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Old 04-23-2003, 09:00 PM
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Post stay 400 or go 455

Would it be easier to sup up a Pontiac 400 or a 455 on my desktop dyno I get close readings but the 400 has more ponies and the 455 has more torque. The problem is I want to get as much as I can of both. Its going in my 77 lemans so torque is nice but I plan on going with 3.73 or higher gears and dont know if a 455 will rev high enough. I currently have a 1975 400 with 5c heads although I hear those arent great. I can get a fairly built but possibly stuck 455 with modified 6x heads for 300.00. Unless the guys dad tries to jip me on it. I know there are better judges of pontiacs than me on this site, What way should I go? I have always wanted a big old 455 but my 400 might be a better choice I dont know. what do you all think? Thanks

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Old 04-24-2003, 05:06 AM
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3.73's are the stiffest gear you would want to run with a 455. Most racers that I've talked with say that they have the same results with 3.31's. They just change the slick diameter. 400's are great motors and will accept more gear but you're right about that 75 400. they're not as good as an older 400. Most guys would prefer running 455's if it's a street/strip car. You can't beat the torque they put out. 6X heads are great flowing heads andwork really well on 455's. They also keep the compression ratio down so that you can run pump gas. What do you mean by stuck? Is it locked up? What are your plans for the car? Street? Strip? Or both?
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Old 04-24-2003, 05:22 AM
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For the street, cubic inches are king. However, pontiacs aren't meant to rev high and they in no way will keep up with a chevy. On the other hand, if you know how to build 'em, you don't need revs. A 455 with 6X heads (there are two types of 6X heads, so compression will matter on which you get) will run decent compression and are good flowing heads. But I don't think that I'd run that stiff of gears. I'm running 3.08 in my 74 firebird, and it can hold it's own pretty well. However, I set the red line at 5200, because you cut down on the life of your block at much above that.
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Old 04-24-2003, 06:01 AM
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adryan16 brought up some good points (cept that chevy comment <img src="graemlins/nono.gif" border="0" alt="[nono]" /> ) LOL.

There are actually three versions of 6X head;

The 6X head was installed on the 350, 400 and 455 Engine during the mid to late 70's
Stamping location will determine the cc's of the later 6X heads are as follows:

#4 is 91 cc's (Installed on both 350's and 400's)
#8 is 98 cc's (400)
#11 is 114 cc's (455)

There are two drilled bosses for an A/C bracket(over the end exhaust port) on 6X's, looking at the head from the exhaust port side. At the other end is a lone boss (not drilled) with a # stamped on it.
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Old 04-24-2003, 04:10 PM
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go with the 455,while the year of 400 that you have could still go good,it will not put up with the same abuse the 455 will and you can always balance the motor.And i can tell you that my brother built a pontiac 400 that not to many Chevy could catch let alone keep up to on the street,and yes you actually can get them to rev pretty decent,you just have to build it properly.
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Old 04-24-2003, 04:19 PM
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I would go with the 455 for sure. you can run a little higher gear ratio 3:36-3:55 and it will still pull great off the line. you can design what ever torque and power curve you want with the 455 and you'll still have big cubes for HP. check with of the cam companies and they'll set you up. Even better you might want to consider using a 700 r 4 trans. the low first gear ratio is unreal. so you can run like a 3:08 or 3:36 and leave plenty hard. Example 700 r 4 with a 3:36 is like having a 4:11 gear and you still have over drive for the road. I was skeptical on the 700 r 4 trans until i tried it. WOW! I just did a 74 vette 350-350hp with a 3:36 and it flys will haze the tires for a block.
good luck
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Old 04-24-2003, 08:33 PM
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Ok if this guy ever calls me back (he was supposed to call 2 weeks ago.) I plan on buying the 455 or finding another one. they are hard engines to find around here. The problem is I have that 400 and a perfect crank sitting here and I know where to buy some real nice parts for it. So the longer it takes to find a 455 the better that 400 looks. Either way I go I plan on doing a full rebuild. Pistons, rods (if needed), crank (if needed, at least cut or polished), head work, etc. The car will be mostly stop light to stop light womping on the rice and some strip use. no highway or distance driveing.
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Old 04-26-2003, 09:54 PM
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First off adryian 16 my 400Pontiac has walked all over big block Chebies on the strip and that was with junk 2 barrel Catalina heads.And whoever said you can't turn a Pontiac up, well I'm not afraid to turn mine to 6200 and have on a fairly regular basis for the past year ( tire smoke smells good in third and fourth gear) The 75 block has one of the better cranks Pontiac offered (the 74-76's) were lighter than the earlier cranks from 67-73. this helps for it to rev a little quicker. Also a 350 Pontiac crank can be modified to work in a 400 for even faster and higher revs, but when doing this make sure you have the rotateing assembly balanced. There are several cams out there for Pontiacs, research them carefully because Pontiac respond better with dual pattern cams with a wide lobe separation. The 068 Ram Air III was one of the finest cams ever used in a Pontiac and this cam was also used in the 455 HO's built in 71-72. Use a good dual plane intake, either a 68-72 cast iron or Edelbrock Performer with a quadrajet, and HEI ignition.The best heads to use would be a pair of 6X's from a 350 or if you can find them a pair of 96 D-ports from a 71 GTO or Grand Prix. Hope this helps and go for it.
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Old 07-05-2003, 07:01 PM
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Thumbs up 455

NO DOUBT , 455 YOU'LL BE GLAD YOU DID AFTER IT'S ALL SAID AND DONE . :







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Old 07-06-2003, 03:26 AM
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Check out some of these:
http://www.boyleworks.com/ta400/psp/featuredcars.html
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