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Old 03-21-2013, 04:59 PM
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building a Pontiac 400 high for performance street

I am working on a plan for my 1976 trans am. It has a 10 bolt rear end with 4:10 gears and a (original?) Borg warner super T10 4 speed and rear tires are 295/50/15. The engine I picked up is out of a 76 automatic TA with 6X-8 heads. I also got a bare set of 6X-4 heads with the motor. I do not intend to keep the rear gears since I want something highway friendly at 70mph. Still want to be able to fry them big tires if i ever feel the need to. Mostly I just want a very good street performer with that lopey idle and lots of power I have no intention of ever racing the car. I would like around 300 to 400 horse power....but 15mpg on the highway would be nice too. I have been reading a few books by Rocky Rotella and Jim hand. Keep in mind I just got this car and I am still learning. I need a real good plan before finding a quality machine shop to do the work. Also don't think a stroker kit or aluminum heads are needed for my goals.

Can I get 9.1 to 9.5 compression without milling heads or boring more than .30 over?
What is a good cam and rear gear for my goals?
Do I need to port or mill my heads?
Where do I find the RPM 5140 rods for $250 a set that I keep reading about?
Are things such as stainless valves, enlarging the 1.66 valves to 1.77, porting, 7/16 bbc screw in studs and roller rockers worth the extra money with the goal I have in mind?

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Old 03-21-2013, 05:05 PM
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Also would like to stick with an intake that won't give me trouble with the shaker hood, such as the stock one or a performer. If needed I read there is a kit that allows use of the shaker with a performer rpm.
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Old 03-21-2013, 05:23 PM
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You didnt say what engine you have 400? 455?
Mr. P body sells the 5140 rods for about 259 a set
Also butler performance sells them.
Porting (mild) will help...dont attemp porting untill you have done some serious homework on porting.
Milling may be necessary and desired
Gotta get a gear ratio for the rear... 3.08 or 3.23
What engine do you have ?
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Old 03-21-2013, 05:27 PM
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Sorry, I had it in the title but forgot to mention in the message that it is a 400 that I want to have bored .30 over...so about a 406?
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Old 03-21-2013, 05:32 PM
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Cool.
you can get good power from a 400 without breaking the bank.
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Old 03-21-2013, 05:39 PM
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You will need to CC your heads to see EXACTLY what they are.Dont trust the charts you see on website. Your lucky to have 6x-4s and 6x-8s
You dont need to go clear to 9.5 to one for good power. You can stay under 9 and still make good power by running a lunati Voodoo or comp cams XE grind. They tend to "make" compression.
Or go to 9.0 - 9.5 and run a summit 2801 or similar.
I have 9.45 to 1 and I am running a Crane 272 - h 216/228 at .050 112 LSA.
My dynamic compression is around 7.5 pretty close to the edge.
I also decked my block to .005 and am running the 5140 s with sealed power forged slugs.
I started with a 65 389 block and used 400 pistons ( 4.120)
Its for the light blue sled in the picture
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Old 03-21-2013, 06:26 PM
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If the 6x 4 heads do cc out to 93cc as the charts say what is the best way to lower compression with out stroking the motor or boring it to the max? Or is a stroker kit the best way to do it? I don'twant a 461 stroker if I am going to be stopping at every gas station I see. Since I am on the subject, 91 octane is the best I see around my area. So 9.5 is the max cr I want to run. Maybe even a bit less.
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Old 03-21-2013, 06:49 PM
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The old 400 GTO's were 10.75.1 compression with the old heads. They ran really good and from the factory were rated at 360HP.
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Old 03-21-2013, 06:55 PM
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Quote:
Originally Posted by 76TAmatt View Post
If the 6x 4 heads do cc out to 93cc as the charts say what is the best way to lower compression with out stroking the motor or boring it to the max? Or is a stroker kit the best way to do it? I don'twant a 461 stroker if I am going to be stopping at every gas station I see. Since I am on the subject, 91 octane is the best I see around my area. So 9.5 is the max cr I want to run. Maybe even a bit less.
93 CC heads put your static at 8.23, even if you run a small cam you would be OK on 87 octane
Boring raises compression if same such heads are used in formula
Stroking the engine if same such heads are used in formula
Both increase cylinder volume.
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Old 03-21-2013, 07:08 PM
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Keeping it simple , Be sure the line bore is checked, Bore it .030 and have it plate honed .
Forged rods and pistons would be "overbuilding" it but would give good peace of mind.
Run the 6X 4 heads, milled only enough to clean them up. Do some MILD porting and bowl cleanup.
Run the pontiac quadrajet intake and carb
HEI
Comp cams XE 268 should work nicely ( 51-223-4)
Change the rear gear to a 3.55 or 3.23
You will need to run the comp springs
Be sure to used screw in studs.
Cams that use .480 ish lift need enough spring pressure that it will pull out press in studs , be sure to use screw ins.
Headers and duals will help a lot.
Duals are needed for sure.
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Old 03-21-2013, 07:11 PM
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From what I have read anything over 9.5 cr can give detonation problems with today's lower octane gas. I don't want to have to add any additives to the gas or risk ruining the engine. I as curious what all the people still running all the older Pontiac high compression motors are doing to avoid detonation. I was offered some reasonably priced #13 and 48 heads but passed.
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Old 03-21-2013, 07:15 PM
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Keep and run the 6X heads. They are good heads and flow well. Save your cha ching for other goodies.
Like I said , the 93 CC will give you around 8.25 static and the Comp XE 268 , will give around 6.86 dynamic.
Well within a safe range for even 87 octane with an easy ...proper tune
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Old 03-21-2013, 07:35 PM
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Quote:
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Keeping it simple , Be sure the line bore is checked, Bore it .030 and have it plate honed .
Forged rods and pistons would be "overbuilding" it but would give good peace of mind.
Run the 6X 4 heads, milled only enough to clean them up. Do some MILD porting and bowl cleanup.
Run the pontiac quadrajet intake and carb
HEI
Comp cams XE 268 should work nicely ( 51-223-4)
Change the rear gear to a 3.55 or 3.23
You will need to run the comp springs
Be sure to used screw in studs.
Cams that use .480 ish lift need enough spring pressure that it will pull out press in studs , be sure to use screw ins.
Headers and duals will help a lot.
Duals are needed for sure.
6X heads come with screw in studs so that helps. I do want to use the 5140 rods for peace of mind, plus I was told it isn't much cheaper to resize factory rods and upgrade to ARP bolts. I was also thinking about speed pro forged pistons with 6.7 cc valve reliefs at 4.15 bore.

