Hi!

I'm looking for some credible research or paper concerning the true horsepower of this legendary 1969 ZL1 all-aluminium engine. The factory specified ~435hp sounds way too low and there are some sites that specify the power being around 500+, nearly 600hp.

Is there any credible research made concerning the true output of the engine? If so, any advice where to obtain it?

Reason for asking is our (Finnish) legislation...we can tune any C3 up to the horsepower rating of the most powerful C3 and old SAE gross hp ratings are further toned down by a factor of 0.7. In this case the most powerful C3 would be ZL1, but the factory spec 435hp would allow legally only 0.7 x 435hp = 304.5 hp I'm looking for some proof that the engine had more power and thus, try to crank up that legal limit

-JJ-

 

The story I heard on the ZL1/L88 (same motor, just the ZL1 had the aluminum block and heads, think the L89 was the L88 with aluminum heads only) is that at the time of production, the insurance companies were getting very nervous insuring high horsepower cars for the street. It seems people tended to wreck these cars more frequently, go figure.

The GM Board of Directors was also concerned with this and Zora feared he would not be able to build the motor if he revealed the true power. What he did was tell the board that the motor did indeed develop 435 hp at the RPM listed, but that RPM was down in the 4-5K range. The motor obviously was capable of much more.

I have heard of the same 600hp figure you have and seen it in some books as well. Unfortunately, I think you might have a hard time convincing the government that GM was lying at the time and they should accept your word over the 'published' specs.

Good Luck though.

 

GM rated the early L-88s at 430 SAE gross horsepower at 5200 rpm. That figure was later carried on to the second design L-88 and ZL-1, but I'm not sure I've ever seen any GM documentation that shows that they ever put a published rating on these engines. If they had, it would most likely have remained at 430 horsepower.

I've posted the following information before so I know it is in the archives somewhere...

There is a quote from an engineer assigned to the project (I don't recall the name... I can post it later or you can check my previous posts on this subject which includes the engineer's name) who stated that every ZL-1 engine that they tested went out the door between 500 and 525 SAE gross horsepower. I find this figure reasonable for a factory assembled engine. Now with some cylinder head clean up... Valve seat work... General attention to detail in machining and assembly... I'd say you're looking at another 50 horsepower or so under optimum conditions. But if you're asking what the output was from the factory, the 500-525 SAE gross horsepower figure sounds just about right.

For reference, Wayne Walker put the engine for 1969 Corvette #29219 (the well known Daytona yellow ZL-1 Corvette) on the dyno when the car was first restored... I recall the horsepower to be in the 523-525 range (the article appeared in Corvette Fever way back when). Another dyno run of a second design L-88 (basically a twin to the ZL-1 with the exception of the aluminum block) was in the 525-530 range if I remember correctly (also a Corvette Fever article).

Sounds like the engineer knew what he was talking about...

Regards,

 

I tried to find the info you were talking about from the archives, but without any luck. If you could post the info here, it would be greatly appreciated.

Any idea where to get that Corvette Fever article online version?

Also, I remember seeing some website, where an ZL1 engine was restored to factory specs and then ran in the dyno...I remember that SAE gross horsepower in that test was somewhere around 523hp. Too bad I do not have the link to this website anymore Anyway, the engineer you were talking about, he really knew the truth then.

-JJ-

 

I read the same corvette fever article,just cant remember which issue.

 

If you look at the 1969 BB horsepower ratings, I believe you'll see the L88 listed as 430 HP and the engine for the 3X2 BB (that you could buy with virtually any accessory) was 435 HP (was this the L89?)

The purpose of this was to thwart the person who just wanted to buy the highest horsepower Corvette. The person buying the 435 HP car was actually buying the second most powerful engine. The L88 by far produced the most horsepower. It took careful reading of the engine specifications to see that the L88 was rated at a very low (relatively speaking) engine rpm. At red line, I thought I read somewhere that the L88 was 550+ hp from the factory. Anyhow these are somewhat notional numbers. Someone who knows exactly will probably contribute some accurate numbers.

 

You''re right, the 435 was the tri-power version ad the L-88 was the 425 I read the same story regarding the rationale for rating it lower.

 

Can you play the same game GM played and put a rev limiter in that keeps the rev's down thus keeps your hp readings low? Number of other ways to keep the hp down: a tiny 2 barrel carb, retarded timing, exh inserts that almost block the flow, etc.