i got a 357 with 230/236 cam with 1.6 rockers, ported/polish afr 190cc heads/hei distributor/hooker shorty headers.. edelbrock 750cfm carb. holley mechanical fuel pump.i went and got dyno'd today and it ony pulled 288.83rwhp 306.4rwtq.. these numbers should be around 350rwhp.. whats up with this.. ok on the dyno it shows max power at about 5200rpms but it completely stops and drops off to about 150rwhp and then rises back to about 280 at 6,100rpms. i'm thinkin fuel or ignition related maybe.. what do you guys think.. sometimes its got a miss at exactly that rpm by the way. but never 3 times in a row.. what do you think ?

corey

 

you have an afpr?

 

This story remids me A LOT of another board memeber about a month ago (advanced tech board) who was having a huge drop-off in a limited RPM range on his engine. Long story short, it was a problem with his MSD setup. Not really a problem with the box itself, but with the dial-retard system he had wired up incorrectly. He chased his tail for MONTHS across 2 different motors with the same parts on top of them before he finally diagnosed the problem dead-bang.

Long story short- if it's in a limited RPM range it IS DEFINITELY ELECTRICAL IN NATURE, and almost certainly ignition-related. There is nothing mechanical (inside the engine or fuel delivery) that can cause problems in a limited RPM range and then recover again in the upper RPMs. Only electrical problems can do this.

I'm sorry that isn't a SPECIFIC suggestion but if you keep this advice in mind, you will have a good chance at diagnosing the problem more quickly.

 

I don't have an msd or any type of aftermarket ignition, just a new HEI distributor/coil/cap/rotor. Think that could be the problem? maybe I need to get a msd??


Thanks
Corey

 

It would help some by getting an ignition box.

Did you change jets and timing on the dyno?

What was the afr?

What is your exhaust system and compression?

 

The first run was horrible at 240rwhp, i moved the linkage for the accelerator pump to recieve the most gas and it jumped to 288rwhp. I messed with the timing a little but it didnt reallie gain much. No the jets are not changed its just a new edelbrock 1407 750cfm mechanical secondaries with electric choke. Im not sure of the afr as i dont have a gauge. My exhaust consists of hooker shorty headers with slp loudmouth / no cat. The Compression ratio is 9.5:1 with speedpro forged pistons. Its a Piece Help ME!! I dont know what the hell to do .. lol.. 280rwhp is embarrassing for my setup.. thanks

corey

p.s. i only have a perfomer rpm intake i need a victor jr. but i dont have enough hood clearence still working on getting a cowl hood.. ANYBODY GOT ONE FOR SALE ? ? ?? !

 

when you go get your car dynoed, don't they usally have technicians there that tweak your car a little bit to get the most of it? But yea i would say there is a big problem cause those numbers don't sound close at all, but i don't know enough about this stuff to tell ya whats wrong, but whatever you do, good luck!!!

 

i didnt get it dyno tuned i just dynoed it and messed around with it myself.. i knew it wasnt running right so i wanted ot hook it up real quick just to see what it pulled.. as you can tell there is spots during the dyno the machine wouldnt even pick up its just blank. and if i shift at about 4,000 it feels quick than going to 6100rpms lol


heres a pic of the dyno..

sorry i had to take a picture of it with digital camera as i never had the need for a scanner before lol

http://www.geocities.com/fullcollapse69/crappydyno.jpg

for some reason on my computer it wont work unless you type it on a new window.. i dunno prolly just my retarded computer but if it dont work try that.

corey

 

any suggestions ??

 

An out of the box carb needs to be tuned. I know holley's, don't know edelbrocks though. I'm sure it needs more gas on the secondary side. You will have to read your plugs to make changes. Go up 2 jet sizes and make another run, or go to the track and make a pass. If it goes faster, makes more power, then keep going up in jet size until you slow down, and the plugs get some color on them. Right now I'm guessing that they are white. Ask the dyno place if they have a wideband o2 sensor to hook up in your exhaust.

Some longtube headers would help power some also.

 

anybody know what kinda jets these things come with stock ? ?

corey

 

You will have to order the correct calibration kit for that carb. Look at summit or the edelbrock website, or call the edelbrock tech line, they should be able to help.