H. P. Versus Fuel Injection

[Jack A.]

I'm restoring a 61 315 H.P. Corvette that has fuel Injection. In rebuilding the engine I was toying with the idea of kicking up the H.P a bit with a 327 crank a LT1 or Duntov Cam and some porting. I contacted Jerry Bramlett who is obviously one of the great Guru's on the Fuel Injection systems, He advised against it in that it negatively impacts the vacumn which will decrease the effeciency of the fuel injection system. I respect Jerry's opinion greatly but was just wondering if anyone out there has tried to what I planned and how it turned out?

Thanks,
Jack 35730

[John D.]

Re: H. P. Versus Fuel Injection

Jack, Listen to Jerry Bramlett. He has a lot of experience and knows his stuff for sure. Meanwhile you better do some reseach as you say LT1 or Duntov cam. I mean you car came with a Duntov 3736097 cam.
If you want to know about the LT1 cam there are a 1000 posts here on that subject. Just push the search button on top of the page. I bet a stock 61 FI car done properly though will blow your doors off with your proposed set-up. Been there a few hundred times. Good luck, JD

[Bruce B.]

Re: H. P. Versus Fuel Injection

I have a 57 283 250 HP FI car and when I purchased the engine we were not sure what cam was in the car.
As it turns out is has the 327 350 HP which was used from 1965 through ??.
It is a hydraulic lifter setup and it has sufficient vacuum to run my 4360 fuel unit.
The engine feels strong although I have not yet taken it for a shakedown ride, other then up and down the driveway.
You might consider this cam although I miss the rattle of solid lifters.

[Duke W.]

Re: H. P. Versus Fuel Injection

The LT-1 cam produces about the same idle vacuum as the Duntov, so your FI unit should have no problem handing the LT-1 cam. The 30-30 cam is another story since it loses 2-3" of manifold vacuum at the same idle speed compared to the typical 12" at 900 that the Duntov and LT-1 cams produce. Your OE cam is the Duntov.

If you have a real '61 315 HP FI with 461X heads, head massaging and the LT-1 cam will turn it into a 7200+ RPM screamer, without affecting idle quality/characteristics and only a slight loss of low end torque if you keep the 3" stroke crank, and it will make more low end torque with a 327 crank.

Search archives for "327 LT-1" to explain what is needed over and above good head massaging. This is a '65 L-76 engine, all original components and appearance that has an 80 percent torque bandwidth of 2100 to over 6000 (90 percent at 2500) and close to 300 SAE corrected RWHP. The limitation on power was the 7200 maximum valvetrain speed with the OE 068 valve springs. FI will probably shift the torque curve up the rev scale because of the single plane manifold architecture. In particular you need some durable connecting rods. The OE 283 and 327 rods will just about guarantee a big blowup at the very high rev levels that good massaged 461x heads and the LT-1 cam will allow the engine to make useable power.

The new Eagle cap screw small bearing rods appear to be as durable and light as the Crower Sportsmans and are half the price.

You may also have to do some minor block relieving to clear a 327 crankshaft.

Duke

[Jack A.]

Re: H. P. Versus Fuel Injection

Hi Duke,

Thanks for the reply. We've corresponded on this subject previously. I'm probably being overly cautious but I want to use the original Fuel Injection and don't want to do anything that will hinder its function. You are obviously better versed in this than I am, So you don't see any problems with what you've suggested and what I want to do? By the way it is a real 315 H.P. It has every correct numbered piece including the 461X heads. I was very lucky to find it for what I was able to get it for.

Jack

[William C.]

Re: H. P. Versus Fuel Injection

I can tell you from personal experience (about 35 years ago) that the 30-30 cam will give you fits in an FI unit with a cranking signal valve as the cam doesn't have enough vacuum at idle to keep the valve closed, and when it opens the engine floods and dies. Just a real PITA. Stick with the 315 spec stuff and you will have a system you will be very pleased with.

[Duke W.]

Re: H. P. Versus Fuel Injection

Hi Duke,

Thanks for the reply. We've corresponded on this subject previously. I'm probably being overly cautious but I want to use the original Fuel Injection and don't want to do anything that will hinder its function. You are obviously better versed in this than I am, So you don't see any problems with what you've suggested and what I want to do? By the way it is a real 315 H.P. It has every correct numbered piece including the 461X heads. I was very lucky to find it for what I was able to get it for.

Jack

No I don't see any problems, but achieving the potential performance requires a closely managed project and extreme attention to detail. Let the machinist run amok and don't sweat the details and you could end up with the typical disaster that most guys get into when restoring an engine.

