[pontiacs-r-us]

I have 65 389 that is going to require a .060 over-bore.Thoughts on using original std.400 pistons?What compresstion issues will I run into using the orig.#76 heads?Thoughts on cam selection?I have a Comp Cams EX-252 (214-224@.050 w/110 cl), or the orig.066,or a 068?This will be used in a G/P w/200r4,and 3:42 rear.Thanks Guys for your suggestions,Kenny

[ho428]

The stock compression chart list it at 10.5:1 now, but based on 70cc I don't see how. If the heads are 70 cc as advertised your compression will be around 10.0 as is, using std 400 pistons .010 in the hole and a.040 head gasket it sould be about 10.5
You can get a cometic .074 gasket and get down to around... 9.5:1 I think.
Cheaper than dished pistons but the gaskets ain't cheap.

I have some pretty good TRW std 400 pistons if you're interested, run very little. I have no use for them. Most 400 blocks need punched out.

You could do a head swap for bigger valves, and 72-75 cc chambers if you want the compression down.
But I'm sure there are people on this board that know much more than me on reworking 389's though.

Can't really help you on cam selection.

[PONTIAC LARRY]

You can use the original heads if you just get the regular 8 valve relief style replacement style std 400 pistons . The extra valve reliefs are for the use of 389 or 400 heads on a 400 and will also lower the compression into the mid 9.5:1 range maybe lower. Don't use a XE Compcam , they suck. Too much cylinder pressure (detonation) and short power band and noisy Iv'e heard. The factory 067 grind would be best in such a heavy ride. Dont be scared of inexpensive ,cast pistons.. it will still be a Super unleaded fuel engine , but with reasonable timing you should not have any problems assuming you use a 160 or 180 degree thermostat. This is also the least expensive way to build that engine too.. 389 pistons are high !

[Mr. P-Body]

The multi-valve relief pistons may "fit" but they are a poor choice if a quality build is what you're after. We use the L2262F (std.) and "dish" it with a simple dish of 16 CCs (3.25" x .100").

Larry has obviously not used the XE cams in lower compression applications. They hardly "suck". We use XE262H as a "replacement" cam for any application where 10:1 or higher and an 068/744 cam would have been used, once static compression has been reduced to below 9.5:1. Our 600 HP (93 octane) street packages use XE solid rollers.

NOTE: All changes made to reduce detonation without reducing compression will not accomplish the desired goal, and WILL reduce overall performance. While it may be "possible" to super-tune it to run well with a higher ratio, it's not real practical. Perhaps Cliff will stop in here and explain the details necessary to do it. He's more capable of it than anyone else I know. Unless one is "pressing the edge", the potential problems and comlpexity far out-weigh any gains.

Jim

[PONTIAC LARRY]

Originally Posted by Mr. P-Body

The multi-valve relief pistons may "fit" but they are a poor choice if a quality build is what you're after. We use the L2262F (std.) and "dish" it with a simple dish of 16 CCs (3.25" x .100").

Larry has obviously not used the XE cams in lower compression applications. They hardly "suck". We use XE262H as a "replacement" cam for any application where 10:1 or higher and an 068/744 cam would have been used, once static compression has been reduced to below 9.5:1. Our 600 HP (93 octane) street packages use XE solid rollers.

Jim

Jim,
You are right on me not running one.. but I don't discount on a 7.6:1 smog-era Pontiac that it wouldnt make good power. we are talking about a 10:1 389.. and I think it only fair to say that letting someone know all there options to make there own choice is right.
Apparently , a "quality" rebuild by some implies that you have to have a custom , expensive "pro" engine builder "do it right". So all the cast/hyper pistoned 9:51 engines in the world built by very long established national rebuilders and OEM ..lack quality ?
I see half the world split between "Brand name " ,"espensive is better" cheerleaders and the rest of us that sometime's use cast pistons and generic brand cams in our rebuilds lack all the quality according to some...if the guy wants to triple the cost of his engine...go for it.. but I still would not use a 110 LS cam in it..
JMO friends

[pontiacs-r-us]

