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

itb-volvo

Member
Joined
Jun 14, 2003
Location
P-town Or
We're looking for first hand experiences of people running thin Cometic MLS headgaskets on a stock b230 bottom end...

1. What thickness headgasket did you use?
2. Has your bottom end been rebuilt or is it the original, untouched, 250k mile bottom end with the carbon cleaned off the 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?
4. Did you attempt to measure how far the pistons stick out and what did you come up with for squish clearance?
5. How high have you revved the motor with that setup?
6. Have you ever experienced what MAY have been the pistons hitting the head? Has anyone experienced that in one of these motors yet?

For the General Leif Chumpcar(www.facebook.com/GeneralLeif), we are able to run any gasket we want, so we pulled the head to put a Cometic on. Now we are trying to figure out how tight we want to go... Our engine has fresh bearings in it, but it's not "blueprinted" or anything special inside. Just new bearings and rings and a quickie hone. We will be revving it to a usual max of 6-6500rpm for hours on end(36hr race in July!!!).

Thanks for any input you have on what you've done!
Kyle(KLR142) and Marc
 
subscribed.... I havent picked a gasket yet....

I have a block getting blueprinted now. 4 layer bearings if available. 3 If not.
2.5 RSI W/ 158MM Hbeams.
Shooting for 0 deck...
 
Thus far I've used a .036 and a .034. I do know someone trying out a .028 and .030. All of them fresh rebuilds.

All were sprayed with Hylomar.

Only issue I had with any of them was a .036 with a V cam. Belt broke (was new to boot - long story) and the exhaust valves kissed the pistons. Made a half moon showing in the carbon (totally disappeared when wiped clean), but enough to trash 2 of the valves.

Only "rev' I recall was in the 6-7k range while adjusting an MBC.
 
Do you know where they set their deck height when they did rebuilds?

Also ive read that rods stretch is figure to be .004 for every 1K RPM? I reckon i read that somewhere and cant recall if it was OEM rods or H beams?

Best squish below .030?

So with a zero deck height... .028 @ 7K? = .002 away from hitting everyting and making a big ol mess.
 
I think "tight squish" occurs under .040" anything beyond that and you're increasing quench. If you want to reduce detonation just get under .040". .004" rod stretch is a general rule of thumb. Nothing anyone has measured.
 
It was late and i was going from memory. Thanks for clearing that up.


So assuming rod stretch @ .004/1K rpm x 7 k & HG @.040- .028 with zero deck height.. 0.012 ( vs .002 as i originally figured)

I guess im looking to be somewhere around .036 with mine. Im not planning any time above 7K for a while. More stroke = Less revs but more torque down low. I'll take that tradeoff. Plus im hoping that H beams stretch less than stock rods...
 
You could have your block decked and run a stock one.

@ OP .. Are you remving the engine for rebuild/ freshening? I was looking into lemons/ chump and they made the rules lockdown style on chump this year.

how do the stockers hold up under abuse....Oh wait. I abuse the snot out of my orig motor with 247k and ODO INOP. HG is leaking around edges but still runs... no mix of coolant and oil.

Do you know compressed thickness on stocker? I get all OEM parts @ cost ( dealer employee perks)

If its a little on the thick side u can have him set the slugs above as well.
 
On my 2.5 stroked 16v, i ran the .045 cometic with + deck on the pistons, tho I didnt measure, it was minimul. With oil fed to the rear of the head, I could spin mine almost to 8k rpms befroe I shifted, power was strong to that point. We did tune the intake and exhaust runners for a low 7k peek, and the motor did great with Hydraulic lifters.

Im not sure how much more boost tq is made with .2 litres spread across 4 cylinders, but the long rods should flatten it out. Mine had great off idle tq, but I never drove the 2.3l to get a comparison.



It was late and i was going from memory. Thanks for clearing that up.


So assuming rod stretch @ .004/1K rpm x 7 k & HG @.040- .028 with zero deck height.. 0.012 ( vs .002 as i originally figured)

I guess im looking to be somewhere around .036 with mine. Im not planning any time above 7K for a while. More stroke = Less revs but more torque down low. I'll take that tradeoff. Plus im hoping that H beams stretch less than stock rods...
 
Thus far I've used a .036 and a .034. I do know someone trying out a .028 and .030. All of them fresh rebuilds.
Stock rods/pistons or aftermarket? Sticking out of the block and measured to be such, or not measured? How high have the engines been spun?
Also ive read that rods stretch is figure to be .004 for every 1K RPM? I reckon i read that somewhere and cant recall if it was OEM rods or H beams?
"Word on the 'net" is that you shoot for ~.004" for every 1,000 rpm and add another .004" for safety. This may or may not be with a built bottom end. And it may or may not be more specifically for one engine than another.

On my '91, I run a .040" Cometic gasket on an untouched, now 198k mile(headgasket done at 150k with head work) b230 that supposedly had the pistons sticking up almost .010" according to those doing the work. I've had it up to 7k without issue and routinely hit 6500 with multiple track days, autox, drag racing, etc. I want to hear more actual stories!
I think "tight squish" occurs under .040" anything beyond that and you're increasing quench. If you want to reduce detonation just get under .040". .004" rod stretch is a general rule of thumb. Nothing anyone has measured.
Yes, under .040" is really required to start reaping the benefits, but the tighter you go, the better it is. Think about it, would you rather have your air and fuel mixture all in the center of the combustion chamber, or would you like some stuck in between the pistons and the squish pads of the head where it struggles to do anything? My '91's setup, above, is not very resistant to detonation and I have to keep the engine temperature on lock down to prevent it. I want to pull the head, make sure all edges are rounded and put a thinner gasket on it. And put in a larger cam, haha.


