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Discussion Starter #1
Well after working inside the car for a while trying to fix up the interior and get the car up to par I started to think about performance. I have looked through many threads asking the same question but i'm no mechanic by any standards, and i'm learning as I go along while using my service manuals religiously. I have a friend whose a mechanic who will be helping me with the engine and performance aspects though. So my car supposedly had/has a l48, but when looking at the numbers on the engine, it looks like it isn't a corvette engine. The engine id pad is really hard to read so I can't completely identify it, but it runs good, supposedly has about 120k miles and doesn't leak anything and has an auto tranny. I was told that the engine and trans were rebuilt about a year ago. So my first mod was going to be exhaust. Aside from a new exhaust, what would be the next best things to do to net me some horses, despite replacing cylinder heads or anything like that. What carb? intake? cam?

I don't want to build a race car, but I want to get a little more pep. Thanks for your help guys
 

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How many $$ do you want to spend?

I'd probably think about Headers, cam and head shave to up the compression!

anyone know the comp. ratio of a L48?
 

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Well I think that i'm going to do things in stages, but i'd like to know what things to do and which ones would be best.

What headers would you suggest? and cam?
 

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If money is tight there is a lot too be said for just cleaning up the original rams horn headers, cleaning up casting marks on the inside. otherwise reputable brand headers....as for cam depends on what use the car will see!
I'd go for a good low to mid range performer.....get in contact with a cam manufacturer and they'll find one to suit you.

yeh I'd start with the exhaust first and slip in the came the same time you do the inlet manifold......upping the compression at the same time if you choose!

hold off on the carbie you might not need any more fuel for a while with these mild mods.

that being said....you should feel quite a significant improvement with this done.

:cheers: Liam
 

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I was just having this conversation with Rjent. I also have a 76 L48. THe comp ratio is 8.5 / 1.

The most obvious bolt on for HP are headers and intake.

The one I just learned about (and you lifelong mechanics take it easy on me for just learning this) is roller rockers. For $150 you can get a set of roller rockers from jegs. In a couple of hours you can install them. Assuming your lifters, studs, and valve springs are in good shape. Our later model engines have a shoulder on the rocker arn stud so you do not have to worry about valve lash or any of that. Re-install you valve covers and drive it that day. According to the comp cams website you can gain up to 30hp.

That will definitely add a pep in your step.

When you want to go big, add a cam and heads. If you want to save money, you can get your heads machined to increase compresion. A friend of mine had his big block heads machined for $95.
 

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Discussion Starter #6
Cool, thanks for the tips. Would installing a 650cfm holley cause problems with only exhaust, headers, and possibly intake done?

I wasn't aware that rockers could free up that much horsepower.
 

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Cool, thanks for the tips. Would installing a 650cfm holley cause problems with only exhaust, headers, and possibly intake done?
I do not think it would cause any problems at all. I also think that 650 is a bit small if you are "upgrading", and that you wouldn't see much of a difference from your stock quadrajet.
 

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Discussion Starter #8
Thanks Jason, it's funny how I kept telling myself before I bought the car that I would keep the engine stock, but am now finding myself wanting to do work on it.
 

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Thanks Jason, it's funny how I kept telling myself before I bought the car that I would keep the engine stock, but am now finding myself wanting to do work on it.
For a while I thought the same thing. It was running great, and I was having sooo much fun driving it that I was not going to spend any $$ on it. Two years later, I want POWER!!!!!!!!!!

More than likely I am going to do the Roller rocker thing. I will let you know how it goes.
 

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good idea, stingin 76.
I have roller rockers ( Yella Terra brand, Australian I think)
8.5 :1 compression ratio could most certainly do with improvement.

as for the quadrajet, Aren't they good for something like 400HP:huh:
I have a 650 spreadbore Holley and don't like the design much at all!
everytime you take off the float bowls they dump fuel all over the intake manifold,there is also a risk of fire if the gaskets decide to give it in!

I have a mild cam, don't know the specs.....still sound abit lumpy at idle though, edelbrock performer manifold, block hugger headers, the biggest valves I could fit in, agood port job and roller rockers

My 650 keeps up Fine.....this would be a similar set up to what you would be upgrading too .....


The whole reason I bought the vette was because I didn't have the time to complete other project cars I had on the go at the time........now I've already had the car apart twice.

have fun when doing it thats the main thing..... I hate working on cars when it dosn't involve making them go faster or handle better.......somehow oil changes just don't do it for me:D
 

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good idea, stingin 76.
I have roller rockers ( Yella Terra brand, Australian I think)
8.5 :1 compression ratio could most certainly do with improvement.

as for the quadrajet, Aren't they good for something like 400HP:huh:
I have a 650 spreadbore Holley and don't like the design much at all!
everytime you take off the float bowls they dump fuel all over the intake manifold,there is also a risk of fire if the gaskets decide to give it in!

I have a mild cam, don't know the specs.....still sound abit lumpy at idle though, edelbrock performer manifold, block hugger headers, the biggest valves I could fit in, agood port job and roller rockers

My 650 keeps up Fine.....this would be a similar set up to what you would be upgrading too .....


