1970 LT1 Carburetor Question

[Bob H.]

My car has sat for awhile so although it runs good, I am doing preemptive maint. I bought a K&B kit for the 70 LT1 and the power valve is an 85. It has a 65 in it now. Which is correct?

[Joe L.]

Re: 1970 LT1 Carburetor Question

My car has sat for awhile so although it runs good, I am doing preemptive maint. I bought a K&B kit for the 70 LT1 and the power valve is an 85. It has a 65 in it now. Which is correct?

Bob------

I believe the original was supposed to be an 85. However, if the car runs good now with the 65 I don't think I'd change it.

[Bob H.]

Re: 1970 LT1 Carburetor Question

thanks. and should the secondary match. Both are 65 now and I see 85 is correct. It runs fine so I guess I will go pick up the 65

[Timothy B.]

Re: 1970 LT1 Carburetor Question

Bob,

Joe always gives good advice but if you have a stock engine just use the 8.5 power valves without spending any more money, they will work fine.

Make sure the gaskets are correct and the valves are tightened good so they don't leak fuel into the engine.

[Bill B.]

Re: 1970 LT1 Carburetor Question

It is interesting that the following LT-1 Holley Carb data book list the following:

1970 & 1971 - Pri Jets = #70, Sec Jets = #76, Power Valves = #85
1972 only - Pri Jets = #68, Sec Jets = #73, Power Valves = #65

So, it appears Chevy leaned out the mixture for '72 and lowered the intake manifold vac threshold for when the power valve enrichened the mixture (to 6.5" Hg requiring more throttle opening before enrichment). Suspect the ever-tightening emissions requirements for the change?? Increased fuel economy requirements?

Even more interesting is that the Compression Ratio dropped from 11.0 to 1 to 9.0 to 1 in 1971, so if it were a CR related change, I would have expected the leaner settings to start in 1971, not 1972.

All I know is that mine drinks gas like there is no tomorrow and my wife hates riding in it because her clothes stink of exhaust after a quick ride.

[Joe L.]

Re: 1970 LT1 Carburetor Question

It is interesting that the following LT-1 Holley Carb data book list the following:

1970 & 1971 - Pri Jets = #70, Sec Jets = #76, Power Valves = #85
1972 only - Pri Jets = #68, Sec Jets = #73, Power Valves = #65

So, it appears Chevy leaned out the mixture for '72 and lowered the intake manifold vac threshold for when the power valve enrichened the mixture (to 6.5" Hg requiring more throttle opening before enrichment). Suspect the ever-tightening emissions requirements for the change?? Increased fuel economy requirements?

Even more interesting is that the Compression Ratio dropped from 11.0 to 1 to 9.0 to 1 in 1971, so if it were a CR related change, I would have expected the leaner settings to start in 1971, not 1972.

All I know is that mine drinks gas like there is no tomorrow and my wife hates riding in it because her clothes stink of exhaust after a quick ride.

Bill-------

There were no fuel economy requirements for 1972. Those did not begin until MUCH later.

As far as the exhaust odor goes, do you have a fully and properly functioning AIR system? That makes a BIG difference in exhaust fumes. As I have mentioned previously, I discovered this one day when I was out driving my 1969 top-down and my AIR pump seized, instantly breaking the drive belt. Thereafter, I immediately noticed a much greater exhaust fume condition, even with the top up. It made driving the car almost miserable. Replaced the pump and all was well. That's one of the reasons I never recommend removing or disabling the AIR system on cars so-equipped.