Joe Randolph's stroker article in the most recent Corvette Restorer

[Joe C.]

Re: Joe Randolph's stroker article in the most recent Corvette Restorer

Hi Joe C:

I think even those with NCRS disease would be very interested in the details about your engine in it first incarnation (with ported OEM heads). As I recall, the only visible clue that the engine was not stock was the headers. I know you also used the LT1 intake, but that is not easy to detect with the air cleaner on.

So, with the exception of the headers, the appearance of your engine would be just fine for folks with NCRS disease, but as I recall the peak power was exceptional. It's a good example of what is possible with a vintage 327.

I think your engine is a very interesting comparison to what I am building, and is a great example of Taylor's Similar Engine Theory that Duke talks about. As I recall, your peak power is in the same range (400+) as what I hope to achieve with my 383. I'll probably have more torque at low rpm due to the larger displacement, but I may not have more peak power.

To me at least, this is all very interesting stuff.

Joe,

In it's second iteration, it had port matched rams horns, a Comp "Nostalgia Plus" 30-30S cam, lots of internal mods which are "trick" and therefore proprietary, ported 461's, the LT1 intake and 750 cfm dual feed. That cam change was responsible for considerable flattening of the torque curve and resultant bottom end torque closer to the 327/300 engine than the original L76 config. The primary reason is that the N+ 30-30S has faster ramps than the original 30-30 cam and thus more "area under the curve" even though 0.050 durations and valve lift @ POML are the same for both.

In its present form, the engine develops about 480 HP @ 6564RPM if you use the 15% deduction between SAE net flywheel and RWHP, yet it makes about 360 ft-lbs torque @ 2500 RPM with peak torque of 430 ft-lbs sustained between 3500 and 6000 RPM with slow fall off above and below those points. See attached Dynorun showing torque/power at the rear wheels:

[Gene M.]

Re: Joe Randolph's stroker article in the most recent Corvette Restorer

Joe C,
Wow, that is a very flat torque curve from 2700 RPM and up. A lot of power for 327 cubes. How is it coming off stop lights?

[Joe C.]

Re: Joe Randolph's stroker article in the most recent Corvette Restorer

Gene,

I'll take this to another thread titled: "Response To Gene Manno's...............

[Stuart F.]

Re: Joe Randolph's stroker article in the most recent Corvette Restorer

Tom;

It's beautiful.

I had more fun building and driving my first car; my 50 Chevy coupe, than any other car I've had since. Considering that I dropped my first V8 in that car in 1956 (a 55 V8 w/2 barrel carb). There were no "how to" articles in any of the car mags back then so I had to learn every thing on the fly. I didn't even know anyone with any other V8 engine in an early Chevy.

Brings back a lot of fond memories.

Thanks.

Stu Fox

[Joe R.]

Re: Joe Randolph's stroker article in the most recent Corvette Restorer

Joe,

In it's second iteration, it had port matched rams horns, a Comp "Nostalgia Plus" 30-30S cam, lots of internal mods which are "trick" and therefore proprietary, ported 461's, the LT1 intake and 750 cfm dual feed. That cam change was responsible for considerable flattening of the torque curve and resultant bottom end torque closer to the 327/300 engine than the original L76 config. The primary reason is that the N+ 30-30S has faster ramps than the original 30-30 cam and thus more "area under the curve" even though 0.050 durations and valve lift @ POML are the same for both.

In its present form, the engine develops about 480 HP @ 6564RPM if you use the 15% deduction between SAE net flywheel and RWHP, yet it makes about 360 ft-lbs torque @ 2500 RPM with peak torque of 430 ft-lbs sustained between 3500 and 6000 RPM with slow fall off above and below those points. See attached Dynorun showing torque/power at the rear wheels:

Joe C:

That's a really impressive dyno plot!

If I'm understanding your posting correctly, that plot is for your current configuration, which I believe has aftermarket heads and headers. Do you have a dyno plot for what you call the "second iteration" configuration that had the ported '461 heads and rams horn exhaust manifolds? Or possibly the ported '461 heads with headers?

I remain very interested in seeing data that shows the power production differences between ported OEM heads and good aftermarket heads. Similarly, I'm interested in the differences between headers and rams horn manifolds. I have seen very few apples-to-apples comparisons on these topics. There are lots opinions out there, but very little useful data.

