I recently bought a 1991 Corvette from a forum member. He had purchased from his uncle so he couldn’t really help me with issues I was having early on. When you buy a modified vehicle you should be ready to face issues. The car is equipped with AFR 195 L98 heads, Accel Superram intake, Comp 218/224 cam, 1 3/4 headers. The car had been mail order tuned and would not pull/rev past 5000 rpm. Fuel pressure was set very high and the actual chip from PCM NC was not even installed. I checked basics like fuel pressure, valve springs and even changed to Bosch 30lb injectors from Accel 30 lbs. That of course meant pulling the plenum on the Superram which actually was a good thing as it had vacuum leaks. Finally had the car tuned by Henderson Performance Technologies in New Braunfels. Results were disappointing to say the least. 279 horsepower and 369 lb ft torque. The car was actually running pretty good but the horsepower peaked at 4300 rpm. The low horsepower peak had me looking for other issues. I found that the lower gaskets for the runners on the intake were for a stock tuned port and were smaller than the SR runners in addition the intake to head gaskets were smaller than the AFR ports and had silicone globs protruding into the ports. I pulled the intake to fix these issues and decided to check the camshaft position with my degree wheel. Believe it or not the camshaft centerline was in a 90 degrees atdc. It turns out that the lower timing chain gear was off one tooth which is 16.3 degrees. Sorry for the long post but it’s a lot to explain. I have fixed the issues and re-dynoed. Cam is now in at 109 degrees .For fun before I post the results let’s see some guesses on what the new numbers are. I was guessing/hoping for 40-50 horsepower more and similar torque. Let’s hear some numbers and explanations all in the name of learning. I can tell you it had a bit of a rowdy idle for the size of the cam before. Correct cam timing has smoothed the idle. All comments welcome.

 

Brother, I've gained wealth of information from knowledgeable members on this forum. My posted are intended to help contribute to the accurate information on the site. Therefore, I really can't make an educated guess on power increases as a result of your cam mis-installation and/or the gobs of silicone in the intake ports.

One thing I would suggest on a build like this: Once the engine is assembled properly, install a wide band O2 sensor in the exhaust to monitor that your AFR is in-range for max horsepower and performance. And to ensure reliability, drivability and longevity.

 

I too have learned a lot from forum members and appreciate learning from the experiences of others, good and bad. Thanks for your reply. The dyno sheet displays the Afr but I do have plans to add a wideband gauge in the future.

 

Original dyno sheet with incorrect cam timing

 

So, good parts thrown together is worse than average parts working in unison. Looks like your upgrades were thrown together.

Based on what you found and fixed, especially the cam...My guess is 325HP at 5500 RPM and 375 ft/lb at about 4K

 

good fixing! 330 HP

 

So true!
Thanks for the guesses. I will say I was surprised by the final numbers. Let’s get a few more opinions and I will post the final dyno results.

 

I will post final dyno sheet around noon today. I wish more forum members would take a shot and maybe share some similar experiences of trying to solve issues of a poor running acquisition. It can be disheartening to purchase a car, ship it across the country only to have it run and or drive badly.

 

Pure guess on my part but I say 350 hp and 380 torque. Your post unfortunately reminds me of the many years Ive been in the hobby, 50% of my time was fixing POs "work".

 

what size AFR heads ?

 

Compression ratio?....How about 345hp/405lbft

 

331/382

 

Final numbers

 

Thanks for all the guesses. Heads are 195cc with 64cc chambers so around 10:1 maybe on a 350 ci?

 

Now let's see the trap speed to see if there dyno numbers are accurate.

Joking aside, that actually seems a bit high to what I'd expect... but also not out of line. Auto or manual and what gear was the pull done in?

 

Manual and 4th gear I assume. Unfortunately the closest track to me shut down so Texas Mile will probably be the easiest way to confirm the actual horsepower although I do have a Dragy.

 

I also know that HPT/Corey Henderson is well known and respected when it comes to C4 ZR1’s and custom tuning in general. But either way I was more interested in the difference between the first and second dyno numbers. (Same dyno of course) I will say that the numbers changed mainly from the cam timing but also to a lesser extent from the correct intake gaskets and I did add an underdrive crank pulley when I put it back together.

 

Well, I got both RPMs spot on.

 

Street port or Race (competition) port heads? How much spark advance did it like?

 

great job ! congrats
superram air leaks sucks ):

369hp at wheels is impressive or is it calculated at crank ?

i have same parts as you on auto except for the most imprtant parts, heads !!! (hope 1 day)

what about your lower intake is stock, ported stock, big mouth, I sent to port bigmouth intake for the afr195cc

are you using 1.5 or 16.rr ?

tb ? 48, 52 or 58 ?

regards