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76 L-48 performance upgrades: anyone been down this road? (Read 9173 times)
May 11th, 2011 at 10:50pm
jim   Ex Member

 
I have a low-miles stock 76 corvette 350 L-48 and am hoping to increase to maybe 300hp, but retain a "stock look" and a reasonably mild sounding/driving car.  Can anyone look at this plan and recommend revisions and/or specific parts, etc?

1.  I have a great exhaust guy who will cut Y-pipe and cat and fabricate a mild true dual system.  I'd rather not have headers.  I can keep the L-48 iron exhausts or replace with a higher performance GM iron exhausts if there's something which fits around the accessories in the tight C3 compartment.

2.  Retain the existing L-48 iron intake or replace with the L-82 alum intake or other GM intake, but swap the Quadra-Jet for an older (pre-emissions) QJ or perhaps an Edelbrock "Quadrajet replacement" carb with a base to match the QJ base holes on the existing iron intake (again unless there is a better GM intake I could swap out).

3.  Whatever I do with carb/intake, I've ordered the K&N #66-1202 X-Stream Top Filter (black not chrome) which essentially replaces the stock lid on the snorkel air filter  housing with a similar black lid but with an integrated top element to improve flow.

4.  upgrade to a Crane "101" hydraulic cam reproduction
(222/222 dur.; .447/.447 lift; 114 deg. separation) and double-roller timing chain.

5.  retain the stock (electronic) distributor but fit with a Blaster coil, re-curve kit, and performance module.

6.  Can I stop there, or do I need heads with 1.94 or 2.02 intake, maybe something like the GM 461 castings but with accessory bold holes?  Anyone want to weigh in on whether heads are necessary and, if so, any specific recommendations?

sorry for all the questions, but I'm a rookie....
 
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Reply #1 - May 12th, 2011 at 5:38am

blue 77   Offline
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Jim, welcome on board.  You have joined the BEST corvette forum on the internet.  Glad to have you.  There are many members here with all the knowledge you could want on your project and even better they are very free with advice and more than willing to share it with you.  I'm sure some of the real performance minded guys will chime in very soon to help.  Good luck!

Dale
 

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Reply #2 - May 12th, 2011 at 6:47am

TX 73 gone   Offline
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Hi Jim,

I just finished boosting the HP in my 73 and it sounds like you're on the right track.  I like headers but the factory horns will flow just fine for you. Definetly an intake and carb combo will help. You can get an up to date HEI ignition for $50 that will look just like the one you have. If it's original, I'd replace the whole thing.  The cam sounds perfect and will give you low end torque and good power up to 5200. As for the heads. That's a yes, you need to replace the smoggers with something better. I found camel humps for a good price but no accessory holes. I'd search for a good set ot vortec heads and since you want to change the intake, this is the perfect time to do it as they do not interchange. So, Vortec heads ( 64cc will boost comp ) intake, carb and disty and you should be good to go.  Cool

Good Luck, Charlie
 

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Reply #3 - May 17th, 2011 at 1:45pm
nevr2ol   Ex Member

 
Hello, I am a new member to the forum and take great interest in Jim's desire for more power. Like Jim, I have a 76 with a 4 speed. An engine builder I know suggested a set of Patriot Freedom aluminum heads for my vette. At first I was a bit leery because of their reputation but he assured me their quality had gotten better. Although they are cast in China, they are finished and assembled in Rainbow City Alabama. I was pleased when the heads came in. They were very clean and actually flow better than advertised. I know they don't add the power like a set of AFR heads would, however for a set of finished heads for 799.00 they are a bargain. All of the springs and rockers added to the heads are top of the line products and I can actually break the tires loose in 2nd gear ftrom a dead start. Just a thought and good luck with your build.
 
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Reply #4 - May 26th, 2011 at 3:01am
jim   Ex Member

 
Thank you Dale, for the nice welcome; Charlie for the helpful feedback; and Nevr2ol (great moniker...!) for mentioning Patriot heads.  Sorry for the delay -- I'm recovering from surgery.

Again, starting with a completely stock (numbers matching) L-48 motor, I'm hoping to hold onto the stock intake and Q-Jet, and use iron exhaust manifolds, but behind those convert to true dual exhaust to help her breath.

The cam I've selected is 1965-68 L79, 327/350hp GM specs:
GM 3863151 (hydraulic)
222/222 Duration; .447/.447 Lift; 114 LSA
Comp Cams #12-106-3; Crane #967601

My research shows I clearly need to change those smogger heads (GM 333882 with 76cc chambers).  I've looked at using the GM 3927186 (“186” or "Powerpack”) heads which have the accessory holes (which I need) and come with valve size 1.94/1.50 or 2.02/1.6 and 64 CC chambers.

