IH 392 Emissions style head chamber volume cc?

[sdowney717]

10 years ago, I shaved the heads .050 and it detonated like crazy, so big mistake.
So I stacked gaskets and it has run fine since.
I recently torn it down to replace bearings , seals, do valve work, rings.
I cc the chambers and I get 80.75cc.
I used a syringe and clear flat plastic.

The pistons are h996cp .030, and the d cup measures 8cc.

I have been thinking decking the block is better to keep quench low.
I could grind out the combustion chamber sides to gain back a few cc's then have the deck done to zero clearance.

So been looking at dynamic compression ratio and wondering what is oem for the 392?
http://www.rbracing-rsr.com/compradvhd.htm
Also what is the adbc degrees for the oem cam?
It is needed for the dcr calculation.

 

[sdowney717]

I have a set of stock IH 392 improved cooling heads.
I just cc'd the chamber at 98.1 cc's.

Using a digital caliper I measure the distance between head gasket surface and chamber between the valves and the difference comes up at .061, so my .050 surfaced heads had already been .010 surfaced perhaps.

I could actually mod these to fit the non ic engine by drilling 7 holes. And blocking one water port. I could be block by tapping steel plugs, then drilling and tapping another steel plug.

 

[Robert Kenney]

I was just reviewing my information on 392 c chamber volumes.
This case it is also an ic head and 91cc. From Mark peitz.

Since IH used the same grind across all sv's I have data from my own cam degreeing that says intake closing @ 22* abdc .050 lifter rise.
Another here got tc 17* abdc @ .050 on a stock clevite replacement.

 

[FDChappie]

Are you using the oem steel shim gaskets or the felpro composit gasket. Iirc you'll gain about .032" with the with the felpro gaskets.

I did a 345 with .010 off the heads and (man I should have written this down as my memory is getting fuzzy) .035 off the deck. No ping on regular, but premium need for towing, just about like it was before the rebuild.

 

[sdowney717]

I use the felpro gaskets.
I measured the height of both heads.
Ic uncut head reads 3.438
non ic cut head reads 3.388
which is .050, so must be a .050 cut.

 

[sdowney717]

I was just reviewing my information on 392 c chamber volumes.
This case it is also an ic head and 91cc. From Mark peitz.

Since IH used the same grind across all sv's I have data from my own cam degreeing that says intake closing @ 22* abdc .050 lifter rise.
Another here got tc 17* abdc @ .050 on a stock clevite replacement.

Hi, that is a lot of volume then going into the cylinder dynamically which makes for good low end torque. My calc from that web site came up with 25* abdc.
So in the right region.

I definitely got a good 98cc's. I plan to recheck.

I originally cut these heads too much, but I have learned since then. My original idea was bump in compression for more efficiency, but that got dashed quick!

I am wondering what is the max dynamic compression ratio these engines can run using 87 octane? A static calculation seems to yield 8.6 cr using the 80.75 cc's on the cut head.

I have done some grinding on the exhaust, I enlarged-smoothed the bowls and opened the runners a little. I left the intakes alone.
I also smoothed around the intake valve in the combustion chamber.

These engines are in my boat. I swing a 22 by 20 prop.
I have noticed theses engines pull very well at low rpm, but higher rpm the really top out I think about 3500 rpm. But palmer specs these to 4000 rpm and 265 hp. I don't know what cam is in the port engine, but this starboard engine is 151985r5, an oem cam. For all I know this engine was a standard rebuild someone put in the boat, as they did not retain the adjustable solid tappets or oem cam.


Here is the bsfc and rpm torque and hp chart from them.

 

[sdowney717]

https://www.rbracing-rsr.com/compstaticcalc.html
I can not get the online static calculators to give 8 to 1.
It keeps coming up around 7.5 to 1 oem.

Bore 4.125, stroke 3.656, gasket 0.040, deck height 0.035, piston top 8, combustion chamber 98.

