Piston / Build question

[James Neidig]

So I rebuilt my 88 TII Shelby Z from the bottom up. Stock forged crank cut 10/10, Clevite Bearings, TII rods, MP perf head gasket, 804 injectors, block bored 20 over... I plan to run a stage 3 SMEC with a max boost of 15 psi. I will add a 2 stage controller that is switchable between a G valve set at 15 psi and line pressure which should open the wastegate around 6 or 7 psi...

Here's where I think I royally screwed up... I used a set of Sealed Power/Federal Mogul pistons. I am not seeing anything good about these. They are not the H code pistons, but I still have now read enough to make me scared of them. Please weigh in... Thanks, Jim

[cordes]

I have some of the older cast Sealed Power pistons and they have done well. Just tune with prudence and they should hold up fairly well.

[Mopar318]

Well, with a good tune they dont hold much over 20psi. I just pulled my engine apart, and all the top rings were broke in pieces, and one pistons had a broken ring land.

I think you will be fine with 15 psi, but if I spent all the money like you I would spend the extra 400 and throw in some forged slugs for insurance.

[rosie]

Brian Slowe has a smokin deal on some JE's that IMOHO would be perfect for the build you described. No copy/paste on my phone with the link but I'll bump it so you can find it in "new threads"

Rosie

[1984rampage]

Yea I had those in a fresh rebuild with a stock mitsu running 12PSI.. Wasn't even beating on the car and lost the pistons.. I'd get rid of them :/

[James Neidig]

Just found the post on the JE's and replied to him. Thanks for the input. I am pulling it back out to change the clutch and turbo anyway....so what's a few more bolts to turn?!?

[James Neidig]

One more question... my machine shop simply took stock bore and added 20 thousanths to it when they bored it. Will a set of 20 over pistons be fine or will I need to go back through the whole process again?!? Again, 15 psi max here...

[cordes]

One more question... my machine shop simply took stock bore and added 20 thousanths to it when they bored it. Will a set of 20 over pistons be fine or will I need to go back through the whole process again?!? Again, 15 psi max here...

Since you are now going forged you will most likely need another trip to the machine shop. You will need to check the clearances as the forged pistons require a greater clearance than cast.

[Directconnection]

never just toss them in...always check your piston to bore clearances.

JEs are made "smaller" on purpose so the stock rings can be file fitted.

Also, just adding .020 to the bore of what they measured was not a good thing to do at all....

JE's are kick-azz.... but if you cannot use those in the FS section I reccomend
TU's forged Wiseco's with pins, clips and RINGS for $450.

[James Neidig]

never just toss them in...always check your piston to bore clearances.

JEs are made "smaller" on purpose so the stock rings can be file fitted.

Also, just adding .020 to the bore of what they measured was not a good thing to do at all....

JE's are kick-azz.... but if you cannot use those in the FS section I reccomend
TU's forged Wiseco's with pins, clips and RINGS for $450.

I may be a bit off on that, as the machine shop did wait to bore it until they had the pistons on hand, so they may have bored it off of the piston dims. I guess now I need to know what clearance I should have. I would prefer to not remachine it if at all possible. Can I measure the bore and order the pistons and rings off of it? I think I recall Forward Motion telling me he can order them in any size... Is this accurate?

[Directconnection]

I may be a bit off on that, as the machine shop did wait to bore it until they had the pistons on hand, so they may have bored it off of the piston dims. I guess now I need to know what clearance I should have. I would prefer to not remachine it if at all possible. Can I measure the bore and order the pistons and rings off of it? I think I recall Forward Motion telling me he can order them in any size... Is this accurate?

No, not accurate.... sorry.

You get the piston(s) measure them, and fit them to the bore. The pistons are all made with the clearances in them. meaning: a standard bore 3.445" "bore" will have a piston measure smaller than 3.445". It may be 3.4420 for a wiseco, and 3.4435 for a stock mahle cast.

[trannybuster]

Well Im sure custom pistons take a bunch more time to get. If you already bored .020 for cast then .020 forged piston will need more clearance so you wont need boring just hone BUT if there is at least .003 and you run synthetic oil exclusively that would be okay....Venolias and Weisco will run at .003, JE should also, check though. Is you use Weisco you can order them with stock wrist piston off the shelf from TU instead of dealing with getting rods reworked.

[Directconnection]

Unless Venolia's have changed, they need at least .006" clearance as some were running .007" back in the day.

JE's are .003... yet I had mine a tad more per Fm's suggestion at .0035.

For the most part... clearances are built INTO the piston, not the bore. You open up the bore if you wish to exceed the manufacturer's reccomendation.

[Mopar318]

Wouldnt you put the cylinders at 3.465 if its a .020 over cast or forged? I just thought they made the forged smaller for the clearence issues.