If I ever manage to get my 383 on the dyno, I hope to compare four combinations of exhaust (rams horn with open exhaust, headers with open collectors, rams horm through factory exhaust, and headers through factory exhaust). At one time I thought I would also try to compare ported '462 heads to a set of aftermarket heads, since I have both types available on different engines. However, I decided I don't really want to do all the work involved with swapping heads just to get some data.

I think that some solid data on original-vs-aftermarket heads, and rams-horn-vs-headers would be very useful for those of us with NCRS disease, so that we can have some idea of how much power we are leaving on the table if we decide to use original parts.

[Joe C.]

Re: Joe Randolph's stroker article in the most recent Corvette Restorer

Joe C:

That's a really impressive dyno plot!

If I'm understanding your posting correctly, that plot is for your current configuration, which I believe has aftermarket heads and headers. Do you have a dyno plot for what you call the "second iteration" configuration that had the ported '461 heads and rams horn exhaust manifolds? Or possibly the ported '461 heads with headers?

I remain very interested in seeing data that shows the power production differences between ported OEM heads and good aftermarket heads. Similarly, I'm interested in the differences between headers and rams horn manifolds. I have seen very few apples-to-apples comparisons on these topics. There are lots opinions out there, but very little useful data.

If I ever manage to get my 383 on the dyno, I hope to compare four combinations of exhaust (rams horn with open exhaust, headers with open collectors, rams horm through factory exhaust, and headers through factory exhaust). At one time I thought I would also try to compare ported '462 heads to a set of aftermarket heads, since I have both types available on different engines. However, I decided I don't really want to do all the work involved with swapping heads just to get some data.

I think that some solid data on original-vs-aftermarket heads, and rams-horn-vs-headers would be very useful for those of us with NCRS disease, so that we can have some idea of how much power we are leaving on the table if we decide to use original parts.

Joe,

Yes the plot above is in it's current configuration. I have some older plots but I don't think they will be a valid comparison between a 327 and a 383 because the camshafts are different and the static compression ratios are different, as well as the other modifications I made on the inside. Further, the first two versions were plagued by ignition problems which was finally cured by installing a Pertronix ignition and a MSD 6AL module.

One very interesting observation is that all other things being equal, the big aluminum heads make a lot more torque across the board and yes, even at very low RPM than the ported 461's (183cc). The conventional wisdom says that throttle response suffers with big heads but I can tell you unequivocally that the reverse is true. Of course, the big ports sustain that big torque as you can see from the plot.

When you post your dyno results, I will be more than happy to join in the analysis. I have to read my notes from the last 10 years to refresh my memory as to exactly what the config was when the 2 older sets of dynoruns were made in 2008 and 2011. It's possible to extrapolate the plots as the engine layed down later when it was in 3rd gear due to the lighter loading which forestalled the ignition problem I was having at the time. The highest peak power using the ported 461s was achieved in 2011, at 353.7 RWHP @ about 6250 RPM in 3rd gear. In 4th gear on the same day, the plot was similar, except that ignition problems cause the engine to lay down at around 5500 RPM.

I wish you the best of luck when you fire and dynotest your engine. Do you have a time frame in mind?

[Mike E.]

Re: Joe Randolph's stroker article in the most recent Corvette Restorer

It's too bad most chassis dyno runs seem to start at around 2500 rpm. It seems like we would really like to know what it's doing in the lower ranges. Joe C's torque curve is really impressive I must say. The heads must make a big difference, the 461's can only flow so much air.

My daily driver is a older AWD BMW 550i twin turbo V8, it develops 450 ft-lbs. @ 1750 rpm and give the car a real kick in the butt and makes a hoot to drive for a 4 door grocery getter, not as much as Duke's Tesla P90D, still respectable. In the 1/8 mile it would clean my C5 Z06 clock, a lot would of that would be attributed to traction.

I'll go along with Duke, the low end is where we feel the difference and make the car more fun to drive on the street.

Mike

[Duke W.]

