Jay M

You may have seen this post last week http://forums.corvetteforum.com/zerothread?id=764700

Since then I have added Thorley headers, 3" exhaust and Dynomax mufflers.

I dyno'd the car again today and only gained 28 HP.


This is last weeks run and this weeks run on the same page. It seem like I should be making more power. I took the air cleaner off to see if that was causing a problem, but it made no difference.

I plan on taking it to a dyno shop that knows carbs next week, maybe he can figure it out.

Here's the engine dyno chart for reference:


Any other ideas?

BTW- the new mufflers sound pretty awesome.. downright intimidating. :) The neighbors are gonna hate me.

~Jay

Les

That's a decent gain but I"m wondering if your fuel line might be the problem. When I bought my cam from Ultradyne, Harold Brookshire strongly advised stepping up to 1/2" fuel line. Does your car pull strong through all gears or does it start nosing over at high RPMs in 2nd gear or higher? That's what he said would happen if fuel delivery wasn't sufficient- you're right about at the 500 HP mark & that was a ballpark number he threw out for when it's time to move up to 1/2" line. Just a thought- good luck.

Jay M

Thanks Les,

It feels pretty good throughout the range. It doesn't feel like anything is wrong. It doesn't sputter or have any misses. In fact wouldn't have known anything was wrong if I didn't dyno test it.

I have an appointment with a good dyno tuner for next week. All the guys in town only tune fuel injected cars. Hopfully this guy can figue out the problem.

~Jay

Budman68

Did they run a wideband O2 during the run? That will tell alot. Please post that if possible. Clutch slippage, torque convertor silppage, tires slipping on the dyno. That is a huge difference, but still alot of power to the ground.

Les

Sure Jay, I'll be looking forward to Part 3 results. I'd also love to hear what your 3" system sounds like- did you go w/ Ultraflos?

1Bad69

whats your fuel pressure like at WOT? do you have a guage hooked up?

Jay M

Budman,
They didn't use the wideband Co2. That was $40 extra. I just wanted to know how much power it produced. My eyes were watering so I think it may have been too rich. If there was clutch or tire slippage, would the chat be as consistant as it is?

Les,
The new exhaust is a little loud. A different kind of loud than the 2 1/2" with Flowmasters. The Flowmasters are loud all the time even under WOT. They also have a horrible resonance at 1500 to 2000 rpms.

The 3" with DynoMax Ultra Flo mufflers is very deep at idle with occaisonal crackles. At cruise speed it settles down a bit with slightly less resonance than the Flowmasters. At WOT it is awesome... like a full on race engine! A sound that says "DON'T F*** WITH ME!!!!!" LOL ...Pretty cool :)

The Thorley headers are very quiet. I don't hear any of the rat-tat-tat that that people complain abou twith headers.

After I get to close to 400 rwhp, I may put stock mufflers on and learn to drive like a normal person and enjoy quiet cruising...you know...act my age ;) . But for now I feel 18 again! Enjoying cruising through parking structures and setting off car alarms!

~Jay

Jay M

No, but that might be an issue. I also still need to verify that the throttle is opening all the way.

How would low fuel pressure affect the dyno results? would it be an even drop all the way across?

~Jay

1Bad69

well my pressure was at like 2psi on the dyno runs...put in an autometer guage under my cowl so i could see what was happening while i was driving...same thing...so i put on a 130gph mexh pump with a regulator and the pressure now stays at 6...i guess it is safe to say that you would be starving your engine of fuel?

seemed to run a bit better after the pump change...picked up a bit of torque at the wheels..HP was roughly the same...

toddalin

We also have and love the Thorley headers with the Ultraflow mufflers (2-1/2") and we also love the sound. :iagree:

When I changed the stock rams horns to the Thorleys, I told my wife that it would get louder. It got quieter and she was extremely disappointed as she wanted it loud! The metal on the Thorleys is so thick, the sound doesn't get through or resonate the header. Definitely a quality header.

Budman68

Rich = less horsepower. Jet your carb secondaries down.

427Hotrod

You're heading the right way. I'm sort of curious about how quickly it falls off on the top end. After 5200-5500 it is going down fast. That's where HP is going to come from...how long it hangs on and makes power.

From looking at the TQ curve, it appears to be a relatively mild cam. It makes great TQ down at low rpm. What kind of cranking compression does that dude have?

Total timing?

I would suspect valve float or lifter pump up (is it solid or Hyd roller?) but I don't see the characteristic breakup at the top end. It just noses over.

A/F ratio check is needed. Might be low fuel pressure..maybe. But another sign of "running out of air" is when the mixture keeps getting richer. Vacuum keeps increasing as RPM goes up and airflow is restricted. I doubt your heads are much of a restriction, but that ole Torker II ain't the best thing out there. I know you're hood clearance limited, but it would be fun to try a 2" or even a 1" spacer on it to see the effect of increased plenum.

For sure make sure carb is opening.

Keep working on it..you'll get there! Those ponies are hiding in there somewhere!


JIM