I don't recommend the 30-30 cam for ANY road engine, FI or carbureted, but the LT-1 cam provides the same idle vacuum as the Duntov. They both have about the same effective overlap, but the LT-1 cam opens the exhaust valve earlier and closes the inlet valve later - neither of which have any real effect on idle. Idle quality/characterisitics is all about overlap, and the more overlap the lower the idle vacuum at a given idle speed.

The Duntov cam was a good design for the small port 3" stroke engines, other than I think it would work better on a road engine with less overlap.

The big port 461X heads and then the increase in stroke to 3.25" significantly change the optimum valve timing for a high performance road engilne. The 30-30 was way too much, but GM recognized the issue, designed the LT-1 cam and when it was released, it replaced the 30-30 in service parts circa 1970 and is the best design for big port heads and strokes over 3". The Duntov cam remained for another 20 years or so.

BTW DON'T increase the size of your OE valves to 2.02/1.60. Concentrate on the head massaging. I've seen massaged 1.94/1.50" valve heads outflow 2.02/1.60" heads. It's all in the details, and I don't think the larger valves will even fit any less than a 4.000" bore.

Duke

[Mike M.]

Re: H. P. Versus Fuel Injection

duke is correct. you'll probably hit antifreeze if ya try to install 2.02 valves in your 461x heads.mike

[Duke W.]

Re: H. P. Versus Fuel Injection

Mike - grinding out early 461X heads to the larger 2.02/1.60" valve size won't "hit water" as these castings were OE machined to the larger valve size beginning in 1964 for SHP/FI engines.

The problem is that I don't think the larger valves will clear the cylinder walls on engines with less than 4.000" bore, which would preclude 283 blocks with stardard 3.875" bores or a slight overbore.

Duke

[Mike M.]

Re: H. P. Versus Fuel Injection

i checked with my buddy whose heads hit water. seems the machine shop was installing case hardened seats, not the 202 valves.thanks for correction duke.mike

[Tim S.]

Re: H. P. Versus Fuel Injection

Years ago, I used an LT-1 cam in my 63 fuel car with excellent results. Great power across the powerband and it would rev like a 302 Z-28 I had. But....if I were to do another one today, I would check with one of the cam manufaturers. Modern technology for camshaft lobes and valvesprings will allow you to have the best of both worlds. To have a cam that creates good vacuum yet has RPM capabilities and good midrange torque, is only a phone call away. I have found the people on the tech lines to be very helpful when they have acurate information on your combination. This way, you can have a cam that idles like a stocker, plenty of vacuum to keep the F.I. unit on the lean stop, and yet pulls like a freight train when you want to pour it on. In addition, I am a big advocate of the dyno. It allows for control of the engine for cam break in, seating the rings, monitor exhaust gas temps, and fine tune the combo. Then, you know the combo is right on when you go through the effort to install it. My last engine(427 400hp) was $400.00 to dyno. Just my thoughts.........hope it helps.
tim

[Duke W.]

Re: H. P. Versus Fuel Injection

Since you have experience with this how about if you call up a cam manufacturer and ask them what they recommend. There are literally hundreds of aftermarket cams out there from a dozen or more manufacturers. Which one? Where do you even start? Do you really think some kid on the other end of the phone line understands vintage Corvette engines?

Dyno testing tells you what performance characteristics you end up with, but it doesn't tell you what to expect. Most "engine builds" are based on pure guesswork, and many end up with performance characterisitics that are not very suitable for a road engine.

This is where engine system engineering comes in. Design - analyze - test, which I have discussed extensively on this board and others.

The first order of business is head massaging. Then pick valve timing that yields the best torque bandwidth, and I definitely do not recommend anything that requires higher that OE valve spring characteristics in order to keep valvetrain loading and longevity at OE levels. Once valve timing is choosen, the maximum compression ratio range that the engine will tolerate can be determined, and the later the inlet valve closes, the higher the target CR range.

I've tried many different representative cams on various Corvette engine configurations in engine simulation programs, and nothing beats the LT-1 cam for torque bandwidth, top end power and rev range while maintaining OE idle characteristics and good driveability for SHP/FI engines. With OE valvetrain components and massaged heads it yields useable power to over 7000 revs, whilie maintaining the critical 80 percent peak torque at about 2000 revs, which is necessary for a good, responsive road engine.