Re: Joe Randolph's stroker article in the most recent Corvette Restorer

I've been harping forever about starting dyno runs at 1000 or at least no more than 1500, but dyno operators often refuse for no good reason. It won't hurt the engine and won't hurt the dyno. They also want to end the pull when the power flattens out rather than going to the engine speed requested by the owner. The point of a dyno run is to determine engine output across the full useable operating range, which is off-idle to the redline that is determined by the owner, not what's on the tach. It may be higher or lower depending on engine components and the owner's confidence and road tested understanding of maximum useable revs. For my "327 LT-1" configuration I recommend a normal limit of 7000 and an absolute limit of 7200, which is the point of incipient valve float with the OE valve springs. Power peaks at 6500 with a little rolloff to 7000, which increases signficantly beyond 7200, likely due to false valve motion.

Before embarking on a chassis dyno test the car should be "tuned" SOTP with plenty of road testing. You want to get the most aggressive detonation-free spark advance map possible, which means getting full centrifugal in at the lowest possible RPM down to about 2500.

A dyno run starting at low revs takes about 15 seconds - about equivalent to flooring the throttle at low revs in third gear and letting it run to the redline. This is easy to do on the road at least up to medium revs, and you can test the upper end in second gear. This is to ensure that the engilne pulls smoothly with no detonation to the redline.

I recall going around and around with a dyno operator about ten yeas ago when I did a chassis dyno test of my Cosworth Vega. The guy finally agreed to start the pull at 1000 and go to 7000, but warned of dire consequences. The test was done in "track trim" with open exhaust and no fan on 87 PON fuel. The engine was stock internally with 8.2:1 true CR (8.5 advertised) that I computed from taking the appropriate measurements when the head was off for a refresh. The cams are reindexed to what is essentially L-79 valve timing, and it has an aggressive centrifugal spark advance curve. Upon flooring the throttle it sounded like a tractor engine, but pulled without protest of any kind. It began to really "sing" through the open exhaust at about 5000 and made about 110 lb-ft at 5000 and 122 RWHP at 6500 with a little rolloff to 7000, SAE corrected.

Advertised SAE net at the flywheel is 107 lb-ft @ 4800 and 110 HP @ 5600. (My estimate is that the single catalyst exhaust system generates about 15 psi backpressure at high revs, which is huge. A SHP small block is only about3 psi through the 2.5" undercar exhasut system.) The low rev start revealed a shallow but fairly long "hole" in the torque curve from about 2000-4000, which I believe is a result of the OE bi-wye header. As is typical of headers, you get more torque/power in the mid to upper rev range, but take a hit down low. I think the engine would have a more road friendly torque curve with a streamlined cast iron exhaust manifold. If the pull had started above 2000 I would not have seen the hole, which confirmed my SOTP feeling that the low to mid-range was weak, which, unfortunately is where you spend 99+ percent of normal road driving.

I agree that modern turbo engines make big torque at low revs, but there is lag, and the biggest problem is the transmission. I had a recent experince with a Mercedes CL 250. If you floored the throttle at 40-45 MPH cruising in seventh it must have taken the transmission two seconds to figure out and engage the proper gear. (In addition it had and unbeliveably harsh, very un-Mercedes like ride - a total PoS.)

With the Tesla maximum (and prodigious) torque is available instantaneously at any vehicle speed - no turbo lag, no tranmission trying to figure out what to do. It's really awesome and redefines the term "throttle response"!

Duke

[Joe R.]

Re: Joe Randolph's stroker article in the most recent Corvette Restorer

Joe,

Yes the plot above is in it's current configuration. I have some older plots but I don't think they will be a valid comparison between a 327 and a 383 because the camshafts are different and the static compression ratios are different, as well as the other modifications I made on the inside. Further, the first two versions were plagued by ignition problems which was finally cured by installing a Pertronix ignition and a MSD 6AL module.

One very interesting observation is that all other things being equal, the big aluminum heads make a lot more torque across the board and yes, even at very low RPM than the ported 461's (183cc). The conventional wisdom says that throttle response suffers with big heads but I can tell you unequivocally that the reverse is true. Of course, the big ports sustain that big torque as you can see from the plot.

When you post your dyno results, I will be more than happy to join in the analysis. I have to read my notes from the last 10 years to refresh my memory as to exactly what the config was when the 2 older sets of dynoruns were made in 2008 and 2011. It's possible to extrapolate the plots as the engine layed down later when it was in 3rd gear due to the lighter loading which forestalled the ignition problem I was having at the time. The highest peak power using the ported 461s was achieved in 2011, at 353.7 RWHP @ about 6250 RPM in 3rd gear. In 4th gear on the same day, the plot was similar, except that ignition problems cause the engine to lay down at around 5500 RPM.

