Angle plug head question for Joe?

[Lynn H.]

Re: Angle plug head question for Joe?

You hip youngsters know all the lingo!!!! (I didn't know what that meant either)

[Dick W.]

Re: Angle plug head question for Joe?

Duke, I sold that engine over 30 years ago. Went into a mid-engine Corvair. I know that I ordered the part #'s listed in the Chevrolet Power Manual. Piggins put me on these heads.

[Clem Z.]

Re: Angle plug head question for Joe?

some times these heads were called "tubo heads" beacuse GM used them on the stock block turboed indy car engines back in the day

[Clem Z.]

Re: Angle plug head question for Joe?

Which casting number/part number did you buy, Dick?

Same question for you, Jerry. Based on the machining features of your 492 castings, which finished head assembly of the three are they.

AFAIK = as far as I know. Sometimes my fingers get tired!

Theory says that the closer the spark plug is to the center of of the combustion chamber, the shorter the combustion time for greater thermal efficiency - closer to the themodynamic ideal of heat addition at constant volume.

Also, the closer the plug is to the exhaust valve the more detonation resistance at a given CR.

The Chevrolet engineers certainly knew the above and decided to run some experiements, which lead to the angle plug heads. Some racers may have known this or gotten wind of what was up and done their own work by welding up the plug hole and redrilling it, but that would require a very good welder and machinist.

Besides, I believe that in 1969 the block and heads had to be "production" parts for T/A racing, so such a modification would have been illegal. Later on the rules were made more liberal - like dropping the requirement to offer a production 5-liter engine and allowing destroking, which began in 1970.

Same applies for next year in ALMS GT class. Though the GT Corvettes will be based on the ZR1 aluminum frame rail chassis and bodywork, the engine will be a 5.5 liter naturally aspirated LS based on a production 4" bore block, which means the stroke will be about 3.34" - about the same as our favorite 327. What goes around comes around!

This year's 6.0L GT2 engine used the 4.125" bore racing block from the GT1 engine, destroked to 6 liters.

Duke

next years GT-2 corvettes will go back to direct injection that they started out with but other car makes in the class pictched a bitch and the corvette had to back to port injection for the last couple of the races

[Terry M.]

Re: Angle plug head question for Joe?

I am trying to figure out when the " angle plug head" was available for racers to use on the Camaro. My recollection was that it was sold to racers as an over the counter service item in 1969 and available on the production Z-28 for the 70 model year. Was it available earlier in any configuration or part number?

I can remember seeing these heads in a display in the Chevrolet parts department where I was making purchases. I wish I could remember exactly when, but all I can tell you is that it was after February 1970 because I was seriously considering getting a set for the LT1. They were being sold as a complete head assembly -- valves, springs, retainers, and studs – the whole nine yards. And I recall thinking the price was reasonable, but for the life of me I can't remember the number. Just as well, because it would make us all sick anyway.

Edit add: Because of other landmarks in my life I am sure I saw these heads in the parts department before June of 1973.

[Joe L.]

Re: Angle plug head question for Joe?

I am trying to figure out when the " angle plug head" was available for racers to use on the Camaro. My recollection was that it was sold to racers as an over the counter service item in 1969 and available on the production Z-28 for the 70 model year. Was it available earlier in any configuration or part number?

Jerry-----

There were 2 part numbers for the angled plug small block cylinder heads. The first was GM #3965784 as has been mentioned by others. The part number for this cylinder head implies a late 1969 or early 1970 release date. However, this cylinder head used casting number 340292. That number implies a 1973 release date. I suppose it's possible, though, that there was a different casting used for the "original" 3965784. This much I can tell you for sure, though: the 3965784 cylinder head was not released into GMSPO SERVICE until mid 1973. It may have been available to "racers" through some "back-door" channel prior to that time, but no one could go into a GM dealership and purchase these heads prior to that time. Curiously, their availability from GMSPO nearly aligns with when I would have expected the 340292 casting to be released.

The GM #3965784 cylinder head was the head which was referred to as the "Turbo" head. It had no provisions for heat cross-over. It was NEVER used in ANY PRODUCTION application.

The other cylinder head which was available was the GM #336746. This head was based upon the 3991492 casting which dates to about early 1971. However, the 336746 finished part number implies a 1973 release date. As a matter of fact, the 336746 was first available "over-the-counter" at GM dealerships in mid-1973. Whether it was available through some "back door" channel prior to that time I do not know. But, it was first available to retail/wholesale customers in mid-1973. While it is possible that the previously described GM #3965784 MAY have been originally produced using something other than the 340292 casting, I don't think that the 336746 was ever manufactured from anything other than the 3991492 casting.

Basically, the 336746 was the same as cylinder heads used in PRODUCTION (and, in fact, utilized the same casting as those heads), except it had the revised "angled plug" location. Like all 3991492 castings, it had a heat cross-over passage. However, the 336746 cylinder head was NEVER used for any PRODUCTION application.

I purchased a set of the 336746 cylinder heads in early 1975. I still have them. They are an EXCELLENT cylinder head for street use. I would not part with mine for anything.

Later part numbers for angled plug heads were GM #14011058, released in 1982, and GM #10134392, released in about late 1991. I don't think that either of these were ever used in PRODUCTION, but it's possible they were. I have not researched that.

