Headers on 468" how much HP gained?
 

This is a question relating to a car motor, but I'm sure some of the boat engine gurus are playing with cars too. The motor is in our 1966 Vette. It is a 468 Chev, 11:1 comp, Chevy "signature series" aluminum heads, matched dual plane intake, 850 holley DP carb, comp hydraulic flat tappet cam (244/244 @ .050, .550" lift), and comp roller tipped rockers. We ran it at the strip last year and turned 13.45 @ 110 MPH with a 2.3 60 foot time. That was with street tires and stock exhaust. We have beefed up the rear end and added a set of Hooker headers and 8" slicks. I have heard of huge HP gains with headers over stock manifolds. How much can be expected and what do you think the car will turn? I know this is a boating website, but come on HP is HP and cool on land and water.

I had a pro street 55 Chevy with similar power. I would think you would pick up 40-50 HP over stock manifolds.

You should get Mr Gaskets "desk top dyno"it is a lot of fun for stuff like this and I feel it is fairly accurate.

Kurt.

66 Vette?
Be careful with big power on a Vettes at the drags ('specially with slicks). When the rear suspension hits the bump stops, you'll snap a U-joint on a halfshaft. Can do some significant damage if it is the outer U-joint. Go to HD aftermarket drag-rated halfshafts and U-joints. Also can use longer urethane bump stops with a hole drilled in them - this allows softer "bottoming" and avoids the traction "spike" at the bottom that blows the U-joints.

mike

Thanks for the tip. We are running solid hardened U-joints, hardened yokes, and larger half shafts. We also added a heavy duty differential cover. We don't plan on drag racing very often. Just something to do at "test and tune" on friday night. We just want to get a time slip with about 12.50 or 12.60 and then we'll put the street tires back on.

a lot depends on your first gear of your trans and rear end gears. if they're not steep enough to make the engine rev, a freer exhaust could make it fall on it's face off the line espically under the extra load from slicks. unless your running a health stall converter. i would think with 4;10's or 4;56's gears you will be there. leagal disclaimer ," i may be wrong so don't bash me as this is just a guess from past experience."

That`s fun stuff! When I was in high school I had a 72 Pinto with a small block Ford,tunnel ram, Nitrous, 9"rear end with 4.57 gears on a Detriot Locker:D It was my everyday, only car!It would run the 1/4 in 12.1 at 119 mph on STREET TIRES!

I still to this day have dreams about that car!...great memories:)

Kurt.

Some good mods. I was runing a 433 rear gear with reworked 400 turbo with stall also did HD mods to rear then started taking out axles but i was shifting at 8600 man. body auto. Alum. diamond elkins sp? heads .125 angle cut lots of fun stuff, brings back memorys. love the old rides. :D

We're running a 3.90 gear with 4 on the floor. The m21 4-speed may not be the best for drag racing, but it's the way to go on a street driven muscle machine. The clutch is a centerforce 2. A 12.5 sec. time would be great, but we will be happy with whatever it does. It is very original looking and most people think it is stock. It even has factory air! We know the slicks will give us the ability to really see what it can do. With street tires first gear is a joke. Smokin tires baby and trying to go sideways. The people at the strip think we are nuts taking a sweet vintage car out and hammering on it. Its a hell of a lot more fun than car shows though.

I had some L88 stuff but i still have a complete 68 stamped 427 435 saved from one of the old vettes. If you put those inverted trailing arms on you can get more tire under the wheel wells. I ran hoosiers on the street.

Have fun :D

You don't have enough rear end gear to hook up the tires right away. I'd suggest you run fairly high air pressure in the tires and look for some spin off the line. Concentrate on the 330' times and let the engine spin. With the combination you listed, you should have a single plane manifold or a smaller carburetor. A smaller carburetor and the dual plane manifold will probably like the slicks better.