Hi Everyone,

Like most everyone else on this board, I'm constantly making changes in my engine compartment. I just removed a 850 cfm Speed Demon carb from my 502 and opted to install a brand new Holley Commander 950 multiport fuel injection system which is now up and running, but I'm now very concerned with other parts that may have worked quite well before, but may now be robbing me of performance.
Here's my current setup: Chevy 502 with Edelbrock aluminum rectangle port marine heads. Compression is 8 3/4 and I'm using a stock 502 cam as far as I know. Holley MPFI single plane highrise intake and stock GM 502 exhaust manifolds. I'm running a 3inch exhaust system with Dynomax mufflers, but the diameter backs down to 2 1/2 after the mufflers due to my wanting to run a Hellwig rear anti-sway bar. I understand that I'm bottle-necking the exhaust due to the diameter drop which I plan on changing very soon, but what kind of power and torque do you think I'm losing while using the stock 502 manifolds and the current exhaust?
You might also be wondering why my compression is so low. I bought the engine from Chevrolet like this. Someone had ordered it with intentions of supercharging and the deal never came about. I found it and grabbed it. The engine was dynoed at 508 hp at 5700 rpm and 531 trq at 3900. I don't know if the engine was dynoed with headers or exhaust manifolds? I would also like to add a centrifical supercharger in the near future, but I'm trying to get this car running as well as I possibly can right now before I open up another can of worms.
Please tell me what you think. I'm not a racer and I really depend upon the members of this awesome forum to keep me from believing everything I read in the magazines which I have been getting in a great deal of trouble with for the past eleven years.
As far as an improvement, I was instructed by a friend to find a good set of shorty headers - 2inch primaries going to a 3inch collector. I was told that the difference between full length and the shorties was not that great as far as power loss. Does this sound reasonable and would running 1 7/8 primary compared to a 2inch offer better performance? I was running full length Hooker super comps on a previous big block in this car and they hit everything they weren't supposed to. They were a trip to hell and back. That's why I'm really leaning towards the shorties this time.

If I've left any info out of this topic that would help you to help me, please let me know. I can't begin to tell everyone how helpful you've all been in the past and I look forward to any suggestions you can make. I also have so many more questions to ask.

Sincerely Grateful,

Paul

Didnt know 502 came with exh. manifolds? but they are costin you a bunch of power. As for headers dont go with anything less then 2". The diff between shorty and full length is the shorty will loose some bottom-end but will make about the same top-end power. And the 2 1/2" is killin it. Here's an example I like to use: friends 70 Chevelle, 454 - with 2 1/2" exhaust and turbo mufflers it ran 12.0@110, with a 3" system and Dynomax turbos it ran 11.5@115, and thats on a 454, there would be a bigger diff on a 502, it was around 50hp loss. Go 3" duals minimum!
Also stick a real cam in it, nothin crazy, but 240s - 250s duration works well on the street. Usually a single plane and a cam swap will get around 100HP more on a 502. Also dont forget the fuel system, these big motors like everything big, you cant just run parts that work well on a 350 (like 2 1/2" exh.)and expect them to work on a 502 - these things make plenty of TQ.
Good luck graemlins/thumbsup.gif

No doubt the manifolds are killing power.

1-3/4" is as Large as you want to go, thats a basically Stock 502" Motor.

Emphasize power in the range that you use it!

[ 06-13-2004, 09:24 PM: Message edited by: Drag Fabricator ]

From what I've read from posts on several other sites is that the show is over(expansion of exhaust gases)after the mufflers. So for a big block, use 3" up to the mufflers and the 2 1/2" tail pipes will work fine. ;)

As far as I know, GM uses 2 1/8 headers in all their dynos. Do not go any smaller then 2" plus if your blowing it later on you should be thinking ahead and going 2 1/8 or bigger headers and 3 1/2 exhaust. Plus go with a bigger cam as mentioned above.

Lee

2 1/8" alright now we're gettin brave, graemlins/thumbsup.gif but I agree with a blower they'd work well,
but I wasnt gonna say it, because someone would give a 1 1/2" hdr recommendation. ;)
The only thing I can say to top that is we tried a set of 2 1/4" dyno header
on my 502 and it picked up like a switch from 4500+rpm. But that doesnt
mean it would pick up ET at the track, although the mph would go up. :D
I guess I dont need to mention my 4" exhaust do I ? We could change this
topic to "bigger is better" ;)

Hi Everyone,

Thanks for all the replies. I really do have quite a lot more to consider than I thought. To be quite honest, I didn't think a 4inch exhaust would even fit under a first generation.
I guess I'll take a look at a larger diameter header as well as a suitable cam. If someone has a suggestion as far as cams, I'm also definitely interested in hearing. I don't want something so extreme that it loses it's street manners. I take long cruises every chance I get. My Thanks to all, Paul

Ditch the manifolds but leave everything else alone. You really dont have the compression to run a large cam, the stock one is probably the best one for your C/R. Bigger isnt allways better even when you already have a 502. D)