[Badss540]

Good Morning, I'm going to start the rebuild of the 71 GTO 400 ci 300 HP for my 67 Firebird and I'd like to get a little more (350hp) from it but stay close to stock as I can.
The block will be 030 over with the stock style pistons which are 8.5 to 1, with 96 cc heads that will be massaged on the intake and exhaust.
I have a 1968 spreadbore manifold ( will that work?)that will also be ported a little bit with a Carter carb that will be rebuilt by SMI with the specs from the build.
I'm using the Nodular crank cut 10/10 and getting new rods ( eagle)
TH400 with stock style converter, 308 posi with a 14 inch rim/tire
Want to stay with a Hydrolic cam.
Using stock style exhaust manifold.
Thanks for any help and input.

[steve25]

You should deck the block to have zero deck height and mill the heads .030" to get you to at least 9 to 1 compression, 9.4 would be ideal, but the heads would need to get milled .060" on both the deck and intake flange so things will bolt back up.
A decent bowl port job on the heads and a factory type 068 cam with High lift 1.65 rockers will probibly net you closer to 400 HP even thru the exh manifolds, but at some point you should step up to the better flowing RA type manifolds, if not headers.
A stock port matched 68 intake and a properly jetted Q- JET carb is fine for your needs.
You want to run a HEI distributor with the Vac advance hooked up.
The only other area that will need to be attention is the 3.08 gears if you go cam wise bigger than a factory 067 cam specs, the 068 cam will work far better with a 3.42 to 3.55 rear gear!
Take things in steps and build a strong short block first that will let you go with a top end parts down the road that will let you make 600 HP if you ever want to, and you will never have to yank the block out of the car to do so!

[paint guy]

For my 69 GTO vert, I had my 71 YS GTO block rebuilt with the same intention as you (about 350 hp, just a nice cruiser motor) with an .0030 overbore. I reused the 96 heads and kept the compression at around 8.5 (maybe even a little less) with the intention of running regular gas. 87 octane and no pinging even on hot summer days. No port work on the heads, just some casting flash clean-up and gasket matching using a Performer manifold (this was probably a mistake except for the weight savings) a Melling cam 2801 style, and R.A.R.E. exhaust manifolds with a 2-1/4" exhaust. HEI distributor, 3.23 gears and a T-400. Certainly not the fastest car in town, but it's no slouch either, and does what I want it to do. ( I have driven this car on vacation to northern Minn, also make sales call in this car) As someone used to small-block chevies and high revs, I remember my engine builder telling me "you'll be surprised at what a low-compression Pontiac motor will do." He was right. IMO, some of the best money spent was the exhaust manifolds.

[locomotivebreath]

I built my 400 similar to as described above . It's the original engine for my 68 gto and all parts carb to oil pan where reused except I stepped up to 2.5 ram air manifolds . And made 412hp and 482ftlb . Was a little lean so I'm sure more was on the table. I used a small ra3 style hydraulic roller cam and my compression is right at 10:1 so 93 is a must. The #16 heads had a mild port job ( 230cfm @ .500) basically it's a ram air style engine and makes 16.5 inches of vac.and idles nice. Hydraulic roller was just for piece of mind but not necessary . You'll get a lot of comments to stroke it and I could have done that for the same money I have in the 406 but like you I was just after a good stout street motor.

[locomotivebreath]

I forget to add I did have the block zero decked and used eagle rods,probe pistons , and Harland sharp 1.5 roller rockers . If you can work a roller cam into the budget I really feel it's worth it . It'll seem real cheap if ya wipe a flat tappet cam ! Saw May neighbor do this on a sbc made my mind up right there. Tomahawk had some killer baby rollers out , check out the motor rocky rotella did in his book , that the motor for you !

[screamingchief]

Please read my post in your thread over @ YB.com. (saw that one first today)

But to recap for the members here,,,dont use the 8 valve relief 400 cid pistons!!!

Cant stress that enough.

Engine wont be 8.5:1 CR with those,more like 7.5:1 CR.

HTH

Bret P.

[Badss540]

Thanks, would the 067 or 068 work better with this setup?

