74 L-82-trying to get a little more power

[RickT]

Ok so the engine is pretty much stock. The dist. has been changed out ( no more points) but everything else is stock. The engine was rebuilt less than 10,000 miles ago and sounds good and tight.

This set up from the factory is what,260 hp or so? How hard is it to get this up to 325 hp or close to it? I don't want to build a hot rod but just needs more than what it has.

How much extra hp will some good headers and free flowing xhaust get me?

What about an after market intake and diff. carb? It has the stock Q-jet and it runs fine. How many HPs will this get me?

What else can be done to get the hp up? I don't really want to tear into the engine but if I have to I will.

Rick

 

[Rodney Gold]

Headers and a carb/intake will get you minimal power unless you can get the compression up , use good heads and a decent cam. Not to say you wont have a power increase with the intake/headers combo , but it wont be cost effective.
You could probably skip the intake/carb purchase and use stock and rather spend the money on a set of heads,cam and headers.
I recon you can easily pick up 70 hp with that , even with a "conservative" (270) cam

 

[TJay]

I can imagine with just with a new rebuilt with 10.000 mi you might not want to buy new heads. But as stated above, heads, headers & cam are you best shot.
You could change the rear gear for the extra take off speed with what you have now. No increase in hp, but faster pick up, you will lose MPG and rev a bit higher pending what gear you go, just something else to consider.

 

[Vette79]

Keep the Qjet. Since it was rebuilt, look at headers and exhaust first. How about going with an aftermarket stall? But as mentioned previously, if you really want serious HP then you'll have to look at a head, cam, intake combo.

 

[Evolution1980]

No need to replace the carb. Just have it tuned once you have the other parts in place.

What about increasing your torque instead of HP? I reckon most people would rather have a torque-y engine over HP increases...they just don't know that. :cool

A different rear-end, as stated above, might satisfy you, but with the tradeoffs also mentioned.

I don't know much about the exhaust manifolds on the 74 L82, but I'm guessing they are somewhat restrictive relative to what a decent set of headers can get you today.

Heads are an expensive upgrade, but can definitely add big numbers quickly. Ya get what ya pay for...

Or........consider adding a nitrous setup for the occasional burst. That's usually a last resort though. But a mild NOS setup might fill your occasional(?) itch.

 

[Hib Halverson]

As "Evolution 1980" suggests, I'd keep the Quadrajet but retune it.

Then, add a modern short duration hydraulic roller cam, pocket-port and poiish the heads, install an Edelbrock Performer, headers and either a low restriction cat or (if you're plated in a state with no emissions testing) no cats and dual exhaust and you'll be at that 325hp level.

 

[RickT]

So it seems that if I want to get the HP up to around 325 there's pretty much no getting around replacing the cam. I don't really want to change the rear end and raise the RPMs since I like to cruise at 70-75 and I am not looking to smoke the tires everytime I take off. I just want more power to keep up with these newer C5/6s and show them that these old Vettes can run a little too.

Oh,I don't have to worry about cats.

Rick

 

[RickT]

Say Evolution,I also have Vic KP,I know yours is a Vegas. Just finished the Big Bore kit-stage 3 cams and S&S air box. It runs like it should now!

Rick

 

[Rodney Gold]

Well, you could add an underhood supercharger -- and in fact your engine is probably an ideal candidate if its under 9:1 comp ratio. The good thing is that you can remove the SC and the motor is back to "original" , you will get substantial power increases this way....but it isnt going to be cheap.
Be careful of a cam change - dont get carried away and be careful of your compression ratio when selecting a cam...if you are a low comp motor you have limited choices.
The best bet is to buy a power package , like an Edelbrock performer where you have matched components , ally heads etc and just add the headers.
There is also another problem when souping up the car, and that is matching the drivetrain to the power delivery...to get the best out of hotted up motor , you will need to change your stall speed on the convertor if yours is an auto , to something a bit higher than stock - a 2000rpm will do the trick.
If you want to get more torque , the only real way to do so is to add cubic inches , either stroke your engine to a 383 or drop in a 400 cu inch lump. (or go the SC/turbo/NOS route - those 3 fool the engine into thinking its bigger than it is)
Nos is the cheapest way by far and the simplest to get a huge boost , the disadvantages are that it is not a gradual power delivery , the nos itsself is expensive and it doesnt last long and of course , if a fuel problem arises , you will most likely melt the engine as it goes lean
It might also be a plan to drop in a turnkey high powered motor and remove and store your old one. You lose very little this way as the modification is reversible , your car goes back to stock when selling it and the turnkey motor can be sold as well ...essentially you lose the difference tween the motor new and 2nd hand.
A corvette is a performance car ... I don't see the point of driving one unless it can frighten you on occasion.....