I wish you the best of luck when you fire and dynotest your engine. Do you have a time frame in mind?

Hi Joe C:

I'm not suggesting that we try to compare my 383 build to your 327, since my build is not even completed and may end up being a poor performer despite my efforts. However, my target has been to try and match the GM performance ZZ383, which is rated at 450 HP at 5400 rpm (it was 425 HP when I started my project). If we simply use the ZZ383 as a reference, we can see that the Similar Engine Theory appears to hold. Namely, that for two engines that are otherwise identical except for stroke, the one with the shorter stroke will develop the same peak power but at a higher rpm.

To me this was a surprising concept when Duke first brought it up, but I think it is better known among racers. The basic idea is that you can make big peak power from a small displacement engine if you wind the smaller one to higher rpm. I think your engine demonstrates this very well. I would not have thought it possible to get 450+ HP from a 327, but you have demonstrated that it is.

That being said, my focus is on street driving with only an occasional run to redline. So, I wanted more torque at low rpms and I am using increased displacement to try and achieve that. By most racing standards, my 280HR cam is a bit small for a 383, but I have made that tradeoff with an eye toward the configuration I will be driving, which is rams horn exhaust manifolds running through factory exhaust.

That's why I was interested in any data you have on rams horns vs. headers, and ported '461 heads vs. aftermarket heads.

As for when my engine will be dyno tested, I'm hoping to get that done by the end of this year, but my current work/family schedule leaves very little room for "Corvette time," so I can't say for sure. I'm embarassed that it has taken literally years to build a single engine, but that's they way things have worked out.

[Duke W.]

Re: Joe Randolph's stroker article in the most recent Corvette Restorer

Hi Joe C:

To me this was a surprising concept when Duke first brought it up, but I think it is better known among racers.

I don't think that's true. In fact I think the concept is mostly unknown to those who have not read or been told of Taylor's Similar Engine Theory. When I first read it, I paused to think, and after some thinking it made sense. That was long before inexpensive PC-based simulation programs (long before PCs for that matter), but it's certainly born out in engine simulations and real world results.

Many racing classes have maximum displacement rules. This calls for an "oversquare" bore/stroke ratio that provides large piston area that will run up to very high mean piston speed. Such a configuration will produce maximum power per unit of displacement. That's why F1 engines have bore/stroke ratios on the order of 2:1, but such engines have fairly narrow power band sweet spots, which explains why F1 gearbox intergear ratios are on the order of 1.1.

Good road engine performance calls for good power over a much wider speed range, which favors large displacement, mildly tuned engines (in terms of specific output) with very flat torque curves, and for a given displacement, a long stroke engine will usually provide greater low end torque.

That's why I've always said that road engines and racing engines are totally different animals. For a given given bore and stroke, tuning for maximum power at the highest possible mean piston speed compromises low speed torque to the point where such an engine offers poor performance and fuel economy in real world road driving. A 750 HP (at 18-20K revs) naturally aspirated F1 engine of 2.4 liters sounds impressive, but they barely make any power below 6000 and would be a lousy road engine.

The LS7 represents state-of-the-art in naturally aspirated road engine performance, and the current LT-1 is actually even better since it porvides about the same torque up to about 4000 revs with less displacement. They feature nearly "square" bore/stroke ratios. The pushrod architecture with aluminum major components makes for a package that is both smaller and lighter than a typical 5-liter DOHC V-8, yet they make similar or better top end power (other than a few exotics) with greater average power across the range, much better low end torque/power, and better fuel economy due to decreased internal friction from less sliding surface area (fewer bearings and valves).

It all depends on your objective. If you want to retain original vintage components and idle behavior there are limitations to how much top end power you can achieve, but increased stroke will provide more power in the lower rev range where the engine is running 99+ percent of the time, and massaging vintage heads will increase top end power, so you get a significant gain across the entire rev range while maintaining OE appearace and general operating characteristics including idle behavior. That's why I refer to them tongue-in-cheek as "cheater motors". No one can detect the modifications.

