I've seen where certain cars had different carbs and/or cams for the stick vs. AT cars.
Why? / What is the difference ?
Does an AT car require something extra/less to compensate for the TC drag at idle ? Or ?

There are carb/cam combos for 442s based on stick or AT, but SBO cars (exc. W-31) all got the same carb/cam regardless of trans. Does this only apply to higher powered engines ? Or was it just a $$ issue for the SBOs ?

Just wondering....

 

Some cars supplied with A/T had a slightly more powerful engine than stick models in the '50s & '60s.. This was to compensate for the power loss through the auto trans.

Automatics are best suited to engines with lots of low rpm torque, could be the cams were profiled for this in the the auto versions.
Roger.

 

Think it has something to do with vacuum the perfomance stick shifts required less vacuum as they had less items that needed vacuum to work so the cam was a bit better. The automatics had more items that needed the vacuum so the cam was milder. Could be other reasons also.

 

There are a number of factors. Idle speed, vacuum, performance, strength of the AT, etc. For example, in 1968-69, the AT 442s got a milder cam (and only 325 HP) as compared to the MT cars (with 350 HP). On the other hand, the beefed TH400 in the W-30 cars allowed both AT and MT W-30s to use the same cam and thus have the same 360 HP rating, but neither power brakes nor A/C were available. Interestingly, the 1969 W-32 cars used the same cam as the MT cars and had the same 350 HP rating. Power brakes were available on the W-32 but not A/C (though the latter may have been due to problems routing the O.A.I. hose around the A/C compressor - yes, I know the H/Os had A/C in 1968).

Then, there's the 1970 model year, where the MT W-30s got the 328 deg cam and were not available with power brakes or A/C, while the AT W-30s got a milder cam and could have PB and A/C. Of course, Olds just lied about the two having the same HP rating...

 

The cams and distributor curve were based on auto/ manual trans and gear ratio. The differences were not really noticeable, it was mostly to get them to spool up correctly!

 

I wondered about the 'strength of the AT' , but kinda dismissed it because the difference in power between the stick & AT cam/carb combos is typically like 5-10%. So unless the AT's were running within a hair of failure load with the AT combo, I couldn't imagine that those extra 5-10% would make a difference.....but the 'beefed up TH400' kinda refutes that...

When I see 'PB', I think vacuum...aka the cam. I'm not sure how A/C fits in unless its cooling related.....or maybe the A/C running load at low RPMs (idle) contributes to the lack of vac with the 'hotter' cam.

This is what I was thinking. That somehow the MT combo had a narrower/'peakier' power band due to having 4 gears as opposed to 3 wider gears in the AT (M20/21 vs. TH350/400).

 

I always thought the "no A/C" thing was on the opposite end -that it was because the compressor would spin too fast at redline, and that putting a reduction pulley on it would make it not work in the normal driving range.

-Eric

 

Ahhh...Interesting idea....but was redline different between the AT/MT config ?

 

Don't know about the redline itself, but I think that the stock TH 400 will shift a good deal lower than the average hotfoot, even if you try to hold it back by holding it in 1 or S.

- Eric

 

No A/C might be because of the different rear end gears too.
Larry

 

Actually, the A/C DOES relate to low vacuum. The flapper doors in the HVAC box under the dash are vacuum operated. If the vacuum levels are too low, the air won't blow out of the correct vents. On the heater-only cars the flapper doors are all cable operated.

Eric is also correct, since A/C cars were limited to 3.23:1 gears, allegedly due to the compressor RPM limit.

 

And, I suspect, not only the compressor's limit.

Ever look at how long that run of fan belt to the compressor is?
Considering the average driver's propensity for routine maintenance - both then and now - if you imagine that belt poorly adjusted, whipping around under load at 6,000 RPM, it just isn't pretty. Not allowing A/C is a good way to avoid the warranty department having to have that argument a few thousand times.

- Eric