trying to get some horsepower.

[vetteKID]

ok.....its time for alittle winter money spending. I just sold my other classic car (mopar) and i decided throw half into the vette and half into another car. heres what i got planed..........internally stock L-48 (performer manifold) by the way.

-650cfm holley spread bore carb. (#8055)
-Comp cams 268H .454 lift.

what do you guys think?

the cam right? headers first?

 

[Bob Chadwick]

I'm no expert on this by any stretch of the imagination bit I have read heads, cam and intake are the way to go on the L48. Heads first, I think primarily due to compression but also valves, then the other two, though I don't know in whay order.

Why the carb? Are you having problems with the Q'jet? There will be other opinions but from whay I have read, the Q'jet can hang in there if stroked by someone who knows what they are doing.

Having shared my limited knowledge, the experts will pipe in and I look forward to hearing what they have to say because I have an L48 as well.

 

[vigman]

Heads/Cam/headers/carb/ignition

In that order...

Aluminum heads ( pick your poison there .. the edlebrocks are good)

While your down that far.. do the cam & timing chain..seals etc.
( Have the radiator at least rodded out & new water pump/hoses)

Put it all back together... and feel the new power.

Add headers next... and if you feel the need. Carb!

Then cool Igniton...


Vig!~

 

[Mako]

ok.....its time for alittle winter money spending. I just sold my other classic car (mopar) and i decided throw half into the vette and half into another car. heres what i got planed..........internally stock L-48 (performer manifold) by the way.

-650cfm holley spread bore carb. (#8055)
-Comp cams 268H .454 lift.

what do you guys think?

the cam right? headers first?

Opinion time

Headers and mufflers first definitely. Then put the car on a dyno with a wide band O2 sensor and dial in your Qjet. That should net you a good 20+HP and do it on the relatively cheap too.

I see no advantage to tossing a properly working Qjet out on a stock long block engine. When you install ported heads and a roller cam, then we'll talk, but until then, keep the QJet, it's a fine street friendly carb when dialed in.

Header tip:
Do not buy ceramic coated headers right off the bat. Instead buy uncoated headers and then fit the pipes to the car and the exhaust system first. Once the pipes are all dialed in fitment wise, only then send them out to be coated.

Hooker Super Comp headers are one of the best performing "off the shelf" headers you can buy and can be ordered with the AIR injection tubes for something resembling a smog legal setup.

Walker "Turbo" mufflers are surprisingly good performance mufflers and are a quarter of the cost of a Borla or what have you. Have your exhaust shop pick the largest muffler that will fit properly.

You *really* want a exhaust shop with a mandrel bender to fabricate your 2.5" pipes. Stretch benders are hell for crushing the tubes way down to exhaust choking diameters/cross sections.

Now assuming you have the need for more speed, then get into the engine proper. The cam you've mentioned is a nice not too over the top cam. If your willing to use after market valve covers, I would also add 1.6:1 roller rockers to the shopping list.

Adding the cam and the roller rockers will get you another 25HP or so.

Once you have cam, headers and good mufflers in place, dyno tune the carb on a Dynojet to get the air:fuel ratio dialed in.

One more place to find power is by ditching the stock cooling fan. Replacing it with an electric will free up anywhere from 10-20HP - seriously. I have the time slips buried in my desk somewhere to prove that.

I dumped my fan and picked up .2S and +2MPH. I did that on track experiment after seeing some convincing dyno tests in Hotrod magazin back in '99. It's imperative that you still keep the fan shroud and ensure that all the air seals are in good working order regardless of fan type!

You should be able to net a cool 40-60HP for ~$1800 by doing all the above. If that doesn't put some fire in your shorts, nothing will

CYa!
Allen

 

[vetteKID]

i already have exhaust........2.5 true duals chambered dumping before the rear axles, I also have the performer Intake manifold.
My Q-jet is giving me problem, and i really love holleys and trust them. i dont have enough money to do heads right now, and i really wouldnt get heads untill i rebuild the engine. my price range would at the most 500$, and i figured those would be the best bang for my buck, so it was either headers or cam. but the carb is a problem, it gives me problems when flooring it and is hard to start, and also i would like to change over to a electric thermo.

so i guess my question is more of what are the best bangs for the buck under 500$?

