[racerboy]

I had my 70 TA out over the weekend and noticed a bit of pinging when I started to give it any king of pedal. I just picked this car up last year. It has a numbers-matching WS RA III with original #12 heads. That engine went through a standard rebuild about 10 yrs ago. There are only about 5k miles on it since. Anyway, I have a bunch of receipts and it looks like it the previous owner went with stock (resized) rods. I was thinking about pulling the motor and going through it. My plan would be to replace the rods and maybe put in a HR cam. I would want to continue running the factory heads, realizing that i am going to need a bit of a dish to bring the compression down to pump-gas friendly range. I see that Butler carries an Icon forged piston with a 14cc dish. Does ani have experience with this brand? I wouldn’t order any pistons until I got the heads off the engine and CC’d them to find actually combustion chamber volumes, but figured I’d at least start a conversation to get some feedback. Thanks!


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[Gary H]

I have use the Icon forged pistons in probably around 25 - 30 Pontiac engines. IMO they're a great piston for the money, well made, spot on measurement wise, and also use a thinner ring pack than the original or forged TRW type pistons. It's my go to piston for all the street engines I build for folks. Note: the piston pin boss is narrower than stock and you cannot use a stock rod with them unless you narrow the small end of the rod, or machine the pin boss wider in the piston. I normally use aftermarket Eagle style rods so that not an issue

[steve25]

If you still have the original carb on the motor they are set up to limit the how far the secondary’s can open, in the passed I had found on guys 69 RA 400 bird that is caused his motor to ping also .
When the limit tab was removed his ping issue nearly fully cleared up!
It seemed that the angle of the secondary’ throttle blade was effecting the fuel distribution enough in the manifold plenum to cause some cylinders to ping and knock.

[racerboy]

Originally Posted by Gary H

I have use the Icon forged pistons in probably around 25 - 30 Pontiac engines. IMO they're a great piston for the money, well made, spot on measurement wise, and also use a thinner ring pack than the original or forged TRW type pistons. It's my go to piston for all the street engines I build for folks. Note: the piston pin boss is narrower than stock and you cannot use a stock rod with them unless you narrow the small end of the rod, or machine the pin boss wider in the piston. I normally use aftermarket Eagle style rods so that not an issue

Good to know! I would definitely be going with an aftermarket rod, even with a mild build. They are just so much more affordable than back in my bracket racing days in the early 90s on a shoestring budget.


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[racerboy]

Originally Posted by steve25

If you still have the original carb on the motor they are set up to limit the how far the secondary’s can open, in the passed I had found on guys 69 RA 400 bird that is caused his motor to ping also .
When the limit tab was removed his ping issue nearly fully cleared up!
It seemed that the angle of the secondary’ throttle blade was effecting the fuel distribution enough in the manifold plenum to cause some cylinders to ping and knock.

This car does have the original 7040273 carb. How easy/hard is it to remove this tab? Also, on a side note, is this why the RA III was rated at 345 hp in the TA, but 366 in the GTO?


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[steve25]

Yes, that’s the reason for the different hp ratings. Between what is the same motors!
GM back then had a hp to weight ratio limit in the F body cars that would be exceeded otherwise.

The limit tab is easy to bend so as to not function.

Sorry, I do not have a Carb to show you a picture of it , but it’s been talked about here so I am sure you could do a search to find pictures and more info.

[racerboy]

OK, thanks. I'll take a look. I found this image on another forum.

[GPC]

Gary H, What clearance do you use with the Icon pistons for street use? Thanks

[Gary H]

Originally Posted by GPC

Gary H, What clearance do you use with the Icon pistons for street use? Thanks

If I remember right .0035. I get them, Ross, and Autotec piston clearances recommended confused in my head. Each comes with their recommended clearances on the box.

[MarkS57]

Originally Posted by racerboy

OK, thanks. I'll take a look. I found this image on another forum.

I remember fixing my 68 Firebird 400 with just a pair of pliers.