Even using 92, it is too low cr calculated, anyone can you tell me why?
My deck height is a guess, what is it usually?

If I can not get the cr accurately, how can I determine the dcr, so I can not make any adjustments to the heads without having some solid info to base a decision on.

 

[sdowney717]

Theoretically, when I shaved off .050, then put back .040 gasket, my net change is 0.010 tighter, so a slightly higher compression than oem.

I will likely just put the engine back together as I had it.
The other idea was to grind out 10 cc's as in taking away the sides to round out the combustion chamber. It seems 10 cc's is possible in the combustion chamber.

That would make the chamber open and get rid of the quench.

That would still have it a little higher cr than what it is now. I wonder what it would be, if you could trust the cr calculators, then you would know.
Any thoughts as to that would work without detonation of regular gas?

 

[Robert Kenney]

So lets build a hypothetical marine engine from scratch that would mimic what you have after taking .050 off the heads.
A quench configuration. .040 +/- .010 piston to head surface.
8.6? Think that is what you said you thought you had. For kicks lets say up to 9.0-1.

Peak rpm @ wot 4000. Peak hp @ 3900-4000 or propped for 4000 wot rpm (very important)

cammed appropriately for rpm range. (same as IH did) this really won't effect running peak ve or peak torque cylinder pressures or octane requirments

timing 32-34 total initial and mechanical advance.

Octane requirements would be 87 r+m/2. Tops 89 @ 9.0-1 compression.

On the odd occurrence that you encounter detonation or ping. Recurve the advance to come in later.
Install 2-3 colder on plugs.

Now I have read your problems and suggest not adding 2 head gaskets. This will eliminate the quench effect and reduce the detonation resistance of the assembly. I have been building marine application engines for years and the formula is the same as what IH did for their trucks.. Only the rod ratios are oddly big which will cause more dwell of the piston at tdc. This can require less timing but that's it really.
Still pinging? Pull some timing out.

 

[sdowney717]

so lets build a hypothetical marine engine from scratch that would mimic what you have after taking .050 off the heads.
A quench configuration. .040 +/- .010 piston to head surface.
8.6? Think that is what you said you thought you had. For kicks lets say up to 9.0-1.

Peak rpm @ wot 4000. Peak hp @ 3900-4000 or propped for 4000 wot rpm (very important)

cammed appropriately for rpm range. (same as IH did) this really won't effect running peak ve or peak torque cylinder pressures or octane requirments

timing 32-34 total initial and mechanical advance.

Octane requirements would be 87 r+m/2. Tops 89 @ 9.0-1 compression.

On the odd occurrence that you encounter detonation or ping. Recurve the advance to come in later.
Install 2-3 colder on plugs.

Now I have read your problems and suggest not adding 2 head gaskets. This will eliminate the quench effect and reduce the detonation resistance of the assembly. I have been building marine application engines for years and the formula is the same as what IH did for their trucks.. Only the rod ratios are oddly big which will cause more dwell of the piston at tdc. This can require less timing but that's it really.
Still pinging? Pull some timing out.

That would require decking the block and using the other set of heads to get a low quench of .040, I know that is desireable to do.
I really don't know what I have now for a cr, just going by what the calculators say, but discouraging stock oem numbers come up with 7.5 instead 8.

Back 10 years ago, after shaving head .050, when the motor was running in slip no load, ran fine. Ran fine when revving up with no load. So we took it out, idled out into the chesapeake bay. Then when I opened the throttle instant detonation and also constant, sound horrible. Really even just a little throttle was constant detonation.

So I retarded the spark and no effect. No matter how far retarded it continued to ping horribly, very surprised at that.

Thing is with boat, your always under heavy load, and also the gas gets old since it sits in the tank. And of course the engines are in a tight bilge space, so the air they breath is hot like a desert. All those things are good at making the engine detonate.


