Duke and I traded a few emails recently regarding L88 HP, and I thought the subject might be interesting to folks on this Board. I have an old Chevrolet Engineering Dept. dyno test dated 10/64 of a 427 engine that is spec'd similar to L88 specs, but actually not quite as wild (slightly smaller exhaust valves and slightly less cam). This particular dyno test compares exhaust system effects. The engine made about 510 HP at 6500 rpm WITH CAST EXHAUST MANIFOLDS AND 2.5" TAIL PIPES IN PLACE ! With 36" head pipes (headers) and a special venturi-shaped collector the motor made about 560 - 565 HP. All this from a "milder" L88 type engine, and in 1964 - pretty impressive numbers. I suspect the '67 - '69 engines did even better...
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Re: L88 Horsepower
Everett,
Interesting numbers. GM always claimed near 550-560 HP with all of the 1st design components. Looks like they were close. That would have been with the correct original 1st design L88 cam that was used in 67 and very early 68?
Was involved in a few restoration 67 L88's a few years ago and with that correct 1st design cam, they produced just about exactly the same numbers on the dyno. I think the original cam number was 3879605??? It may be included in your documentation? It would be interesting to know if that was the same cam used for the 10/64 test.
Michael -
Re: L88 Horsepower
Michael - the cam and valve specs from the 1964 test are; lift of 0.560" exhaust, 0.530" intake, 1.72" exhaust valves, 2.19" intake valves (no cam duration specified, only "Mechanical-lifter cam"). Other specs are; single Holley 4-bbl 850 cfm, transistor ignition. If I recall correctly, didn't even the 1st design L88 heads and cam have more lift and bigger exhaust valves? And then of course the open chamber heads had even bigger valves.Comment
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Re: L88 Horsepower
Everett,
Have to run for a while but when I return, I'll dig out the paperwork on the first tests of the 67 L88 so we can compare. The cam lift numbers sound vaguely familar but I thought I remember the intake lift being slightly higher.
Interesting note: The engine that was built to exact 67 L88 specs for the 11 mile red coupe only produced something like 530 HP, if I remember the numbers correctly. Not sure why the drop in the numbers.
MichaelComment
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Re: L88 Horsepower
Everett,
Still haven't found the paperwork on the early L88 but I did just happen to remember something about the valve sizes you mentioned. The smaller valves were used in the first tests because those first very early L88 engines had cast iron heads, not aluminum, which would explain the 2.19 and 1.72's.
Of interest was the fact that the original L88 testing was done as much for passenger car as it was for Corvette. In fact, the original intention was for Nascar racing in passenger cars. As late as 1965, the L88 was still scheduled to be available in the early part of the 66 Chevy model run but all that was stopped before it got off the ground. A lot of the L88 specific parts remained available for Chevy for years afterward. The L88 road draft tube, for example, was listed in the HD section of the parts book under a different number than the one for Corvette.
I think you're correct on the early 605 cam being of a higher lift/longer duration than the 2nd design 535 cam for 68-69. Will find and post soon.Comment
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Re: L88 Horsepower
I thought the original L88 cam had .560/.540 lift. I was also told that the original L88 heads went up to 1.84 exhaust from the cast iron heads 1.72 but that horsepower in the as cast configuration was the same because the L88 heads necked down just past the valve seat. From my own unported heads, I can verify that the 842 castings had a horrible valve pocket shape. The later 074 and 076 (D port) heads were far superior.Comment
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Re: L88 Horsepower
I just dug out some original paperwork on the L88 cams and there WAS an earlier version than the 67 cam. It was originally designed for Nascar and supposedly had a slightly less aggressive plot than the 67 did but that's all the paperwork had to say about it. I suppose it was a diffferent layont for a much different torque curve to suit the nearly constant RPM of a Nascar stock car that ran at a nearly fixed RPM instead of the wide range of RPM that an SCCA road race car would need.
The 67 cam, part number 3879605, was a little different than both the Nascar cam and the later 68-69 L88 cam. It had .5586 int and .5800 exh lift with 352 deg int duration and 364 exhaust. (all @ .020 lash)
The 68-69 cam, part number 3925535, was .540 int and .560 exh with 354 deg int duration and 360 exh. (all @ .020 lash)
I don't remember for sure why the change in late 67 to the 535 but I seem to remember a number of problems with valve train durability and the slightly less aggressive 68 cam may have been a partial remedy for it. I'd guess the ramp speeds were reduced a bit with the new cam.
