Higher Compression, Harder the Start?

[Zrush]

I have a dumb question, but I'm going to ask it anyway. Is it normally harder to start a car with high compression?

Vicky

[sblake01]

Remembering my V8 musclecar days whenever we went too high compression wise we had to install a high torque starter and the best battery you could find. Of course we're talking 11-1, 12-1, 13-1 etc. You could buy gas with a high enough octane in those days. Maybe those are extreme cases but generally I would have to answer yes.

[2ManyZs]

Yup, the higher you go, the higher the cylinder pressures will be.

Of course, no. of cylinders/cylinder volume plays and important part in it as well. In other words, a small bore engine with a high compression ratio won't be much harder to turn over than a large bore engine of the same number of cylinders with a lower ratio.

That's why you'll see high torque or gear reduction starters used on big block V-8 engines that are running lower compression ratios than say, an L engine that is actually running a higher ratio.

That's also why you'll see a 24 volt, gear reduction starter on a diesel engine too, as they run 16:1 compression and higher with very high cylinder pressures to ignite the fuel.

[Zrush]

Originally posted by sblake01

Remembering my V8 musclecar days whenever we went too high compression wise we had to install a high torque starter and the best battery you could find. Of course we're talking 11-1, 12-1, 13-1 etc. You could buy gas with a high enough octane in those days. Maybe those are extreme cases but generally I would have to answer yes.

Thanks Stephen and 2ManyZ's.

That's kinda what I thought. Scott's car seems so "tempermental" when it's turning over, but my bone stock 240Z always cranks right over with no fight.

Vicky

[texasz]

So it sounds like an L28 with a 10:1 CR would be ok with a stock starter. Right?

The engine will be an F54 block, NO boring over, flat top pistons and a stock N42 head.

[Zrush]

Do they even make a high torque starter for our Z-Cars?

Vicky

[2ManyZs]

10:1 shouldn't be too much trouble with the stock starter, however, you should upgrade the battery to the highest CCA you can get in a group 24 for those times it might decide to be ornery about starting. This could be part of Scott's trouble, the battery might be one of the lower CCA batteries and it's not supplying the amps needed...

I'm not sure, but I think the ZX's had a slightly higher torque starter than the earlier cars. Someone else will have to jump in on that one...I'm not very well versed in what the ZX's had or didn't have.

Higher torque aftermarket starters are available last I knew, but they would probably be pretty pricey...

[Zrush]

Scott has the Optima Red Top battery. I think it's either the 720 CCA or the 800 CCA. That's pretty potent as far a cranking amps. I'll let him know about the beefier starter possibilities.

(I'm sure he'll just love hearing ME tell him what he should do to the car "HE" built)

Thanks guys for all the valued info:classic:

Vicky

[Alan Pugh]

Isn't the starter on the auto's a little higher in torque value than the manual? I know they are different but I can't remember what exactly.

[mdbrandy]

The later 1978 280Z has a 'gear reduction' starter. Is that classified as high-torque?

[TXZ]

The Datsun gear reduction starter with the addition of an adapter is used as the preferred retrofit for high performance Amercican V8 motors.

[mdbrandy]

Originally posted by TXZ

The Datsun gear reduction starter with the addition of an adapter is used as the preferred retrofit for high performance Amercican V8 motors.

Yup, I was reading in "How to Modify Your Datsun OHC engine..." last night that these gear reduction starters started on the late '78 280's, and apparently went through the 280ZX series. So they ought to be fairly easy to get?