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Discussion Starter #1
Just took apart my 427 too find out if I had a head gasket leak and sure enough I did. But that's not all I found. Time for new pistons a bore and rebuild haha. The mains and rod bearings were blue hot. Cranks still standard and it had standard bearings. What kind of clearances would be ideal for a lake boat. I ran 15/40 syn and I got a 10 quart pan no cooler 70psi of oil press and usually 220F of oil temp after a couple good passes. Also what can you tell me about my cam? It looks like a custom grind.

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Discussion Starter #4 (Edited)
Looks like it got into detonation. Most likely what took out the head gasket and the piston.
Cam is 635 lift 262 @ 050, more than likely ground on 114 lsa. with an iron distributor gear.
I think she was a little high on comp for 91 octane. I was told its around 10-1. When I buy new pistons ill make sure it's pump gas friendly. I noticed it did like the timing a bit retarded like 6* base and the stiffer spring in the destribitor. Pistons were TRW L2239N and heads are 990s

As for the cam would you keep running this one or switch it? Seemed to really pull hard around 4-6500 rpm. I didn't sounds as lopy as my brothers 285 Hyd roller. I don't wanna take away perf with two big of cam.
 

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I think she was a little high on comp for 91 octane. I was told its around 10-1. When I buy new pistons ill make sure it's pump gas friendly. I noticed it did like the timing a bit retarded like 6* base and the stiffer spring in the destribitor.

As for the cam would you keep running this one or switch it? Seemed to really pull hard around 4-6500 rpm. I didn't sounds as lopy as my brothers 285 Hyd roller. I don't wanna take away perf with two big of cam.
Depends on the heads what the compression was. 10 to 1 is doable with aluminum heads. More 9 to 1 with iron.

Cam depends on the rest of the build, like heads. If the cam is ground on 114 LSA it will idle a little smoother than a similar cam ground on a tighter angle.



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Discussion Starter #6
Depends on the heads what the compression was. 10 to 1 is doable with aluminum heads. More 9 to 1 with iron.

Cam depends on the rest of the build, like heads. If the cam is ground on 114 LSA it will idle a little smoother than a similar cam ground on a tighter angle.
Pistons were TRW L2239N and the heads are 990s. I think that's closer to 10-7 or 11-1.
 

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Discussion Starter #8
Closer to 11.5.
Maybe 11 to 1 if it had a composite head gasket. Way passed pump gas compression with an iron head
what would you think I was making HP wise before? And would there be much of a drop in power with 9-1 comp hollow dome pistons which will lighten up the rotating assem which getting balanced again. Would my cam be too big for 9-1 comp?
 

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Those bearings look stained like that when new. Just a piston & head gasket it appears.
 

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Discussion Starter #10
Those bearings look stained like that when new. Just a piston & head gasket it appears.
Bearings are clevette 77's. my cylinders are scratched enough to feel with the finger nail. So it's off to the engine shop to get hot tanked and bored 30 over
 

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Isn't L2239N closed chamber? 990's open chamber 116-118 cc.?


You must have crappy gas in Canada, I run those same (heavy) pistons with 109 cc iron heads and a .020 head gasket on 91 pump 38* locked and have never had a detonation problem.(your results may vary)
The 77's in mine aren't blue, is that a car (spec)motor with a stock oil pump making 70 psi?
Mine is .025 rods .032 mains with a mellings hv and 20/50 val.With 220* oil...maybe 70 psi...solid [email protected] 6800
 

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Discussion Starter #13
Isn't L2239N closed chamber? 990's open chamber 116-118 cc.?


You must have crappy gas in Canada, I run those same (heavy) pistons with 109 cc iron heads and a .020 head gasket on 91 pump 38* locked and have never had a detonation problem.(your results may vary)
The 77's in mine aren't blue, is that a car (spec)motor with a stock oil pump making 70 psi?
Mine is .025 rods .032 mains with a mellings hv and 20/50 val.With 220* oil...maybe 70 psi...solid [email protected] 6800


Yup those pistons are closed chamber design ive been told and Were run with open chamber heads. The block is a 286 casting 4 bolt with a melling HV pump. Here's the clearances from the build sheet. Rods .002-00225 mains #1 -.002 #5-.0025 Pistons were .004-008 and ring end gap .018 As for fuel I'm not sure lol
 

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WHAT? You didn't know that GM assembled thousands of BBC with CC pistons and OC heads.? Specially crate engines.
And how do you get 11.0-1 compression with pistons that are 11.0-1 with closed chamber heads and he has open chamber?

Yup those pistons are closed chamber design ive been told and Were run with open chamber heads. The block is a 286 casting 4 bolt with a melling HV pump. Here's the clearances from the build sheet. Rods .002-00225 mains #1 -.002 #5-.0025 Pistons were .004-008 and ring end gap .018 As for fuel I'm not sure lol
Kinda tight on the bearings, .0025 is the usually accepted number for rods and .003-0035 on the mains with a straight line bore.....Not so sure on the fuel? That's an opps, even at 10.0-1 91 octane be about the minimum although for some reason i get away with close to 11.5-1 and 91.
 

