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Domed Pistons


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These photos were taken as progress shots of my 2.8L rebuild.

Pistons are Ross domed .040 overbore

I'm still debating head choices. Will be N47, E88, or N42 depending on the least amount of work.

I will retain and retune my SUs and will be using Isky's L-490 camshaft.

My mechanic says compression will be about 10.6:1

 

Any of you guys seen domed pistons cut like this?

No speculative answers please, thanks.

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Guest Dustin M

that's not a typical domed piston, but i'd assume it would have to rely on the higher compression, while still allowing valve, and spark plug clearances. It's an odd design, with a few radical edges, probably not the best for flow while in the combustion chamber, but at that point, it won't hurt much, if any.

 

I'm more interested in their balancing. I'd expect to see a higher side load on the piston skirt because of weight in one area.

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My mechanic says compression will be about 10.6:1

LEngine says that with flat top pistons and a felpro gasket, the CR is 10.3, so I don't think you're going to see 10.6 with those reliefs cut into the pistons.

 

Why did your mechanic choose those pistons? Is he worried about interference between the valves and pistons? From what I can see on the Isky website, the L490 has a lift of 0.490". Unless you are going with oversize valves, I don't see why you can't use that with an N42 head and flat top pistons. That's about what I did (not an isky cam, but otherwise about the same).

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how much do those stick up above the deck (if at all)?

 

IMO the best head without doing work to it (aside from the closed chamber P90) is the N42. big valves, square port, decent flow.

 

 

I'll have to get that verified by my mechanic.

I read the thread "big and nasty headwork" and was leaning toward the N47 since this is supposed to be a "hot" street, not race motor.

I'm probably cutting it close at 10.6:1 compression, but I think the cam at 290/.490 will allow that to work.

 

I'm hoping Mr. Mortensen, Coffey, and Ruschmann will chime in.

 

I realize now, I probably should have posted this in the L6 forum.

Obviously, I've read more than I have posted.

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LEngine says that with flat top pistons and a felpro gasket, the CR is 10.3, so I don't think you're going to see 10.6 with those reliefs cut into the pistons.

 

Why did your mechanic choose those pistons? Is he worried about interference between the valves and pistons? From what I can see on the Isky website, the L490 has a lift of 0.490". Unless you are going with oversize valves, I don't see why you can't use that with an N42 head and flat top pistons. That's about what I did (not an isky cam, but otherwise about the same).

 

 

The donor engine is a 77, 2.8 and has dished pistons.

I specified cast flat tops because of cost.

The forged domed pistons were thrown into my deal.

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Helping him, that would be saying his motor setup is not gonna work like he thinks it is, and needs to do more research or he his throwing money away, those pistons arent cheap! You need to fit pistons to heads, when a good motor builder builds an engine, they fit EACH piston to EACH combustion chamber, Ive written LONG articals on the subject.

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If you read through all the threads that Braap and others have commented on about head and piston choices its very obvious that you would want to match pistons to your head. Works the same way as the aerodynamics, slapping on a whale tail wont do much by itself, its the total package.

 

I think his comment did help. If WISHIHADAZ is spending alot of money on machining and parts, its important that he knows what his machinist is doing and why.

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brian i wasnt saying you where wrong... i agree with you and i know you have to match everything. i know its a complete assembly that every part has to work together.. its just the way you come across (at least to me). i would just maybe point the guy in the right direction than just stamping his engine build with big "WRONG" and toss it to they side. why not direct him in the right direction so he can maybe get the best possible head with those pistons?? what head would you put with those pistons??

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brian i wasnt saying you where wrong... i agree with you and i know you have to match everything. i know its a complete assembly that every part has to work together.. its just the way you come across (at least to me). i would just maybe point the guy in the right direction than just stamping his engine build with big "WRONG" and toss it to they side. why not direct him in the right direction so he can maybe get the best possible head with those pistons?? what head would you put with those pistons??

 

Looks like WishIhadaZ didnt mind.

 

Just a general question, about how far is the piston away from the head at TDC? For example a flattop and a p90.

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Any of you guys seen domed pistons cut like this?

No speculative answers please, thanks.

 

And how does your post help my situation?

I'm not a thread basher, but really; this is the kind of stuff that makes people do it.

Your post was totally irrelevant!

 

Seen plenty like that, not on an L series but seen plenty. Your initial question has been answered a few times by other members. You already said ya like the N47 head, even after the P90 and N42 were suggested.

 

You obviously have plenty of money to throw into your project. Relax and enjoy the progress. Hopefully your engine builder is as good as ya think and everything should be fine. I would personally ask the supplier why those pistons were thrown into the deal instead of the flat tops you originally wanted. Make him tell ya what will work with the pistons he send ya since he obviously knows something we both are unaware of.

 

I wish you the best of luck and success with your build, it looks great so far. If I did'nt have 5 kids and a wife with Epilepsy, I'd have a motor like that. Sorry if my first post threw ya off ballance and pissed ya off. Concentrate on the build, not people like me.

 

Sincerely,

Dave.

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