[pontiarrg]

I have been talking to a machinist who is telling me about turning cranks on the highside and lowside to affect deck clearance. Will this really affect compression? If so What needs to be done? I was thinking instead of milling 6x-8 heads to 89 cc just changing the grind on the crank. What effect does this have on performance vs rpm range? I know that a unmentionable engine builder does this to his 350 buildups to get more torque and higher compression. What is the straight scoop. thanks Pontiarrg

[pontiarrg]

I have been talking to a machinist who is telling me about turning cranks on the highside and lowside to affect deck clearance. Will this really affect compression? If so What needs to be done? I was thinking instead of milling 6x-8 heads to 89 cc just changing the grind on the crank. What effect does this have on performance vs rpm range? I know that a unmentionable engine builder does this to his 350 buildups to get more torque and higher compression. What is the straight scoop. thanks Pontiarrg

[pontiarrg]

Have i blundered again... The normally Verbose experts on the py forum have remained unusually silent on this topic.... Is this a forbidden subject.... I have milled my cranks for years on different sides for chevy engines but this pontiac thing is new to me. someone please advise as i really have no other place to go...

[paul 67gto]

Im no expert, this is just my two bobs worth.
What you are talking about is stroking the crank,this will cause the piston to travel slightly higher up in the bore,increasing compretion and reduceing the deck hight.
Be aware by not decking the block and using standard height gugeon(spellcheck)the piston will be right up into the bore releif which may cause piston rock.
You will gain few inches also.
I think compression gains will be slight, rev range should be fine.
Remember Im just a novice so dont rely to heavily on this info.

[wholio]

I think you are talking about offset grinding. You can gain compression and stroke, keep in mind you will be reducing the rod journal size a little. In the chev. engine I go to a standard small journal from a large journal with an offset grind to gain inches. It's easier and cheeper to deck to zero.

[pontiarrg]

Yes i have done this with many chevy engines as well but it seems to me that these pontiac motors are a whole different animal. I am not sure what this will do but I was looking in to building a 400 that i have here with a offset grind on the crank and a set of 6x-8 heads milled from 101cc down to 94cc (flat milled). By changing the grind I am Hoping to use the L 22620 pistons to have a final comp ratio of 10.0. I am very concerned about what effect this will have on valve geometry and/or combustion. bottom line is has it been done and how much should i mill the offset and where?

[pontiarrg]

I Can't believe that nobody has tried this. I hate to waste a good crank trying this on the fly. PLEASE somebody tell me if i am wasting my time pursuing this. I am really curious if this can be done with pontiacs. I have seen a 350 with 46 heads that was built by a very disliked builder on the west coast that had a funky crank we surmised was turned on the low side and engine failed because of high rpm valve crash into a piston. But untill the motor was overrevved it ran like a banshee. The powerband reminded me of a 2 stroke engine but WOW. This was a 350, I want to try a 400 then a 455 and see what happens.

if it aint fixed don't broke it

[grandville455]

hey this is off the subject but how far do you have to mill the 6x-8 head to get 89cc and what has to be done to it ...do you have to mill the intake side too?...putting them on a 455

Grandville455

[pontiarrg]

I have milled a set a 6x-8 heads about 52 thou. i checked and found that they are at 87cc. Now if i am measuring right who knows. I filled them with water and measured it with a syringe. On a set of regular 6x-8 i found 101cc. Maybe some of the eggspurts will help us out. by the by i milled the whole surface as i did not know whether to mill the intake or exaust. Hope there are no manifold problems.

if it aint fixed don't broke it

[Will]

Something about the question, or this discussion strikes me as strange.

In the last couple of years I've screwed together a few motors and talked with a couple of crank grinders. The guys I talked to use the terms "high side" and "low side" to describe the finished diameter of the crank journal. A crank that is ground on the "high side" will have slightly larger journals than one ground on the "low side" and thus the resulting clearances between journal and bearing will be smaller. A "low side" crank may give you as much as .003 - .004" clearance, while a high side crank might only have .001 - .0015"

As for offset grinding a crank to change the stroke, well, a crank is a crank when it comes to that. It can be done on any crank. But keep in mind that you can only change the stroke by the same amount that you are taking off the journal, and this will only change the deck height by 1/2 the amount taken off the journal.

To clarify what I'm saying for those who may not follow - if the journal on your crank is in fine shape (doesn't really need to be ground), then it would be possible to increase the stroke by .010" by offset grinding the journal such that .010" is taken off the inboard side of the journal (the side closest to the crank centerline) and no material is removed from the outboard surface of the journal. This has the effect of moving the centerline of that journal .005" out from the centerline of the crank and will put the piston that much higher up in the hole at TDC.

If the surface of the crank is bad and it needs to be turned at least .010" all the way around to clean up, then you'd have to take off at least .020" to achieve the .010" stroke increase and the .005" higher piston height.

This is an interesting approach to zero decking a block, I've never thought of doing it this way. There is no reason it can't be done. The displacement increase will be minimal and won't have a significant effect on power output (you're talking about changing a 400 from 3.75" stroke to a maximum of 3.79" using .040" bearings if they're available on a good crank). The compression increase could be worthwhile if the pistons are already sitting down in the hole a ways. I would not want to end up with the pistons protruding more than about .005" from the deck surface in any case.

The real question in my mind, is which way is cheaper to attain zero deck? Offset grinding the crank or simply decking the block.

[grandville455]

i thought if you milled anymore than 25 thsds you also have to mill the intake side otherwise the intake wont fit when u bolt it up?

Grandville455

[Beebe]

I have been told more than once that you must mill the intake as much as the heads to maintain a proper mounting angle.

[Beebe]

Forgot to mention that you should measure lifter to rocker distance , as you might need to get custom pushrods .060 shorter , I know somebody makes a special pushrod for this situation,

[grandville455]

hmmmmm ,maybe i should just find 6x-4's and be done with it then,lol i'm getting a headache thinking about it

Grandville455