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Discussion Starter #15
And how do you get 11.0-1 compression with pistons that are 11.0-1 with closed chamber heads and he has open chamber?


Kinda tight on the bearings, .0025 is the usually accepted number for rods and .003-0035 on the mains with a straight line bore.....Not so sure on the fuel? That's an opps, even at 10.0-1 91 octane be about the minimum although for some reason i get away with close to 11.5-1 and 91.

I've heard those pistons with closed chamber heads would the 12-1 comp range maybe higher. I usually run shell v-power and its 91 octane. We have 92 and 93 but its sometimes hard to find when your out at the lake. As for my block its been line honed.
 

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And how do you get 11.0-1 compression with pistons that are 11.0-1 with closed chamber heads and he has open chamber?


Kinda tight on the bearings, .0025 is the usually accepted number for rods and .003-0035 on the mains with a straight line bore.....Not so sure on the fuel? That's an opps, even at 10.0-1 91 octane be about the minimum although for some reason i get away with close to 11.5-1 and 91.
Like any other piston, it depends on the chamber CC, distance in the hole, and head gasket, You figure it out.
You seem to do a lot of things that defy logic. But then.....you're special

The specs on the L2239:
C.H.=1.760"
D.V.=44 cc
D.H.=.450"
C.R.=13:1
Weight=750/760



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I missed the op having pistons with more dome. Mine are the L2268. No entry for 109 cc heads but it looks like it lands right on 11.0-1. The L2239 is 10.84-1 @ 116cc. OP has thicker head gaskets. Why would OP have detonation issues when i don't? Not even with one head milled .030:rolleyes:
Nothing 'special' about my pile...other than the guy who supervised the build....although he did say the .020 head gaskets would be cutting it close.
Been told several times 11.0-1 and 91 octane won''t work.
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I missed the op having pistons with more dome. Mine are the L2268. No entry for 109 cc heads but it looks like it lands right on 11.0-1. The L2239 is 10.84-1 @ 116cc. OP has thicker head gaskets. Why would OP have detonation issues when i don't? Not even with one head milled .030:rolleyes:
Nothing 'special' about my pile...other than the guy who supervised the build....although he did say the .020 head gaskets would be cutting it close.
Been told several times 11.0-1 and 91 octane won''t work.
View attachment 496833
Because you're special. We all know that. Mere mortals can't run the compression, and you have a god for mentor, we don't. You forgot to mention you run 40* of timing and 15 to 1 AFR as well.

In fact your special that you KNOW OP's head gasket thickness and he never mentioned that. THATS HOW GOOD YOU ARE.:)sphss



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Because you're special. We all know that. Mere mortals can't run the compression, and you have a god for mentor, we don't. You forgot to mention you run 40* of timing and 15 to 1 AFR as well.

In fact your special that you KNOW OP's head gasket thickness and he never mentioned that. THATS HOW GOOD YOU ARE.:)sphss
Awww, you 'pecial tooo! lol
So i guess 11.0-1 is to much for even Terribles 91 octane?
And 40* is to much?
ARF? Never checked, 'god' says the plugs look fine in winter, a little fat in summer.

Didn't say i knew OP's head gasket thickness, i said 'thicker'(than mine) composition vs steel shim...re-used a few times. I did forget about the fllycut. I didn't cc the pistons when i was done but the 2 i weighed lost almost 6 grams...+2cc's.
DSC0026777.jpg

So you are saying it won't run on 91 octane and not hurt itself?
I don't want to have to buy racing gas and i sure as hell don't want to blow it up, i only have 100 hrs on it.:notsure:
 

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Awww, you 'pecial tooo! lol
So i guess 11.0-1 is to much for even Terribles 91 octane?
And 40* is to much?
ARF? Never checked, 'god' says the plugs look fine in winter, a little fat in summer.

Didn't say i knew OP's head gasket thickness, i said 'thicker'(than mine) composition vs steel shim...re-used a few times. I did forget about the fllycut. I didn't cc the pistons when i was done but the 2 i weighed lost almost 6 grams...+2cc's.


So you are saying it won't run on 91 octane and not hurt itself?
I don't want to have to buy racing gas and i sure as hell don't want to blow it up, i only have 100 hrs on it.:notsure:
That's the point. You are ASSUMING again, I don't see where he mentions composition head gaskets.
Nobody even mentioned the ridiculous cam you run in that thing. Think that might play a role in the gas you can get away with?

Are you suggesting that the OP just hones the cylinder and replace the damaged piston? There is little doubt what you would do. Just wondering if that is your suggestion to the OP? If not, what is.



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