zacht

iTrader: (18)

i know it says sbc bbc....my dad has a 70 gto 455 car and wants to do upgrades...he has been out of it a while and asked me to research some things...

from the papers he has with it...it has a few mods already.

455 .030 over
#15 heads (small valve)
roller rockers
headers (smaller ones)
dual exhaust with turbo mufflers
comp cam ---280 adv duration .480 lift
th400 with B&M 2400 holeshot converter
12 bolt with 3.08 gears.
msd hei

we dyno'd the car last year, and found the secondarys werent opening...we got that working...

dyno'd 236hp/336tq to the tires, figured that isnt bad...he's wanting a new intake/carb setup for it...most i can tell is go with a edelbrock performer (or performer rpm) intake with something spreadbore around 750-800 cfm..


and we would also like some advice on general pontiac upgrades.

i want him to do an LS swap...but he's not feeling like doing it just yet...

cambirdracing

iTrader: (4)

Don't screw up a GTO with a LS engine. The cam is too small for that big of an engine. And you need at least a 6X head with bigger valves. And probably more gear, somewhere around a 3.73. Go here and ask those guys, they will help you out more than you would expect:

http://forums.highperformancepontiac.com/

A good bunch of guys over there with tremendous amount of knowledge.

ramairetransam

iTrader: (18)

butler performance

Felix C

I have been considering an old school BB build into a late 70s F-body. Did Pontiacs as a youngster and so have a soft spot for those.

The factory intake is considered to be equivalent to the Edelbrock Performer except the inherent weight savings from aluminum and the ability to cool swifter compared to cast iron. There is a High Performance Pontiac manifold test if you wish to Google it.

I am leaning towards the RA IV intake reproduction because I had good service from Quadrajets and it has a built in air gap due to the separate heat crossover plate. There is no Edelbrock Pontiac Performer Air-Gap as there is for Chevrolet engines.

Valves are too small on the #15 for a 455. Depends on how much he wants to invest. A set of low compression 400 heads would work better unless he leans towards aluminum heads.

Then there is the camshaft. 268H is for good flowing heads and exhaust.

One of the nicest street cars I have ever driven was a 1971 Trans Am with a 455HO. It was super smooth and did not need any gearing at all to pull strongly. Perhaps a modern version of that engine-your 455+HEI, aluminum round ports, hydraulic roller copy of the HO cam(#068) valve events but with more lift,etc. is what you are looking for. The SD-455 VEs might be useful.(#041)

455 will produce 100ft-lbs more than an LS1 and probably 100hp less But it will all be down low considering a TH400 is 2.48 1st gear and the 3.08s means you want torque down low.

Good luck and keep us posted. I am budgeting myself to see if this goes forward.

Here is a good link with casting nos, applications, valve sizes and flow nos! http://www.strokerengine.com/PontiacInfo.html

Ironic the 6x heads are highly touted now. We thought they were garbage back when used Pontiacs were plentiful in the junk yard.

zacht

iTrader: (18)

i've done some research as well, and found that the 15 heads are small valve and 87cc chambers to keep compression down...it would have to have a set of heads to keep the compression about the same. About the cam, i've agreed that it is WAY small for that engine...looking at the ram air IV cam...that thing sounds 2x the size of whats in there...

it'd be nice to see him go with something butler or kre performance for it...

and on the intake, i didnt know if one would be better or not...sounds like it is what it is with the stocker...

guess if he's to start anywhere it would be with heads/cam...after making this thread i've read a lot more and it seems like the 455 thats in there was something pontiac put together to get down the road...lol...

maybe he can drop some coin on some heads and a different cam...either way...236hp/336tq wasnt too bad on the dyno i figure around 340hp/440tq at the crank through that th400 and all.....and those 3.08s get him down the road at around 12mpg...

also idk how much more gear that thing needs...read alot that the 455's dont like much rpm/gear...guess if he had a better combo for power he might not need more gear...

cambirdracing

iTrader: (4)

My 68 Bird with a 455 ran it's quickest time with a 3.90 gear, quicker than a 4.10 gear. I had a 77 formula with the same 455 but different cam and got 25 on the highway, it had 2.41 gears. I ran this cam in it:

Crane Cam

Good mid range torque and HP, excellent for 455 SD, fair
idle, moderate performance usage, mild bracket racing,
3000-3400 cruise RPM, 9.5 to 10.75 compression ratio
advised.
H-278-2 (part # 283801)
2000-5600
In 222 278 114 2 40 .000 .467
Ex 234 290 56 (2) .000 .494

Had great low end torque and idle, and as you can see, great mileage with the right gear.