If you want to generate maximum power from a vintage block without retaining other vintage components you can get impressive numbers at high revs with aftermarket heads, mechanical roller cams, and headers with open exhaust, but a reasonable road exhaust system will reduce the numbers significantly and mechanical roller lifters usually start munching needle bearings after about 20K miles of road use, so they aren't very durable.

It's an apples to oranges comparison.

Duke

[Joe R.]

Re: Joe Randolph's stroker article in the most recent Corvette Restorer

I don't think that's true. In fact I think the concept is mostly unknown to those who have not read or been told of Taylor's Similar Engine Theory. When I first read it, I paused to think, and after some thinking it made sense. That was long before inexpensive PC-based simulation programs (long before PCs for that matter), but it's certainly born out in engine simulations and real world results.

Many racing classes have maximum displacement rules. This calls for an "oversquare" bore/stroke ratio that provides large piston area that will run up to very high mean piston speed. Such a configuration will produce maximum power per unit of displacement. That's why F1 engines have bore/stroke ratios on the order of 2:1, but such engines have fairly narrow power band sweet spots, which explains why F1 gearbox intergear ratios are on the order of 1.1.

Good road engine performance calls for good power over a much wider speed range, which favors large displacement, mildly tuned engines (in terms of specific output) with very flat torque curves, and for a given displacement, a long stroke engine will usually provide greater low end torque.

That's why I've always said that road engines and racing engines are totally different animals. For a given given bore and stroke, tuning for maximum power at the highest possible mean piston speed compromises low speed torque to the point where such an engine offers poor performance and fuel economy in real world road driving. A 750 HP (at 18-20K revs) naturally aspirated F1 engine of 2.4 liters sounds impressive, but they barely make any power below 6000 and would be a lousy road engine.

The LS7 represents state-of-the-art in naturally aspirated road engine performance, and the current LT-1 is actually even better since it porvides about the same torque up to about 4000 revs with less displacement. They feature nearly "square" bore/stroke ratios. The pushrod architecture with aluminum major components makes for a package that is both smaller and lighter than a typical 5-liter DOHC V-8, yet they make similar or better top end power (other than a few exotics) with greater average power across the range, much better low end torque/power, and better fuel economy due to decreased internal friction from less sliding surface area (fewer bearings and valves).

It all depends on your objective. If you want to retain original vintage components and idle behavior there are limitations to how much top end power you can achieve, but increased stroke will provide more power in the lower rev range where the engine is running 99+ percent of the time, and massaging vintage heads will increase top end power, so you get a significant gain across the entire rev range while maintaining OE appearace and general operating characteristics including idle behavior. That's why I refer to them tongue-in-cheek as "cheater motors". No one can detect the modifications.

If you want to generate maximum power from a vintage block without retaining other vintage components you can get impressive numbers at high revs with aftermarket heads, mechanical roller cams, and headers with open exhaust, but a reasonable road exhaust system will reduce the numbers significantly and mechanical roller lifters usually start munching needle bearings after about 20K miles of road use, so they aren't very durable.

It's an apples to oranges comparison.

Duke

Hi Duke:

In my view, there are two key questions that haunt those of us with NCRS disease who also want more power:

1) How much would be gained by substituting headers for the cast iron rams horn exhaust manifolds?

2) How much would be gained by using modern aftermarket heads instead of ported vintage heads?

I think the answer to both of the above questions is "less than it would otherwise be if you are running through factory mufflers," but I don't know how much less. Given that the whole point of a "stealth" engine or "cheater" engine is to have better performance while also maintaining original appearance, the comparison should really be done with factory mufflers, not open exhaust.

At present, I suspect that even with factory mufflers, the above two changes would each net some power, but I don't know how much. For question #1, I hope to get some actual data if I ever manage to get my 383 on the dyno. Regarding question #2, I have opted to use aftermarket heads that are carefully disguised to look like vintage heads, based on the belief that modern aftermarket heads offer a performance benefit that makes this effort worthwhile. However, I simply don't know how big the benefit may be.

[Tom P.]

