Re: [Amc-list] rpm, "cruise speed", manifold vacuum, spark advance

[Tom Jennings <tomj@xxxxxxx>]

farna@xxxxxxx wrote:
> My 4.6L feels the same way -- cruising at 70 "feels" better than cruising at a lower speed, and I'm sure gas mileage is better. Vac gauge says the sameas yours (reads a bit higher), except when pulling long or steep hills, which need a bit more throttle to maintain the higher speed. I'm going to put slightly shorter tires on next time to effectively increase gear ratio and slow it down slightly -- a 215/65 instead of the current 205/70. The speed reduction in high gear is only 3 mph, so it won't make a lot of difference (or was that with a 215/60? will check before buying!). If you want to maintain a 60 mph cruise speed you might consider the same, but if mileage bears out the vac gauge you may want to just drive 65. Certainly not slowing anyone down or running over anyone! In my case 65-70 is just a bit fast for most of the rural roads around here, especially when you round a curve only to find a farmer pulling out with a large slow moving tractor and a semi in the on-comi
ng
>   lane! 

Yeah that sounds like mine. The odd thing is, these tires are within 
0.3" of factory stock, 6.500x15's. I'm fine with 65mph cruise, unless 
the mileage has tanked. Ask me in a week :-)

> 
> I bet your tach is correct. Calculations don't take into account wind resistance, tire size variances, and/or gear train loses. I've always found that tachs usually read 50-200 rpm more than calculations, depending on engine size, speed, and trans type.

Well this is an ooooold tach... late 1960's. Who knows... I have a 
clip-on digital job I'll compare it to. (All those digits! It must be 
accurate! Erm, ... I'll at least see if they agree or not!)


> I don't think the advertised torque is necessarily at the peak. 

Yeah, like advertised curb weights, which I assume, without any real 
evidence, is a way for the shippers to give factories a discount under 
ICC rules; legislated $/lb, so we agree it weighs less... torque; is it 
part of the taxable HP calculation? rpm x torque...

The TSMs says 1600 - 1800, but software, and the calculator in my 
backside, says it's around 2400, though the software says it's fairly 
flat over a broad range.
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