And all my simulation work is based on "SAE net" output, which takes into account losses from the exhaust system and front end accessories. Then chassis dyno testing allows me to validate the models and refine them based on test results. Lab dyno data is of less value when trying to predict "as installed" performance characteristics because it doesn't take exhaust system pumping and front end accessory loss.

When it came to the 300 HP configuration, there was NO aftermarket cam that could significantly increase power and extend the useable rev range without screwing up the smooth, low rev idle, so I designed my own - in fact, I designed two - one for manual transmissions and one for Powerglide, and they don't look even remotely close to ANY of the several hundred available aftermarket cams.

Duke

[Jerry G.]

Re: H. P. Versus Fuel Injection

Very interesting. I also have a 315 HP 283. It needs to be bored out to clean up the cylinders. I was thinking about going with a larger bore rather than a longer stroke. I'd like to go to 4.00" and end up with a 302. Keep the 461X heads but pocket port them and go with the LT1 cam. I figure it's going to have more torque than a 283 just because it's larger displacement. So I guess this is a bore vs stroke question. Your thoughts?

[Duke W.]

Re: H. P. Versus Fuel Injection

Peak torque is a function of displacement and compression ratio, so the old adage - you can't beat cubic inches - is valid.

Another very important point to remember is that all other things equal, two engines that are identical other than stroke will produce about the same peak power at about the same mean piston speed, but the longer stroke engine will produce more average power from off idle to the end of the useable power bandwidth because of the greater displacement, and this is really important for a road engine - less so on a racing engine that will spend most of its time in a fairly narrow rev range that defines the top end power bandwidth.

That's why I like the idea of installing a 327 crank in a 283, especially the 315 FI with the OE 461 heads. It's a "bolt-on" deal other than possibly some clearance issues, which can be easily addressed with a die grinder, and with well massaged 461X or later big port heads a 3.25" stroke small block will make useable power to the OE mechanical lifter/valvespring valvetrain limiting speed of about 7200

7200 revs corresponds to a mean piston speed of about 3900 FPM with a 3.25" stroke, but 3900 FPM is about 7800 on a 283, so the valvetrain will give up before the heads, and you are leaving a lot on the table. You can extend the rev range with the optional off-road valve springs, but will you really want to rev the engine to over 7500?

On the other end of the spectrum a 3.48" stroke 350 is only running about 6700 at 3900 FPM, so the extended rev range of a mechanical lifter cam is still useful, but if the stroke is increased to 3.75" 3900 FPM is only about 6200, so the extended rev range of a mechanical lifter cam is not necessary unless the heads flow better than the best massaged OE heads.

(As a point of reference HD diesel engines from the huge Wartsilas on ships to automotive size HD diesel engines are rated/governed in the range of 1100-1800 FPM, while NASCAR and F1 are running at about 5200 FPM at peak revs, and the LS7 at 7000 is running at about 4700 FPM.)

For SHP/FI 283s I generally recommend the Duntov cam, but I've also recommended that the lobes be reindexed to something like 110/118 rather than the OE 108/112. The 110/118 indexing reduces overlap and closes the inlet valve slightly later. In fact at 110/118 the Duntov cam is essentially a mechanical lifter version of the L-79 cam, albeit with a little less lift.

I think most early 283s have thick enough cylinder walls to support a .125" overbore, but they should be sonic tested and at this overbore there is likely no chance that the block will tolerate another cleanup overbore of even .020".

Forged 327 cranks are available and usually fairly cheap because nobody wants them. Of course, many have been ground, which destoys the Tufftride on SHP/FI cranks, but a surface hardening treatment can be reapplied. So my recommendation is to go with a stroker rather than boring out the OE 283 block to the limit. With a .030" overbore and 3.25" stroke, you'll have a fairly torquey (relative to a 283 or 302) 311 CID engine.

Duke

[Tim S.]

Re: H. P. Versus Fuel Injection

Duke,
My experience has been with Comp Cams. Regardless of engine make or age, they have done a fine job in my opinion with cam selection. Yes, the LT-1 cam is great. Modern grinds have faster ramps and set the valve down easier to increase average port flow with out increasing duration and the drivability problems that follow. Furthermore, the new beehive springs reduce valvetrain weight to enhance RPM potential without increasing spring pressure. The abilty to custom select cams or custom grind cams allows a person to overcome changes made such as when one wants to lower compression ratio. Your comments about SAE net testing and tuning are right on. I suggested the dyno for the simple fact that the engine is "pretty well" sorted out when it comes time to fire up the car. No doubt, the dyno does not replace fine tuning or an eye for detail at the end.
Best regards
Tim