[79firebird_99TA]

Hi all,

It looks like I just landed a `68 GTO 400 block that is going to be built. The guy that I'm buying it from is building it. I have to decide on a cam.

I will be using my 6x-4 heads, stock 4bbl intake w/ q-jet, stock exhaust manifolds. The car has the BW Super T-10 4 speed with stock rear end.

The bird will be driven on the street once or twice a week. I will also be on the highway doing 75 mph during those times.

What hydralic cam should I get? Is Summit OK...such as a 2801? I want this car to run like a bat exiting hell while having good street manners.

[79firebird_99TA]

Hi all,

It looks like I just landed a `68 GTO 400 block that is going to be built. The guy that I'm buying it from is building it. I have to decide on a cam.

I will be using my 6x-4 heads, stock 4bbl intake w/ q-jet, stock exhaust manifolds. The car has the BW Super T-10 4 speed with stock rear end.

The bird will be driven on the street once or twice a week. I will also be on the highway doing 75 mph during those times.

What hydralic cam should I get? Is Summit OK...such as a 2801? I want this car to run like a bat exiting hell while having good street manners.

[Brian Baker]

2802 might even be good, since you're running a 4-speed.

[firechicken]

What gears in the rear?

[79firebird_99TA]

I have no idea, firechicken. The rear end is stock. The only thing I know, is I remember reaching for 5th gear while on the highway at 3000 RPM (if that tells you anything). It's been 8 years since she's been on the road.

[firechicken]

I think a '79 could have a 2.41 3.08 3.23 or even a 3.42 ratio in a stock rear. Quite a variance. You should find out for sure as this will greatly affect you camshaft selection.

[krisr]

Easy way to check your rear end is to put the rear on axle stands, spin the tires one revolution and mark and count how many times the diff yoke spins, that will give you a rough idea on gear ratio.

[ponchoV-ate]

<BLOCKQUOTE class="ip-ubbcode-quote"><font size="-1">quote:</font><HR>Originally posted by firechicken:
I think a '79 could have a 2.41 3.08 3.23 or even a 3.42 ratio in a stock rear. Quite a variance. You should find out for sure as this will greatly affect you camshaft selection.<HR></BLOCKQUOTE>

I always wondered that when the guys at the local speed shop would ask me that when I had question about a cam for my T/A; why is it so? So should I choose a cam based just on my rear-end ratio, which is 3.70:1, or base it off the gearing I get using my Richmond 5-speed, which combined with it's 3.27:1 first gear multiplication is similar to that if I had a Muncie Rockcrusher and 4.56:1 gearing in the rear?

1981 Turbo Trans Am
-'75 Pontiac 400
-Richmond Street 5-speed/3.70's
-Holley 650cfm 4-barrel on 1/2in. spacer, blocked exhaust crossover, 160 degree thermostat, Blackjack 1-5/8 in. 4-tube headers, Thrush 2-1/4in. dual exhaust w/ Thrush California Turbo mufflers, no A/C-no emissions; drunk bitch induced front-end damage, placed on indefinite hiatus.

1974 Grand Am
-original 400/4-barrel
-original M21 4-speed
-dad's first new car, sitting in his garage since '86.

[firechicken]

You would base your cam selection off your total gearing taking into account your very low 1st gear ratio. The numerically higher your overall gear ratio, the more camshaft you can run without negativly affecting your cars ability to move easily from a stop or low speed. Generally speaking, more gear = more cam.

[Z Code 400]

'79,

What is your compression Ratio??? What will you honestly do with the car???

If you can provide more technical information, we could get closer to a basic recommendation...Robert

"If I had better junk in my garage, I know I could go faster."

[79firebird_99TA]

Basically the static compression ratio figures to be 8.5:1 and the rear end I'm not sure about. I'll jack it up and figure it out tonight. I was told that the fact that the tires are 26" tall, it is around 3000 RPM at 65 MPH, that it's a 3.73:1 rear end. Does that sound concievable for stock.
Like I said, I'll know for sure tonight.

[Z Code 400]

8.50:1 will really limit your camshaft choice and your rear axle must be properly matched for good performance.

With a 26.0" tire, a 3.73 gear would turn about 3150 @ 65 mph, but you should pull the cover to be sure.

3.73 is a steep gear for a moderate compression 400 in my opinon. That would put you at 4800 at 100 mph. Not bad for 1/4 mile, but pushing a mild camshaft.

I'm not a fan of Comp Cam's Extreme Energy Series, but I really like their Dual Energy line. I would recommend the DEH 265 based on compression ratio alone, but I will wait for more information from you later.

Best of luck...Robert

"If I had better junk in my garage, I know I could go faster."

[79firebird_99TA]

Hi Robert,

It looks like I have a 3.08 rear end gear ratio. Also if I do no milling on the heads then I'll have 8.4:1 CR and if I do mill, it will go up to 9:1.

[BAD ANDY]

Bigger doesn't always mean better. Daily driver?, Vaccume brakes?, Stall converter?, How fast do you want to go? Sounds to me like you had a good runner before. If it were me I'd go a couple steps over stock with a little more lift than durration and go for it!!

[79firebird_99TA]

Not a daily driver and was a dog before with the 350. It's a 4 speed...and I'll put it on the highway once a week probably. Yes, I do have vaccum assisted power brakes.