Re: Joe Randolph's stroker article in the most recent Corvette Restorer

Joe makes some good points-------------real world vs theory generated computer modeling. And reworking vintage heads/block vs aftermarket heads/blocks.
Since I haven't, and do not have the funds to invest in rather pricy aftermarket parts, I've always been relagated to working with factory parts. For example, as I've explained, the heads on the SB400 in the 56 are 66 vintage 462 heads which have been somewhat reworked and no doubt they do not flow as well as a set of improved aftermarket heads. But they sure seem to work great with my combination.
As for headers vs iron manifolds, there can be no question that headers flow better than iron manifolds. BUUUUUUUUUUUT, when all the gas pressures get back to the mufflers, will there be any significant improvement since it would be expected that the restriction of the muffler would be the same for an exhaust system with either headers or manifolds. True, the gases are going to flow more freely through headers, but once the gases reach the rest of the system with stock mufflers, has there been a significant gain? It would seem to me, and along with my PERSONAL experience, that the entire exhaust system needs to be more free flowing and less restrictive mufflers should provide an added benefit.
I once had a stock 56-57 stainless exhaust system on the 56 and I always felt that performance was much less than it should be. FINALLY, I tossed the stock 56-7 system and went with 2 1/2in manifolds, 2 1/2in pipe all the way to the ends of the tail pipes with 2 1/2in generic turbo mufflers. The difference was night and day.
Now, back to heads. IF, I replaced the 462 heads which have been reworked with some (supposedly) better flowing aftermarket heads, and retained the SAME exhaust system, would there really be a significant improvement in performance? Last, always keep in mind that my above engine is fed by a Rochester (also somewhat modified) FI unit which has an air meter that flows somewhere in the range of 600cfm.
I think the ONLY way I could gain there would be to go with a dual air meter FI unit. Anyone got one of those that they are willing to part with????

[Gene M.]

Re: Joe Randolph's stroker article in the most recent Corvette Restorer

Would not a dual air meter FI unit destroy the stealth look? Headers and custom exhaust is another "give away". Yes it would be faster but original look would be gone. I can see a lot of guys will enjoy the new NCRS Street class of judging when it gets to practice.

[Duke W.]

Re: Joe Randolph's stroker article in the most recent Corvette Restorer

I've got one reliable data point on headers vs. manifolds - a '65 L-79 that was converted to a "327 LT-1". With headers and open exhaust it made about eight percent greater peak torque and three percent greater peak power on a lab dyno, but was weaker at the low end. The header primary tubes were 1 5/8" that is small for the level of power, which was in the 360 SAE gross range.

The additional torque/power is due to wave dynamics generated by the headers that creates negative pressure at the exhaust valve duing the overlap period over about half the RPM range, which starts the inlet process early. The peak is probably in the area of three psi, which is about equal to the exhaust backpressure of the base OE exhaust system, so most of the header effect would be negated by backpressure, which would cut the gains substantially in the car with the OE exhaust system. Headers usually reduce low end torque by creating positive pressure at the exhaust port at low revs, so you trade off a loss at the low end for more at the top end, which is not a good thing for a road engine.

For a given configuration, power is approximately proportional to head flow, but aftermarket heads as shipped may not flow any better than massaged OE heads, and may not be any better after similar massaging. Also, if the only flow improvement is above 0.5", which is true of many aftermarket heads, there is no improvement with any OE camshaft since maximum lift at the valve (small blocks) is in the range of 0.43 to 0.44 at 1.44:1 rocker ratio, which is the true rocker ratio at maximum lift.

So careful system engineering analysis is required to select parts that are complimentary, and simulation programs are a good tool to compare various configurations. Absolute torque/power numbers are not exact, but comparisons to a baseline are usually valid.

My experience with EA 3.0 is that it is usually within a few percent on top end power, but the real engine power rolloff above the peak is not as fast. Predicted peak torque is usually high by about eight percent. The least accurate area is low end where predicted torque may be as much as 20 percent lowerer than actual torque, but generally the configuration that yields greatest predicted average torque/power across the range is the config. that will produce the best average when tested on a dyno.

Another note on headers. They need a high overlap camshaft to be effective at all, so installing a set on a 300 HP engine with the OE cam is a total waste. In fact, top end power may actually be less because the exhaust gas has to traverse several feet of small tubing which increases friction compared to almost immediately being dumped into a much larger pipe as is the case with manifolds, and the low overlap severly limits the range that wave dynamics are effective.