The pistons sit in the hole maybe 0.035, I will measure when I put it together. Then you have a gasket of .040, so already piston to head is at
0.035+ 0.040 = 0.075.
So only way to fix that is deck the block to zero so quench is then .040.
Anyway that requires moving big heavy block to a shop.

'cammed appropriately for rpm range.'
are you suggesting a bigger cam with a abdc of like 50* to 60*?
What cam would be appropriate you think?
The current cam crams a lot of air in since the intake is closing at 22* to 25* abdc, so moving to a bigger cam, that would lower the dcr and it would develop more power at a higher rpm?

What would happen if I left the quench at 0.075 using a single head gasket, the current shaved heads and went to bigger cam, would it detonate on 87 octane?

With the doubled up head gaskets, that puts the cr at maybe 8 to 1, and I know that works ok with no pinging.

 

[sdowney717]

I rechecked the cc's.
This time I put a smear of grease in the head and around the valves to keep them dry so they wont rust, etc...
Second time I get 96.7 cc's

then checked next chamber, I get 94.5 cc's.

So I would guess these 392 average out around 95 to 97 cc's.

At the most error with me pumping in a syringe 9.5 times, I can imagine not more than 1 cc variation total and more like 0.5cc, and I was careful to line up the plunger properly as the pharmacist explained how to use them. I was told to measure from the bottom of the rubber cone in the syringe. So from cone tip down to where the rubber meets cylinder wall is the Mark.

 

[sdowney717]

I checked the cc of the felpro gasket, and it is 14.4 cc's.

I am going to try and figure out what the cr ratios are myself separate from the online calculator. IH gasket is not round, so must be affecting it somewhat.

 

[Mark Pietz]

I rechecked the cc's.
This time I put a smear of grease in the head and around the valves to keep them dry so they wont rust, etc...
Second time I get 96.7 cc's

then checked next chamber, I get 94.5 cc's.

So I would guess these 392 average out around 95 to 97 cc's.

At the most error with me pumping in a syringe 9.5 times, I can imagine not more than 1 cc variation total and more like 0.5cc, and I was careful to line up the plunger properly as the pharmacist explained how to use them. I was told to measure from the bottom of the rubber cone in the syringe. So from cone tip down to where the rubber meets cylinder wall is the Mark.

I used a graduated cylinder. I wouldn't stress over the difference between your results and mine. Like you, I did mine several times to make sure I got it right (still believe I did). So the question is to account for variations. I'm talking through a paper as*hole here...my heads had been lightly surfaced - that would account for some of it, no idea how much. Previous valve jobs would cause slight recession of the valve - that could increase volume. I had new valves (most, anyway), that would have the opposite effect. Or some slight change in the factory's molds, who knows. Robert will weigh in, I'm sure, but I think the bottom line is that's why we cc these things in the first place - so we know what the reality is, and then build from there. I discovered that the "d" recess in the silvolite piston top had a much different volume than the d in the original piston, by several cc's. One's natural assumption they'd be the same was a major error - see my rebuild for that discussion.

The difference between 91 and 94 is significant, so it's good that you found your reality.

 

[Robert Kenney]

Read my post again. What I am saying is that you should not be having the problems you are having at your existing engine setup unless you have overlooked something. These palmer marine engines were given a big safety margin to ensure their ability to run on crap fuel and not self destruct. A small increase in cr would easily be dealt with through the normal variables.

With a .040 thick head gasket you are at .075 quench distance? Sounds like you had steel hg's originally and you whacked .050 from the heads? Mistake #1 of not working out quench or.

You say you retarded the timing. To what? I suspect it was a wag with no real verification of the setting. I don't think you knew if the fuel was any good.
#2 not documenting your testing. You have no way to know where you were while experiencing detonation.

Oh did I say that I build marine application engines? I get the operating parameters.


I'll step out of this because it sounds like you won't be happy with my answers ever.

 

[sdowney717]

Ok, figured this out. The cr difference is 0.9 greater after I shaved .050 from the heads comparing a single versus a doubled up head gasket.