The whole reason I bought the vette was because I didn't have the time to complete other project cars I had on the go at the time........now I've already had the car apart twice.

have fun when doing it thats the main thing..... I hate working on cars when it dosn't involve making them go faster or handle better.......somehow oil changes just don't do it for me:D
Keeping in mind that I am not trying to break any 1/4 mile records, or even go to a drag strip with it, Edelbrock sells a whole performance package
http://www.edelbrock.com/automotive_new/mc/power_package/power_package_main.shtml
That I think would be more than adequate for a regularly driven car. I am much more interested in Tourque that I am horsepower.

Here is my .02

1. My car's brakes can be locked up at any speed. This makes a brake upgrade a very low priorty, and more for looks than anything else.

2. I have driven my car 120mph and everything felt good and safe. So again, any further ugrade of the steering and suspension would be for looks only.

3. My low end tourque sucks. I can barely pull off a brake tourque let alone spin the tires without the brakes. It is quite embarrassing.

So my whole goal as far as modding my engine is going to be for tire spinning purposes only. The other performance gains that come with that goal will all be a bonus.
 

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I was just having this conversation with Rjent. I also have a 76 L48. THe comp ratio is 8.5 / 1.

The most obvious bolt on for HP are headers and intake.

The one I just learned about (and you lifelong mechanics take it easy on me for just learning this) is roller rockers. For $150 you can get a set of roller rockers from jegs. In a couple of hours you can install them. Assuming your lifters, studs, and valve springs are in good shape. Our later model engines have a shoulder on the rocker arn stud so you do not have to worry about valve lash or any of that. Re-install you valve covers and drive it that day. According to the comp cams website you can gain up to 30hp.

That will definitely add a pep in your step.

When you want to go big, add a cam and heads. If you want to save money, you can get your heads machined to increase compresion. A friend of mine had his big block heads machined for $95.
A 30 HP increase on roller rockers alone is quite a claim. I'd say 5 HP is more realistic on a mild engine. One area where they are really good is in reducing valve train friction (that's where the net HP increase comes from) and therefore reducing overall engine oil temperature. I would definitely investigate the lack of adjustment claim and make sure that is true. The roller rockers may have a slightly different geometry than the stock stamped rocker. Adjusting the valves on a hydraulic lifter engine is easy anyway and is usually a one-time event. Speaking of geometry, there may be roller rockers available with a different ratio, such that you can get a little more lift at the valve. These are good as long as you are not looking for high rpm.

There is a phrase..."the power is made in the heads". Small block heads are relatively cheap, about $900.00 or so I believe for aluminum. Your present head design is 30 plus years old. You can get a more modern high-torque, light-weight, higher compression head in one shot by getting new Edelbrocks, Brodix or Name-your-brand heads. I just did it on mine. Do some research. To shave your heads and have to go through the work of removing your cast-iron manifolds, buy new head and intake gaskets, dump your anti-freeze, break off a few exhaust manifold bolts, etc. just to gain 5 HP isn't worth it. You shouldn't re-use head bolts, so there is another expense. If the old heads are off...well it's time to freshen them up, blah, blah, blah...more money wasted.

IMHO, your thought to buy a power package from Edelbrock is a good one because the components are matched and proven. You won't end up with a set of heads that are good for 300 HP and a cam that could go 500, but has no torque.

Probably more than two cents worth. ;)
 

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A 30 HP increase on roller rockers alone is quite a claim. I'd say 5 HP is more realistic on a mild engine. One area where they are really good is in reducing valve train friction (that's where the net HP increase comes from) and therefore reducing overall engine oil temperature. I would definitely investigate the lack of adjustment claim and make sure that is true. The roller rockers may have a slightly different geometry than the stock stamped rocker. Adjusting the valves on a hydraulic lifter engine is easy anyway and is usually a one-time event. Speaking of geometry, there may be roller rockers available with a different ratio, such that you can get a little more lift at the valve. These are good as long as you are not looking for high rpm.

There is a phrase..."the power is made in the heads". Small block heads are relatively cheap, about $900.00 or so I believe for aluminum. Your present head design is 30 plus years old. You can get a more modern high-torque, light-weight, higher compression head in one shot by getting new Edelbrocks, Brodix or Name-your-brand heads. I just did it on mine. Do some research. To shave your heads and have to go through the work of removing your cast-iron manifolds, buy new head and intake gaskets, dump your anti-freeze, break off a few exhaust manifold bolts, etc. just to gain 5 HP isn't worth it. You shouldn't re-use head bolts, so there is another expense. If the old heads are off...well it's time to freshen them up, blah, blah, blah...more money wasted.

IMHO, your thought to buy a power package from Edelbrock is a good one because the components are matched and proven. You won't end up with a set of heads that are good for 300 HP and a cam that could go 500, but has no torque.

Probably more than two cents worth. ;)
Your .02 is always welcome.

I am just learning about this stuff and don't have the experience to not believe the claims of company websites. I apperciate all of the input I can get.

You are absolutlely right about being able to get different ratio rocker arms. I think that the stock ratio is 1.52. Moving to a 1.6 will give a little more lift for longer duration.
 

