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Old 04-24-2006, 01:16 PM
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75 vette L48 upgrades!!!!!

Here goes. I have a really nice 75 vette with 49K miles on it. Sweet driven car but it just lacks the power. Comes stock with estimated 8.5:1 compression and a whopping 165 HP I would like to boost my power up around 300 or so without spending a lot of money. Any suggestions on cams,intakes,carbs,head work etc...Any imput would be greatly appreciated.

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Old 04-24-2006, 02:07 PM
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go with the eldrbrock top end kit says 410 hp. that should be enough for the street. cost about $1200 . put 3 in exhaust all the way back. and get some headers.
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Old 04-24-2006, 03:52 PM
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Doc here,

Any intake you may be considering, you best be sure it will fit ( physically in the engine bay).

All Corvettes of that Vintage Have a Hood Clearance problem. BE a bummer to get it on there to find the hood won't close anymore..

Your options then are : Aftermarket Hood scoop $$$.$$, A Ray type Hood $$$$.$$$, or pull it and return to stock.

I thought this was a 1980, not a 75 (as per your prior postings) Or is this another?

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Old 04-24-2006, 03:58 PM
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When you upgrade your engine you need to consider the transmission and diff gear.

For example, if you have a 3.08 gear with an automatic and stock converter then you need to build your engine with that in mind.

A 350 with 8.5:1 will have slightly dished piston and 76cc heads. You can make fairly good improvements with your current heads and block but you will be limited with those heads for a number of reasons. Namely poor flow, big combustion chambers, smallish valves, stamped rockers, weak springs, and press in studs that will pull out with heavy springs.

If you don't what to modify or replace your heads and what to keep the stock drive train and you don't what to spend too much money then your choices are limited.

The biggest cam you cam get away with using the stock valve train is a CompCam 252H. Then use an Edelbrock Performer intake with your Q-jet carb, install a set of full length small tube headers (doug thorley, 14 gauge with 3/8 inch flanges), install 2.25 to 2.5 inch exhaust with some hooker Areo Chamber mufflers (not to loud) and a H-pipe right before the mufflers. I know the Performer intake fits under stock 73 hood.

You can skip the headers if you install a CompCam DEH255 cam. It is a cam designed to work with stock exhaust manifolds and valve springs. You will give up some power without headers but it will be much quieter in the car without headers. But still upgrade the mufflers and exhaust pipe diameter.

This will run nice with an automatic transmission and a 3.08 diff with stock heads. Should get close to 300 hp and will get better mpg. Plus it will idle smoothly and spin the tires hard off the line.

If you can. Pull the heads and do a some mild bowl work and give them a quality valve job. This can add another 20 or 30hp right there.

For more power you really need to replace the heads with some 64 cc combustion chamber heads with 160cc to 180cc intake ports (darts or afr). Then install a CompCam 260H cam with the stock torque converter or a 268 with a 2000 stall. Anymore cam than that then you will need to lower the gear which will effect the drive on the freeway.

Later, consider a 383 or 400 cid if you what to keep the 3.08 gear.

With 3.08 gear you need to build low rpm torque not hp. Don't try to make a 400hp engine. Try to make a 500ftlb of torque at 2500rpm and don't worry about the hp.

Last thing. When installing a new cam make sure to use the cam break in additive in the engine oil. Motor oil has been reformulated over the past few years and it is now missing additives that are needed to prevent flat tappet wear. Oil for spec'd for diesel truck still has it for a few more years.
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Old 04-25-2006, 08:12 AM
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yes this is another sorry about that there confusion
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Old 04-25-2006, 09:52 AM
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Another idea is to put a nitrous plate system under your current carb, around $500.00 total. you can turn it on and turn it off when you want. It can be removed if you sell later. And you'll still have a # matching Corvette.
I did this on my '63 Covette and loved it.

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Old 04-25-2006, 07:06 PM
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if you can do the engine work or have a buddy who can or if you can afford to pay to have it done you have a great opportunity to make some very good upgrades with out spending a bunch of money.pull the motor and have the block machined and get new rings for your old pistons after honing the cylinders and having your block zero decked to increase c.r..also have your heads rebuilt and possibly some porting done and here again cut the deck surface for more c.r..you should have no problem attaining 9.5-9.8 c.r. and by reusing your block,heads and pistons it allows youto spend that money in other beneficial power building area's such as a new powerful roller cam and retro fit lifters.there are a few ways you could go here and many people will tell you to get new aluminum heads but they are not necessary.you can end up with very real power or penny pinch and make ok power.
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