 

[73shark]

Per the 1971 factory specs an LT-1 (cam, heads, pistons, intake, and Holley) is good for 330 hp net. Since you are already at 9:1 CR, you just need intake, carb, and cam/lifters and you're set. There are probably cheaper equivalent intakes, carbs, and cam/lifters than the OEM stuff that are as good or better since technology has come a long ways in 37 years. What ever you choose, you'll have to pay more $s for more ponies.

 

[Evolution1980]

Per the 1971 factory specs an LT-1 (cam, heads, pistons, intake, and Holley) is good for 330 hp net. Since you are already at 9:1 CR, you just need intake, carb, and cam/lifters and you're set. There are probably cheaper equivalent intakes, carbs, and cam/lifters than the OEM stuff that are as good or better since technology has come a long ways in 37 years. What ever you choose, you'll have to pay more $s for more ponies.

Did the 71 LT1 use the same heads and pistons?
Also, weren't the SAE ratings different back then? Sometime around '74 or so they changed over to the newer/current ratings, which were lower, no?

 

[73shark]

1971 was when they lowered the CRs in order to start using unleaded gas in preparation for using cats in 1975. According to my parts book, the '71 Lt-1 and '74 L-82 used the same head & pistons. The L-82 cam was the same as the 350-350 cam. Of course that 350 hp was the old gross rating. Probably more like 300-310 net. Which reminds me that the 330 hp I quoted for the '71 LT-1 was a gross rating (not net) and went to a 255 hp net in '72. Which means that the '74 L-82 at 250 hp wasn't far off the LT-1. So won't gain much by going to the solid cam and Holley.

However being the original owner of a '73 L-82, I can tell you that a stock '70 350-350 could take me (and did on several occasions). So I'm thinking that the high compression engines may have been closer to their gross ratings.

 

[petes74ttop]

Ok so the engine is pretty much stock. The dist. has been changed out ( no more points) but everything else is stock.

What else can be done to get the hp up? I don't really want to tear into the engine but if I have to I will.

Rick

You say the distributor has been changed out? Is it still stock but with something like a Pertronix conversion kit which just replaces the points?
If so get an Accel Kit and recurve the distributor so your all in at about 36* at 2,800 to 3,000, this will make your Vette pull better for about $ 10.00. PG.

 

[RickT]

I am pretty sure it's like HEI dist. Just checked and it's a Delco Remy dist.
No points or coil wire.
I did reroute the vac. advance from the carb. to the intake.

Rick

 

[Vette79]

I just want more power to keep up with these newer C5/6s and show them that these old Vettes can run a little too.

Rick

Good Luck with that.

 

[Vettehead Mikey]

What about an after market intake and diff. carb? It has the stock Q-jet and it runs fine. How many HPs will this get me?

Probably zero. There's very little you can do in terms of bolt on horsepowr for smog mtotrs. Low compression and flaccid cams are the biggest weak points.

 

[black_81_vette]

sure theres alot you can do ...... turbo charge it,run a paxton or other super charger.. or just spray the hell out of it.

 

[73shark]

I am pretty sure it's like HEI dist. Just checked and it's a Delco Remy dist.
No points or coil wire.
I did reroute the vac. advance from the carb. to the intake.

Rick

It still has a mechanical advance doesn't it? If so, then recurve it like Pete said. Really wakes up the bottom end. Also put as much initial advance in as you can.

 

[RickT]

I am going to put the timing light on it later today and see what's up.
So I set the idle at 2800 RPMs,right? Then set the timing.


BTW,I have the 74 350 L-82 and it's 9.1 comp. so should I be running regular or ethel?


Rick

 

[Vettehead Mikey]

That's a pretty weird way of setting the timing especially if you have no idea what the advance curve is. Follow the factory specs and procedures until you know.

If you are asking whether to use regular unleaded (87 octane) or high octane (91-93) gasoline, your engine was built to run on 87. Putting higher octane than that is a waste of money with NO benefits.

There's lots of myths out there, high octane in low perf. engines is one of them.