[72SSConvertibleGuy]

Hey guys...I recently got a 72 SS 396/402 and my father-in-law and I have been working on the engine. It's a numbers matching car, but someone did a poor tune-up on it sometime before we got it. The question I have for you is---

Does anyone know what kind of vacuum reading we should get on the car in park at idle (700rpm)? It's an air injector reactor engine, if that makes any difference.

I know this is kind of a specific question, and my knowledge of engines is layman at best, but my father-in-law is very good, and he's having a tough time getting this thing tuned...

Any feedback would help immensely, and if I need to provide more info than I did here, let me know...

Thanks again everyone for all of your help...It means a lot to a newbie owner..

John

 

[427L88]

I'm bumping this up John, as I truly have no idea what a stock 402 would idle at, other than well north of 10-12" Hg. Check your timing to see if its set at the stock spec, and then change it to 12-15 BTDC, while checking your total advance with the engine at 4000 rpm to ensure it doesn't go much over 40. ( Disconnect the vaccum advance).

I'm guessing the idle vaccum should be 14-17" Hg, but that wont happen unless you have enough timing, and then you can tackle carb tune issues.

 

[MrBill66Malibu]

John,

Like Gene said is a good start. What readings are you getting now? Is the reading steady or fluctuating? If there is a aftermarket cam in the engine that will affect it's vacuum too.

 

[CLMSS396]

I get about 15-16 in my 396 with a mild aftermarket crane cam hyd. (114 lsa) using a vacuum guage at 750 rpm idle.

Charles

 

[427L88]

Yes, steady or fluctuating reading makes a difference.

 

[Jerry70]

Any feedback would help immensely, and if I need to provide more info than I did here, let me know...

)

John

John, more information about why you're asking would help us help you. What vacuum readings are you getting? Is the reading steady or does it fluctuate? Fast or slow? Probably most important, what is the problem? Symptoms? Is the engine totally stock (especially the cam)?