Thanks guys.Im glade we can all agree to disagree.Also Im thankfull that the Pontiac market is strong enough that we have many choices.I may be ahead to build something else since this is not a #matching block.If I do,I think the dished forged piston is the way to go because of CR.I have dished TRW's in the past to retain orig. heads.I also have used the cast one's in low compression stock rebuilds with good results.(I have friends and customers on low budgets also)I saw where KB has forged pistons now,and they offer a dished(-14cc)forged piston(none for std.400 or 389's)This is good news for us,if quality is good.As for cams I felt that the EX-262H wasnt the best choice because of CR..I have the EX-262 for a 8:1 400 rebuild.Larry,I have a EX-274H in my 455,and like it very much.Thanks Guys.If anyone has this type engine,chime in and tell us about your combo and how it works.As Im shure I will run into this again and have to retain a #matching block.Thanks again,Kenny

[ichabod]

My 65 GTO 389 # 77 heads tri-pwr was done 60 over, 5yrs ago. Used 400 cast pistons and 744 cam. Everything else was left stock. I do have a 4sp. 4:33 gear. I use 93 plus 5 gals of 100 LL av. gas for a full tank. So far not a problem. I have also used 1gal of 110 VP race gas per tank.

[Mr. P-Body]

Larry,

It appears you have the "cheaper is better" outlook. If you had any idea how many burned pistons, cracked heads, broken rings, turned rod bearings... on and on... that come from the "just as good only cheaper" mentality, you wouldn't be so quick to erroneously call me "out". One of my most important "jobs" is cleaning up messes behind other "builders". BTW, the guy that shoves the pistons in the hole may or may not be the "builder". An engine builder's job is to do all the math, all the machine work, selecting the correct combination of pieces and POSSIBLY assembly. If all you did was put it toether, you are the "assembler". The word "builder" encompasses a LOT more than assembly.

Nowhere did I say anything about "custom" pistons. The Speed Pro (TRW) forgings are quite thick in the head, and are a very good candidate for such a build. A "simple dish", turned into them on a lathe, is more than adequate to reduce compression. There are no GOOD hyper-eutectic pistons available for the Pontiac. The KBs are marginal, at best. We've had no experience yet with the KB forgings. They are significantly more money than the Speed Pro. The hyper-eutectic pistons sold by Sealed Power/Speed Pro are FAR superior to the KBs. We use them in the lower level circle track engines. Unfortunately, SP doesn't offer them for the Pontiac. Cast pistons are fine for a driver. Most here are looking for improved performance, which you cannot get from that 8-relief piston. Flame propegation is out to lunch. Detonation or a lean condition will cook them in a heartbeat.

Several of our customers will argue with you over the effectiveness of an XE grind in a sub-8:1 engine. If you're still hung up on the LSA, you need to study a bit more. Comp specifically says you cannot compare older designs to the modern ones using the conventional "numbers". Other builders have tried to alter the XE approach without the desired results. And, if you've never used one, isn't it a bit presumptious to say they "suck"?

When talking about a 10:1 ANY SIZE Pontiac, detonation WILL occur if the proper octane is not used. This is why we recommend lowering the compression.

We build Pontiac engines from "stock" to TA/FC. The winner of "The People's Choice" award at last year's GTOAA Nationals had one of our "resto" engines. Stock as a rock! (Oh, except the lowered compression and the XE262H...) About 1/2 of our engines are restorations or mild street. Pidgeon-holing us as "Brand name" "expensive is better" clearly illustrates you don't know anything about us or our shop. Not EVERYONE bases their engine build on how "cheap" it is. Most want quality, which, for the most part, cannot be "had" based strictly on price. ("quality" is defined as "meets the requirements for the application", not "expensive is better")

My purpose in posting on sites like this one are not to promote any one brand, shop, etc. It's to provide ACCURATE and CURRENT information. This hobby (it IS a hobby, you know) is loaded with myth and superstition, and arm-chair professionals. Two statements we hear all the time that cause us AND our customers grief are "just as good, only cheaper" or "the same as".... For the most part (if you are a decent "shopper"), you get what you pay for.

