Too much compression on pump gas?

[cdn66satellite]

Good day,
440 with 88cc eddy heads will Ross pistons #99503 be too much compression for pump gas? Thank you

 

[Cranky]

The cam will have a lot to do with your cylinder pressures too. You can build a 11-1 motor to run on pump gas if the combination is right. The static compression is only one part of the equation. So, exactly how quick do you want your ride to be?

 

[lewtot184]

11:1+ compression, open chamber no quench, domes. i don't think so.

 

[eric383]

X2 Cranky. How about piston/deck height? Have you tried this calculator?
http://www.summitracing.com/expertadviceandnews/calcsandtools/compression-calculator

 

[cdn66satellite]

Well the thing is, I have a bare 440 block. I found a rotating assembly with those Ross pistons and was just wondering if it'll be too much for pump gas and street use. Also, I have a purple 484 cam.

 

[eric383]

I see those are dome pistons. It depends on deck height/ piston height. I'm thinking you should mock this up and see where the piston height is. Maybe someone else can add to this.

 

[cdn66satellite]

I see those are dome pistons. It depends on deck height/ piston height. I'm thinking you should mock this up and see where the piston height is. Maybe someone else can add to this.

Thats the thing, the pistons arent local. Its either I buy em and use, or pass them up

 

[lewtot184]

edelbrock makes those 88cc heads specifically for people using quench dome pistons, which the ross's aren't. there will be a dead spot in the chamber, opposite the plug, and domes impede flame travel. poor combo and there ain't no cam, gadget, or gizmo on the planet that will save a poor design.

 

[cdn66satellite]

edelbrock makes those 88cc heads specifically for people using quench dome pistons, which the ross's aren't. there will be a dead spot in the chamber, opposite the plug, and domes impede flame travel. poor combo and there ain't no cam, gadget, or gizmo on the planet that will save a poor design.

Thank you for the information! Big help, thanks guys

 

[383man]

edelbrock makes those 88cc heads specifically for people using quench dome pistons, which the ross's aren't. there will be a dead spot in the chamber, opposite the plug, and domes impede flame travel. poor combo and there ain't no cam, gadget, or gizmo on the planet that will save a poor design.

I agree. I used the KB quench pad pistons once with 906 heads and got it to work ok but one thing is that its alot of work on the head chambers and each piston height to get a decent quench # in every cylinder. I agree with "lewtot184" as its not worth the effort to me in using the 88cc open chamber heads and pop-up pistons if you dont have to. It can be done but if you can somehow get flattop pistons and closed chamber Eddy RPM heads it works great and is so much easier to setup. In fact its so simple to get good quench with closed chamber heads and the flattop piston and it does not effect flame travel at all. And with the felpro .039 gasket if you set up zero deck height you will be golden ! If you can drop the pop-up pistons as I prefer flattops in most engines other then a Hemi. Sometimes you have no choice and may have to run pop-ups but if you dont have to then its so easy to set up a nice cyl and head chamber deal with flattops and great flame travel.

But with aluminum heads and good quench I have seen guys running up to 11.5 comp and getting away with 92 pump and no ping. But its all in the combo as the intake vlave closing also is very important for cyl pressure. In my opinion with good quench and the cyl press controlled I still would not push it past 11.0 running pump just to be save in a driver street car. In fact I run 10.6 staic comp with my aluminum Indy EZ heads. And I run 37 total timing all in by 1800rpm with no ping at all. Good luck , Ron

 

[Kern Dog]

PLEASE do not use a cam of any kind to "band-aid" your combination. I was all over the Mopar forums in 2012 and 2013 trying to get my 493 to run right on CA 91 octane gas. My compression ratio was near 11.0 to one with mimimal quench and my engine detonated at anything over 3/4 throttle even with the timing at 31 degrees total. I was not willing to pull the engine to install dished pistons so I asked for alternatives. Several people suggested that I install a camshaft with a later intake closing. The theory is that the later the intake valve closes, the less the cylinder pressure at low engine speeds. It makes sense but there are drawbacks. The cams made with a later intake closing also seem to have tighter lobe centers and more overlap. This is bad for low speed operation or cruising. I do like to run it hard, but I also like to cruise it and take road trips. For drag racing, my combo was actually pretty good. For a nice street car, my combo was really out of whack.
The bigger cam requires a looser torque converter. This is so the engine isn't loaded too early in the rpm range which would lead to poor throttle response. The loose converter was a pisser for cruising. I will freely admit that my car was faster than before at wide open throttle but not much fun for just cruising around or on the freeway going anywhere.
I ended up pulling the heads and then putting in thicker head gaskets. Several thought I was making things worse because they felt that I would lose any "quench" that I had. The gaskets made a world of difference. ZERO detonation now and I am able to run more spark advance. The car runs like a raped ape. I'm tired of the rough idle of the big cam though. I have a MP 284/528 solid that I am going to use. This will be a great match to the tighter 11" converter I have in the car now.

 

[HT413]

What kind of deal are we talking about here? Do you already have those 88cc heads? If you're getting a screaming deal, why not sell those pistons, buy new and just rebalance? You'd probably lose a few hundred bucks in the deal, but if the deal can support that and still be a value, then maybe it works.

 

[GTX MATT]

What kind of deal are we talking about here? Do you already have those 88cc heads? If you're getting a screaming deal, why not sell those pistons, buy new and just rebalance? You'd probably lose a few hundred bucks in the deal, but if the deal can support that and still be a value, then maybe it works.

You would be at 11-11.5:1 with those pistons and a .051 head gasket with stock Chrysler rods. Drop 2 tenths of a point if using aftermarket rods. This is too high with pump gas and no quench.

 

[Meep-Meep]

Several factors need to be included. Compression ratio and cam choices as mentioned plus fuel distribution, overall mixture strength and inlet charge temps. A good start for pump 91 is 9.5:1 with about 175 PSI of cranking pressure. You can squeeze close to 10:1 if you have a very efficient chamber and very good fuel distribution.

 

[rumblefish360]

OK, it's a small block but the same example exists.

KB-107.5cc valve reliefs
Zero deck slugs @ .030 overbored.
.038 head gasket
Edelbrock 63cc chambered heads.

Runs on pump gas, no problem. It has very good quench.

Hyd. Cam used, MP's purple 292/.509
Current cam, Comp cams 294S/.525 (solid lifter)

The rest is a 4spd manual and 4.10's.