What's the thinnest b230 Cometic you've run?

brian smith said:

Finally, I get it...

Enlightened am I.

Thank you.

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Who?

John V said:

Who?

Click to expand...

Thanks John, for the photo showing the quench pads as being co-planar to the HG surface.
And for picking up on the "poking out" measure.
And to everyone else who tried to esplain me this characteristic of our 8v heads.
If you could have seen the underside of mine, you might better understand how I could possibly think that the quench pads were above the plane of the HG...

Color me bad(d)

1. What thickness headgasket did you use? .027
2. Has your bottom end been rebuilt or is it the original, untouched, 250k mile bottom end with the carbon cleaned off the pistons? original 90k 230ft, uncleaned pistons
3. Did you do anything to prepare the block for the headgasket like is recommended or did you leave it alone and just scrape the original junk off? carefully scraped off the junk
4. Did you attempt to measure how far the pistons stick out and what did you come up with for squish clearance? yes, with my eye. just a tad over flush
5. How high have you revved the motor with that setup? just before 7k
6. Have you ever experienced what MAY have been the pistons hitting the head? not that i can hear. Has anyone experienced that in one of these motors yet? i don't know

It sounds like one hand clapping.

pretty sure the pistons are hitting the head, i think i just have a hard time hearing it. somethings gotta be broken

Alright, I'm going to resurrect this three year old thread since it applies directly to what I am working on, and I really want this all double checked. So i've measured .006" piston protrusion, plan on just running a stock 6500 rev limiter so figuring .026 rod stretch, do I order a .036" head gasket? Also, where is everyone getting cometic's these days since RSI seems to be non responsive?

I just found them here from google

I set my B230FT to 4 thou out and used a 36 thou Cometic MLS HG for 32 thou clearance. H-beams, so I'm not as worried about stretch. Nothing but smiles and detonation resistance. I ordered my Cometic from my local dealer.

I ordered a Cometic for a b230 from Summit sometime last year. Never used it though. I can't remember if they had all the options for b230s.

Another example, my 94 squirter block in the DD:

Approx. 140K miles on the bone stock bottom end

Factory pistons were poking out .007" to .009" (pics in my build thread, I believe)

Bought a 036 Cometic from RSI back in the day

After review with TF, I weenied out on the 036 (due to the piston poke out) and bought a 040; Hylomar lightly coated and torqued using the method on TF's pages. Approx. 15K miles now in 3 years without issue; engine has not been north of 6500 RPM.

Considering that most of the automotive forums (that I've viewed) report study results showing that .035" is the sweet spot to prevent combustion of the mixture out beyond the quench pads.... mission accomplished.

I recall a conversation with a local V8 engine builder here in Georgia.....said he built lots of SBC's for the dirt track boys down here. A particular engine which had built with .030" quench was found (after a season of racin') to have the P/N from the top of the piston "written in the carbon on the bottom of the head" Obviously those parts were getting awfully close to one another...... but that is a different construction engine (V8, with 2 rods / pair of mains) and who knows what the piston weight or rod type/strength was? I think if I were building an NA torque motor, I wouldn't be afraid of going .024" or .027".

Nothing really unique to the redblock here, boys. Plenty of proof of the benefits of tight quench construction to improve your chances to avoid detonation and the nasty things that happen as a result.

This is a pretty old thread but it has peaked my interest in raising compression. I'm planning on install a 114938 - Billet HD VX Street Performance Camshaft from IPD and since I'll be learning how to do that for the first time I may as well learn how to install a head gasket. Because I'm just planning to wing it in my garage I won't try to figure out the piston protrusion, stretch, valve clearance or have a machine shop smooth out any surfaces.

Can anybody suggest a Cometic gasket thickness that will work with the new camshaft, that is very unlikely to cause any damage to the motor considering nothing being measured, and I will feel an increase in performance? I drive the car pretty easy and it has an automatic trans. I'm just looking for some more grunt while getting onto highways and while towing my trailer. Something less than .040?

Has anyone else been having a hard time finding head gaskets for a b230 on the cometic website?

Oh and I have an '87 245 with the stock head.

Thanks for your help.

squish quench or whatever you want to call it is not a thermal thing it is about creating a high turbulence combustion chamber and not having any dead areas of fuel mixture that get exposed to the fire AFTER cylinder pressures have increased beyond the auto detonate level.

