Zero-decked 4.1?

[UncleDave]

According to the builder, this setup should result in approx. 9:1 CR with 46cc GN1 aluminum heads. This is not my first BV6, but it is my first 4.1, and I don't recall ever seeing a zero-decked Buick turbo V6... Slugs are custom Wiseco forgings; I was planning on using the Fel-Pro 1026 HG's. Would this be OK, or is it looking for trouble?

In case you're wondering about the build, it's a .020-over 4.1 "291"casting, standard Turbo crank, steel caps, K1 stock length rods. And yes I got a build sheet, lol...

 

[bison]

I've run out of the hole. Zero deck is not uncommon. What is the dish on the piston? If it's less than 30cc you will have well over 9:1.

 

[it's just a six]

Running a 0 or close to 0 deck will help supress detonation. Gives you some sort of quench area.

What is the crushed measurement of the Felpro gasket?

I run a positive deck myself.

 

[UncleDave]

I've run out of the hole. Zero deck is not uncommon. What is the dish on the piston? If it's less than 30cc you will have well over 9:1.

What is the crushed measurement of the Felpro gasket?

Dish volume is 35.5cc. According to Fel-Pro the 1026 compressed thickness is .032. And this thing will be running a bit of cam, so I don't want to be running into valve-piston clearance issues either.

 

[charlief1]

What's the part number of the pistons Dave? Looks like I may have found what I was looking for in a piston design for the 4.1.:biggrin:

 

[novaderrik]

does anyone make an off the shelf reverse dome piston for these engines that would give the same compression ratio?
that way, you'd have all sorts of quench..

 

[novaderrik]

does anyone make an off the shelf reverse dome piston for these engines that would give the same compression ratio?
that way, you'd have all sorts of quench..

 

[charlief1]

Looked for about 2 years and never found an off the shelf piston that would work. If there's one out there I'd like to find it.

 

["More Boost"]

im running a "291" block in mine. (dont forget cam bearings are diff from 109)
if you run arp head studs 4.1's are diff. than 109
I got a good education when i built mine, of course you prob. already know these things anyway. just trying to help...

 

[UncleDave]

Charlie, the part number is AW-03149. They're custom forgings, there's nothing forged available off the shelf for these motors.

As far as cam bearings, More Boost is correct, and it's same thing you run into with an earlier non-109 block without groove behind the #1. Found that out the hard way when I rebuilt the original '84 HA motor last year; ended up making a transfer tube connecting the galleys at the rear. Using the correct cam bearings is MUCH easier!

 

[charlief1]

Thanks Dave. Now all I need to do is call them and they should be able to duplicate them. Makes it much easier to get the pistons that way.

 

[bison]

8.88:1

 

[UncleDave]

8.88:1

Perfect, thanks.

Quick Q regarding running out of the hole: Wouldn't this require machining a relief in the head? Not that I'm planning on doing this, just curious.

 

[charlief1]

Depends on how far out it is Dave. Minimum clearance, if I remember right, is .010 between the head and the piston. If your head gasket thickness is .030 compressed then you can run .020 out and be fine. This also gives you good squench characteristics.

 

[BlownV6]

Depends on how far out it is Dave. Minimum clearance, if I remember right, is .010 between the head and the piston. If your head gasket thickness is .030 compressed then you can run .020 out and be fine. This also gives you good squench characteristics.

No expert here on this combo , but in general .010" piston to head clearance is way to close and will hit!! .040" is more of a standard clearance. Mike

 

[UncleDave]

No expert here on this combo , but in general .010" piston to head clearance is way to close and will hit!! .040" is more of a standard clearance. Mike

I just talked with the builder and he recalls I may be as much as .002 out, he believes that with .040 Cometics I should be fine. I'm going to gauge it tonight just to be sure, cuz I don't want to leave anything to guesswork. Then I can order the gaskets and finally get this beast put together. Thx!

 

[Alky V6]

No expert here on this combo , but in general .010" piston to head clearance is way to close and will hit!! .040" is more of a standard clearance. Mike

+1.
Figure a steel rod can grow .010". I don't know what a piston grows. An aluminum rod can grow .020". Then you have piston rock. Carbon buildup? Of all the written material I've read on the subject of deck clearance, .040" is a safe minimum. If good quench action is the objective, just stay under .060".
If you're going to play under .040", you'd better know what you're doing.

 

[9SECVSIX]

I ran the 1026 gasket with a 0 deck clearance in one of my Stg motors .didn't have any problem but I wouldn't chance going any less than .038"-.040"

 

[UncleDave]

I'll probably go with the .060's to be safe. Thanks everyone.

 

[bison]

Perfect, thanks.

Quick Q regarding running out of the hole: Wouldn't this require machining a relief in the head? Not that I'm planning on doing this, just curious.

I ran as much as .012 out before i saw some light shadowing on the head where the piston would just barely rub the carbon off the head on the rock with a .040 compressed gasket. .030 would be the absolute minimum id run. Id run it tight. They run better that way.