PAX

Jim

[1qikta]

I dumped a mess from another builder into Jim's lap a few years ago..No Atlanta area shop would touch it.
Due to the lack of a local Pontiac machinist I initially chose a roundy round shop that had the " If you aint running Saturday night you aint next" mentality. A year later it was half ass done and lasted less than 100 miles. By that time they had changed ownership and I had no recourse.

Soon after I called Jim (thru Cliff Ruggles).There is much more to the story but you get the point.This past experience has built a heck of a relationship with Jim and lot of good business.

Thanks Jim!

[PONTIAC LARRY]

Originally Posted by Mr. P-Body

Larry,

It appears you have the "cheaper is better" outlook. If you had any idea how many burned pistons, cracked heads, broken rings, turned rod bearings... on and on... that come from the "just as good only cheaper" mentality, you wouldn't be so quick to erroneously call me "out". One of my most important "jobs" is cleaning up messes behind other "builders". BTW, the guy that shoves the pistons in the hole may or may not be the "builder". An engine builder's job is to do all the math, all the machine work, selecting the correct combination of pieces and POSSIBLY assembly. If all you did was put it toether, you are the "assembler". The word "builder" encompasses a LOT more than assembly.

Nowhere did I say anything about "custom" pistons. The Speed Pro (TRW) forgings are quite thick in the head, and are a very good candidate for such a build. A "simple dish", turned into them on a lathe, is more than adequate to reduce compression. There are no GOOD hyper-eutectic pistons available for the Pontiac. The KBs are marginal, at best. We've had no experience yet with the KB forgings. They are significantly more money than the Speed Pro. The hyper-eutectic pistons sold by Sealed Power/Speed Pro are FAR superior to the KBs. We use them in the lower level circle track engines. Unfortunately, SP doesn't offer them for the Pontiac. Cast pistons are fine for a driver. Most here are looking for improved performance, which you cannot get from that 8-relief piston. Flame propegation is out to lunch. Detonation or a lean condition will cook them in a heartbeat.

Several of our customers will argue with you over the effectiveness of an XE grind in a sub-8:1 engine. If you're still hung up on the LSA, you need to study a bit more. Comp specifically says you cannot compare older designs to the modern ones using the conventional "numbers". Other builders have tried to alter the XE approach without the desired results. And, if you've never used one, isn't it a bit presumptious to say they "suck"?

When talking about a 10:1 ANY SIZE Pontiac, detonation WILL occur if the proper octane is not used. This is why we recommend lowering the compression.

We build Pontiac engines from "stock" to TA/FC. The winner of "The People's Choice" award at last year's GTOAA Nationals had one of our "resto" engines. Stock as a rock! (Oh, except the lowered compression and the XE262H...) About 1/2 of our engines are restorations or mild street. Pidgeon-holing us as "Brand name" "expensive is better" clearly illustrates you don't know anything about us or our shop. Not EVERYONE bases their engine build on how "cheap" it is. Most want quality, which, for the most part, cannot be "had" based strictly on price. ("quality" is defined as "meets the requirements for the application", not "expensive is better")

My purpose in posting on sites like this one are not to promote any one brand, shop, etc. It's to provide ACCURATE and CURRENT information. This hobby (it IS a hobby, you know) is loaded with myth and superstition, and arm-chair professionals. Two statements we hear all the time that cause us AND our customers grief are "just as good, only cheaper" or "the same as".... For the most part (if you are a decent "shopper"), you get what you pay for.

PAX

Jim

Jim,
First off, don't assume I believe "cheaper is better" , I use forged pistons in most of my builds as well. This man did not mention any racing , if his SCR is lowered to a mid 9:1 and has a stock curve in the distributer he would be OK. Why not just put a stroker kit in it and put alum heads ? if money is not an object. I have seen plenty of the damage you describe and also much damage on forged pistons as well. Lots of factors to contribute to that. I have been building engines and great combinations for over 20 years , ranging from stock , street/strip , strip only with a great record of reliabilty and performance. I have not and never will run a hyper in a Pontiac.. factory ones seem to last OK , seen some of the cheap claimer stuff break on SBC's. Of cource Comp says thing's to sell there camshafts and if you are a "follower" ..so be it.. I don't knock their roller grinds. There has been little to nothing shown to me on the track that the streetable XE hyds outperform the tried/true "older" grinds whether they are Mellings or Summit Racing etc.. It is a matter of preference not quality , Comp's quality is not better than OEM or most generics. I am not attacking your shop or you , merely stating options for a person to choose from . So don't try to label me or assume anything about my knowledge or quality that you do not know about. Good Day.

