poncho_1119

Greetings!

I recently purchased a 1975 corvette convertible with a the standard 350 engine (non L82). As you all know, the 350 that year put out a less than impressive 165 HP. My question is, what are the steps to getting this engine to the 330 or 350 HP of the earlier C3 models? Just wondering how much work I have ahead of me.

Thanks!
James

Stewart's74

1) Exhaust (duals)
2) Headers
3) Intake
4) Cam

These 4 things can easily get you close to 300.

poncho_1119

Thanks! I have dual exhaust now, but I believe the original catalitic converters are still in - do these need to go away? Any recommendations for new exhaust, headers, intake and CAMs? Should I try to keep these parts original corvette parts?

Stewart's74

I could be wayyyy off here but I think you have a 2-1-2 exhaust set up. If you have no smog restrictions in AZ ditch all the emissions stuff.
There are literally hundreds of options for you as far as intake and cam go.
Most members here use an Edelbrock performer or performer RPM intake. I personally like my 268H cam, but I also went with a higher than stock Stall converter.
A Comp Cams 260H cam is a good starting point for a stock tranny and a new intake.
Keep asking questions, you'll learn real fast here on the forum.
I am living proof of that. :cheers:

poncho_1119

Great - thanks again. If anyone else has any advice on increasing HP- I'm all ears!!

Tom73

I may be mistaken but I believe that Phonex AZ has full emission testing, even for a '75. If that is true you are sc***d. If not, then go with true dual exhaust, that first year for Cat Converters really did mess up the engine efficency. Then add a good cam. Those two changes alone will add a ton more power. Later you could look at heads and an intake.

tom...

poncho_1119

Tom,

I'm going to get my emmissions test next week and if its good for 2 years, I may consider siwtching out the pipes and then readdressing it in 2 years. How much more HP would you guess that the pipe change alone would add? And then how much more for the CAM, then intake, then headers? Just trying to get a breakdown. Sorry for all the questions - I'm learning...

Thanks,
James

Scudd

I have a 75 L82 4speed with no emission controls(cats, smog).It has dual exhaust, headers, and a new edelbrock carb/ intake. Stock it was rated for 210 hp. I have no idea how much its at now . I'm too scared to have it tested. All I know is when I race my buddy who has a 96LT4 6speed, rated at 330 hp and he kicks may azz(my car also weights less). I would say good luck getting it to 300 to 330 with just intake, headers, exhaust, and cam. It might take Juice to get the engine to that kind of HP and I dont think that old of a motor will take the abuse for very long. Good Luck....

poncho_1119

Interesting. I would think that a few modifications to make the motor more like the early 1970 350 would increase the HP to the same range and not cause any more abuse on the motor than the same HP puts on the earlier versions. I guess my question is, how do I get my 350 more like the earlier engines. Is it just exhaust, headers, intake, CAM - or is it much more to it?

Thanks,
James

Tom73

Those engines were rated at GROSS HP, yours is rated at NET HP.

tom...

Jvette73

The earlier engines like the 1970 had higher compression due the cylinder heads having a smaller combustion chamber. If you really wanna make good power with the typical engine mods that are being discussed here, bumping up the compression with different heads is a good idea. My original 73 heads were 76cc chamber. I swaped them out for 1969 year heads with 64cc chamber. They were also milled .012 which makes for even more compression. Originally my engine had 8.5to1 comp. With the older milled heads im probably closer to 10.5to1. I also ported and polished them which help im sure. You dont need a monster carb for a 350. My meager Holley 600 gets me deep into the 13 second bracket in the 1/4mi.

TheVin

exhuast wise if you have to keep your cat look at the new free flowing ones the import racers use--just a thought--I have a 75 also with mods--better than factory ratings but still no Lt1 or c-5---but Damn C-3 look so good....

Ganey

See Why Exhaust is problem for HP on 75-81
-what many refer to as my Exhaust topic. http://www.corvettefaq.com/c3/ganeyexhaust.htm

You need to state trans. & rear gears (stock for example is fine) for cam.

75Rag

I have a '75 L-48 with 203 rwhp. All I've done is 2.5" true duals (still have cats) and a Lars re curve kit for the timing.

more on the way ......

ROD NOCK

Just make sure you 'match' your mod components! Think of it as a whole picture. You may just buy a couple items now, like exhaust and intake, but have a plan to your goal, and stick to it. It will be based on your budget. Some study is advisable first.
There's a ton of such material here under the 'search' feature, and at Corvettefaq's.
A good start is reading Ganey's exhaust article! Take your time and good luck! :chevy

poncho_1119

Thanks Ganey! Great discussion - very informative.

James

Pete76Shark

On my 76 L-48 I took the cat off, gutted it and put it back. I want to dyno it to see what she comes in at. IF I decide to go with headers and 2.5 duals I have a few questions.
Will the Dynomax headers clear the older style A/C compressor or will I have to amke modifications.
Also where do I look for the bolt on pipes from the headers back to my Borla's ? does Summit sells these or do I have to have a muffler shot make'em up ?

Thanks for your help

poncho_1119

Pete,

I can't help you with that, but I am very intersted in your HP test to see what just removing the cat will do. Please send me an email if you have that test done (poncho_1119@yahoo.com).

Thanks,
James

nunus79

Based on weak memory, I think gutting the cat netted me ~25 hp gain. That's based on 1/4 mi mph calculation. It can be very restrictive!

After you get that resolved, a new cam should be first on your list. Good Luck!

pillowmeto

if you add some heads you can get a big increase, but do exhaust, headers, intake, and cam first or simotaniously. Also a holley carb couldnt hurt. A 268XE by comp cams is the biggest/ most popular cam to use. Im gonna go with a 272 and hope for the best, i got it plus the hydrolic lifters at carlisle for 25 bucks so nothing to lose right. Also some new rear gears drasticly help acceleration, but youll run higher rpm's you probobly have a 3.0, you can get up to 4.33, most people dont go above 4.11. But since the rpms are higher, you lose out on top speed, but mostly gas milage will suffer alot.

MAtt

MAtt