After my engine rebuild my first trip to a Chassis Dyno was a bit of a disappointment. Max horsepower was just over 290 and max torque
was almost 370. I kept the engine looking stock with stock intake and
exhaust. I think thats the limiting factor. I dont want headers or a new
intake. Maybe a less restrictive air filter or better flowing mufflers.
you see the details on the rebuild and dyno sheet on my webpage, but I expected better numbers. Another forum member posted 330hp but had
a high rise intake and headers.
:confused:

 

Pat, the air cleaner and mufflers won't help an L36 in any way that you can feel "seat of the pants" :( Been there, done that.
290 at the rear wheels is good for a close to stock L36! You're actually getting close to the 390 at the crank rating from GM.

I don't think you can get much more power out of it without headers. They would make a bigger difference than anything else.

 

Pat you went too lite on the cam. You need more but maybe lift limited now depending on springs used and retainer to seal clearance.

There might be a Crane available that will bolt in if you or your machinest remembers what everything was set up at in the way of springs/retainer to seal clearance.But then things start to multiply there also when trying to use a Qjet that is not modded by a carb shop.

I bet it is a sweeter engine overall though as compared to the factory cammed L-36.Do you agree?


[Modified by mountainmotor, 7:40 AM 3/22/2002]

 

Thanks Guys,
I went easy on the cam selection due to all of the vacuum accesories on my car. The same forum member that posted the 330hp this year said that he
got 290hp last year with headers, but an different intake. :confused:
Overall I am pleased with the rebuild and the car is running great.
I just dont see how the engine cannot be stronger than a stock L36?
I'm guessing that GM's rating of 390 was over rated!

 

Carb rebuild... Timing curve... maybe fedex can fit your car in their truck and take it to lars... :jester

Actually i wonder if you could find a GM high perf. intake and drop it on... it'll still say GM, and paint her orange

Could port and polish heads and exhast manifolds...

Just out of curiosity did you run a valley pan and crank scrapper? How about a Heat preventative gasket between intake and carb? How about mufflers? Are they Still stock?

 

Pat,
If you wrap them manifolds that you have in the car that will yield you some 20hp-30hp depending on the ambient conditions. This might be in violation of your stock look though so I'm not sure if this is the right way to you to go. But it's definitly an easy hp uppper. :D I have dyno sheets from Windsor Automotive to prove the hp increase but the thing was he was using wrapped headers. I'm sure that wrapping manifolds will be good for a couple.

 

The engine is stronger! The HP rating in '69 was gross but the chassis dyno is using SAE net which was instituted in '72. The SAE rating is roughly 20-25% LESS than pre-'72 HP ratings. So using SAE net, your engine would rate around 300-310 at the flywheel. Factor in the drivetrain loss of .2 on the chassis dyno and the stock motor should rate somewhere around 250 at the rear wheels. If you posted 290, that's a 16% gain!

On the intake & headers, those two items along with heads & cam are the secrets to HP & TQ. If you are unwilling to upgrade in those other areas, you will be hard pressed to squeeze any more out of your engine without a power adder (i.e. N2O, blower, etc.)

Mark

 

Mark, this isn't entirely correct. Unlike the HP ratings used back in '69, the chassis dyno has always been "net". It can only be net because you can't chassis dyno a car without a drivetrain and accessories ;) If you chassis dyno'd this car back in '69, it would give you the exact same results it gives today. No 20-25% correction is necessary.

As far as I can tell from my car's 1/4 mile performance, the stock L36 was putting out around 270-280 net HP at the crank. Heck, the thing runs out of breath at 5200 rpms, so how much could it make by then? IMO, the 390 rating was a fantasy, and 340-350 gross is more realistic.

 

Pat, I checked out your rebuild page and I noticed you have an Edelbrock #1901 carb. Have you modded the carb at all? The jets and rods that come in the carb are very tame. (narrow jets, fat rods! :) ) You should be able to achieve noticeable gains in performance by changing jets and rods. MJ

 

Change to a Demon carb........MORE hp.

 

I'm with ZD75BLUE - carb rebuild / recurve kit.
Big Blocks are pretty good w/ air flow - so your heads & exhaust are fine....
Also, you can pick up extra HP with 1.71" roller-tip rockers.
I'm looking at getting the Crane - steel w/roller tips for mine :D
That - with a little bit more lift from a slightly more radical cam should give you the 'boost' you're looking for ! :cool:

 

Thanks again everyone.
Mnjack,
The carb is new out of the box with no mods. Initially the linkage was not opening at WOT, but I have fixed that problem. What parts would I need
to order to improve the carb. Which jets and rods and is this a diy project?
Also I was told that the stock air cleaner is fairly restrictive. Anyone have
input on that K&N lid/filter?

 

To reiterate what Mountain motor said "you went to lite on the cam" I do not believe you are going to see much of a HP gain untill that situation is dealt with. Motors are big air pumps, more air fuel mixture in, expent gas out, more power. If the cam does not allow for much of either, like in your case, then the other power adders won't have much effect because they are based on the more air in and out law.

Even with the power everything you have there are several bigger cams that would give you a marked improvement. After that you can go after the headers, intake, carb.

 

Pat, there have been a few threads recently about setting up Qjets in general and the Edelbrock #1901 in particular. Lars is the expert and he has given us tons of info and time. His carb tuning paper and data are available at the corvettefaq.com website. He has also provided detailed instructions for carb tuning (along with instructions for "technical procedures") . The secondary rods are the easiest thing to change. The hanger is held down by a tiny screw on the top of the carb. Changing secondary rods is about the same level of difficulty as changing the air cleaner :). You will need to take the carb apart (or at least take the top off) to change the primary jets and primary rods. This is not very difficult especially with detailed instructions. The well-illustrated book by Doug Roe is a big help also.

