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Oh what the head gasket!

Did you measure it in the front/back side of the piston, or on the inside or outside? Keep in mind the piston can rock in its bore because it's actually a little barrel shaped so when the top heats up and expands it doesn't seize up. So you have to measure several times to try and get a consistent number, and try to measure above the wrist pin on both front and back, so it can't rock in that direction. The reason I am saying that is because .036 is still a lot. Also, be absolutely sure you are at TDC, use the balancer mark, if it's 3 degrees off of TDC thats getting almost .002" error already. I also try to measure several pistons.
 
folkenheath said:
Did you measure it in the front/back side of the piston, or on the inside or outside? Keep in mind the piston can rock in its bore because it's actually a little barrel shaped so when the top heats up and expands it doesn't seize up. So you have to measure several times to try and get a consistent number, and try to measure above the wrist pin on both front and back, so it can't rock in that direction. The reason I am saying that is because .036 is still a lot. Also, be absolutely sure you are at TDC, use the balancer mark, if it's 3 degrees off of TDC thats getting almost .002" error already. I also try to measure several pistons.
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Are you talking about the piston to cylinder wall clearance? The 0.036" I gave you was height to deck.
 
You measuring at the dish? As far as I've been able to determine, stock compression height (deck height) was always .025". I just assumed that was measured at the highest portion of the piston, never considered the dish which was prevalent on stock motors.

.040" quench is considered ideal, which is what GM ran (minus the stupid dish pistons): .015" shim head gasket plus .025" compression height.
 
Chevy305 said:
Are you talking about the piston to cylinder wall clearance? The 0.036" I gave you was height to deck.
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No, talking about the distance to the tp down in the hole, you can get a lot of different measurements for the deck height to the piston top depending on how and where you measure.

Also, I just looked up the spec for block deck flatness in the Chiltons, it lists .004". So as long as you are under that I would say you are OK, assuming you don't use a thin gasket. The problem is, if you really are .036" plus a .041" gasket would be a .077" quench, pretty poor, but as long as your compression isn't too high you are probably fine, better slightly less power than a blown gasket.

I think I ended up finding a .028" felpro gasket that did work fine for my 355 a few years ago, because my bottom end was horrible but I wasn't putting any money into it, PO used crappy recon rods and the piston was .070 in the hole before the gasket! I do have a set of stock GMPP .051" gaskets for aluminum heads, and some nice valve seals I never used, but they are for a ZZ4 head, so it would depend on if they have the same diameter at the guide OD.

Certain GMPP ZZ4 engines actually used a piston with a .020" shorter compression height (wrist pin center to piston top) to reduce the compression, which made the quench bad but still worked fine for that power level and compression.
 
folkenheath said:
No, talking about the distance to the tp down in the hole, you can get a lot of different measurements for the deck height to the piston top depending on how and where you measure.

Also, I just looked up the spec for block deck flatness in the Chiltons, it lists .004". So as long as you are under that I would say you are OK, assuming you don't use a thin gasket. The problem is, if you really are .036" plus a .041" gasket would be a .077" quench, pretty poor, but as long as your compression isn't too high you are probably fine, better slightly less power than a blown gasket.

I think I ended up finding a .028" felpro gasket that did work fine for my 355 a few years ago, because my bottom end was horrible but I wasn't putting any money into it, PO used crappy recon rods and the piston was .070 in the hole before the gasket! I do have a set of stock GMPP .051" gaskets for aluminum heads, and some nice valve seals I never used, but they are for a ZZ4 head, so it would depend on if they have the same diameter at the guide OD.

Certain GMPP ZZ4 engines actually used a piston with a .020" shorter compression height (wrist pin center to piston top) to reduce the compression, which made the quench bad but still worked fine for that power level and compression.
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I put a straight edge across the cylinder and measured the difference with a feeler gauge. I measured on the outer side of the piston which is the tallest part since the inside center is dished.

So since the block is within spec, what should I do with the Patriot heads? Have them surfaced and run them with a thicker gasket? Or start over on a new set like these?:

This RHS head uses all Comp Cams valvetrain components and specify compatibility with hydro roller cams, and would be only a little more than having the Patriots redone. They flow a hair more on the intake and virtually the same on the exhaust:
http://www.compperformancegroupstor...ore_Code=RH&Screen=PROD&Product_Code=12052-02

This is the AFR Eliminator which flows more than Patriots but at an additional $600 over getting the Patriots worked over:
http://www.airflowresearch.com/index.php?cPath=24_25

Or these Brodix heads, which are even more than the AFRs:
http://www.jegs.com/i/Brodix/158/1011019A/10002/-1?parentProductId=755722#moreDetails

Or these sexy Darts which are priced like the AFRs, but flow about the same as the Patriots:
http://www.jegs.com/i/Dart/301/11121112P/10002/-1?parentProductId=744642
 
Chevy305 said:
I put a straight edge across the cylinder and measured the difference with a feeler gauge. I measured on the outer side of the piston which is the tallest part since the inside center is dished.