I think James and Adrian have run .028" gaskets on stock b230s for just runabout cars, but they didn't rev them high. Or did they? Eh? Eh?
 
Stock rods/pistons or aftermarket? Sticking out of the block and measured to be such, or not measured? How high have the engines been spun?
"Word on the 'net" is that you shoot for ~.004" for every 1,000 rpm and add another .004" for safety. This may or may not be with a built bottom end. And it may or may not be more specifically for one engine than another.

On my '91, I run a .040" Cometic gasket on an untouched, now 198k mile(headgasket done at 150k with head work) b230 that supposedly had the pistons sticking up almost .010" according to those doing the work. I've had it up to 7k without issue and routinely hit 6500 with multiple track days, autox, drag racing, etc. I want to hear more actual stories!

Yes, under .040" is really required to start reaping the benefits, but the tighter you go, the better it is. Think about it, would you rather have your air and fuel mixture all in the center of the combustion chamber, or would you like some stuck in between the pistons and the squish pads of the head where it struggles to do anything? My '91's setup, above, is not very resistant to detonation and I have to keep the engine temperature on lock down to prevent it. I want to pull the head, make sure all edges are rounded and put a thinner gasket on it. And put in a larger cam, haha.


I think James and Adrian have run .028" gaskets on stock b230s for just runabout cars, but they didn't rev them high. Or did they? Eh? Eh?

I think this is why another member complains about the term squish. It is really a reference to an anti detonation trick. Quench or lots of it is why people go beyond .040". They are kind of two different things but attained through the same machining practices.
I don't know why someone would go beyond .030."
 
I used a .030 on my '97 B230FK. The stock shortblock had already 180k miles on it.
I preped the block face using a sharp bladescraper, the head was planed in a machineshop.
I cleaned the bolt holes and removed any crud using compressed air and a used headbolt.
I just slapped the head on and installed it using brandnew lightly oiled TTY headbolts.

It was a complete succes. It cured some pistonslap noises on cold startup. the cometic held up so good that i managed to drive at least 200km (highway, light load on cruise control) with only very little coolant in the system....(level just at waterpump height) The reason that the engine lost coolant? a blown perished rubber waterpumpseal between head and pump. After arriving home i let the engine cool down slowly, did the repair, refilled the engine with coolant. NO HG damage. ready to go.
I never reved it to the limiter though, 5000, maybe 5750rpm? With a T-cam in there it was pointless anyway.
 
Very cool. Thanks for the feedback. Did you take off extra material from the head to get your compression up or just resurface it for proper sealing? How has the performance(fuel consumption) been in addition to the reduction in piston slap?



I'm hoping to hear some more, I know there's more out there!
 
I did the .030 with 50 thou shave off the head on my NA b230, with the K cam, it actually makes a noticable difference...
YES! This is what I'm looking for. Hell yeah! I'm going to do the same on my Beige Bomber '87 DD. Shave .050" off, put on a thin gasket and toss in the H cam for some awesomeness(I was thinking of maybe doing even more and grooving it, just so someone can actually do it on here and take notes... :-P). What fuel system are you running and how is it liking it? Running premium or something else? Did you measure where the piston tops were in relation to the block's surface before installing? How high do you rev it?
 
YES! This is what I'm looking for. Hell yeah! I'm going to do the same on my Beige Bomber '87 DD. Shave .050" off, put on a thin gasket and toss in the H cam for some awesomeness(I was thinking of maybe doing even more and grooving it, just so someone can actually do it on here and take notes... :-P). What fuel system are you running and how is it liking it? Running premium or something else? Did you measure where the piston tops were in relation to the block's surface before installing? How high do you rev it?


I thought I said 060...oh well.
Al's old POS was some skinny rod POS from the junk yard, pistons were like all B230 NOMINALLY flush with deck. I think that was LH2.2....Ran the best pump gas at whatever convenient gas station he happened by....

K cam.... and 4.88 in the rear end....Borg Warner T5 with the only gearset worth paying for: 2.95 first

The motor was just some interim lowest budget imaginable thing since he was planning all along to move to what is called Group 5 which is a class for 2wd cars with turbo but the imbecile owners of one of the corporations that sanction rally on a whim said "No turbos for newbs"
275 n.a. hp for example is prefectly safe in their "reasoning" but a stock old B21T is "tooooooo risky, near certain death!"
So it was just some old POS..

It went REAL good as the total package Compression, K cam, specific gearset, axle ratio.

We were both kinda big eyed say "Daaaayum what's it going go like with the turbo motor?"
 
I think this is why another member complains about the term squish. It is really a reference to an anti detonation trick. Quench or lots of it is why people go beyond .040". They are kind of two different things but attained through the same machining practices.
I don't know why someone would go beyond .030."

Because of the inexorable logic always operating which guides so much car-thought:
If this much________ is good, then WAY FAWKIN MORE IS LIKE OMG!!!!!!!!!!!:omg:

036-040 is long established---2 1/2 to 3 decades ago as very very effective at mitigating detonation..


less,is TONS BETTER-ER!!!! is ASSERTED by many completely subjectively---and I'll bet most asserting the AH-mazing stuff went from stock whatever fat ol spongy gasket, to whatever they 'figured out" without ever doing the 036-040 thing.

Solid reasoning, as always.
 
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