Your Edelbrock #1901 Qjet comes with .69 primary jets, 36B primary rods, and DR secondary rods (DR rods have .057 diameter tips).

Your original Qjet #7029215 had .71 primary jets, 45 primary rods, and AX secondary rods (AX rods have .0397 tips).

Your rebuild bigblock has a carb that is ideally set up for a 350 pickup truck! (just an approximation on my part :) )

When I put my #1901 on the vette I noticed an immediate improvement in startup and idle, but less "umph" when I floored it. I just rebuilt the old carb and will swap out the jets/rods on the Edelbrock real soon.

I would be interested to see what Lars would recommend for your rebuilt setup. Perhaps more aggressive jetting than stock would be appropriate, but stock is usually a good place to start. I just ordered some rods and jets from GMpartsdirect.com jets + primary rods + secondary rods might cost you $25 - $30. You could get equivalent or better results with a new Demon carb, but it would cost a lot more, plus I am not even sure it would fit under your hood with the adapter you would need to use. Why not at least explore the potential of your existing carb first? People have also given rave reviews to his distributor kit (as in, recent post estimated 50hp gain!!!) but I havent gotten around to that yet.

Hope this helps, but you should really get advice on this from Lars! :)

(Also, I am not disputing any of the cam advice you are getting above, but rejetting your carb is a fairly simple operation) MJ


[Modified by MNJack, 10:49 PM 3/22/2002]

 

Can anyone give me some cam recomendations that would be better suited to my engine. Preferably from Comp Cams. I will need adequate vacuum for power steering and power brakes.

 

Sometimes it's a matter of practicality. Your engine will work just fine and get you where you want to go. Adding hp for the sake of adding hp can get expensive and you really have to ask yourself what it is you want. Do you want a 600 hp full blown racing engine that shakes when it idles or do you want a driveable Corvette with plenty of power for daily driving....or somewhere in between. It's a tough decision on where to draw the line. If you have a big block, you do have the basic component to push that 600 hp. Do you really want to spend the effort, time and money to get what you "think" you want? The more hp you have, the less driveability you'll have. Along with that extra hp comes a heavier clutch, special gas and on and on and on. I think your quickest, cheapest and easiest "fix" is improving the breathing of your engine. Carbs, headers and air filtering system aren't that expensive. You can also go for the latest hot set up in ignitions and you'll be where you want to be....maybe. But, you're probably talking a thou or two to get all this done. Good luck in your decision.

 

You probably did not see my engine rebuild page.
What I want to do is make the most of what I already have.
I want the engine to remain looking stock. I would be willing to do a cam
swap if it will make that much of a difference with stock intake and exhaust.
I will definitely do some mods to carburetor as mentioned above and
also the distributor upgrade.

 

Pat, cam is a good one. I would not change it out. This is a Ganey recommendation for my L-36 set-up. Intake .224/exhaust.230. Lift isn't real high (low.500's) but the stock intake is done by 5300 rpm anyway.

Your main problem right now is your carb. Had a 1901,it is set up from Edelbrock as a compromise at best. Lars did some work on it but it still isn't as good as an original. I finally got Lars to re-jet another Q-jet from an early '80's truck and that was the ticket! Easy seat of the pants 50 horsepower! Now I must change to electric fuel pump as it's suffering starvation at high rpm's (4300-5500).As mentioned, big block is a big air pump!

Not sure what kind of distributor you have but all advance needs to be in by 3000 (approx. 36-38 +/-).

K&N airfilter maybe good for a couple horsepower. I use the standard K&N kind, not the one that acts as a lid.

My next step is Hooker Super Comps (1&7/8 primaries) bought directly from Jet-Hot Coatings. This is hopefully where I realize the full potential of this motor.Also, add a Dr.X X-pipe directly behind the trans. crossmember. 2&1/2" exhaust with Dynomax super Turbos or Flowmasters with 2&1/2 inlets AND outlets (will need a piece of 2&1/2" polished stainless for exhaust tips. This is available from custom shop down her in FLA.. Let me know if they can't find any wher you live).

Summary, IMHO: Good Cam selection for your motor/compression & rear gears. Need different Q-Jet or at least have that one worked on by Lars. Distributor curved properly. Exhaust work as stated above. Finally, that 3.08 rear gear is not the best for the "stop-light Gran Prix". 3:36. 3:55 or even 3:73 would improve acceleration.

One question on those heads. Did they have any problem stuffing those valves in there without shrouding the valves?

Regards,Mark


[Modified by marky mark, 1:32 PM 3/27/2002]

 

MY 66 L36 , stock cam , 308 rear gears turned 13.7 et @ 102 MPH,,,,Oldies day at NE dragway ....following mods, Alum Endlebrock heads , 780 Holley, wieland alm high rise, MSD dist & ing, MSD 1.72 rollet tipped rockers,...I had no traction in first gear 2.6 60 foot times .....I will be going with Comp Cams XE 262 CAM , the opreational range is 1300/5600 rpm with a 5800 rpm redline......not a bad et for a 9.5 compresion ratio 308 street driver :) :flag

 

Thanks Mark,
You can see a photo of the bigger valves seated in the heads on my engine rebuild page. The photo was taken before they cleaned up the chamber edges.