Want flat tops for pump gas 523.

Got my 460 in the shop getting a 4.3 assembly. The aluminum heads are 93cc. With flat tops at zero deck, the compression will be a bit high for 91 octane, around 11.5 to 1. With dished pistons, 22cc, the compression is a on the low side. Does anyone know of a piston that will put this engine in the 10.5 to 11.0 to 1 range?

Victor L wrote:Got my 460 in the shop getting a 4.3 assembly. The aluminum heads are 93cc. With flat tops at zero deck, the compression will be a bit high for 91 octane, around 11.5 to 1. With dished pistons, 22cc, the compression is a on the low side. Does anyone know of a piston that will put this engine in the 10.5 to 11.0 to 1 range?

What connecting rod length and cylinder heads are you using...?
What is your block deck height...?

The rod would be 6.7, but I do not know the deck height. My machinist wants to cut the pistons down to get the desired volume. We haven't ordered the parts yet. Just thought I could learn a little bit more first, and hoped to find an "off the shelf" piston. I will contact my supplier on Monday.

Victor L wrote:The rod would be 6.7, but I do not know the deck height. My machinist wants to cut the pistons down to get the desired volume. We haven't ordered the parts yet. Just thought I could learn a little bit more first, and hoped to find an "off the shelf" piston. I will contact my supplier on Monday.

A custom piston is where you're going to get 12 cc dished pistons.
Flat tops are available from a number of places and a 12 cc dish is only about 3 5/8" diameter dish by 1/16" deep considering an intake notch being there.

[quote="rmcomprandy"]

Victor L wrote:A custom piston is where you're going to get 12 cc dished pistons.
Flat tops are available from a number of places and a 12 cc dish is only about 3 5/8" diameter dish by 1/16" deep considering an intake notch being there.

Sounds like your machinist is on the right track, just chuck 'em up in a lathe and cut a dish like the one RM outlines above. Unless the pistons have a super thin deck which I doubt you will be fine.

Steve

Victor L wrote:Got my 460 in the shop getting a 4.3 assembly. The aluminum heads are 93cc. With flat tops at zero deck, the compression will be a bit high for 91 octane, around 11.5 to 1. With dished pistons, 22cc, the compression is a on the low side. Does anyone know of a piston that will put this engine in the 10.5 to 11.0 to 1 range?

Are you sure about that? I have a 521 with flat tops and large Edel heads, the ratio comes out to be 10.5 to 1
Most of the 18 to 22cc pistons are used with 72 - 74cc heads for pump gas. Run your calculator again.

Dave

you say head are 93 cc let us guess Pro Comps?

the Coug wrote:you say head are 93 cc let us guess Pro Comps?

As long as one is not intending they're engine to be a race engine, Pro Comps CAN be a pretty good option.

rmcomprandy wrote:

the Coug wrote:you say head are 93 cc let us guess Pro Comps?

As long as one is not intending they're engine to be a race engine, Pro Comps CAN be a pretty good option.

Guess is all in how you define a racing engine... guys called a worked over flathead Ford four cylinder a race engine too... just not much of one...

what is the dynamic compression ratio? Wouldn't that play a bigger role on max compression ratio for pump gas.

Is there a compression ratio calculator available? How about a dynamic compression ratio calculator?
So far, I go by what I am told, and get mixed answers.
And yes, I got taken advantage of and let a machine shop, Daves Performance Engineering, in Fresno Ca. assure me that Pro Comp heads were the best heads I could get, and paid over $2000 for them. So now I am trying do the best with what I got. My car actually ran very strong before spinning a bearing.
I might have dual valve reliefs machined into my pistons, so P51 heads could be an option in the future.
So is there a calculator, or a chart to help me figure the ratio?

Victor L wrote:Is there a compression ratio calculator available? How about a dynamic compression ratio calculator?
So far, I go by what I am told, and get mixed answers.
And yes, I got taken advantage of and let a machine shop, Daves Performance Engineering, in Fresno Ca. assure me that Pro Comp heads were the best heads I could get, and paid over $2000 for them. So now I am trying do the best with what I got. My car actually ran very strong before spinning a bearing.
I might have dual valve reliefs machined into my pistons, so P51 heads could be an option in the future.
So is there a calculator, or a chart to help me figure the ratio?