[Michael H.]

Re: Angle plug head question for Joe?

Jerry-----


There were 2 part numbers for the angled plug small block cylinder heads. The first was GM #3965784 as has been mentioned by others. The part number for this cylinder head implies a late 1969 or early 1970 release date. .

Joe

I think you're chasing the wrong part number. The correct part number for the original angle plug head was 3965742. Not 3965784 as mentioned in other posts. (one of mine)

The 3965742 angle plug head was definitely available to the general public in 1971.

[Bill M.]

Re: Angle plug head question for Joe?

Joe

I think you're chasing the wrong part number. The correct part number for the original angle plug head was 3965742. Not 3965784 as mentioned in other posts. (one of mine)

The 3965742 angle plug head was definitely available to the general public in 1971.

From Hot Rod 12/73, p.51: "When the current angle-plug head (Chevy part no. 3965742) was introduced in 1970..."

The article is covering the new (as of 12/73) 340292 head.

Found another Hot Rod article: angle plugs introduced on Hall's Trans-Am cars at St. Jovite 1970.

[Dick W.]

Re: Angle plug head question for Joe?

Bill's post makes sense to me. I know that I was living on the DelMarVa pennsula when I built that engine. I left there in late '72, so it had to be several months prior when I finished the engine.

[Michael H.]

Re: Angle plug head question for Joe?

Bill's post makes sense to me. I know that I was living on the DelMarVa pennsula when I built that engine. I left there in late '72, so it had to be several month prior when I finished the engine.

I think we've narrowed it down further than that. I just dug out a GM price book dated 3 January 1972 and the 3965742 is shown as being available. (to anyone) The GM price to the dealer was exactly $50. each. (no list price shown)

And lets not forget the scan of the GM page I posted way earlier in this thread, dated 16 November of 1970, that shows the 3965742 cyl head.

[James W.]

Re: Angle plug head question for Joe?

some times these heads were called "tubo heads" beacuse GM used them on the stock block turboed indy car engines back in the day

I bought and installed a new pair of those turbo heads on a 355ci engine that I had in my 1968 Camaro back in the early 80's. It was a great running engine.

James West

[Duke W.]

Re: Angle plug head question for Joe?

next years GT-2 corvettes will go back to direct injection that they started out with but other car makes in the class pictched a bitch and the corvette had to back to port injection for the last couple of the races

Next year there will be just one class called GT, which will basically be the same as this year's GT2. GT1 is history.

The port port injection sure didn't seem to hurt the Corvette's performance in the last couple or races. ...what a wild finish at Laguna Seca - more bumpin' and grindin' than a NASCAR short track race. Next year should see some great GT racing.

Duke

[Duke W.]

Re: Angle plug head question for Joe?

Found it. The first listing of the 3965784 angle plug head, dated 11-16-70 at the bottom.
I have a stack of GM info from 1969 and there is no mention of this cyl head. The previous head listed in 69 was not an angle plug casting.

I have a similar hand typed list titled: "302 - 327 - 350 - 400 Heavy Duty Parts" dated nearly a year earlier - 1-16-70 along with sections on engine preparation. These were basically early drafts of what became the Chevrolet Power Manual. The parts list includes 3987376 (1970), which is the OE replacement head based on the 492 casting. It also lists 3958604 (1969). No casting number listed, but this is probably an OE service head based on a previous casting.

So it appears that the first slant plug head (3965742) based on the 492 casting showed up during the 1970 racing season, which meant it was homologated with SCCA, but that doesn't necessarily mean it was actually released and available to the general public through GMPD the first time it showed up on a T/A engine at a race.

Duke

[Michael H.]

Re: Angle plug head question for Joe?

I have a similar hand typed list titled: "302 - 327 - 350 - 400 Heavy Duty Parts" dated nearly a year earlier - 1-16-70 along with sections on engine preparation. These were basically early drafts of what became the Chevrolet Power Manual. The parts list includes 3987376 (1970), which is the OE replacement head based on the 492 casting. It also lists 3958604 (1969). No casting number listed, but this is probably an OE service head based on a previous casting.

So it appears that the first slant plug head (3965742) based on the 492 casting showed up during the 1970 racing season, which meant it was homologated with SCCA, but that doesn't necessarily mean it was actually released and available to the general public through GMPD the first time it showed up on a T/A engine at a race.

Duke

Duke

The 3958604 and 3987376 numbers that you posted are for regular production heads as used on 64 and later hi perf 327's and 350's. Nothing special or HD about these.

You are correct. The very first over the counter angle plug head was a 3965742. It became available some time in 1970 but I believe it was later 1970.

[Bill M.]

Re: Angle plug head question for Joe?

Duke

The 3958604 and 3987376 numbers that you posted are for regular production heads as used on 64 and later hi perf 327's and 350's. Nothing special or HD about these.

You are correct. The very first over the counter angle plug head was a 3965742. It became available some time in 1970 but I believe it was later 1970.

Michael and Duke:

Found another Hot Rod article dated 4/71, p.120: "Because of the unavailability of the rumored Chevy slanted-plug heads..."

The article is about a Canadian racer modifying straight-plug to angle-plug heads.