[Vengeance Race Engines]

Icon forged are a good piston. I like them better than the Speed Pro stuff in basic builds. I have used many, and not just in Pontiacs. If you need the 14cc dish, then run with it. DSS makes them as well, with more to choose from. Just got a set of DSS flat tops for a 459 I am doing out of a 428 block. Nice pistons.
As in any 4032 material forging, clearance will depend on application, but minimum is usually .0035" in stock builds. I run them between .004" and .005", min. to max. depending on application. I HAVE gone more out of necessity in some instances with no issues, but don't usually recommend it. Hope this helps.

[pontiacmark]

With my stock #12 heads I have been considering the Icon dished pistons as well. I did check on Butler’s site and they are showing as not available in any bore size. Although I would prefer to buy from them, are there any other vendors that carry Icon? It will probably be this summer before I am ready to buy anyway, but just curious.

[OG68]

I bought mine from Summit.

[Gary H]

Originally Posted by pontiacmark

With my stock #12 heads I have been considering the Icon dished pistons as well. I did check on Butler’s site and they are showing as not available in any bore size. Although I would prefer to buy from them, are there any other vendors that carry Icon? It will probably be this summer before I am ready to buy anyway, but just curious.

I get all mine from KRE. If Jeff doesn't have them in stock he has them drop shipped to me in a couple of days. I've never had a problem getting any of the advertised sizes. They've always been in stock either at KRE, or Icon

[racerboy]

I just did some digging through the paperwork I received when I bought the T/A last summer and it shows that the engine was rebuilt with XPC 411NP30 pistons. A Google search showed that these are cast replacement flat-tops with 4-valve reliefs. I'm assuming that answers my pinging question. Summit still sells them for $136, which is about $30 cheaper than what Gary (fellow who owned car before me) paid 12 years ago. I guess I better start making some calls to look for rods and pistons.

[racerboy]

So I dug a little deeper through the paperwork and it looks like Gary had a rod knock in 2011 (2 years after CarQuest rebuilt his motor) . The new shop pulled the motor and did a complete rebuild. I don't know what pistons they used this time around as the only item on the invoice says PO400AKIT. This kit cost $1102 in 2011, so maybe these are foged? There is a receipt from another shop that did the balancing and the piston weight is 683 gm and total rod weight is 885 gm. I'm guessing these are still cast rods, but am not sure.

[racerboy]

Here is the ‘balancing’ sheet that was included in paperwork.

This is probably a dumb question, but there’s really no way to know if the block might need a clean-up bore until I get it out of the car (or at least get the heads off it), right? There are only about 5000 miles on it since this second rebuild was done (2011), and it was bored .030 the first time it was rebuilt (2009) so I’m hoping it just needs a hone, but I guess anything is possible.


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[racerboy]

I reached out to previous owner and he sent me the following photo of the short block after it was rebuilt in 2011. I think these are flat-top pistons with the valve reliefs, but no dish.



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[geeteeohguy]

Originally Posted by racerboy

I reached out to previous owner and he sent me the following photo of the short block after it was rebuilt in 2011. I think these are flat-top pistons with the valve reliefs, but no dish.



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Those are the dreaded '8 relief' jobber pistons which have a rounded shoulder as well. They provide low compression AND detonation as well as being fragile. You will be money ahead to replace them with pretty much anything else.

[racerboy]

Thanks Jeff. I was also going through the notes of the build and is has a Mellings MTP-1 camshaft, which based on everything I found online, is actually lower performing than the stock 068 cam! I am not sure why it was rebuilt with what I would call less-than-optimal parts. I have all the receipts and it still cost $4900 for the rebuild in 2011, so it really should of had better components. I just don't think the PO was a real hardcore engine guy, and he was steadfast in keeping everything as original as possible. I feel like the engine guys took a little advantage of him. I think I should just bite the bullet and plan on getting a stroker kit. I have another thread going about possibly dropping a built 428 I have into the Trans Am just so I can drive it this summer and spend some time/dollars on the original RA III engine.