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 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.

Your results probably would have yielded more torque and power with a cam of equal duration and overlap, but with more lift...................and so a "bigger" cam, which is where I was going in my reply. Since the major part of flow restriction is across the valve seat, some more lift would increase flow considering your heads are fairly big @ 200 cc.

It looks like your Iron Eagle heads will accept up to .600 lift using a hydraulic roller with their standard springs. It would be interesting to see flow ratings with valve lifts up to .600 and I suspect that the rating @ .600 would be close to that @ .500 lift. Assuming that's true, I'd be looking for intake lift of something like .550 (mine is .610, but mine is a solid roller of longer duration). I don't remember which rockers you used, but a very strong performance improvement can be had by increasing the rocker ratio on the INTAKE side. Exhaust lift is not as important considering your restricted exhaust with those rams horns. If you don't already have them, then consider boosting your intake rocker ratio to 1.6 or 1.7:1. Not sure if Comp has a hydraulic roller intake lobe that yields more than .525" lift @ 0.050/221 duration. Maybe the "Extreme Energy" series, or a custom cam using a high lift/low-moderate duration intake lobe.

My guess is a .550-.600 lift intake would be good for another 40-50 HP. Try it on your EA sim program.

[Joe R.]

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

Your results probably would have yielded more torque and power with a cam of equal duration and overlap, but with more lift...................and so a "bigger" cam, which is where I was going in my reply. Since the major part of flow restriction is across the valve seat, some more lift would increase flow considering your heads are fairly big @ 200 cc.

It looks like your Iron Eagle heads will accept up to .600 lift using a hydraulic roller with their standard springs. It would be interesting to see flow ratings with valve lifts up to .600 and I suspect that the rating @ .600 would be close to that @ .500 lift. Assuming that's true, I'd be looking for intake lift of something like .550 (mine is .610, but mine is a solid roller of longer duration). I don't remember which rockers you used, but a very strong performance improvement can be had by increasing the rocker ratio on the INTAKE side. Exhaust lift is not as important considering your restricted exhaust with those rams horns. If you don't already have them, then consider boosting your intake rocker ratio to 1.6 or 1.7:1. Not sure if Comp has a hydraulic roller intake lobe that yields more than .525" lift @ 0.050/221 duration. Maybe the "Extreme Energy" series, or a custom cam using a high lift/low-moderate duration intake lobe.

My guess is a .550-.600 lift intake would be good for another 40-50 HP. Try it on your EA sim program.

Hi Joe C:

I agree with all of your points.

To answer your questions, my heads have intake flow of 264 CFM at .500" lift, 270 CFM at .550" lift, and 261 CFM at .600" lift. So, they would probably respond to more lift than I used. My cam has .525" lift, but I did use 1.6 rockers on the intakes only, bringing intake lift to .560".

The lobes on my 280HR cam are an older design and are less aggressive than the latest offerings from Comp Cams. This was an intentional choice because I was concerned about long-term reliability with the really aggressive lobes. This concern may not be warranted, since I drive my Corvette only about 1000 miles a year. However, my hope is to drive it for at least 20 more years.

Even with the milder lobe profile of the 280HR, for extra insurance I used top-drawer parts in the valve train, including full roller rockers, beehive springs, and hollow-stem intake valves. The idea was to make the valve train as strong and light as I could, just to reduce the strain on it. Much of this was probably overkill, but the only downside of over-doing it was cost. In terms of measurable performance, these extra-cost changes probably don't add anything, so it's mostly a longevity consideration.

I suppose that if I end up wanting more power without compromising the idle characteristic, I could swap in a cam that has similar duration but more lift. The existing valve train would probably handle that just fine.

[Joe C.]

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

Hi Joe C:

I agree with all of your points.

To answer your questions, my heads have intake flow of 264 CFM at .500" lift, 270 CFM at .550" lift, and 261 CFM at .600" lift. So, they would probably respond to more lift than I used. My cam has .525" lift, but I did use 1.6 rockers on the intakes only, bringing intake lift to .560".