When aluminum heads were added in place of the cast iron heads for 67, (66?) the valve sizes changed also. The exh valve was increased from 1.72 to 1.84 and up again to 1.88 for the open chamber 2nd design 69 heads.
I'll try to post a picture of a 66 427 L88 that has cast iron heads. It also has the large passenger car idler pulley so we can assume that it was going to be for a Nascar full size Chevy. If I remember correctly, it also has the passenger car style road draft tube with the strange bends at the bottom, unlike the Corvette tube that exited straight without bends.Comment
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Re: L88 Horsepower
Everett, the numbers I always heard from numerous sources including Vince Piggins were 525 to 565 hp. These were basically stock engines with dyno headers and carbs jetted accordinglyDick WhittingtonComment
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Re: L88 Horsepower
In researching the history on my 67 L88 the guys at Traco who were "blueprinting" the motor for Guldstrand ran the engine fresh out of the car and the engine peaked at 560 hp. They were apologetic that they could only get 640 hp after reworking. The engine was tested with the headders provided by Chevrolet with the car.Comment
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Re: L88 Horsepower
So if I understand correctly, it made 560 HP in "stock" factory L88 configuration, with headers in place, and it made 640 HP after the rework, with headers in place. The reason I ask is to confirm if the headers were in place for BOTH tests, as my original post was primarily addressing the HP ratings with various exhaust systems which the Engineering Dept. graph illustrates. What did Traco do to get the 640 HP? Also, is Traco still in business (I know this has been answered here before, but I can't recall)? Thanks for the info on your L88 - it is quite interesting.Comment
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Pic of L88 with Iron heads *NM*
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Re: L88 Horsepower
For what it's owrth, in January I completed the rebuild of the motor in my '69 L88. My motor did not need any radical work, so I decided to build it as close to stock as I could. All my original hardware was re-used except for cam, rods, and pistons. Unfortunately, I was not able to locate NOS examples (despite posting here and many emails that some of you who read this probably got), so I ended up going to Crane's restoration series for the cam. We put this on a Cam Doctor and found the grind to be very close to the original specs for the 535 cam. Likewise the rods and pistons were as close as we could find to factory specs, with the exception that we went with .030 over pistons. My heads/intake had never been ported and polished, so I elected to not do this during the rebuild also.
When we put the motor on the dyno after the rebuild, we got 520 HP @ 6000 RPM (standard correction to 29.92 inches HG and 60 degrees air temp) through an original set of Kustom headers that my mechanic had (which actually did silghtly better than the dyno headers). I really wanted to do some pulls with the stock side exhaust to see how much difference they made (I've heard of a 100 HP penalty), but unfortunately the small dyno room we were using would not accomodate them.
Here's a photo (with the dyno headers).
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Re: L88 Horsepower
Is it an open chamber or closed chamber? Did the power drop off above 6,000? Most that I have dealt with will make additional hp at 6,500. Noticed thermocouples in dyno headers. For curiousity were the EGT's pretty equal. There were fuel starvation problems to certain cylinders (me is a gittin' old and cannot remember which) with the intakes that had the deviders cut out. The carbs had to be "stagger" jetted to balance the air/fuel flow. If you did not, on oval track engines, the tops of the pistons did not last very long before they became major porous as in holes burned in them.
For information the F..d 427 side oilers in race trim were not making but about 540-550 hp in '66. I stood beside (can you say stupid) these engines when they were being dynoed. All the controls and guages were on a panel directly behind the Clayton dyno. I cannot remember if this was SAE corrected hp or not. Loooooong time ago. I do not posess the memory that Joe, Clem, Duke, and numberous others on the board.Dick WhittingtonComment
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Re: L88 Horsepower
Closed chamber heads. Power started to drop off at 6000, but we only ran it to about 6100 - at least that is all it shows on my sheets. I wasn't there for the actual dyno runs, so I'm not sure if it was run past that or not. I don't see any EGT info on the dyno sheets, could it be called something else?Comment
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Re: L88 Horsepower
The correct name for EGT is really exhaust gas temperature. I am curious as to why the hp fell off. With open headers I would have expected to see a little more. Maybe the carb was lean with the headers. Maybe Clem or Duke could address this more. At least the open chambers I have seen made more hp to 6,500 and some beyond depending on the level of preparedness.
Just last evening I was quoted hp #'s from a Traco prepared 68 L-71. 585 hp. Pretty stout for an engine in a street car.Dick WhittingtonComment
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