Diamond piston,s web site has a good one and so does Eagle Rods. I hate to hear you got took on your heads, guy should be horse whipped if he did that to you.

sskwb wrote: what is the dynamic compression ratio? Wouldn't that play a bigger role on max compression ratio for pump gas.

Not really ... Although that would be PART of it, octane limitations are also determined by other things beside static cylinder pressure.

Victor L wrote:Is there a compression ratio calculator available?

Save you the trouble

4.40" bore, 4.3" stroke = 523
93cc head
Flat top with single notch = 3cc
Zero deck
.041" thick head gasket

CR = 11.04

How this will run on the street as far as detonation is concerned has a lot to do with the gasoline used, piston to head clearance, piston and head design, cam, operating temp, charge temp., converter, gear, tune (ignition curve & A/F ratio), spark plug heat range, and a few other things.

Try not to get sucked into the whole dynamic CR thing, seems to be another internet legend. It is just one piece of the puzzle and determining the right intake closing number is NOT as straight forward as some will have you believe.

I'd say if you were running this before without detonation issue, is no reason it won't again. I an assuming the cause of the spun bearing has been determined?

Simply put, thank you,

What is the intended use besides being streetable? My last motor was a pumpgas 523 with 11.02:1 compression.

Victor L wrote:Is there a compression ratio calculator available? How about a dynamic compression ratio calculator?
So far, I go by what I am told, and get mixed answers.
And yes, I got taken advantage of and let a machine shop, Daves Performance Engineering, in Fresno Ca. assure me that Pro Comp heads were the best heads I could get, and paid over $2000 for them. So now I am trying do the best with what I got. My car actually ran very strong before spinning a bearing.
I might have dual valve reliefs machined into my pistons, so P51 heads could be an option in the future.
So is there a calculator, or a chart to help me figure the ratio?

Pro Comp heads CAN be fine. Most people bashing them have never ACTUALLY had a pair and are relating information from somewhere else like their buddy's , sister's, boyfriend who knows about such things.

People who try to sell them under false pretenses are also part of the problem.

If you want a race type head then something else would probably be better. For an improved version of factory iron heads but, made of aluminum ... they can serve you well.

dfree383 wrote:Get real Randy, I normaly won't argue with you....... The Procomp stuff is Junk, might as well be running a set of worked factory Iron Dove's, it will make the same power........ and we both know it.

Well, we'll just have to agree to disagree, Dave.
Looking at invoices from people who PAY for their head work and can't do it themselves, I know that Pro Comp heads are "dollar for dollar" a better alternative than a large chamber OEM iron head.

By the way ... how many Pro Comp heads have you owned or A-B tested to definitively have that wrong opinion...?

dfree383 wrote:

rmcomprandy wrote:

dfree383 wrote:Get real Randy, I normaly won't argue with you....... The Procomp stuff is Junk, might as well be running a set of worked factory Iron Dove's, it will make the same power........ and we both know it.

Well, we'll just have to agree to disagree, Dave.
Looking at invoices from people who PAY for their head work and can't do it themselves, I know that Pro Comp heads are "dollar for dollar" a better alternative than a large chamber OEM iron head.

By the way ... how many Pro Comp heads have you owned or A-B tested to definitively have that wrong opinion...?

You already know I won't own them, By Choice and I've finger enough of them to know their are some very bad flaws in them. Besides for what this guy paid for his...... he could have had a much better set of heads and been money ahead.

Well, what this guy paid for his heads is a different story. As I said, "People who try to sell them under false pretenses are also part of the problem".

I have performed that very A-B dyno test with a customers "street rod" engine.
The 466 had P.I. bowl ported heads ... we change them on the dyno to bowl ported Pro Comp heads with the same valve sizes as the P.I.'s and milled slightly to have the same chamber volume ... same pushrods, same rockers even the same valve springs.
EQUAL torque and a bit more horsepower was the outcome; probably because of the better exhaust ports.

As a side note ... I did a pair of Pro Comps for Adney and he sold them to a trusted member here to put on a street driver / once in a while strip "car/truck", (well a vehicle), which now has over 12,000 trouble free miles on it.