My opinion is that headers are only useful for serious racing engines. The OE exhaust system, especially 2.5" manifolds and 2.5" pipes is very low backpressure for an OE system, but the off-road mufflers or some aftermarket straight through mufflers may provide some advantage on an engine the makes 300 or more SAE corrected RWHP on a chassis dyno.

Duke

[Joe R.]

Re: Joe Randolph's stroker article in the most recent Corvette Restorer

Joe,

Excellent article and very well written! However, I'm surprised that in the short block portion of your 2-part article, you didn't mention which pistons you used, as well as explaining the meaning of compression height as it impacts piston-to-deck-clearance. Given the fact that the majority of folks that populate this website have no engine building experience, alas, neither do they have much knowledge of what goes on inside of an engine, such a discussion would have proven very educational to many of the folks with "NCRS disease".

As you know, I am not as much a fan of long stroked engines as I am of squeezing every ounce of torque and power from a fixed displacement. Notwithstanding the fact that displacement is proportional to torque, and that you did a fine job in designing your engine, a camshaft change alone can make a dramatic difference in torque across the entire rev range. For instance, we know that the stock 461 heads using 2.02/1.60 valves respond VERY well to mild porting and respond even more to more radical porting. I had gotten mine to flow 255/196 cfm @ .600 lift which defines the practical limit of lobe lift for a design camshaft. I can tell you that simply porting the heads as well as adding a high lift solid roller cam without any other changes will flatten and raise the torque curve across the rev range. Of course, making further changes to a small displacement engine will further raise the torque curve and sustain it to higher RPM's thus increasing peak power as well as average torque.

I look forward to your dyno results as well as your follow-up article.

Hi Joe C:

I finally got my engine on the dyno and I thought those who have been following this thread would be interested in the results. I acheived my goal of matching the GM Performance ZZ383, which was 425 HP when equipped with a dual-plane intake. In my Restorer article I mistakingly stated that the ZZ383 rating had been increased to 450 HP, but it turns out this was for a long block assembly with no intake, and the intake used to get the 450 HP rating was a single-plane intake. I'm sure I could get another 25 HP with a single-plane intake, but I used a dual-plane intake like the original ZZ383 crate engine.

Note that the 424 peak HP I achieved was with open headers, which corresponds to the way most engine dyno results are reported. However, I spent some extra $$ for another day of dyno testing to try and get some real test data on a topic that has been debated endlessly on this TBD and others. Namely, how do open headers compare to other exhaust system options that can be used on the street? My theory was that adding mufflers to headers would likely cancel out the beneficial effects of headers, but it turns out I was mistaken. The attached plots show the results of comparing four options:

1) Open headers
2) Headers with low-restriction Corvette N11 mufflers
3) Open ram's-horn 2.5" factory exhaust manifolds
4) Ram's horn manifolds with factory N11 mufflers

Hopefully the attached comparison plots are sufficiently readable. I think there is a lot of useful information here if you study the plots.

What is not shown is the effect of a cam change. My cam is a relatively modest hydraulic roller with 224/224 degree duration at .050" and .525" lift. My Engine Analyzer simulations suggest is that a bigger cam gives better results with open headers, but worse results with the iron manifolds and the factory N11 exhaust system. I did not have the budget to try an actual cam swap for the dyno testing, but I suspect that the Engine Analyzer simulations are correct. In other words, a big cam can yield impressive results with open headers, but with iron manifolds and a factory exhaust system, it actually performs worse than a smaller cam.

Readers should note that my engine is more than just a stroked L79. The cam is a roller cam, the heads are Dart Iron Eagle 200cc heads that have been externally disguised to look like stock '462 heads, and the intake is a 1967 Z28 intake that looks a lot like the correct L79 intake but flows better. The carb I used is a new 750 CFM Holley.

I'm not sure how my results compare to a bone-stock 327 L79 that has simply been stroked to a 383 and has pocket-ported '462 heads. My guess is that I might have gotten an extra 25 HP with my roller cam and aftermarket heads, which suggests that simply stroking an L79 to 383 and pocket porting the heads might yield 400 HP with open headers. If so, that's a lot of bang-for-the-buck with changes that are a lot less extensive than what I did. And, the resulting engine would be externally indistinguishable from a stock L79.

In any event, I had a lot of fun developing this "stealth L79" for my '67 Corvette, and I plan to write a more detaiked follow up article about the build for the Restorer.