Engine performance upgrades....

[Ala75Vette]

I'm a relatively new member to this forum, and I've really appreciated hearing all the things members are doing to enhance the performance of their C3s. I have a '75 350 L48, and, as probably most of you know, the '75s were at the low end of the C3 hp curve as Corvettes go. I want to do some 'minor' top half enhancements to my engine -- someday maybe I'll get a 383 stroker, but it's not in the near term plans -- but I'm not sure how to proceed. I gather getting new aluminum heads and a performance cam would be a good thing to do, but the mechanic I use wants me to get flat head pistons and a host of other engine internals. From what I've heard on this forum and heard 'around' the Edelbrock Performer RPM heads are the best, and Eckler's has a small block 260 High Energy cam that looks like about what I'm looking for. But the Edelbrock heads may be overkill for what I want, and I'm not sure what all else I should get along with heads/cam, anyway (push rods, rocker arms, etc.). This is almost certainly not a 'new' topic, but any advice ya'll can give would be appreciated.....I'd like to spend no more than $3K, but $2K is more realistic, and I'll do most of the labor...

 

[Dave L.]

crate engine?

did you consider a crate engine.for 2-3 thousand i can think of several decent crate engines.most come with some type of warranty and all new parts.that is the route i am going to take down the road.when rebuilding you are talking down time,dealing with machine shops and getting the right combo.my mechanic freinds all like the crate motor deal.just my $.02.:s

 

[rpounds]

First of all, welcome to the CAC. I'm very glad to see another '75 L-48 on the forum.

The performer and performer RPM heads are basically identical, the main difference being the performer heads having provision for exhaust gas recirculation. If this is necessary for retaining the smog systems in your vehicle (depending upon state smog laws) then, by all means, don't hesitate to go with these heads. Bear in mind that there are a number of head manufacturers out there. Edelbrock makes a great product, but there are others to consider, such as AFR, Dart, etc.

If you don't mind, I would like to point out a few things to keep in mind. You didn't mention your final drive ratio. I will assume that you are running the stock TH400 transmission and 3.08:1 differential.

In order to keep from being disappointed in the performance, I would stick with heads that have a rather smallish intake size. Something like 170 CCs would be good. With a higher rear axle ratio, you want to keep your low end torque up. The smaller intake runners help cylinder filling at lower RPMs, which translates into low end torque.

Stock '75s have a horrendous compression ratio. They came with 76cc combustion chambers. Be sure to select heads with a 64cc combustion chamber. This will raise your compression ratio by one full point . . . maybe more. You'll like the results of that.

Next, be very careful of the cam selection. This is the area that will disappoint you the most. Too much cam and you will lose your low end . . . again, that is death for a high rear gear ratio. You launch will be sluggish and you will end up being disappointed. Think about what RPM range your engine normally lives in. With a high rear gear ratio, you need most of your power/torque between idle and 4500 RPM or so. So select a cam that gives you the most oomph in that range. Check out the Summit 1100 or 1101.

Make sure that you use new lifters. I would always recommend new pushrods with new lifters. With new heads, you may also need new pushrods of a different length than your old originals.

Roller rockers are not completely necessary, but are a nice benefit.

To help your launch, think about a mild stall converter . . . maybe a 2200-2500 or so. You'll be surprised at the difference.

I hope some of this helps. I'm no expert by any means, but I've been there, done that with my '75. Went through a lot of money and disappointment before I found a combination that I was really happy with.

Good luck,

Ron

 

[Bullitt]

Ron has given some excellant advice. Burgular's advice about crate engines is too, as well. Just to let you know, that camshaft that you are looking at in Eckler's is made by Comp Cams or Crane. I can't remember which one, right now. So, talk to their tech guys before deciding on a cam. Things like rear gear ratio, compression and weight of the vechile are things to factor in, when selecting the right cam. For general FYI, a lot of Corvette retailers sell stuff made by other manufacturers. The difference? You end up paying more for things in "Corvette Catalogs." So it pays to shop around.

--Bullitt

 

[Ala75Vette]

Thanks guys! The car I've got has a non-original 4-speed, but from all appearances it was acquired from another '75 or so (according to the vette shop here in Huntsville). I'm relatively certain my rear end is the stock 3:08, also, based on some speedometer work (gears in the tranny) I've had done recently, and the fact that I'm pretty sure it started out an automatic (which had the 3:08 rear end). Thanks for the suggestions, I'll let you know which way I go.....

 

[Ganey]

Ala75Vette

See what many refer to as my ex. topic:
http://corvetteactioncenter.com/forums/showthread.php?s=&threadid=4373

W/ ex. fixed & a 4spd., Comp Cams 268H is min. rec. cam if you drive hard.
That will get your car running like a CORVETTE !
Many good heads are available.

:cool


PS Comp Cams 260H is min. for stock auto.

 

[Ala75Vette]

Thanks, Ganey !!!!! Great post on exhaust systems..... I learned more (truth) in ten minutes than I've heard from so-called 'experts' in the past several years. This has got to be the best vette (and automotive) online forum around.....