The lobes on my 280HR cam are an older design and are less aggressive than the latest offerings from Comp Cams. This was an intentional choice because I was concerned about long-term reliability with the really aggressive lobes. This concern may not be warranted, since I drive my Corvette only about 1000 miles a year. However, my hope is to drive it for at least 20 more years.

Even with the milder lobe profile of the 280HR, for extra insurance I used top-drawer parts in the valve train, including full roller rockers, beehive springs, and hollow-stem intake valves. The idea was to make the valve train as strong and light as I could, just to reduce the strain on it. Much of this was probably overkill, but the only downside of over-doing it was cost. In terms of measurable performance, these extra-cost changes probably don't add anything, so it's mostly a longevity consideration.

I suppose that if I end up wanting more power without compromising the idle characteristic, I could swap in a cam that has similar duration but more lift. The existing valve train would probably handle that just fine.

FYI: You can port that intake to a 1206 intake gasket as I did, but only if you have the later service replacement with the wider head flanges. I ported my heads to the same gasket with the step going in the proper direction, at the port floor; however, I don't know if the Iron Eagles will tolerate such port size, and if not then you are already at your port size limit since the head port size must be greater than or equal to the intake manifold port size.

You once asked me about Pro Filer aluminum heads, which are very high quality and less expensive than AFR heads. My 195s are ported to 203 cc and flow 285 @ .500, 290 @ .600, 291 @ .700 and 292 @ .800.

[Joe R.]

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

FYI: You can port that intake to a 1206 intake gasket as I did, but only if you have the later service replacement with the wider head flanges. I ported my heads to the same gasket with the step going in the proper direction, at the port floor; however, I don't know if the Iron Eagles will tolerate such port size, and if not then you are already at your port size limit since the head port size must be greater than or equal to the intake manifold port size.

You once asked me about Pro Filer aluminum heads, which are very high quality and less expensive than AFR heads. My 195s are ported to 203 cc and flow 285 @ .500, 290 @ .600, 291 @ .700 and 292 @ .800.

Hi Joe:

I can't recall what Felpro intake gasket I used (I'm away from home and can't check). I do recall that I used the gasket recommended by Dart for the 200cc heads. I compared the runner size on the Z28 intake to the Dart 200cc head and concluded that they were almost identical, so I did not do any port matching at all.

I do have one of those later service replacement Z28/LT1 intakes with the wider flanges, which I picked up cheap as a backup in case my Z28 intake presents the well-known vacuum leaks associated with that design. My hope is that the '67 Z28 intake will seal okay. I like it because it looks almost the same as the original '67 L79 intake. The thermostat placement, temp sender placement, and Winters snowflake are identical to the '67 L79 intake.


Joe Randolph

[Joe C.]

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

Hi Joe:

I can't recall what Felpro intake gasket I used (I'm away from home and can't check). I do recall that I used the gasket recommended by Dart for the 200cc heads. I compared the runner size on the Z28 intake to the Dart 200cc head and concluded that they were almost identical, so I did not do any port matching at all.

I do have one of those later service replacement Z28/LT1 intakes with the wider flanges, which I picked up cheap as a backup in case my Z28 intake presents the well-known vacuum leaks associated with that design. My hope is that the '67 Z28 intake will seal okay. I like it because it looks almost the same as the original '67 L79 intake. The thermostat placement, temp sender placement, and Winters snowflake are identical to the '67 L79 intake.


Joe Randolph

Dart recommends a FelPro 1205 with your heads.

Although the ports on the intake are "about" the same size as those in the heads, the alignment of the two is very possibly not optimal considering the fact that your heads are not stock which means that the port centers may not be in the same location as original. Most often, the port centers are raised slightly on better quality aftermarket heads, which means that if your intake port height is the same as the head port height, the step between the ports will be in the wrong direction. The head port should always be larger than the intake port, with the step located in the floor of the port junction. Optimally, the sides and roof should be perfectly aligned and equally sized. This must be carefully checked prior to assembly. Proper port alignment and sizing ensures laminar flow at the junction. The reason for a step in the port floor is to minimize flow reversion during cam overlap interval, which in your case is not very important.

