Engine Speed on Highway

[jwalkman]

I was wondering if anyone knows how many RPM's my 2.8L is turning at 60+ mph. It is a '86 with a 904 auto and 4.10 gears. The XJ does not have a factory tach and I have tried a couple of aftermarkets and they do not play well with the GM ignition. This seems like a low gear for an automatic transmission even though it has a lock up torque convertor.

Thanks,
Jwalkman

[CanMan]

I was wondering if anyone knows how many RPM's my 2.8L is turning at 60+ mph. It is a '86 with a 904 auto and 4.10 gears. The XJ does not have a factory tach and I have tried a couple of aftermarkets and they do not play well with the GM ignition. This seems like a low gear for an automatic transmission even though it has a lock up torque convertor.

Thanks,
Jwalkman

How tall are your tires? That will effect the RPM's. Im assuming stock, 225-75-15's?

If so, your RPM's would be around 3100rpm's at 65 mph. 60 mph would be about 2900 rpm's. If its a lock up, the rpm's should be a little lower.

Since it is a TF904, it is a 3 spd tranny, and has a 1:1 final drive in the tranny. Thats one reason it seems like a low gear.

TF904 - 2.45 1.45 1.00 Don't know about reverse.

Get us the tire size, and it should be able to be determined better.

[RichP]

An aftermarket tach should drop right in, get one that has the pins in the back for changing the jumpers. I had one in my 82 2.8L S-10, a Sun super tach, worked like a champ, 3 wires, one to ground, one to the dash lights and one to the tach...I think it was like $29.

[jwalkman]

The tires are 225 70R 15.

Thanks for responding

[jwalkman]

I may have to give a Sun a try. I even borrowed a working tach and it would not register on the XJ.

Thanks for the answer.

[MPETESS10]

yea I used a generic tach from walmart on my 93 TBI 2.8 S10 and it had a real simple hookup
hot ground dimmer and signal from ignition and it worked beautifully
I think mine was somewhere around 20 bux as well
but then again I am pretty sure my s10 had a different style ignition and coil setup than the older carbed 2.8's

[NighthawkXJ]

I used a sun on my 1982 s10 2.8l, It worked great, thats what i used as a speedo for a while as i had a electric tranny in a cable style speedo.

It was a snap to hook up.

[RichP]

yea I used a generic tach from walmart on my 93 TBI 2.8 S10 and it had a real simple hookup
hot ground dimmer and signal from ignition and it worked beautifully
I think mine was somewhere around 20 bux as well
but then again I am pretty sure my s10 had a different style ignition and coil setup than the older carbed 2.8's

Pretty much all the distributors have a hookup point for a tach, GM just happens to put a metal connector on theirs and mark it 'tach'... I have not looked for one on the XJ as I switched out the idiot light panel for a gauge panel so I never bothered. There was not any good place to mount the sun tach anyway on my 98 though I almost bought one of those hood mount tachs like GM used on the pontiac Judge GTO's...I just did not want to spend $60 at the time..JC Whitney has or had them a couple of years ago.