1975 350 Modifications
Thread Starter
Heel & Toe
Joined: Sep 2003
Posts: 19
Likes: 0
From: Phoenix AZ
1975 350 Modifications
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
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
Thread Starter
Heel & Toe
Joined: Sep 2003
Posts: 19
Likes: 0
From: Phoenix AZ
Re: 1975 350 Modifications (Stewart's74)
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?
Safety Car
Joined: Aug 2000
Posts: 3,943
Likes: 44
From: Florham Park NJ Port Credit Ontario
Re: 1975 350 Modifications (poncho_1119)
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:
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:
Race Director
Joined: Apr 1999
Posts: 15,136
Likes: 477
From: NM
Re: 1975 350 Modifications (poncho_1119)
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...
tom...
Thread Starter
Heel & Toe
Joined: Sep 2003
Posts: 19
Likes: 0
From: Phoenix AZ
Re: 1975 350 Modifications (Tom73)
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
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
Safety Car
Joined: Dec 2001
Posts: 4,832
Likes: 0
From: Florida
Re: 1975 350 Modifications (poncho_1119)
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....
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Thread Starter
Heel & Toe
Joined: Sep 2003
Posts: 19
Likes: 0
From: Phoenix AZ
Re: 1975 350 Modifications (Scudd)
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
Thanks,
James
Race Director
Joined: Apr 1999
Posts: 15,136
Likes: 477
From: NM
Re: 1975 350 Modifications (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
tom...
Safety Car
Joined: Jun 2001
Posts: 4,004
Likes: 2
From: Severna Park Md
Re: 1975 350 Modifications (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
Thanks,
James
Instructor
Joined: Mar 2003
Posts: 236
Likes: 0
From: Spring Lake mi
Re: 1975 350 Modifications (poncho_1119)
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....
Race Director
Joined: Apr 1999
Posts: 11,520
Likes: 13
From: CORVETTE 77 385 C.I. TEXAS
Re: 1975 350 Modifications (poncho_1119)
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.
-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.
Melting Slicks
Joined: Jun 2002
Posts: 2,609
Likes: 1
From: Behind the wheel of a large automobile
Re: 1975 350 Modifications (poncho_1119)
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 ......
more on the way ......
Pro
Joined: Jul 2000
Posts: 654
Likes: 0
From: Now Frozen in Michigan
Re: 1975 350 Modifications (poncho_1119)
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
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
Racer
Joined: Jan 2003
Posts: 383
Likes: 0
From: Columbia SC
Re: 1975 350 Modifications (poncho_1119)
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
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
Thread Starter
Heel & Toe
Joined: Sep 2003
Posts: 19
Likes: 0
From: Phoenix AZ
Re: 1975 350 Modifications (Pete76Shark)
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
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
Drifting
Joined: Nov 2000
Posts: 1,361
Likes: 0
From: Honolulu Hawaii
Re: 1975 350 Modifications (poncho_1119)
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!
After you get that resolved, a new cam should be first on your list. Good Luck!
Le Mans Master
Joined: Apr 2003
Posts: 7,154
Likes: 1
From: I blame my Dyslexia MD
Re: 1975 350 Modifications (poncho_1119)
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
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MAtt