 

[WayneLBurnham]

In low-buck, "kam is king"

and that doesn't sound so high a lift you should be taxing the valve springs too much...but make sure of that. I've heard it frequently opined just changing the ratio of the lifters and going with roller tipped versions is like a mini-cam change on it's own. Again, you have to be careful of pushrod requirements and valve spring stresses and other geometry issues like clearing vlave covers.

If you have fuel related drivability problems, then sure, the carb is key - but will go for $300+ at a minimum - most of your budget. On the other hand a full rebuild kit for your QJet is probably $25.

Don't forget, going even as deep as a cam/lifter change will eat some additional bucks in gaskets and sealant too - and maybe a trashed bolt or two if it's been a while since anyone's been there.

All else being equal though, that cam change will bring you the greatest improvement.

 

[Ganey]

Ex. is first. 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
Chambered is restrictive & not rec. for performance.

Next is cam. HE268H is good min. for 4spd. & max. for stock valve springs.

Dynomax Cerma coated headers & mufflers.

Holley 600.

Cam will add the most power, cam before headers. All this will put you about 300-320.

:cool

 

[skeetimer]

Mako,
Why do you recommend buying non-coated headers first and then after installing them having them coated? Same deal apply for side pipe setups?

 

[Mako]

Mako,
Why do you recommend buying non-coated headers first and then after installing them having them coated? Same deal apply for side pipe setups?

I've yet to have a pair of headers that fit properly the first time. Inevitably something needs to be bent, dinged or cut or whatever to dial the fitment in properly.

Welding on coated headers is very ugly. You have to grind the ceramic off the steel and the welds end up looking like crap and are prone to pin holes, not to forget that now you have exposed metal at the welds.

Your better off getting the headers properly fitted to the car and dialed into the rest of the exhaust system and then sending them out to your favorite coating house.

That way you have a perfect fit and the pipes will look cherry. You can also send out other parts of the exhaust system to be coated at the same time. For example, I have two pairs of side pipes - one pair with mufflers and one pair without.

When it's time to go fishing for time slips at the track, I will slip off the street pipes and slap on the racing pipes and go hunting for Blue Ovals Both sets of pipes are going to be ceramic coated, perhaps different colors. Classy black or silver for the street and over the top yellow for the track, we'll see.

CYa!
Allen

 

[skeetimer]

Thanks. I will keep that in mind.

 

[Ganey]

While that's basically right about headers, you should not have a problem w/ Dynomax Cerma coated headers.

 

[Mako]

While that's basically right about headers, you should not have a problem w/ Dynomax Cerma coated headers.

A non-stock oil pan, especially a road race type, throws all fitment bets out the window. Dittos for suspension mods that move the steering and A arms around.

I had two pairs of Hooker Super Comps, and both were bent differently and required surgery. It's a long story, but I'm on headers set #4 - 2 Hookers, 1 Stahl, all three out the back, and now #4, Stahl for side pipes. Doing this 4x running is no fun....

That said, my AS&M headers on my Z28 were a perfect fit, so go figure...

CYa!
Mako

 

[lg78VETTE]

I have been reading your discussions and maybe some could help me.I have a78 L82 4spd I put in a comps 268h cam a performer manifold;knair filter and getting ready to install MA true duals and Dynomax ultraflo mufflers all stainless steel.Originaly the 78 was rated at220hp what do you think I will be pusing when all is done.I did not change headers.Even with the original exhaust I can feel and here the diference feels good!What do you think?

 

[Classicvette63]

Headers first, headers second and headers third. Then do what you want. 2.5 or 3" straight pipe all the way back to a good pair of "turbo" style mufflers. Then you will get full benefit from any other mods you do. After headers, the only criteria you have is, how much do you want to spend? Classic

 

[Ganey]

lg78VETTE

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

Engine on dyno about 300+ HP.

Mako
Sure, but he did not say he had a "non-stock oil pan", etc.

 

[MaineShark]

Just remember, opening up the exhause may give you a higher horsepower number, but low-end torque will drop dramatically. and the powerband will move up in the revs, to a less useful area.

Some reduction in restriction is helpful, but too much will hurt more than it will help. I wouldn't go larger than 2.5" on the exhaust.

Joe