[PontiacLars]

Putting my engine back together now and would like some thoughts on power output for my combo.

- 400 +0.30
- New eagle 3.75 crank
- Speed pro forged flat tops 8 valve relief
- Eagle H beam forged
- Edelbrock performer rpm 60599 cylinder heads (72cc)
Unported, so flow around 290 cfm according to Edelbrock.
- Edelbrock performer rpm intake (match ported to cylinder heads)
- Comp cams XE284 hydraulic flat tappet cam
- 1.65 roller rockers
- Dougs 1.7/8 headers (D581)
- 0.039 head gaskets, så CR around 10.5:1
- Edelbrock AVS2 800 cfm carburator

Going in 76 T/A 4 speed 3.42:1 rear end

[68WarDog]

Those 8 relief pistons are junk Someone else can chime in on a replacement. With everything else I see you may be looking at 435-450-hp. In a 400 you'll need a cam in the 248 to 256 @ .050 range to get that 500hp, but others may offer a different recommendation.

[David Jones]

425/450 or so.

[PontiacLars]

Seems hard to make power with these engines. A buddy made 430 hp at flywheel in a 351 cleveland. Ford cast iron cylinder heads and milder cam than mine..
Do standard Ford cylinder heads outflow Edelbrock round ports for pontiac?

What makes these pistons junk? I know there Are ligther and more expensive ones out there, but Are they bad because of the shape on the flat top destroying the combustion?
I thought they where okei as long as one does not rev too high, because of the weight.

[77 TRASHCAN]

Do you know what the part number is on your pistons??? I'm not educated on those pistons, AND not sure that the 8 relief pistons were forged???

The widely known, low performance 8 relief pistons sit down in the cylinder AL LOT at TDC, making the combustion process very inefficient...and they are cast, as far as I know....

It's not always an exact comparison, not knowing how someone else's dyno was setup. HP numbers can be skewed in one direction or another, A LOT!!!

[PontiacLars]

L-2262F 30

Sits 0.014 down according to what I have read.

[tom s]

To make 500 your going need a lot of cam and RPMs to get there.Tom

[Stan Weiss]

I maybe using the wrong numbers but, I get just under 10:1 CR

Stock 4V 351 Cleveland head come with a 2.19" intake and flow around 280 cfm.

Stan

[MarkS57]

Pretty sure L-2262F are 4 valve relief pistons. Those are what I have.

[Gary H]

Those pistons have a thick 5/64, 5/64 top and second ring which rob horsepower compared to more common aftermarket 1/16, or smaller, rings. Also, as Stan mentioned above your compression ratio is a little on the low side with those pistons. Zero decked and 2 valve relief pistons with 5 cc's would probably get you to around 10.75. Both the better rings and higher compression ratio are needed to hit 500 hp

[PontiacLars]

4 valve relief are correct, my mistake.
Would not 0.027 cometic gasket make 0.040 quench allmost spot on?

[steve25]

No, you will not top 500 hp, and you do not have the needed 10.5 compression that you should be running to make good use of Aluminum heads with those 8 notch pistons!

In fact with those 215 cc runner heads you will be making far less average torque then you would had you been running ported 260 cfm iron heads with a 9.5 compression!

[JLMounce]

Yeah that part number would indicate a speed pro piston, should be 4 valve reliefs. Basic forged rebuild piston, nothing wrong with it and certainly not the 8 valve relief piston. People steer clear of those pistons for a variety of reasons, including low piston to deck clearance, number of sharp edges due to the valve reliefs, it's metallurgy etc. It's just a crappy piston in any kind of performance setting.

I also get right at 10:1 compression for your setup if your build sheet shows the pistons .014 in the hole.

I think you're going to be around 435.

[PontiacLars]

Ok, I have the 4 valve relief speed pro forged,.
I use the Summit racing compression calculator.
+6.7 cc pistons
0.014 deck
With 0.027 thick MLS gaskets I get 10.47:1.
worth it over standard felpro 0.039?

