[MetalHead175]

So I've been building my 70 Firebird for quite some time, and gathering info on the way. This is going to be a street/strip car. However I've come to a road block now that it's time for the motor to go in. I have a '74 455 with 4X heads (low compression ones) that I was going to put in it. I also have a '69 400 with 62's and was i believe a factory 350-375hp engine out of a Grand Prix. Both engines are rebuilt, and I won't have enough money to secure heads for the 455. So my question is, which one should I go with temporary before I build a race motor? I'm leaning towards the 400, but I like the torque and cubes of the 455. However, with less money the 400 makes more horespower...Both engines will have the same manifold, ignition, headers and decent sized cams. I will eventually build the 455 to go into the Firebird but I need something to kick around with now. I know nothing about 400's so cam suggestions would be helpful too What do you guys think?

[BILTIT]

The 400 w/62's will be too much compression for pump gas without the right cam to bleed off some cyl. pressure (my 400 w/670's was the same way but i ran a RAIV cam which bleed off cyl. pressures.). Even with the right cam you will need some decent gears and conv. (if auto) to have this thing perform. I would personally put in the 455, even with low comp. it will have torque (more torque = more fun). It will be nice to run with 87 gas too.

[MetalHead175]

Yeah i forgot to mention though that the car has 3.73 gears.

[BILTIT]

I rough calculated the comp. of the 455 at 8.1:1 which is not as bad as you think. It would still pull hard with the right cam, timing, and carb adjustments.

The 400 would be about 10.2:1

[71 Ventura II]

Even with the 3.73 gear your going to be much happier running the 455 over the 400. Don't be "Fooled" by the assumption the 400 rated at 350-? HP can or would be faster than the 455. Running 8.1-1 compression with the right camshaft, intake, ignition, and tires will make for a very strong running car.

EX: We built a 1976 Firebird with a Stock 455, stock iron intake, Lunati Bracket Master II cam .490/.490 @0.050 .230/.230 Adv 292, Comp 1.52 Magnum roller tip rockers, Holley #6213 Spread-bore DP (800 cfm), TH350 w/stock converter, 3.73 Auburn posi, and 275/60/15 Cooper radials. This car could not hook the radials at all and still ran 13.20's at 103 mph. There was alot more ET left in the combo with sticky tires!

We copied an article from HPP magazine, from a build up by Jim Taylor East Coast. On the dyno his engine made 390 HP @5200 rpm and 500+ ftlbs of torque. I can't remember the torque peak rpm, sorry. JD

[MetalHead175]

Torque is what I'm after, is there really a huge difference in just 55 cubic inches? I think this thread helped me decide to do the 455.

[BILTIT]

Its not just the cubes but the increased stroke.

[mikeb]

455 hands down. You'll have to back the timing off on the 400 to stop detonation and it'll be a dog.

[Hard-Timess]

My 400 Bird with Bullet 068 hydraulic cam out performs 455s hands down. See August issue #27 of High Performance Pontiac.

Now, having said that, if you are going to drive this on the street with todays available fuel, put the 455 in with the 068 cam, bring the 4x head down to 89/90 ccs and have fun.

[gold bird]

455 it,s to much fun.

[firebum]

Hard-Timess,

How much off the 4X's to get 89/90/?

Thanks,

Jim

[Ron H]

If you are going to modify the engines the 455 will win hands down.

[MetalHead175]

Thanks guys! 455 it is... I'll let everyone know how it goes once I get it all done!
-Jason

[BVR421]

Originally Posted by MetalHead175

However, with less money the 400 makes more horespower..

you can pull two plug wires off that 455 and it will still beat the 400

Trumans 400 is indeed fast but it is not exactly a motor he just jerked out of a clunker and tossed in his Firebird.

[johnsma22]

You can also just install a 455 crank (mains re sized to 3"), and standard bore 455 pistons in a .030" over 400 block, and stroke it! That will give you the best of both worlds. Longer stroke with the strength of the 400 block. You end up with a 455 on 3" mains.

[JLMounce]

If it's not going to be a car that gets cruised a lot, you may consider swaping the 62's on to the 455.

I know I'm going to get flamed for this, but it's a great way to build power. Yes you'll have to keep a supply of high octane fuel, but especially if you're planning on building a race engine, you're going to need that anyway.

I currently run a .030 over 455 with 62's. The car is just stupid. Way more power than anyone could ever need. That's what makes it so fun.

[MetalHead175]

That's not a bad idea, but I will cruise the car as much as I can. How much would I have to dish the pistons to get it into 91 octane pump gas range?
-Jason

[b-man]

Originally Posted by MetalHead175

That's not a bad idea, but I will cruise the car as much as I can. How much would I have to dish the pistons to get it into 91 octane pump gas range?
-Jason

About 25 to 30ccs, 30 being best. Getting a 455 under 10:1 with 72-75cc heads takes a deep dish in the piston, custom Ross pistons can be made with the big dish.

[JLMounce]

The problem with going that deep of a dish on the piston tops is it really screws with quench. If you need lower compression the 62's on the 455 aren't going to be a very viable option.

[BILTIT]

Yup, i run 30cc dish in my piston with the 670's-72cc chamber. I am not sure i agree with the bad quench idea though.