silverdroptop

Just had my car dyno tested today, it is an 87 Corvette.
I have TPIS ZZ9 cam, Big mouth intake, AS&M semi-siamised runners, ported plenum, comp pro magnum roller rockers 1.52,
underdrive pulleys, air foil, ported 113 Corvette aluminum heads, flow matched Ford 24 # injectors, completely stock exhaust including pre cats and main cat and factory pipes, manifolds, & mufflers and stock computer chip.
car dynoed at 234.5 hp and 315.4 torque.
I was expecting more, I know the exhaust and chip are holding it back but how much more can I expect with headers, exhaust, and cust tune on the chip?

chriswtx

Sounds like something is wrong. I would susspect clogged pre cats or main cat. Even with the stock chip, this is not any better than some stock cars on here. You definatley need to upgrade your exhaust and chip...Also was this a dyno jet or mustang dyno. You cannot always trust dynos. Some are right on the money and others are way off. Go to the local drag strip and see what MPH you are running. This will give you a better idea of your power levels...

silverdroptop

It was on a dyno jet.
I am just waiting for the track to open back up.
It is only an 1/8 mile track but I can compare to my stock times from last year.

85 500 horse

Without doing any modifications to your car, it should run (stock) 240 HP and 345 Ft. Lb. torque. So you definitely have a problem somewhere. Off the top of my head, I'd agree that your cats, since they are all original need to all be replaced with the high-flow design. You definitely need to install an upgraded free-flowing exhaust system. The stock one is restricting lots of power. A custom chip definitely couldn't hurt, tuned to the mods that you have made. A good set of headers will open up more air flow and in return, more power. I'd guess, that if you changed all your cats, added a good exhaust system, a custom chip (not one off the shelf), and headers, you should see about a 30HP increase. That doesn't include what you've already done to your car.

vader86

Stock would be 240 crank, a dynojet measures rear wheel power.
I figure you've gained about 40hp over stock, and you should have gained 2x that from all that work, so something is definitely wrong there.

Either the cam wasnt put in right, something isnt properly adjusted, or perhaps the cats are plugged, but a plugged cat is something you should notice by excess heat in the footwell. Normally, from going to stock to brand new exhaust with headers, you'd get 25hp or so. I dont know if you'll get that if somethings wrong inside.

chriswtx

could also be an incorrectly installed cam...But something is wrong. It will just take some time to find out what it is. Do you have any air to fuel ratio's with that dyno?

rocco16

But...how do you know which ones are right on the money?????


(oh, never mind, I know; the ones that give us the biggest numbers!!!)


Larry
code5coupe

88-406

Upgrade the exhaust! my L98 put down 242/331 but I had headers and an offroad front y-pipe,no cat,stage 2 TPIS chip,airfoil. I made those numbers through the completly stock TPI manifold, 48mm TB and all.

Honestly I dont think you'll see much more till you adress the exhaust and get a chip. Then I would expect you to exceed my numbers.

KM

65Z01

Right now you are building less than 300chp which is way off.

With those mods you still need to do full exhaust, ie FL headers, hi-flow cat and cat-back along with an AFPR. Your stock exhaust is really holding you back and you definitely need more fuel pressure.

Check out the "L98 Mods" thread on my site and you will see what is possible with those mods.

Also, what was your A/f ratio when you were on the dyno? It should have been around 12.5:1.

silverdroptop

Thanks for the replys
I am running an adjustible fuel pressure regulator set at 42psi which is where Rich at Cruzin Performance flow matched the 24# FMS injectors at.
On the dyno it was running just under 13:1 with a flat ratio we turned the pressure down to about 40psi and started to get spark knock so cut that run short and put the fuel pressure back to 42psi and the spark knock went away.
also tried timing settings of 6 8 10 & 12 with 8 & 10 giving virtually the same results so we left it at 8.
I have not checked the TPS setting since I got it running again but dont think it moved any.
I am also trying to find a local shop to run a true dual 2 1/2" exhaust system from the factory headers back.
I will see if that helps and then try to get headers in the spring.
Also should be sending my chip to ski-down-it within the next week.
Any one running a true dual exhaust?
What are your thoughts on it?
What mufflers are you running?

silverdroptop

I have found a local shop that will drop the factory exhaust and install a true dual 2 1/2" system with Flowmasters or any other muffler I want to.
I plan on doing this running off the factory headers for now and eliminating the 3 cats.
What are your thougts on this?
Do you think this will help find some of the missing power?
Thanks

vader86

You will find some of the power, but its the factory manifolds that really kill power, the openings are really small.

88-406

Since you don't want to put headers on right now, you may find decent gains by installing the off/road front y-pipe which will bolt right up to your stock manifolds.

If it were my money, I wouldn't spend cash on custom pipes that were bent to adapt to my stock manifolds.

km

TA

Your numbers are [B]way[/] off from where they should be. Many guys here are making a lot more power with stock head/cam L98s. I'd say you are need of exhaust and a custom tune. Your tune has gotta be way off with the cam, ported heads, 24 lb injectors, etc.

rick lambert

Check out this web site for true dual exhaust. http://www.madvet.com/shop?frame=3.36.928

You can put headers on and a totally stock exhaust, cats etc. But if you're really looking to gain with headers, the stock exhaust is still restrictive, but with headers and true duals you'll notice the difference.

silverdroptop

I just wanted to post an update as to my approach to narrow down the problem with the missing power.
I sent Jesse (ski_down_it) a prom today to reprogram.
I have to give Jesse credit here, He has been very helpful so far and has answered every question I have asked him so far even as far back as a couple months ago when I was getting parts for my combonation together.
The 2nd thing is I am going to try a true dual 2 1/2" exhaust system from the factory headers back eliminating the 3 cats for now and exiting into Flow Master mufflers.
I hope to get the exhaust installed this weekend if everything goes well and when I get the chip back I will have it dyno tested again and see where I stand.
If its still not where it should be then I will take the front back off and recheck the cam timing but I dont believe it is off.

65Z01

You should pick up around 25chp from the exhaust mods that you have planned. BTW, assume a DT loss of 17% for an A4 when calculating CHP from RWHP at the dyno.

Your fuel pressure was likely 3-4psi too low for those mods. A good target A/F is around 12.6:1. After you get the new exhaust on bump fuel pressure to around 48-50psi (idle & no vacuum) and get another dyno pull. Then you will know exactly how much the exhaust was worth.

REDC4CORVETTE

Just a ? does anyone know if the L98 has a limiter in the chip like the 94 and later cars do.
My 94 would not MPH or make much power until I took the rev limiter off.
I have an L98 and the MPH is just not there.
95 no juice to a max of 103 with a 100 shot of juice.
The car goes to the 3/4 mark at the track and just makes ahumming sound.
Not to hijack your thread but maybe someone has the same problem .
I think it's the chip.