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good idea, stingin 76.

as for the quadrajet, Aren't they good for something like 400HP:huh:
I have a 650 spreadbore Holley and don't like the design much at all!
everytime you take off the float bowls they dump fuel all over the intake manifold,there is also a risk of fire if the gaskets decide to give it in!


The whole reason I bought the vette was because I didn't have the time to complete other project cars I had on the go at the time........now I've already had the car apart twice.

have fun when doing it thats the main thing..... I hate working on cars when it dosn't involve making them go faster or handle better.......somehow oil changes just don't do it for me:D
Quote from "John Lingenfelter On Modifying Small-Block Chevy Engines".

"Q-Jets - This is not to suggest that the other carburetors on the market are inferior mix masters. I have won numerous national event titles in NHRA Super Stock using a QuadraJet carburetor. When the Q-Jet is assembled and tuned properly it will deliver outstanding street performance. It's unfortunate that the Q-Jet's perceived complexity baffles many enthusiasts. The Q-Jet's metering rod and jet arrangement combined with its sensitive primary metering circuit is what gives the carb its great street manners capable of excellent part-throttle fuel management. As a plus, few realize the the Chevy Q-Jets are rated at 750 cfm. This is more than enough airflow for upwards of 500 horsepower. A great feature is that secondary metering rod changes can be accomplished in seconds by merely removing one small screw and lifting the hanger."
 

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Your .02 is always welcome.

I am just learning about this stuff and don't have the experience to not believe the claims of company websites. I apperciate all of the input I can get.

You are absolutlely right about being able to get different ratio rocker arms. I think that the stock ratio is 1.52. Moving to a 1.6 will give a little more lift for longer duration.
Thanks, Jason. I will try to make sure my .02 is accurate, but I am human from time-to-time.

Get some books, like the John Lingenfelter one I referenced above. There's a lot of information in there (stock SBC rocker ratio is 1.50:1, roller rockers will reduce oil temp 10 to 15 degrees) and in others. "How To Build Horsepower - Vol. 1" by David Vizard. "How to hotrod Small-Block Chevrolets" is another. And Smokey Yunick's "Power Secrets".

There are many rules of thumb and general concepts that are true on their own, but don't work with all engine combinations. The best thing to do is to really plan out your concept of what you want the car to do, your budget and time allowance. Have patience and spend a lot of time finding out how and what parts and systems work together. A high reving big ported engine does not work well with a 2.56 rear. A lift above 0.420" and stock SBC cast iron heads may not work well together...this is right out of Lingenfelter.
 

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Thanks Fred!

I just ordered some books from David Vizard and John Lingenfelter.
We have a 1975 vette with manual shifting and a 3.70 rear axle ratio. The catalic coverter is gone so a bit more HP than the original 165 I guess.
But still it is difficult to spin the tires without playing with the clutch.
To my opinion the vette should behave the way it looks.
My goal is to reach 250-300HP. But of course torque matters and not horsepower:partyon:

Before spending a lot of money on the wrong equipment and bad configurations I'll do more research by reading (books and the forum)

Stephan
 

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Thanks Fred!

I just ordered some books from David Vizard and John Lingenfelter.
We have a 1975 vette with manual shifting and a 3.70 rear axle ratio. The catalic coverter is gone so a bit more HP than the original 165 I guess.
But still it is difficult to spin the tires without playing with the clutch.
To my opinion the vette should behave the way it looks.
My goal is to reach 250-300HP. But of course torque matters and not horsepower:partyon:

Before spending a lot of money on the wrong equipment and bad configurations I'll do more research by reading (books and the forum)

Stephan
Use the sticky thread at the top for timing and get Cliff Ruggles book on the Qjet mod/tuning.
These will probably help you a bunch until you decide where to spend any money.
:D
 

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be smart, spend on heads and cam if the short block is fine. No need to go apeshit with mods there for "only" 300HP. Stock components will easily live there (and even then, it's usually revs that kill components), don't waste money on junk stuff hyped up in advertising. The real power is in the heads and valve train, if carefully selected to compliment the rest of your engine combo.
 

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@ Twinturbo,

You are right. I can spend my money only once and when you ad up all gains in horsepower by all advertisements I will end up at 1001 HP:surprised .

On my L48 (actually a 4 bolt main engine from a small truck C10 eg) a compression ratio of 1:8,5 isn't much. This weekend I'm gonna buy some new headers. This will result in some gain of HP. New Heads = compression and letting the engine breathe easily will help a lot.

I'm not scared to take my engine apart (check www.stingray75.nl for gear box), but to find the right configuration is difficult. The new ordered books will help a lot. And some searches on this forum will help a lot in finding info.
Edit. Now I see you're from the Netherlands and if I'm not mistaken we have mailed allready together. I'll send you a private mail.

@ 010752

Ok that brings my books spending up to $120. I believe the Q-jet is a good carb so it is worthwile to invest in this book. Thanks for the tip.
Keeps me off the streets for a while.:D

When I've thought of a configuration I'll make a post of it.

And for the timing it is a good suggestion. I've timing light with programmable advance and rpm reading. This makes life easier. The timing will be redone but I dont expect huge improvements.

Stephan
 
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