'65 250 HP Camshaft?

[Eugene B.]

Members,
Just got more bad news from my engine builder. He believes that the camshaft in my '65, 250 HP engine should be replaced when the motor is rebuilt.

Question is: What camshaft replacement can I purchase that is an exact duplicate for the original? The engine builder spoke of a 274 camshaft, but I don't know what he's talking about.

I have a specification sheet that list the 250 & 300 HP camshafts lobe lift at .2658" for inlet and exhaust. No mention of camshaft duration. This doesn't mean much to me, but luckily there are many experts that I hope will respond.

Thanks and best regards,
Gene

[Joe L.]

Re: '65 250 HP Camshaft?

Gene----

For 1965, the 250 and 300 hp engines used the same camshaft. This was GM #3733431. This is the same camshaft that was used for many hydraulic lifter 283 engines. It was discontinued by GM in May, 1967 and replaced by the GM #3896929 camshaft. The latter camshaft had very similar, but not identical, specifications. It was discontinued quite a few years ago and replaced by other camshafts with yet slightly different specs.

I don't know of a reproduction source for the 3733431, although there may be one. If not and you're serious about wanting EXACT original specs, then you'll have to have one custom ground. Most of the big cam manufacturers offer this service, but it may be expensive. Otherwise, I'd recommend that you use the 3896929. It's a better cam than the 3733431, anyway, and no one will know the difference after it's installed in the engine.

The 3896929 IS available in reproduction from Comp Cams and Crane. It's also available from GM as a Crane-manufactured kit under GM #12364051 which includes cam and lifters. It's possible that this kit may have been very recently discontinued, though. If so, the Crane or Comp Cams reproductions are available.

[Harry Sadlock]

Re: '65 250 HP Camshaft?

Joe, I am always amazed at your knowledge!!!

I have the same question on a 1963 250hp engine. I had to replace the cam about 4 years ago. I went to GM and obtained a cam, their guidance, with grind number 12364050 as the original was not available. I recall that the original was 3732798. If I need to change cams again should I stay with the one I have or go with your 1965 solution. What makes me uneasy is last year I heard that grind 12364050 was for the 350hp engine not the 250hp engine

Thanks

Harry
38513

[Joe L.]

Re: '65 250 HP Camshaft?

Harry-----

GM #12364050 is, indeed, a Crane-manufactured GM kit which includes a reproduction of the GM #3863151 L-79 camshaft.

GM #3732798 is the CASTING number for the GM PART #3733431 camshaft that I discussed previously. The closest thing to it available from GM is the GM #12364051 kit which includes a reproduction of the GM PART #3896929 camshaft. The GM #3896929 was used for many PRODUCTION applications beginning in 1967 and became the SERVICE replacement for the 3733431.

[Harry Sadlock]

Re: '65 250 HP Camshaft?

Thanks Joe, see ya at Carlisle.

Harry

[Eugene B.]

Re: '65 250 HP Camshaft?

Joe,
Thank you for your response to my question.

You state that the ...929 cam is a better cam than the original ...431. Can you give me a few specifics why it is a better choice? I'm also wondering if there is a way that I determine the specifications of the ...929 cam?

Thank you again for your response, Joe.

Best regards,
Gene

[John H.]

Re: '65 250 HP Camshaft?

Gene -

The "929" cam specs are 196*/202* duration @ .050", with a 113.5* LSA, lift is about .390". Great all-around cam with excellent low-end torque; used in Corvette base 300hp engines from 1967-1979.

[Duke W.]

Re: '65 250 HP Camshaft?

My specs for the 929, based on actual analysis, of the engineering lobe data, yield 194/202 duration at .050" lifter rise. The 431 is 196/196. The 431 was originally designed for 283s with medium port small valve heads. The 929 adds a little extra duration to the exhaust - all of which is on the front end via earlier opening - in recognition that the later big port heads are exhaust restricted relative to the inlet ports.

Timing numbers at .050" lifter rise, points of max lift and LSA are:

431: (11.5)-27.5/30.5-(14.5), 109.5/112.5, 111
929: (12)-26/75-(15), 108/116, 112

Also the 929 cam reduces peak acceleration by about one-third and peak jerk by one-half, so it is easier on the valve train.

I wouldn't install the 431 cam in a restoration engine if someone gave it to me. The 929 is the way to go. It provides essentially identical torque curve and idle characteristics (maybe even a little better) and is easier on the valve train.

Duke

[Scott G.]

Re: '65 250 HP Camshaft?

Gene:

I have a GM "929" cam which was in my 66 for about 500 miles. It was not the correct cam for the car (it is a 350 HP). So, I pulled the 929 and replaced it with the 350 HP cam. If you are interested in it I will make you a good deal on the cam and the mated lifters.

Scott Goings