I have no idea what normal clean up milling would take off but if I had the taken down to 91cc and zero decked the block I would end up around 8.77 cr. It will have daul exhaust with headers or the ram air type manifolds. If I was to buy the XE 268 cam would it be wise to buy the kit that includes springs, lifters and timing chain?
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Old 03-21-2013, 07:41 PM
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Quote:
Originally Posted by 76TAmatt View Post
6X heads come with screw in studs so that helps. I do want to use the 5140 rods for peace of mind, plus I was told it isn't much cheaper to resize factory rods and upgrade to ARP bolts. I was also thinking about speed pro forged pistons with 6.7 cc valve reliefs at 4.15 bore.

I have no idea what normal clean up milling would take off but if I had the taken down to 91cc and zero decked the block I would end up around 8.77 cr. It will have daul exhaust with headers or the ram air type manifolds. If I was to buy the XE 268 cam would it be wise to buy the kit that includes springs, lifters and timing chain?
Yes, Yes , Yes and Yes. Now your cookin with gas.
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Old 03-22-2013, 07:42 AM
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4.10s were never a Pontiac "factory" gear. T/As of that era with the 4-speed were usually 3.23s or 3.42s. The latter is the best for overall "street performance". Good accelleration and reasonable cruise RPM.

6Xs can be made to "work" on a 400. Milling about .040" off the -4s will yield right at 9:1. Get them "down" to about 88 CCs, 90 at the most (-8s are not suited to this, better left to the larger displacements). The exhaust valve should be upgraded to the 1.77" version. Porting should be done by someone that knows both porting AND Pontiacs. What makes a Chevy "turn on" may "kill" the power in the Pontiac. Jim Hand's "How to Build Max-performance Pontiac V8s" by SA Designs has VERY good porting detail.

With the manual trans, I would more recommend the XE274H over the 268. Still plenty of low-end and adequate vacuum, it will rev well past 5,500, where the 286 will be "all done" before that. If you REALLY wanna get silly, and make a 406 Pontiac a seathing monster, consider the XS series. We use SX274S in many 400s, along with the 6.8" Eagle rod. They routinely rev beyond 6,500 making power. NOTE: If someone tells you you "can't" rev a Pontiac, send them back to the '70s... Remember, when a Pontiac is running, it's making torque. It's very difficult to "hurt" the low-end. Add that to the power peak above 6,500 and you have a very strong street engine with a BROAD power band. I highly advise AGAINST the "K-Kit'. It contains the "wrong" timing set AND valve stem seals. Oh, they "fit", but they're not the ones we would use if building an engine for a customer. The timing set is the cheaper "2112", where the 3112 is called for ("true" roller, not a glorified bicycle chain). The Teflon seals are okay for a race engine, but we use Viton in street engines today. Also, there are other spring providers that have good offerings for the "odd" heights the Pontiac calls for. Reports on the Comp 995 have been spotty.

IMO, the best intake for the 400 is the RPM. This presents a hood issue, as you said. Larry Navarro of WFO Enterprises makes a "drop base" air cleaner housing for this purpose. It allows the use of the "shaker" AND a good intake. I would also recommend the AED 750HO or HOM carb. An MSD "Pro Billet" will cap it off. This combo is well over 400 HP and around 475-500 lbs. of torque.

There will be plenty other "opinions" on this. You will be advised to forget the smaller engine and "stroke" it to 461 or bigger. Good advice, but not MANDETORY. 400 is the engine that made GTO famous, and it wasn't famous for getting beat... A 400 is no punk when properly prepared. Vinny Meyeda goes 6.90s over 200 with a stock-block/crank 406 in his Probe F/C.

Jim
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