Angle plug head question for Joe?

[Jerry G.]

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?

[Clem Z.]

Re: Angle plug head question for Joe?

i don't believe angle plug heads were ever used in production because the need was to get the plug above the high domes on high compression race pistons for better flame travel

[Dick W.]

Re: Angle plug head question for Joe?

Jerry, I believe if you will check the Chevrolet Power Manual of that era, the heads are listed. The best I remember the '70 Camaro did not have those heads. I built a '70 LT-1 engine, in '70) and remember ordering a set of those heads and sending them to Joe Mondello to be reworked.

[Michael H.]

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?

The first angle plug heads became available over the counter in about 1971.

I have the paperwork on this, somewhere, if you need some doc.

In 1971, most organizations did not allow the new GM angle plug heads in production classes so many straight plug heads were converted to angle plug.

Was it a 340292? Or a 39657xx?

I don't remember any of these heads being used on Camaro in the 70's.

[Jerry G.]

Re: Angle plug head question for Joe?

Well the memory is the second thing to go... I purchased an over the counter set of heads for a B production short block motor in 1970, (that I still have) with heads that are casting number 3991492. These are "off- road racing" assemblies. I'm pretty sure I saw them on a 69 Camaro Trans Am car. Were these available for racers over the counter in 1969 for off road service only?

[Michael H.]

Re: Angle plug head question for Joe?

Well the memory is the second thing to go... I purchased an over the counter set of heads for a B production short block motor in 1970, (that I still have) with heads that are casting number 3991492. These are "off- road racing" assemblies. I'm pretty sure I saw them on a 69 Camaro Trans Am car. Were these available for racers over the counter in 1969 for off road service only?

Jerry,

The first info I can find on the new angle plug heads was dated November of 1970. It was a 3965742 and featured "casting beefed-up at valve seat area and relocated spark plug holes". (should have read valve spring seat area)

This would have been the first angle plug head. It may have had a casting number of something like 340282 or 340292?

[Duke W.]

Re: Angle plug head question for Joe?

Well the memory is the second thing to go... I purchased an over the counter set of heads for a B production short block motor in 1970, (that I still have) with heads that are casting number 3991492. These are "off- road racing" assemblies. I'm pretty sure I saw them on a 69 Camaro Trans Am car. Were these available for racers over the counter in 1969 for off road service only?

Synopsis from the 2nd Edition (1976) Chevrolet Power Manual:

The ...492 casting was used for both straight plug service replacement (3987376) and two angle plug off-road heads - 3965742 and subsequently 336746. All of these cylinder head "assemblies" included screw in studs and pushrod guideplates. Both off-road heads have spark plug hole machining that is higher in the chamber and angled. The experiments leading to angle plugs were conducted in "late 1970". The 336746 incorporates machining changes to accomodate larger diameter valve springs.

The 340292 casting has different coring which improves as-machined flow plus other small coring and machining changes and is recognizable by the lack of a head riser passage. The 3965784 head based on this casting was released in 1973. IIRC these heads were informally known as "turbo heads".

No word on when the ...492 casting was first released, but early machined versions were probably the ...376 assembly, which was basically a service replacement and considered "stock". AFAIK the '69 T/A engines used this head with the ...140 cam and ...142 valve springs that fit the production valve spring pockets. The Power Manual validates what Micheal said that the first angle plug heads could not have been released until 1971.

The other thing to look out for is that all ...492 castings are not the same being as how they were used for three different finished assemblies that have distinct identifiable features.

Duke

[Michael H.]

Re: Angle plug head question for Joe?

- 3965742 and subsequently 336746. All of these cylinder head "assemblies"
The experiments leading to angle plugs were conducted in "late 1970".

The 3965784 head based on this casting was released in 1973. IIRC these heads were informally known as "turbo heads".

The Power Manual validates what Micheal said that the first angle plug heads could not have been released until 1971.


Duke

My first guess at the 1971 time of release was off by a year.

The engineering paperwork on angle plugs begins in 1969 and the first heads were available in late 1970 under part number 3965784. We had some of the first sets released and used them during the 71 racing season.

[Duke W.]

Re: Angle plug head question for Joe?

What you say doesn't jibe with the Chev. Power Manual.

Duke

[Dick W.]

Re: Angle plug head question for Joe?

Duke, I purchased a pair in late 1970 or 1971 and had them ported by Mondello. I am sure of that after working the time back.

[Michael H.]

Re: Angle plug head question for Joe?

What you say doesn't jibe with the Chev. Power Manual.

Duke

A lot of things I say here on this board usually don't jibe with a lot of other things or other people but I can usually back it up though.

[Jerry G.]

Re: Angle plug head question for Joe?

Synopsis from the 2nd Edition (1976) Chevrolet Power Manual:

The ...492 casting was used for both straight plug service replacement (3987376) and two angle plug off-road heads - 3965742 and subsequently 336746. All of these cylinder head "assemblies" included screw in studs and pushrod guideplates. Both off-road heads have spark plug hole machining that is higher in the chamber and angled. The experiments leading to angle plugs were conducted in "late 1970". The 336746 incorporates machining changes to accomodate larger diameter valve springs.

The 340292 casting has different coring which improves as-machined flow plus other small coring and machining changes and is recognizable by the lack of a head riser passage. The 3965784 head based on this casting was released in 1973. IIRC these heads were informally known as "turbo heads".

No word on when the ...492 casting was first released, but early machined versions were probably the ...376 assembly, which was basically a service replacement and considered "stock". AFAIK the '69 T/A engines used this head with the ...140 cam and ...142 valve springs that fit the production valve spring pockets. The Power Manual validates what Micheal said that the first angle plug heads could not have been released until 1971.

The other thing to look out for is that all ...492 castings are not the same being as how they were used for three different finished assemblies that have distinct identifiable features.

Duke

Thanks Duke. I'm not sure I understand one part of your response. " AFAIK the 69 T/A engine" what is AFAIK and did the T/A racers take a 492 casting and machine a spark plug hole into them that was angled? I saw some that looked like they had been worked on by clever racers.

[Terry M.]

Re: Angle plug head question for Joe?

" AFAIK the 69 T/A engine" what is AFAIK?

AFAIK = As Far As I Know

[Michael H.]

Re: Angle plug head question for Joe?

What you say doesn't jibe with the Chev. Power Manual.

Duke

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.

[Duke W.]

Re: Angle plug head question for Joe?

Duke, I purchased a pair in late 1970 or 1971 and had them ported by Mondello. I am sure of that after working the time back.

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