[Joe R.]

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

Dart recommends a FelPro 1205 with your heads.

Although the ports on the intake are "about" the same size as those in the heads, the alignment of the two is very possibly not optimal considering the fact that your heads are not stock which means that the port centers may not be in the same location as original. Most often, the port centers are raised slightly, which means that if your intake port height is the same as the head port height, the step between the ports will be in the wrong direction. The head port should always be larger than the intake port, with the step located in the floor of the port junction. Optimally, the sides and roof should be perfectly aligned and equally sized. This must be carefully checked prior to assembly. Proper port alignment and sizing ensures laminar flow at the junction. The reason for a step in the port floor is to minimize flow reversion during cam overlap interval, which in your case is not very important.

I probably could have optimized this aspect better than I did.

I recall that I measured the width and height of the ports on the intake, and the width and height of the ports on the heads. They came out almost identical. I also used the Dart-recommended gasket as a template and compared it to both the intake and the heads. Again, everything appeared to line up pretty well. I only spent about ten minutes on this task and concluded that this was not an area that needed further attention. While I can't say that the alignment is perfect, I can say it is pretty close.

If I was being more thorough, I could have made an exact template of one side (say, the intake) and compared it directly to the other side (head side). If I ever build another one of these "stealth engines" (which would likely be a small block 427), I will be more thorough with checking and fine tuning the intake-head port matching.

[Joe C.]

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

I probably could have optimized this aspect better than I did.

I recall that I measured the width and height of the ports on the intake, and the width and height of the ports on the heads. They came out almost identical. I also used the Dart-recommended gasket as a template and compared it to both the intake and the heads. Again, everything appeared to line up pretty well. I only spent about ten minutes on this task and concluded that this was not an area that needed further attention. While I can't say that the alignment is perfect, I can say it is pretty close.

If I was being more thorough, I could have made an exact template of one side (say, the intake) and compared it directly to the other side (head side). If I ever build another one of these "stealth engines" (which would likely be a small block 427), I will be more thorough with checking and fine tuning the intake-head port matching.

Joe, I know you well enough to realize that you are a stickler for details. Believe me when I say that careful alignment of the intake-to-head port junction is very important. If there is a gross misalignment, then it could extract a high performance penalty. You're an electrical guy and I'm a mechanical guy who is focused on flow paths. Make sure that your intake/head interface is in agreement with what I have posted above. If there is the slightest divergence from optimal alignment, then it will translate to a significant torque/power deficit.

The easiest way is to make sure that the head port size at the intake gasket is larger than the intake port size at the same point. Any downstream step will reduce torque/power significantly. An upstream step will not.

Details....details.........details.

[Joe R.]

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

Joe, I know you well enough to realize that you are a stickler for details. Believe me when I say that careful alignment of the intake-to-head port junction is very important. If there is a gross misalignment, then it could extract a high performance penalty. You're an electrical guy and I'm a mechanical guy who is focused on flow paths. Make sure that your intake/head interface is in agreement with what I have posted above. If there is the slightest divergence from optimal alignment, then it will translate to a significant torque/power deficit.

The easiest way is to make sure that the head port size at the intake gasket is larger than the intake port size at the same point. Any downstream step will reduce torque/power significantly. An upstream step will not.

Details....details.........details.

Hi Joe C:

I'm home now and checked my notes on this. The 3917610 intake manifold ports measured nominally 2.02" x 1.20". The intake ports in the heads measured nominally 2.12" x 1.18". As far as I could tell using just the gasket as a template, the differences were pretty symmetrical around the port, and all eight ports were pretty well aligned.

So, at least the difference in the height of the ports was in the right direction for reducing reversion (head ports larger than manifold ports). I recall that I decided not to try to increase the height of the intake manifold ports due the comparatively small amount of available material that the 3917610 intake is known for.

If I was using the later service replacement intake with the flanges (144044836), I would have been more comfortable making the ports in the intake manifold taller to match the Dart heads.

So, I probably left a little bit of power on the table, but I did not want increase the risk of a vacuum leak, which is already a risk with 3817610 intake in its unmodified condition.