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Old 10-29-2003, 12:06 PM
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400 vs. 455

Hi everyone,

I am a newbie here and this is my first post. I think this site is great and the opinions and answers of some threads are great. You guys really seem to help out everyone. I guess its my turn to ask a question. Any replies will be greatly appreciated.

My son and I have been faithfully working on our 74 gto project car for a while now. We actually have all the performance parts we just need a block. We are trying to chose between the 400 and 455 pontiac. I was wondering if I list the parts and specs we have, if one of you nice fellas could run it through a dyno simulator.

I want to find out the power difference between the two engines. And also the difference in power with E heads vs. our 6X-4 heads.
Ok. so here goes.


-455 block .30 over
and
-400 block .30 over

both w/flattop pistons with 6cc of valve relief
-----------------------------------
Quench dist. on both .45
-Edlebrock heads
87cc chamber
(compression ?)
215 cc intake port
2.11 intake valve, 1.66 exhaust

or
Pontiac 6X-4 heads (ported)
90cc chamber
(compression ?)
200cc intake port
180cc exhaust
2.11 intake valve, 1.66 exhaust

All the rest of the parts will go on either engine-

-Intake is a performer RPM
-Edlebrock 750 carb
-stock Hei ignition

camshaft-comp cams Xtreme energy
installed straight-up
intake-230 @.050 lift
Exhaust-236 @.050 lift
intake lift- .488"
exhaust lift- .491"
1.6 ratio rockers
110 degree lobe separation

Sorry such a long post you guys but i will really appreciate any responses or thoughts on these combos. my son and i will like any input. thanks again!!

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Old 10-29-2003, 06:39 PM
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anyone. help?
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Old 10-29-2003, 08:52 PM
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Compression between the 87 cc heads and the 90 cc heads will be basically the same. The difference is that the aluminum heads on the 455 won't have a problem with pre-ignition while the iron heads will. No amount of porting the 6x's will equal the Edlebrock's out of the box. You will, however, dish out a bunch of cash for the aluminum heads and corresponding round port headers (but it's worth it).

455 compression will be about 10.2:1
400 compression will be about 9:0:1

The 455 will produce more torque and power throughout the rpm band over the 400. Go with the 455 if you have a choice. The extra cubes will also smooth out your Comp cam idle a little bit. Plan on running about a 2500 stall converter with this cam. Remember that the 1.65 rockers(actually closer to 1.72 according to Harland Sharp) will increase valve lift by 10% and effective duration by about 4%. You're getting to an area where power brakes might not work well, but a vacuum can or vacuum pump will solve that if you do want power brakes. I personally like to stay just under 230 degrees duration for the street on a hydraulic flat tappet cam, but we all have a different threshold of what we will put up with.
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Old 10-30-2003, 01:58 PM
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hey 74,
welcome to the forum! it sounds like you will have stout combo either way. i would personally (money provided) go with the 455 E headed block. killer combo. car craft did a build up on that combo (i think even same cam and specs!) and made awesome power. they took a junk yard motor with the stock lower end and kept adding parts. started with like 240 horse and the end result was something like 440 horse and 550 lbs of torque peaking at 3800rpm!!!! all that was changed was heads, cam, intake, carb, and headers. awesome stump puller. im thinking of a similar combo for my 78 TA. they said compression on that was 9.5:1 with the E heads.

the site is http://www.carcraft.com/techarticles...ont/index.html
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Old 10-30-2003, 02:12 PM
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thanks for the replys. bandit, that site is great, i am definately sold on a 455 instead of a 400. you say you have a 78 TA? i had a bandit when i was in high school. that was the best car i have ever owned. you got any pictures? i would love to see the car i used to drive. thanks.
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Old 10-30-2003, 02:19 PM
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i have some pics for you. these are right when i got it back from the paint shop. its amazing how much better it looks compared to when i took it to the shop in primer and bare metal. i did the prep and decals myself and just had it sprayed by my local shop.
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Old 10-30-2003, 02:26 PM
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Old 10-30-2003, 02:26 PM
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Old 10-30-2003, 02:28 PM
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Old 10-30-2003, 02:30 PM
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sorry i had to do my pics like this. but it wont let me do multiple jpegs in one post. last one
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Old 10-30-2003, 05:43 PM
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sweet ride bandit! brings back lots of memories. keep the dream alive
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Old 10-30-2003, 10:33 PM
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74GTO400, a 455 is a good choice for a 74 GTO, I had a hand in setting on up about a year or so ago. It was a .030 over 455 with modified 46 heads (about 9.5-1 compression) a TFX solid lift cam designed by Jim Taylor, with 1.65 ratio Harland Sharp roller rockers, Edelbrock Performer RPM intake, 850 Holley, MSD ignition and headers (I can't remember the brand). It was a four speed car with 3.73 gears. The car ran tire smoking 7.80's in the eighth and was shifted at around 5800. A good head shop that has experience in Pontiacs can port and flow your heads to make excellent horsepower. 455's are known for massive amounts of torque and it's very easy to overcam Pontiac engines. Look for a moderate duration (at .050) cam with a range of up to 5800. Pontiacs respond well to split duration cams with compression ratios between 8.8- 9.8-1. The advantage of a 400 over a 455 is the smaller mains and less rotating mass and will rev higher. The bore stroke ratio on a 455 is very good though and that makes for an excellent street engine. Hope this helps on your decision and welcome to the board and it's good to see more Pontiac folks on here. I've owned a71 GTO for the last 17 years and have seen many combinations over the years. A couple of places to contact for more info is Kauffman Racing equipment (www.krepower.com) and Ken's speed and machine (Pontiac Dude) in Florida.
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Old 10-31-2003, 09:51 AM
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thanks grusome for the feedback. maybe i'll go with the 6X heads and spend more money in the bottom end. i'll just get everything i can out of them. maybe i'll buy E heads later. do you think i will have around 9-9.5 compression with the 6X's on a .30 over 455 with a zero deck? 9.5 is the MAX comp ratio i want. i would rather have 9:1. i think the chambers are around 92 ccs.

do you know the appox. cam specs for that motor in that 74?

i am looking for around 550ft/lbs of torque with this combo. do you think that is possible with the 6X's? thanks again!

Last edited by 74GTO400; 10-31-2003 at 09:59 AM.
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Old 10-31-2003, 07:25 PM
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74 I don't know the specs on the cam but will see if my friend might still have them. I do remember one thing about the TFX cam, even though it's a solid lift cam, periodical adjustment of the valves is not necessary. The 6X heads at zero deck height should yield a 9.5 compression ratio with .042 thick FelPro head gaskets. You can contact Jim Taylor directly on the TFX cams if you want more info on them. He can recommend the right cam for your application. I should have those specs with in the next couple of days.
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Old 10-31-2003, 09:57 PM
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I believe that it works out a little closer to 9.8:1 with 92 cc chamber heads. This site has a built in calculator for computing compression ratio and other things. For the ratio calculator go to the home page; click on knowledge base, 1 engine, 2 engine calculations, 2 engine size and compression. The 30 over bore will be 4.18, stroke on the 455 is 4.21, for dome you are going to enter something between -5 and -7 cc for flat tops with valve reliefs, and the Felpro gaskets will come in at between .042 and .043. And I think you are smart for sticking at no more than 9:1 compression with iron heads. Also this sites ratio calculator works out very close to hand calculations. Only shortcoming is not having a variable for deck height, but since you are going for "0", this doesn't matter. If you haven't worked the 6X heads yet, don't cut them down so far, and leave the chambers about 100-103 cc and you will have your 9:1 compression.
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