[Directconnection]

Wouldnt you put the cylinders at 3.465 if its a .020 over cast or forged? I just thought they made the forged smaller for the clearence issues.

Yes! It just took you many less words to say what I was trying to

Simo: all the oldschoolers running the Venolias in the late 90's were running them at .006-.007 One guy just posted that is in their range, so I'm not totally wrongo.

[trannybuster]

Weisco and Venolias are made of the SAME material, and they require .0035, nothing more. FYI synthetic oils do a much better job than dinosaur guts, better lubrication means closer tolerances. If you made pistons and understood the general populace isnt going to wait for the vehicle to warm up you wouldn't tell them .0035.
Fact-
Fwd told me .0035 is fine for Venolias with synthetic
Weisco has.0035 printed and included with piston kit again with synthetic
Forged pistons are twice as strong..period

Once the pistons and engine are hot both pistons are at the same outer dia, its during startup that is the issue because cast pistons have a steel strut cast into them to control expansion. Yes you can run 20+ psi with good gas but good luck with that, how well is octane monitored at gas pumps? You can run cheaper fuel with forged pistons and keep boost low when you want to save a few bucks commuting to work!
Go forged and you cant go wrong.

[Directconnection]

Weisco and Venolias are made of the SAME material, and they require .0035, nothing more. FYI synthetic oils do a much better job than dinosaur guts, better lubrication means closer tolerances. If you made pistons and understood the general populace isnt going to wait for the vehicle to warm up you wouldn't tell them .0035.
Fact-
Fwd told me .0035 is fine for Venolias with synthetic
Weisco has.0035 printed and included with piston kit again with synthetic
Forged pistons are twice as strong..period

Once the pistons and engine are hot both pistons are at the same outer dia, its during startup that is the issue because cast pistons have a steel strut cast into them to control expansion. Yes you can run 20+ psi with good gas but good luck with that, how well is octane monitored at gas pumps? You can run cheaper fuel with forged pistons and keep boost low when you want to save a few bucks commuting to work!
Go forged and you cant go wrong.

Is this an arguement, or someone giving out factual data???

2618 isn't quite the same for everyone now, is it? Meaning, low to nearly no silicon content..... vs. the high silicon content of the other forging (4032?) ie: low to no silicon means different rate of expansion even though it's 2618, right?

Piston fitting has a lot more to do than startup... it is soley on INTENDED purposes.

We bore/hone for just about every piston manufacturer out there. (Ross, JE, CP, Wiseco, Diamond, SRP, etc) and we do use the factory spec sheet as our guideline, but also custom tailor the fitment per intended usage. Nitrous... or Blower... or Marine... all require different things, same for the pin fitment, as well. That alone, has nothing to do with startup. (or synthetic vs. dino...) You are right that people can "cold seize" a piston being a tool on startup.

[trannybuster]

The only facts that I know of are what I listed under facts. This argument about Weisco or Venolia material was cleared up some time ago wasnt it..? Only a tool would disagree that differnt grades have no effect, thats not me.
You set piston clearence depending on application BUT in the end when absolute growth occurs they are all running pretty much a close tolerance, if not the piston would rattle around and crack the skirt. Oils make a huge difference, I cant agree otherwise.
Whether you or I agree doesnt matter, hes making the right choice going with forged, his decision is on intended application strictly race or street rod.
My Venolias I went with .005 and have had 0 issues street rodding it. I just installed Weisco and went .0035, time will tell, hopefully A LONG time...
Maybe we should start a thread stating clearly
1-clearance
2-oil
3-issues

[turbo84voyager]

I have been running 18 psi in my 84 mini and 91 shadow on Sealed power cast pistons and I have not had any problems. Both motors were built 5-6 years ago so I am not sure if they changed their pistons since. The shadow has been over 20 psi with a 46 trim hybrid when the wastegate froze and knock on wood its fine. If going forged take a look at wiseco's. I like mine. In my opinion it all comes down to tune. I am very cautious about tune and since I am not looking for every last bit of HP I would rather run them a little on the rich side and save the motor.

Looking at your goals, I personally would be to not worry as much about the pistons but to make sure you use a good cal. I don't even run a custom cal in my 84 mini. I have 40+ injectors with lowered fuel pressure. I have had bad experiences with some of the custom cal's available for these cars. Also make sure you have a good working knock sensor.

[James Neidig]

Thanks everyone. I spoke to Mike at Forward Motion today. I am going to pull it down and measure the bore with a good bore gauge. He can get me JE's and rings to work with the bore I have. I will be taking the rods to the machine shop to open up the end for the larger wrist pins as well. Once complete, I will have the option of going with larger injectors, a retune of the stage 3 SMEC, and more boost....but...for now I will keep the top boost at 15psi. Had planned on making Carlisle this year, but it won't be ready with paint & all... Always next year. Thanks again for all the help, I appreciate it!
Jim