'72 LT-1 Throttle Response

[Larry M.]

[Mark #28455]

cold air is denser and makes more power

cold intake air is denser and makes more power. That's why nearly every race car finds some way to duct cold air to the engine. In the stock LT1, there is no provision for cold air intake and the motor gets 180 degree underhood air. In addition, if the exhaust crossover is open, it too adds to the heat of the intake charge. There isn't a really effective modification that you can do that still looks stock. You could duct tape two 4" hoses to the air cleaner inlets and run them to a cool air source.

Good luck,
Mark

[Clem Z.]

2 things to try

richen the carb because the 72 were leaned for emissions and the carb is richer with the choke on and/or block the heat riser crossover in the intake if it is aluminum.

[Larry M.]

Re: 2 things to try

Clem,

Thanks for the tips. The jet sizes in the carb now are the stock 68 primary and 73 secondary. I'm guessing that the '70 and '71 sizes of 70 and 76 would be the ones to use, but to tell the truth, richening the carb would have been one of my last choices. The reason I say that is because the top surfaces of the air horn quickly accumulate black 'soot' (?), which I thought was an indication of a too-rich mixture. Or, is that a symptom of a different problem?

Thanks,
Larry

[Clem Z.]

that is caused by reversion of the exhaust

back thru the intake at low speed most likely from the EGR. try jetting it up

[Larry M.]

Re: that is caused by reversion of the exhaust

Thanks, Clem. I will try the larger jets, and block the heat crossover, however, the car (a '72) never had an EGR valve.

[Clem Z.]

Re: that is caused by reversion of the exhaust

you can still get it even without a EGR valve. try the jets first

[Robert E.]

Re: 2 things to try

Clem, What would one use to block the cross over with? I have a vapour lock problem in the heat of the summer and want to block the cross over off to hopefully keep the heat from my Holley.

BTW, I have a stock '71 LT-1.

Thanks

Robert
41801

[Duke W.]

Re: '72 LT-1 Throttle Response

Did you convert from ported to full time vacuum advance? Rather than blocking the heat riser passage, first try wiring open the valve.

Duke

[mike cobine]

Re: 2 things to try

A thin piece of aluminum or tin shim stock will block the exhaust passage quite well. However, be advised that the cold weather driving will suffer greatly.

If the choke is fed heat from the exhaust manifold, it will heat and open too soon, leaning the carb, and letting it be far too lean for how cold the air coming in is.

If the choke is fed off the intake manifold, it will stay in far too long and keep the carb too rich, wasting gas and fouling plugs.

[Larry M.]

Re: '72 LT-1 Throttle Response

Duke,

I don't know how to tell whether or not I have ported or full-time vacuum advance, or how to convert if needed. Can you give me a resource to refer to?

Thanks,
Larry

[Duke W.]

Re: '72 LT-1 Throttle Response

There's been a lot of discussion on this issue. Try the archives.

Duke

[Larry M.]

Thanks, I'll take a look! *NM*

[Christopher J. Bunsey]

Re: Thanks, I'll take a look!

Ok I have a 76 L-82 4 speed. Would blocking off the manifold riser and rejeting the carb do me any good? If so, What size Jets? Thanks in advance!

[Clem Z.]

you must use stainless steel shim stock

of about .005 thickness as any thing else will burn thru.