That will rock the piston down and increase the measurement, there should be a lip around the front/back of the piston you can put a feeler guage on both sides parallel to the wrist pin and crank. I'll look at your pics and make sure.

So since the block is within spec, what should I do with the Patriot heads? Have them surfaced and run them with a thicker gasket? Or start over on a new set like these?:

This RHS head uses all Comp Cams valvetrain components and specify compatibility with hydro roller cams, and would be only a little more than having the Patriots redone. They flow a hair more on the intake and virtually the same on the exhaust:
http://www.compperformancegroupstor...ore_Code=RH&Screen=PROD&Product_Code=12052-02

This is the AFR Eliminator which flows more than Patriots but at an additional $600 over getting the Patriots worked over:
http://www.airflowresearch.com/index.php?cPath=24_25

Or these Brodix heads, which are even more than the AFRs:
http://www.jegs.com/i/Brodix/158/1011019A/10002/-1?parentProductId=755722#moreDetails

Or these sexy Darts which are priced like the AFRs, but flow about the same as the Patriots:
http://www.jegs.com/i/Dart/301/11121112P/10002/-1?parentProductId=744642
Click to expand...

...

Thats up to you. It's your money, I wouldn't spend $950 on those heads I know that. If it was me I'd resurface them, spec and buy the parts and assemble them myself after lapping the valves and measuring/shimming the springs.

If you don't want to do that, then I would sell those and buy new ones, it wouldn't cost any more depending on the sell price. I don't know anything about RHS heads, they may be good but I'm not sure, and I don't know where they are cast. I'd stick with Dart, Brodix, Edelbrock, or AFR. Look at the edelbrock RPM heads if you are in a hurry, similar to your current heads but cast in the USA and probably cheaper than any of those options. My brother had a set on his 355 and made 434 hp with a flat tappet cam. AFRs are nice because they are CNC ported, but if you get the CNC ported Darts they are more money yet, although probably more power. Dollar for dollar edelbrock is a pretty good deal, just not the most power. For that I would go Dart or brodix.

http://www.edelbrock.com/automotive_new/mc/cylheads/chevy/sb_perf_rpm2.shtml

I haven't compared any flow numbers, but don't forget to look at midlift flow, the valve spends more time at midlift than completely open.
 
I don't think there is anything wrong with the RHS heads. They offer a pretty good value for the money.

One thing I'd make sure is that chamber CC is where you need it. AL heads I'd be looking at 10-10.5:1 for 87 octane.

RHS' website sucks IMO, they have cast iron heads, they are just hard to find on their website. As a for-instance http://www.racingheadservice.com/Cylinder%20Heads/Small%20Block%20Chevy/Pro%20Torker/Vortec/Cast%20Iron.aspx

and

http://www.jegs.com/p/RHS/RHS-Pro-Action-Cast-Iron-SB-Chevy-Cylinder-Heads/743457/10002/-1
 
dyeager535 said:
One thing I'd make sure is that chamber CC is where you need it. AL heads I'd be looking at 10-10.5:1 for 87 octane.
Click to expand...

I agree with Dorian (except I'd run 93 octane with 10:1), let me know all your info if you do decide to order heads and I'll punch it in and see what your static and dynamic compression will be with 64 vs 72 cc, different gaskets, etc.
 
With the modern combustion chambers in cast iron, if fueled correctly (tuned right) 9-9.5:1 is a given with 87 octane. Proper quench helps.

Aluminum (as it acts as a heat sink, robbing heat from the combustion chamber) normally takes another full point of compression before you run into problems with the same octane.

It seemed like it took a long time, but eventually they figured out you need that extra compression to close the gap with the same design iron heads. Oranges to oranges, iron heads make more power than aluminum.

No reason not to build in a safety margin though, which is one reason knock sensors exist. :)
 
The guy that built my engine almost said the exact same thing to me :bow:

dyeager535 said:
With the modern combustion chambers in cast iron, if fueled correctly (tuned right) 9-9.5:1 is a given with 87 octane. Proper quench helps.

Aluminum (as it acts as a heat sink, robbing heat from the combustion chamber) normally takes another full point of compression before you run into problems with the same octane.

It seemed like it took a long time, but eventually they figured out you need that extra compression to close the gap with the same design iron heads. Oranges to oranges, iron heads make more power than aluminum.

No reason not to build in a safety margin though, which is one reason knock sensors exist. :)
Click to expand...
 
