Where can I found information on piston to wall clearance and top ring gap size for Speed Pro forged pistons? I tried to search their website but was not able to find a single piece of information.

 

https://www.thirdgen.org/forums/tech...d-pistons.html

Speed Pro = TRW .
Still use the same part # on pistons

 

Thanks for pointing out that topic. I saw that a while before but I did not remember.

It seems that these pistons use 0.001 wall clearance. What about the top ring gap size?

Am I right if I think that I will receive all of these informations on paper with the piston when I order and get it?

 

On the box

 

Thanks for the picture. Still looking for piston ring gap information because I could not find any on the picture.

Found this information with google:

Can I trust it?

 

Did you try calling them?... or if that dont work call jegs.. their tech guys can pretty much walk you through whats what on most things

 

Not yet. First tried to get some information here from the experienced guys.

 

It's essential to know the material the piston is forged from also. Differences in the material can call for different piston to wall clearances which is why it's essential to know what you have.

For example, pistons forged from 21618-T61 call for more piston to wall clearance than 4032 forged pistons.

Go to BING or GOOGLE and type in the aluminum material number OR the piston part number and spend some time reading the posts the pop up. Homework time.

Jake

 

As I see on the picture from vetteoz, I will found the minimum required piston to wall clearance on the box of the piston that I will order.

 

[QUOTE=giszo;4742914]Thanks for the picture. Still looking for piston ring gap information because I could not find any on the picture.

Found this information with google:

Can I trust it?[/QUOTE]

Nope, not when you read words like most, or generally recommended or usually, etc.

This is an Attention To Detail thing, not a guessing game.

Jake

 

Which of those numbers on the box are you referring to?

Jake

 

Please remember that all of the specs you are looking for depend on the application. A street N/A setup is different than one for boost or nitrous, for example. An alcohol motor will likewise require different clearances than a gasoline motor, etc.

That being said, Speed Pro forged pistons have been around for a bezillion years. They were originally sold as TRW forged pistons and the design hasn't changed much, if any, since then. They're a little bit heavier than newer designs, but they're also built like a brick $H1tH0u5e. Which means, you shouldn't need to agonize over the specs excessively. If the bores are exactly to spec (4.030", for example) and the rings are typical out-of-the-box pre-gapped set for that bore size, you should be within a thou or two of the recommended specs for a typical gasoline N/A application. This is a situation where the "old school" nature of the SpeedPro pistons' design works in your favor. Off-the-shelf stuff should be very close to right, right out of the box.

If you find yourself thinking you need to buy some super-special ring sets or have radical bore surgery on the block you're headed in the wrong direction. Building a SBC with SpeedPro forged pistons should be about as garden-variety as you will ever see as far as specs for clearances and gaps go.

Typical specs for TRW forged slugs in an N/A gasoline application go something like this: 18 thou on the top, 16-18 on the second, 4 thou piston-to-bore clearance. Cast and hypereutectic pistons from TRW/SpeedPro are still in that range but the piston to bore clearance is tighter- typically 1-2 thou.

 

The material maybe not written to the box, but the required minimum piston to wall clearance can be found and that is the advice of the manufacturer who should know the most about it.

 

Thanks for the really nice and detailed explanation, Damon.

To go into a bit more details I'm building a 305 instead of a 350, so my bore size with oversize pistons should be 3.766 instead of your 4.030 example.

The build is going to be a street setup with a better cam than the original factory one and I'm also planning to run occasionally a 50-100hp shot of nitrous on it later.

What do you think about clearances and gap sizes in this case? Still the same as you posted?

 

For a small shot like that, yes, you can still use those specs. Piston-to-wall clearance should be a little smaller just becuase it's in a smaller bore.

 

Thanks!

 

What concerns me is the two different pistons I've been considering call for different piston to wall clearances based primarily on the aluminum material and how the engine is to be used.

Call me ****, but I prefer knowing what the manufacturer recommends. Knowing that, I can refer to their chart, look for the recommended clearance for how I plan to use the engine and provide that range to the machinst. This, by the way, is exactly what I did this week when I dropped of the new block and new pistons at Reher & Morrison's shop in Arlington, TX.

In addition to all that, I always buy my rings +.005 so I can individually set the gap on them. Right now I'm agonizing between Speed-Pro's R19100s and Perfect Circle 315's.

Decisions, decisions.

Jake