Squeezing the fuel mix into the center of the mix vigorously stirs everything up and creates a more homogenous mixt and shares all the fuel mix with the fire.

Any high temps seen in those edges is cause by detonation as they would otherwise be cold spots.

Thanks very much for the info.

Fred Gwynne said:

This is a pretty old thread but it has peaked my interest in raising compression. I'm planning on install a 114938 - Billet HD VX Street Performance Camshaft from IPD and since I'll be learning how to do that for the first time I may as well learn how to install a head gasket. Because I'm just planning to wing it in my garage I won't try to figure out the piston protrusion, stretch, valve clearance or have a machine shop smooth out any surfaces.

Can anybody suggest a Cometic gasket thickness that will work with the new camshaft, that is very unlikely to cause any damage to the motor considering nothing being measured, and I will feel an increase in performance? I drive the car pretty easy and it has an automatic trans. I'm just looking for some more grunt while getting onto highways and while towing my trailer. Something less than .040?

Has anyone else been having a hard time finding head gaskets for a b230 on the cometic website?

Oh and I have an '87 245 with the stock head.

Thanks for your help.

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It's real easy to measure deck height. Straight edge and some feeler gauges that you will need to shim your cam anyways. From there it's just a little math away from knowing what thickness you can get away with depending on your maximum rpm.

Dirty Rick said:

squish quench or whatever you want to call it is not a thermal thing it is about creating a high turbulence combustion chamber and not having any dead areas of fuel mixture that get exposed to the fire AFTER cylinder pressures have increased beyond the auto detonate level.

Squeezing the fuel mix into the center of the mix vigorously stirs everything up and creates a more homogenous mixt and shares all the fuel mix with the fire.

Any high temps seen in those edges is cause by detonation as they would otherwise be cold spots.

Click to expand...

Thank you..I'll contact all the shops in the world and tell them they all have it wrong and that there's no benefit from keeping the corner of the head cool..and I shoot a note to all the OEMs of the world..
Guess that means that under-piston oil squirters are fake improvements too..

Can we please call it quench, which is the proper technical term, not "squish"?

From Webster's online:

Quench:

Transitive verb

a : put out, extinguish
b : to put out the light or fire of
c : to cool (something, such as heated metal) suddenly by immersion (as in oil or water)
d : to cause to lose heat or warmth

both terms are used interchangeably throughout the industry in my experience...

I think squish better describes what happens though. As the piston *almost* touches the head on those quench pad sides, it violently *snaps* the air out of the rapidly closing gap. That creates a lot of turbulence in the central chamber in the already burning mixture. All that added turbulence helps 'quench' the hot spots in the area because the air is moving more. The less close the piston gets to the quench pads, the less 'snap' there is, the less turbulence is created, and the more hot spots are allowed to linger.

And the thickness of the gasket doesn't matter that much, it's the distance between the piston at TDC and the head - the pistons may be above the block, below it, or flush with it at TDC. Measure that, and add/subtract from the head gasket to arrive at the measurement that really matters.

I'm running .036 on the PV (block decked to zero the pistons), .040 on the 16VT, because that head design doesn't really have quench pads so it doesn't really matter much.

JohnMc said:

I think squish better describes what happens though. As the piston *almost* touches the head on those quench pad sides, it violently *snaps* the air out of the rapidly closing gap. That creates a lot of turbulence in the central chamber in the already burning mixture. All that added turbulence helps 'quench' the hot spots in the area because the air is moving more. The less close the piston gets to the quench pads, the less 'snap' there is, the less turbulence is created, and the more hot spots are allowed to linger.

And the thickness of the gasket doesn't matter that much, it's the distance between the piston at TDC and the head - the pistons may be above the block, below it, or flush with it at TDC. Measure that, and add/subtract from the head gasket to arrive at the measurement that really matters.

I'm running .036 on the PV (block decked to zero the pistons), .040 on the 16VT, because that head design doesn't really have quench pads so it doesn't really matter much.

Click to expand...

Thanks for your help. Another newbie question: Can I make a piston TDC by turning the crank with a wrench like I do with my old Moto Guzzi? And can this be done with the engine still in the car?


Thanks

Yes, just turn the main crank bolt clockwise with a ratchet. A breaker bar is easier but isn't essential.

If you're serious about picking a head gasket thickness for tight squish, make or buy a "magnetic deck bridge" and a dial indicator. It's much easier than using a straightedge and feeler gauges, plus you can watch the numbers while slowly turning the crank.