[JLMounce]

I used the .039 gasket thickness you posted in your original post, that corresponds to a felpro 1016 with a 4.3" gasket bore.. I found the specs for your mls gaskets and it looks like it uses a a 4.16" bore. The summit compression calculator doesn't take the gasket bore diameter into account.

With Wallace's calculator I come up with 10.33:1. This doesn't take into account area above the compression ring, but I think that's nominal.

You've probably got a "true" compression ratio of 10.25:1 or so.

Has the machining been done yet on the block? Has the piston to deck height actually been measured? I have those same pistons in my 455 in a +.030 size and although the catalog lists them as being about .020 in the hole, when I measured them, they were a lot closer to the deck. .005 on cylinders 1 and 2 and ,007 on cylinders 7 and 8. With the .027" gasket, if you're piston to deck height is closer than what the catalog might be saying, you might be too tight there.

If you actually end up at about .014 in the whole, that .27" cometic gasket would be a good fit. If you end up much less than that for your deck height, you're probably looking at the standard felpro 1016. In either case I think you're going to nominally be in the 10 to 10.25:1 compression ratio. For what you're wanting to do I think that steve25 is correct in that you're really wanting a bit more compression to utilize those heads properly.

That said, I run right at 10.25:1 on my KRE headed 455 and although I'm certainly leaving a bit on the table, the engine will run on 87 octane.

If 500 is your goal, you're going to need more compression, more cam and more lift from that cam. You really want to be closer to .6" of lift than the xe284 is going to provide.

[Tom Vaught]

If you don't put a .550" lift camshaft in the engine, you should be ok with the .027" thick
gasket as you will still be at a .041 piston top to head combustion distance.
Personally I would do a .040" thick gasket from Butler and live with the lower compression ratio with the gas out there. If you do run a .550 lift flat tappet cam buy some rhoads lifters to kill off some of the low speed duration of the cam.
Better to be a 1/2 point low on compression vs a 1/2 point too high and be forced to run
"premium" gas constantly and not have the ability to drive the car most places. See post #15 above.

Tom V.

[PontiacLars]

Ok, thanks. I have not messured, will do before deciding on gasket.
The Edelbrock heads lists Max lift at 0.575. Is that only due to the springs? Can the springs be matched to a higher lift cam only? Or do the valves need to be longer.
I have read that install height from Edelbrock Are 1.8 inch.

[Tom Vaught]

1.8 spring height is fine. Valves do not need to be longer.
The 406 engine is your biggest handicap to making bigger power.
You will have to spin the engine to get close to 500 hp.
Not going to happen easily.

Tom V.

[dmac]

Originally Posted by PontiacLars

Putting my engine back together now and would like some thoughts on power output for my combo.

- 400 +0.30
- New eagle 3.75 crank
- Speed pro forged flat tops 8 valve relief
- Eagle H beam forged
- Edelbrock performer rpm 60599 cylinder heads (72cc)
Unported, so flow around 290 cfm according to Edelbrock.
- Edelbrock performer rpm intake (match ported to cylinder heads)
- Comp cams XE284 hydraulic flat tappet cam
- 1.65 roller rockers
- Dougs 1.7/8 headers (D581)
- 0.039 head gaskets, så CR around 10.5:1
- Edelbrock AVS2 800 cfm carburator

Going in 76 T/A 4 speed 3.42:1 rear end

If you already have all the parts, you couls mill the heads some for more compression if you have good gas available. And you mentioned something about wanting to keep rpms down, so you would need a lot of CR to get 500hp at low rpm with that many cubic inches. You can get to 500hp a lot easier with more cubic inches. if low rpm is also important. A stroker kit from Butler can get you close to 470 cubic inches for under $2000.

[tom s]

You need a lot more duration,as this is in the street section you will not have a very good driving street car with a 406 500HP engine.JMHO,Tom