[mkpontiac]

Regarding the 8 valve relief cast pistons. Those were installed in my car years ago by an engine shop that was using them to lower the compression ratio. My car originally had an advertised compression ratio of 10.5:1 and used the 066 cam which has an intake closing event at 26 degrees and it pinged when it got hot while using 91 octane. After installation of the cast pistons, which I was told lowered the compression ratio to 9.0:1 and a cam with an intake closing of 31 degrees my engine pings when it gets hot pretty much the same as it did with the original set up. I think the biggest contributor is that the factory piston was down in the hole 0.015 while the “stock replacement” 8 valve relief piston is down in the hole an additional 0.020 or 0.035. I am considering replacing the gasket with a 0.021 thick gasket available at summit. Will this help? I know it will raise the compression but I think the piston is way to low in the hole.

Mark

[PONTIAC LARRY]

Originally Posted by mkpontiac

Regarding the 8 valve relief cast pistons. Those were installed in my car years ago by an engine shop that was using them to lower the compression ratio. My car originally had an advertised compression ratio of 10.5:1 and used the 066 cam which has an intake closing event at 26 degrees and it pinged when it got hot while using 91 octane. After installation of the cast pistons, which I was told lowered the compression ratio to 9.0:1 and a cam with an intake closing of 31 degrees my engine pings when it gets hot pretty much the same as it did with the original set up. I think the biggest contributor is that the factory piston was down in the hole 0.015 while the “stock replacement” 8 valve relief piston is down in the hole an additional 0.020 or 0.035. I am considering replacing the gasket with a 0.021 thick gasket available at summit. Will this help? I know it will raise the compression but I think the piston is way to low in the hole.

Mark

Mark,
What temp are you running at when it pings? Water temp must be managed to stay below 180 preferable around 160. We have 93 Octane here , not sure the limits of 91 octane.
I don't think .020" gasket is a good idea.. What kind of inital/total timing are you running ?

Does it consume any oil thru the valve seals/guides? ]
Thanks

[mkpontiac]

During the winter it runs at 180 which corresponds to the thermostat. In the summer when temperatures get into the upper 90’s and above, which happens nearly all summer in central California it gets up to near 220 and stays there whether I am in stop and go traffic or driving on the freeway. A 160 degree thermostat has not brought about improvement. I have tried a heavy duty thermal fan clutch without resolution. Initial timing is 9 degrees BTDC. Final timing I believe is 30 + 12 vacuum advance if recollection serves me correctly but I have moved it up and down with no improvement. The radiator is a quality 4 core radiator which is about as good as you can get without going to an aluminum one. Although aluminum would be better I believe the copper brass unit should be fine if all else is correct at least it has worked for many others.
I would expect a reduction in pinging going from 10.5:1 down to 9.0:1 and using a cam that has the intake closing event a full 5 degrees later. An ideal quench distance is, from what I have read, about 0.039. The 8 valve relief cast pistons puts me at the original of 0.015 + gasket thickness of 0.039 which equals 0.054 + the additional 0.020 lower piston top which puts me at 0.074 Which is a full 0.035 higher then optimal actually nearly twice the recommended distance. From what I have read the factory piston pin to piston top is 1.72 while the cast piston is 1.70. Doesn’t this make a big difference in heat generation within the combustion chamber? What are the downsides to the thinner gasket?

Mark

[PONTIAC LARRY]

Until that 220 degree temp is brought down, I can't see that pinging eliminated. What year and model is your car? Fan Shroud? Aluminum radiator and a shroud with a 160 stat is likely your answer...
I also would try experimenting eliminating the vacuum advance and trying different advance springs/ intial timing. I use alot of initial timing with a quick advance curve and no vacuum advance with no problems at 9.5:1 but I have 93 Octane and a Aluminum Radiator... Is it pinging at 180 degree also? Part throttle acceleration or full throttle or both ?