[screamingchief]

Honestly,I'm not a "factory cam" kinda guy myself.

Too many better cams out there these days.

Final cam choice is gonna depend somewhat on final CR of the engine,so any suggestions @ this point are going to be more general in nature than specific.

That choice also depends on the goals of the builder.

FWIW

Bret P.

[Will]

As has been mentioned - use good quality pistons with 4 valve reliefs, NOT the rebuilder 8-relief pistons, cut the block for zero deck, mill the heads .030" on deck and intake side. You'll end up just under 9:1 compression which should be fine for what you want. If you want to spend the money, get some custom 2-valve relief pistons and you should be right at 9:1. Sounds like the ports are getting cleaned up so that'll help a little.

A factory '68 manifold is pretty much the best intake you can run. I'm not a fan of Carter carbs, would much rather see you run a Q-jet...

I'm with Bret - I wouldn't run a stock spec cam though you really don't want to go very big with a stock torque converter and 3.08 rear gears.

The 066, 067, and 068 cams were all originally designed for mid 9 and higher compression ratios. They also have hardly any lift. I'd go with a modern profile that uses a more advanced intake centerline to work better with the lower compression and has more lift and thus more "area under the curve."

Something like the Crower 60915 would be an excellent choice, or for better low RPM torque the 60917.

Both of those cams will work very well with manifolds. Definitely get some RA manifolds, they'll make a big difference.

Get your distributor recurved, that'll also make a big difference. Exact timing numbers are unique to each engine, but a curve that gives you 12-14 initial with 32 total all in by 2800-3000 RPM should be real close.

Consider investing in a good quality torque converter, something that will be well coupled below it's stall speed but still give you a 2400-2600 RPM stall when you nail it. Torque converters, IMO, are one of the most overlooked and misunderstood performance parts out there. They can make a huge difference to how your car performs without negatively affecting driveability when properly chosen.

[Badss540]

Originally Posted by Will

As has been mentioned - use good quality pistons with 4 valve reliefs, NOT the rebuilder 8-relief pistons, cut the block for zero deck, mill the heads .030" on deck and intake side. You'll end up just under 9:1 compression which should be fine for what you want. If you want to spend the money, get some custom 2-valve relief pistons and you should be right at 9:1. Sounds like the ports are getting cleaned up so that'll help a little.

A factory '68 manifold is pretty much the best intake you can run. I'm not a fan of Carter carbs, would much rather see you run a Q-jet...

I'm with Bret - I wouldn't run a stock spec cam though you really don't want to go very big with a stock torque converter and 3.08 rear gears.

The 066, 067, and 068 cams were all originally designed for mid 9 and higher compression ratios. They also have hardly any lift. I'd go with a modern profile that uses a more advanced intake centerline to work better with the lower compression and has more lift and thus more "area under the curve."

Something like the Crower 60915 would be an excellent choice, or for better low RPM torque the 60917.

Both of those cams will work very well with manifolds. Definitely get some RA manifolds, they'll make a big difference.

Get your distributor recurved, that'll also make a big difference. Exact timing numbers are unique to each engine, but a curve that gives you 12-14 initial with 32 total all in by 2800-3000 RPM should be real close.

Consider investing in a good quality torque converter, something that will be well coupled below it's stall speed but still give you a 2400-2600 RPM stall when you nail it. Torque converters, IMO, are one of the most overlooked and misunderstood performance parts out there. They can make a huge difference to how your car performs without negatively affecting driveability when properly chosen.

Will, thanks for the info, forgot to say I'll be using the MSD HEI distributor that came with it.

[74Grandville]

if you go with the Carter, i would make sure to port the intake like Cliff R's intake to improve the mismatch of the carb to intake. you could send it to SD if you like as they have CNC program for it. if this is not addressed i think you will be leaving a lot of power on the table.

http://forums.maxperformanceinc.com/...re+bore+spread

[Skip Fix]

I have a similar 400 in the kids old '81 that used the Summit 2801 cam, seemed to work pretty good with flat tops 93cc 6X-4 heads and RA manifolds.