[jscheublein]

I am getting ready to rebuild my RA 3 engine. It will need to be bored and hopefully the corrosion pits from sitting forever will clean up. (It is the # matching engine). I do not plan on running the car hard - just a good restoration. I have heard some people having compression ratio problems - too high 10.75 or higher after boring. Does any one make pistons to lower the compression so I can use all the number matching parts (heads, carb, intake, distributor, etc) This is a manual trans car with 3.55 posi. I have the 48 heads, etc. I would greatly appreciate any help doing this so the car drives on the street without overheating or pinging. Thanks Jim 209-601-4408

[screamingchief]

First thing first,the factory tends to over rate the CR by appx. 1/2 a point of CR,so take that into account.

Frist step should always be to cc the given heads and then decide which piston is going to be the best choice as the head cc is the primary wildcard in the whole deal.

But yeah,the Icon #KB891 14cc D shaped dish forging is a good choice for builds like that.

IMO those are the best "off the shelf" option for this sorta thing.

Stay away from the 8 valve relief cast replacement pistons,some might think that due to their added cc they make a good choice to lower the CR,but the fact that they sit waaayyy down in the bores as SOP completely destroys that situation,where-as the KB forgings tend to sit much closer to 0 deck than the POS 8vr cast pistons do.

And add a set of the budget forged 5140 rods just for good measure too.

HTH

Bret P.

[jscheublein]

I had the original heads cc's and found they were 72 cc. I am not sure how to calculate the compression ratio with that information though. Also, since this is a restored WQ engine I want to use the orignal #48 head. This way for show the car is correct (numbers and date code, etc.) Would you then use the pistons you recommended - and what would be the resulting compression ratio. Thanks for the help.

[tooski]

http://www.wallaceracing.com/

Lots of good info on this site, including compression ratio calculators.

[screamingchief]

Originally Posted by jscheublein

I had the original heads cc's and found they were 72 cc. I am not sure how to calculate the compression ratio with that information though. Also, since this is a restored WQ engine I want to use the orignal #48 head. This way for show the car is correct (numbers and date code, etc.) Would you then use the pistons you recommended - and what would be the resulting compression ratio. Thanks for the help.

Yes,with those dished Icon forgings the CR should be in the mid 9:1 range (I get 9.54:1).

Best part is they sit nice & proud in the bores as SOP so you should'nt even really need to zero deck it or such and you'll still get good quench dynamics with the D shaped dish of those Icon forgings.

Should run well on pump fuel,and will work fine with the rest of the "stock" RAIII combo.

Good luck with it.

Bret P.

[tom s]

I got 9.79 for a 30 over 400 with 14CC dish and 0 deck and .039 head hasket.Should be good with 91 pump gas.Tom

[screamingchief]

Also,do yourself a favor and put all new valves in it.

Last thing you want is an OE 2pc. valve to drop the valve head into those nice new forged pistons because you did'nt spend a few extra $$$ for new valves.

Some items it's just not wise to cut corners on...

FWIW

Bret P.

[screamingchief]

Originally Posted by tom s

I got 9.79 for a 30 over 400 with 14CC dish and 0 deck and .039 head hasket.Should be good with 91 pump gas.Tom

Just for the record,I figured mine with .040"/4.200" headgaskets and the pistons down appx. .010".

Bret P.

[trmjr1]

Jim,

Times two on the Icon pistons with 14cc dish and new valves. I purchased everything from Jeff Kauffman at KRE.

http://www.krepower.com

Tom

[Craig Hendrickson]

One more thing to do: have your machine shop install hardened exhaust seats along with the new valves or the original valves for that matter.

Pontiac did not start induction hardening the cast iron exhaust seats until 1972, so using hardened seat inserts will bullet-proof the heads against valve recession.

Of course this is not required if the T/A will always be a trailer queen or just short drives to local shows. Only miles & miles of high speed (freeway) driving using unleaded gasoline causes valve recession -- like we used to drive these cars. Of course back then we had leaded gas which protected the exhaust valve seats.