Yeah, I'm aware of all that theory, good luck measuring the extra power with the iron though, aluminum will make more power because the compression difference is more substantial, not to mention the weight savings potential. To say it took them forever to figure out they needed more compression to get the power back is BS. They added the compression becuase they could with aluminum. Not to mention the modern EFI engine controls are much better than carbs to keep the proper A/F ratio and add more control for less risk.

http://www.carcraft.com/techarticles/ccrp_0602_iron_versus_aluminum_cylinder_heads_test/viewall.html

And when pushing for power with pump gas I feel you are always better off using premium for peace of mind. Load conditions are always changing and saving 10 to 20 cents a gallon isn't really worth the risk. Especially these days when gas is 3 - 4 dollars a gallon, yet the price difference is still the same at 10 - 20 cents. Percentage wise the cost of premium vs regular went down, because of the fact that gas itself went way up.
 
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I'm with you. Can't find many oranges to oranges comparisons, but the ones I can show a minimal difference in power. At best 5lb/ft.

I still hold some reservations, based solely on variables, but it would appear the modern chambers are the major difference, not the material.

I suspect one major factor for this thinking...early AL heads had the same crummy chambers the iron heads did. GM design kind of proves this, the L98 with AL heads ran more timing than the L98 with cast heads. But neither were "good" chambers. So apparently at one point it was true. But presently, unless there is some variable I'm missing in the tests done fairly recently, the gap is much narrower.

I'd agree then that compression needs to be down around the 9-9.5:1 range for 87 with either material, as long as the chamber is modern.

I would like to see what affect head material has on compression at the lower end of the scale though. The tests I looked at were in the 10:1 range, and it didn't appear that they tried to use the lowest octane available. If heat is an issue, that may very well have been minimized by the octane of the fuel.

If anyone finds an article that tests power production vs. head material and/or octane, I'd like to see it. :) Theoretically, given the same compression, lower octane should make more power, up until detonation. And that too could be influenced by head material, if the "heat sink" theory was true at least to some degree.
 
dyeager535 said:
If anyone finds an article that tests power production vs. head material and/or octane, I'd like to see it. :) Theoretically, given the same compression, lower octane should make more power, up until detonation. And that too could be influenced by head material, if the "heat sink" theory was true at least to some degree.
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Did you see the one I just posted? I think they did a relatively good job there. Now, a dyno isn't real world, so they may have seen detonation at higher ambient temps, loads, high gearing, etc, with the iron heads before the aluminum, but overall there was not a measurable difference between the aluminum and iron of the same head on the same engine.

Here is another article with the same engine on a dyno trying different octanes. Be careful to read the numbers at the same timing.

In the end, just like the head material alone debate, although in theory lower octane will make more power, in reality, it isn't so. And when it gets into the race fuels its a different ball game because of what they due to them. They even have oxygenated race fuel now that is very expensive but produces slightly more power.

http://www.hotrod.com/techarticles/engine/fuel_octane_rating_comparison/

I agree 100% on the modern chambers making a big difference. Even the ignition timing on the new chambers is much less, this creates less loss because the spark starts closer to TDC for less power lost on the way up, yet finishes the spark at the same peak time to create better output. Ideally you would not start the spark until after the piston reached TDC for the most efficiency, but that would require instant burn rates, which just aren't going to happen. Much closer than we used to be though.
 
Well my main concern is testing a static compression ratio. Even in the fuel test it is 10.4:1. My question is what happens at 9:1, 11:1, 12:1 (solely because I'd like to know for race motors)?

Obviously the data could be extrapolated, but as the mechanics of the motor change, the results aren't necessarily what you expect.

In the case of that motor/test, they were running 10.4:1 on 87 octane(!), with no reason to be concerned, with as much timing as they had to play with. Maybe the whole octane/compression ratio requirement "myth" needs to be tested...either those Dodge heads are awesome, or you can run a whole lot more compression than people tend to think. Part of it may be that it's not a "real world" test.

Getting all the variables covered in a "test" would be pretty hard to do.
 
folkenheath said:
Especially these days when gas is 3 - 4 dollars a gallon, yet the price difference is still the same at 10 - 20 cents. Percentage wise the cost of premium vs regular went down, because of the fact that gas itself went way up.
Click to expand...
I keep saying this to people, but it seems like nobody understands what I'm getting at :dunno:.

Premium is way cheaper than regular + octane boost, too. My DD takes premium and I've learned that driving through Indiana and Illinois there are a lot of stations that don't sell it. So it's good to keep an UNOPENED bottle in the trunk (you don't want that stuff leaking on stuff). Sure, I could be mindful to keep my foot out of it for the next 400 miles, but where's the fun?

Anyway, back on topic...
 
My engine currently makes 9.4:1 and I use 93 octane. I also run a lot of timing too.

All the heads I'm looking at are 64cc combustion chambers, the only variable is the head gasket that's recomended with the heads.
It seams that all the previous cylinder heads I mentioned all recomend this gasket:
http://www.jegs.com/i/Fel-Pro/375/1003/10002/-1

4.166" bore
0.041" thickness
9.1cc

So with that my compression will drop to 9.01:1
Am I going to lose a good chunk of power with that loss of compression?
 
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