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Old 09-26-2013, 11:30 PM
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Building the top end of my pontiac 400

I have a 78' trans am with a pontiac 400 under the hood. the engine has 130k miles on it but it still runs strong. I got some freshly rebuilt 6x-4 heads to swap with the 6x-8's that are on the engine now, and i also have an edelbrock performer intake manifold and a set of Ram air restorations factory headers. I'm planning on putting these parts on the engine but i was talking to my mechanic and he's advising that i do the o-rings and essentially rebuild the bottom end of the engine to. This is going to cost me a lot of extra money i don't have. Is it really necessary to build the bottom end. I mean i'm not going to get that big of a hp increase, and the compression is still only going to be like 8:1 or somewhere close to that. Any advice?? thanks
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Old 09-26-2013, 11:47 PM
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why are you changing the parts if you dont want an improvement? If you want an improvement,why not do it all and correct?
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Old 09-27-2013, 12:34 AM
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Originally Posted by vinniekq2 View Post
why are you changing the parts if you dont want an improvement? If you want an improvement,why not do it all and correct?
Agree. If you can't afford it right now, save up and do the mods down the road.
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Old 09-27-2013, 08:15 AM
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Originally Posted by zachfromtheville View Post
I have a 78' trans am with a pontiac 400 under the hood. the engine has 130k miles on it but it still runs strong. I got some freshly rebuilt 6x-4 heads to swap with the 6x-8's that are on the engine now, and i also have an edelbrock performer intake manifold and a set of Ram air restorations factory headers. I'm planning on putting these parts on the engine but i was talking to my mechanic and he's advising that i do the o-rings and essentially rebuild the bottom end of the engine to. This is going to cost me a lot of extra money i don't have. Is it really necessary to build the bottom end. I mean i'm not going to get that big of a hp increase, and the compression is still only going to be like 8:1 or somewhere close to that. Any advice?? thanks
Welcome to hotrodders, Zach.

While I do agree that doing it all once and doing it right is the best way, you can- for the price of the gaskets, coolant, motor oil and filter, and your time and labor- bolt on the new parts "for now". But don't expect a big power increase.

In fact, I doubt you'll even notice the difference between the new heads and the old heads unless the old heads are well and truly flat worn out. The difference between the factory intake and the Edelbrock is a wash, performance-wise. You'll see a weigh decrease but that's about it. The biggest hope for a noticeable change in performance will come from the exhaust manifolds, but unless you are going to install (or already have) a true dual exhaust w/lower restriction mufflers, the power increase will be small.

Pontiac info/sites
Pontiac engine info
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Old 09-29-2013, 09:36 AM
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using a 6x-4 head will not get you any more power at all.
ive tried this!
i am also the type that builds on a budget. and i have used many of junkyard blocks.

the best thing you can do on the lowest budget is to find a set of 72cc heads. 16's are my favorite, same valves and it will jump the compression way up.

BUT... you will need a new cam to really wake it up.

that performer manifold, i would advise to take it off, and apply it to the bottom of a house door that does not like to stay open.
you can find used intakes for cheap.

ive bought some holley intakes for 50 bucks and port matched them.
look this up! its a really cheap way to gain peformance! but it also requires you to cut the water cross over off.

the down fall is, once you wake it up...you can pretty much count on spinning a rod bearing. hopefully AFTER youve had some fun with it.

good luck
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Old 09-29-2013, 09:49 AM
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H0trod is right...think of it this way...with fresh heads your going to have a tighter seal up top. This is going to put more stress on the rotating assembly and if you don't spin a bearing, you could possibly start seeing oil consumption through the rings...they have 130,000 miles...the added tightness on the top could play havic on older wearable parts.

If possible, save up and get all done at once...that way you know what you have and won't be tearing the motor down twice.

Ray
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Old 09-29-2013, 10:01 AM
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Originally Posted by 69 widetrack View Post
that way you know what you have and won't be tearing the motor down twice.

Ray

Sometimes its the only way us hard headed folk learn!
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Old 10-01-2013, 12:47 PM
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I did a top end on my 1970 400 I did my heads and cam and it came out with more power and blow by so much it would push up my dip stick.
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Old 10-01-2013, 01:47 PM
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Originally Posted by GMCTRUCKS View Post
I did a top end on my 1970 400 I did my heads and cam and it came out with more power and blow by so much it would push up my dip stick.
There's your answer, Zach.
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Old 10-02-2013, 02:51 PM
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"Take care of your dipstick" LOL

The quickest way to get more performance out of your stock car is to up the rear axle ratio; not bolt on heads and intakes.
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