Aeroheadracing.com sells what appears to be rebuilt 186 (iron) heads (though the specs are 65cc chambers) for 399.00 assembled with SS valves (2.02 intakes/ 1.60 exhausts), but I can't get seem to get anyone there to help me with a few basic questions, most importantly compression ratio (CR):  The 1976 350cid L-46 engine with stock 76cc heads has a CR of 8.5:1 and if I drop from 76cc chambers to 64cc or 65cc chambers, how much would the CR increase, and would that be too much for a weekend car running pump gas?

Nevr2ol suggested the Patriot heads, and if I choose those instead I'll have the same CR question (above).  Any other thoughts or suggestions on cylinder head selection for this build?  Is it worthwhile to go with aluminum?  Are they as durable as iron?
 
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Reply #5 - May 26th, 2011 at 6:10am

TX 73 gone   Offline
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As long as you don't use one of those super thin gaskets, the 64cc heads should not give you more than 9.5:1. I put flat tops in mineand stuck 64cc heads on it and only had @ 9:1 so I wouldn't worry about it at all. I'd look into the manifolds and see what year stock were better and go for those. The horns work better than the straight ones. Aluminum heads are tempermental and generally need to run hotter than the iron ones. I'd just search until I found a good deal and then jump on it.

Have fun!
Charlie
 

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Reply #6 - May 26th, 2011 at 7:08am

Artsvettes   Offline
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New Jersey

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TX 73 gone wrote on May 26th, 2011 at 6:10am:
Aluminum heads are tempermental and generally need to run hotter than the iron ones.

Have fun!
Charlie


Thats news to me. My 383 aluminun headed engine runs cooler than my 355 iron headed engine........... Cooljack
 

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Reply #7 - May 26th, 2011 at 8:54am

68-73-77   Offline
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I always though Alum heads were better in a higher compression ratio application & they dissipate heat much better. Plus they help with weigh especially in a BB. I only rum 8.75:1 in the vet so I never bothered to switch to Alum heads.  Hp & high compression ratios make heat.....not the type of head. alum just feels hotter because it gets rid of heat faster. My mopar is 11.5 "1 & it get hot especially with the headers
Alan Smiley
 
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Reply #8 - May 26th, 2011 at 9:43am

TX 73 gone   Offline
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My Vette went to a good
home!
Sugar Land, TX

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I've never ran them so I'm just going by what I've heard over the years.  If I was to get my hands on some, I'd throw them on in a second.
 

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Reply #9 - Oct 3rd, 2011 at 6:01am
Ravoll   Ex Member

 
Hi.
Am planning the very same thing over the winter.Bone stock L48 rebuild with valvejob, port matching,CompCams XE262H cam kit with springs and lifters,stamped roller rockers with new pushrods,Tranny rebuild with B&M shiftkit.
Other than that will be keeping all my other stock parts.Intake, Q-jet,stock 2/1/2 exhaust through the cat.Gonna fiddle with the exhaust a bit.Maybe run straight pipes from the cat out the back ,or leave the "Borlas" and empty the cat.Not sure yet.Whatever makes a better sound.

Won't be a "Porsche killer" on the Autobahn,but should accelerate better.

« Last Edit: Oct 3rd, 2011 at 10:04am by N/A »  
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Reply #10 - Sep 18th, 2017 at 3:13pm

76VetteFirstTimer   Offline
Newbie
I Love my Corvette!
Sedona, AZ

Gender: male
Posts: 4
 
Hi all.  I'm about to take possession of a 1976 Vette, 4 speed manual.  I'm wondering if anybody out there is in Northern Arizona and has a recommendation for a good engine shop.  I'm looking to increase horsepower to around 350.

Thanks!
 
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Reply #11 - Sep 18th, 2017 at 3:15pm

76VetteFirstTimer   Offline
Newbie
I Love my Corvette!
Sedona, AZ

Gender: male
Posts: 4
 
Hi all.  I'm about to take possession of a 1976 Vette w/4 speed manual transmission.  I'm looking for a good engine shop in Northern Arizona.  Any recommendations?

Thanks!
 
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Reply #12 - Nov 6th, 2017 at 3:08pm

76VetteFirstTimer   Offline
Newbie
I Love my Corvette!
Sedona, AZ

Gender: male
Posts: 4
 
I'm looking for opinions on the various kits that are available to convert the vacuum headlight switches to electrical.  If you've done this, please let me know what kit you've used, the ease of installation, cost and whether or not you're hapy with the results.

Thanks!
 
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Reply #13 - Nov 7th, 2017 at 9:42am

68-73-77   Offline
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NCRS Member 68,73,77 Corvettes
Newark,Delaware

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My 73 has electric headlights. Jack the previous owner made the kit & used older Pontiac motors.
I have since replaced both motors as they went bad.  If I was doing it today I would use linear actuators or a kit that uses them.
Alan Smiley
 
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