[luckyluc68]

I need help please!!I have the chance to buy a block for building a street strip engine. tThe car is used on a daily basis .I will be using the engine in a 1975 T/A that has a ST10 Borg Warner 4 speed/2.43 1st/1.76 2nd/1.41 3rd and 1.00 fourth gear ratio.Car has a Posi 10 bolt with 3.09 gears.Now these are the choices i have 1 is a W72 complete engine from a 78 T/A with a factory 220 hp to start rebuilding with, 2nd is a 1974 455 block that has barely any where on original cylinder jugs (refresh rebuild)and comes with 6x heads with 240 hp, Torque is higher on this block but also it the weight is heigher.I would like to have a total hp of 420 to 480 hp with good torque to move this heavy T/A..Any stories,advice that will help me decide on which block to buy would be greatly appreciated..thankyou

[luckyluc68]

I need help please!!I have the chance to buy a block for building a street strip engine. tThe car is used on a daily basis .I will be using the engine in a 1975 T/A that has a ST10 Borg Warner 4 speed/2.43 1st/1.76 2nd/1.41 3rd and 1.00 fourth gear ratio.Car has a Posi 10 bolt with 3.09 gears.Now these are the choices i have 1 is a W72 complete engine from a 78 T/A with a factory 220 hp to start rebuilding with, 2nd is a 1974 455 block that has barely any where on original cylinder jugs (refresh rebuild)and comes with 6x heads with 240 hp, Torque is higher on this block but also it the weight is heigher.I would like to have a total hp of 420 to 480 hp with good torque to move this heavy T/A..Any stories,advice that will help me decide on which block to buy would be greatly appreciated..thankyou

[jamaca85]

no argument the 455 more torque, will move that heavy car no problem.

[ontheblocks]

455, especially with 3.08 rear.

[Thumpin455_GTO]

Weight difference between the 455 and 400 is negligible, the power you can get from a 455 more than makes up for it. Add a cam, like the XE268 a Performer RPM intake 750-850 Holley, or Qjet, Headers, and optionaly some ported Iron heads and you will have a fun driver that will still run mid to low 13's with the highway gears.

Nearly the same engine in my 4200lb GTO ran 13.50 with 2.93 gears spinning off the line with BFG Drag Radials. (ULtradyne 280/288 and ported 5C's)

[prostreetpower]

I dont care what u say todd, i still lik emy w72 400 block .....any ways its almost impossible to fin a 455 pontiac in southern Cali..i envy u guys

[78 GHOST]

I have a 455 in the GTO and a 400 in the T/A. Both are at different ends of the spectrum in terms of buildup. The 455 is lumpy and runs high compression #64 heads. The 400 is smooth and runs low compression heads.

The 455 definitely provides more torque, which is what moves ya. It also drinks more fuel and has different manners entirely. It drinks premium only and requires an exact tuneup.

The 400 is no slouch on torque, it just takes a lot longer to come on, not the slam of "Oh Crap!" power the 455 has. The 400 idles smoothly, gets excellent mileage, and is more behaved and appropriate for daily driving. It runs on Regular and is happy with almost any tuneup.. truly a dependable engine.

If fuel $ is no concern, you don't mind the lopey idle.. definately build a 455. If economy and balance are more your speed, try a nicely built 400.

You can build either engine as mild, or as radical as you wish. However, if you go with a 455, you're starting with a large displacement advantage.

Personally, I feel you can build a 455 a little more mildly to achieve the same torque goal as a 400 simply due to the mechanical advantage of the extra cubes.

[Thumpin455_GTO]

I have a W72 in a 78 Bonneville, GREAT ENGINE! Absolutely nothing bad to s ay about them. Moves that heavy tank with 2.41 gears! no problem.

My GTO has a 5C headed 455 and has gotten an amazing 24 MPG with a 2004R trans Q jet and 2.93 gears, 28" tires. 80+ mph just above idle, very docile and great manners untill you stomp it. The Bird had a 11:1 compression 455 that only wuld take race gas and shoved the bird to high 11's with a very mild setup.

I love my 400's including the 71HO in my 76 Chevy shortbox, but I like the 455 better, and any 400 can be a 455 with a crank and 455 pistons. Its so easy to do now its scary. Who needs a 3.25 main anyway?

[PMDRACER]

Go with the 455. No question.

[luckyluc68]

Thanx for the input folks, but im still on the fence...i have heard the 455 has thinner walls and have had overheating probs along with a heavier total weight than the newer w72 400 block. I Read an article that says the 400 would handle todays crummy gas better too.I want to have a "rumpady rump" sound come out of the 3"custom pypes x exhaust,with superflow mufflers.With 6X heads,I am putting in a .050"lift 215/224 exh/intake with a valve lift of .408"/.407".The factory QJ 800cfm from the w72 would sit on a performer intake or a 68 "RAM AIR" intake.The T/A is a original stick 400 car but a 455 stump puller would be cool too.Everyone around me that sleeps ,eats ,dreams pontiac tell me go with a 400. Done right it will be a funner engine all around,but looking here its 455 all the way..man what to do...lol..i have till the weekend to make up my mind..help?stories ,senerios to help me decide please..thanx all

[Thumpin455_GTO]

That cam will idle like a stocker in anything but 350 and smaller. itty bitty is what comes to mind.

I have built 400's and 455's, you can build a 455 from a 400 block and only overbore it .030 to get standard bore 455. The torque you will make with the 455 will far outshine the 400, although the 400 will rev higher. Best run with my ported 670 head 400 was 12.6 @105. Same car same heads cam just a 455 shortblock under those heads and it ran a best of 11.7@115. Of course both are high compression engines, but it was street driven. If you want a great idle you need to go with an 041 RA IV, or something with 230-240 @ .050. The cam you have sounds alot more like an 068, that is VERY mild but a torque monster cam.