With doubled up gaskets, the static cr is 7.924, it works no pinging
with a single gasket, the static cr is 8.863, it fails severe detonation.

Figures I used are for the double gasket, these are cc's

gasket is 14.4 x2 = 28.8
head chamber = 80.75
piston in hole = 7.77 (assuming .035, I will measure)
cylinder bored .030 = 812.34

total volume = 929.66cc
above piston area = 117.32
929.66/117.32 == 7.924 cr

for the single gasket use 14.4 and the calculations = 8.863 cr

it pinged mercilessly regardless of how far I retarded the timing. I knew at the time I had screwed up by shaving the heads. I retarded it so far it would barely run at idle or say it would stall, seriously.
One person at helm, while I moved distributor.
Of course the head had all those sharp edges in the chamber. I dont know if that made it more likely to detonate, probably did.
This time I have softened the radius.

My plan is to put it back together with the double gaskets, I know that works ok.
Alternatives would be to
1. Run a single gasket, grind on the chamber adding some cc's.
2. Have the block decked to zero piston height, run unshaved normal heads and get a cam with a higher adbc.

I think I will wait and if in a few years I am still around, will think on modifying the block, doing number 2

 

[sdowney717]

I used a graduated cylinder. I wouldn't stress over the difference between your results and mine. Like you, I did mine several times to make sure I got it right (still believe I did). So the question is to account for variations. I'm talking through a paper as*hole here...my heads had been lightly surfaced - that would account for some of it, no idea how much. Previous valve jobs would cause slight recession of the valve - that could increase volume. I had new valves (most, anyway), that would have the opposite effect. Or some slight change in the factory's molds, who knows. Robert will weigh in, I'm sure, but I think the bottom line is that's why we cc these things in the first place - so we know what the reality is, and then build from there. I discovered that the "d" recess in the silvolite piston top had a much different volume than the d in the original piston, by several cc's. One's natural assumption they'd be the same was a major error - see my rebuild for that discussion.

The difference between 91 and 94 is significant, so it's good that you found your reality.

Yes, I have no idea if the rebuilder ground the seats on the unshaved heads, most likely they did which would mean maybe a few cc's more. Using a syringe does introduce a small error, my guess is about 1/2 cc at most, if your super careful.

 

[sdowney717]

Other thing is, I can not always keep replacing gas in the boat.
The gas will sit and will go sour. I do use marine stabil now.
Most boats do not get used frequently enough fr the gas to always be pristine. This is just the way it is. If running a lower cr helps then so be it.
I have read gas sits more than a month, it has gone sour. I have gas in the tanks right now from last summer.
This boat is a 37 foot eggharbor sedan cruiser with 300 gallon tank, not a speedy powerboat. Ultimately, the engine needs to run reliably and be ok on crap gas.

 

[sdowney717]

There is an interesting option which gives the quench of 0.040.
Simply use this shaved head with one gasket
zero deck the block

then the static compression becomes 9.5

then put in this cam with an adbc of 68*
http://www.summitracing.com/parts/cca-83-202-4/overview/make/International

Now the dynamic cr is only 7.35 to 1

static compression ratio of 9.5:1.
Effective stroke is 2.73 inches.
Your dynamic compression ratio is 7.35:1 .
Your dynamic cranking pressure is 142.35 psi.
Your effective boost compression ratio, reflecting static c.r., cam timing, altitude, and boost of 0 psi is 7.35 :1.
V/p (volume to pressure index) is 126
http://www.wallaceracing.com/dynamic-cr.php

I am going to keep thinking. I do have another set of pristine heads, so if the above detonated with a zero decked block, , I could swap them on with that new cam to lower the dcr below 7

right now the cranking compression is about that 140 to 145 number, so it is a match.
It will be a future project.

http://www.classicinlines.com/compressionratio.asp
Good read. It says that dcr of 7.35 will work with regular gas.