Question about Rpm's

[MY 85 GT]

Ok i know my rear was changed sometime ago before i got the car the door said it was a Z code 3.08's also in 85 the gt had a 7.5 now it has an 8.5 with 2.73's so im sure my speedo is off. My question is The guys that have 2.73's if your taching 1800 rpm's in 5th gear what speed are you doing? Thanks

 

[89_LX]

Do you mean 8.8 rear, my 89 had 2.73's stock with an 8.8

I remember i couldn't do the speed limit (55mph) in 5th gear without lugging the engine

i got rid of the 2.73 about a year ago but 1800rpm in 5th was around 65mph

 

[LiquidGT]

1800 rpm in 5th with 2:73s? I think I'm doing 75 or 80 mph, I'll check when I drive to work in a hour.

 

[MY 85 GT]

Yeah i meant 8.8 ..lol sorry a typo....Yeah i know my car lugs with 2.73's soon ill throw some 3.73's when i do the H/C/I....

 

[MY 85 GT]

1800 rpm in 5th with 2:73s? I think I'm doing 75 or 80 mph, I'll check when I drive to work in a hour.

Thanks that would be great....

 

[NIKwoaC]

This chart will give you what you need to know.

http://www.fordracingparts.com/download/charts/129.pdf

The "what speed are you doing at 1800" method is not very accurate, as speedometers and tachometers are not extremely accurate and tire diameter differences can throw it all out. Plus, this chart will help you find the right speedo gear so you can get your speedo back on track.

 

[MY 85 GT]

This chart will give you what you need to know.

http://www.fordracingparts.com/download/charts/129.pdf

The "what speed are you doing at 1800" method is not very accurate, as speedometers and tachometers are not extremely accurate and tire diameter differences can throw it all out. Plus, this chart will help you find the right speedo gear so you can get your speedo back on track.

Thanks the chart is very helpful... I want to go with 3.73's I see you have them how do you like them? I will be using them in conjuction with AFR 165 heads...TFS stage 1 cam and Weiand stealth intake...And a nitrous shot from 100-150 ish...lol do you think the 3.73's will be good?

 

[NIKwoaC]

Yea, the 3.73s are awesome. With some better flowing heads, they probably would be even better, so AFR 165s will fit nicely. You'll want to make sure to have some sticky tires, because the 3.73's will vaporize street tires on a healthy motor. I have 225/50-15 street tires on it right now and I have to feather the throttle through first and second to avoid spinning.

 

[MY 85 GT]

Yea, the 3.73s are awesome. With some better flowing heads, they probably would be even better, so AFR 165s will fit nicely. You'll want to make sure to have some sticky tires, because the 3.73's will vaporize street tires on a healthy motor. I have 225/50-15 street tires on it right now and I have to feather the throttle through first and second to avoid spinning.

So should i go with the AFR 185's and a TFS stage 2 cam or 185's with the TFS stage 1 cam? I want the car in the 12's on motor and somewhere in the 11's on the bottle, hopefully as for traction im going to have sub frames..Torque boxes welded...New somekind of Upper and lower A-arms.. Cobra posi unit, 31 spline axles,3.73..Some kind of drag radial or full slick...What else should i get?

 

[LiquidGT]

1800 rpm in 5th with 2:73s? I think I'm doing 75 or 80 mph, I'll check when I drive to work in a hour.

Yeah i meant 8.8 ..lol sorry a typo....Yeah i know my car lugs with 2.73's soon ill throw some 3.73's when i do the H/C/I....

Yep at 80 I'm around 18-1900 rpm, still under 2k. Even with 2:73's my first gear is still useless even second can get hairy. The gear/rpm calculators are they way to go they're fun and pretty acurate.

You could add some good drag springs and shocks to the list.

 

[MY 85 GT]

Yep at 80 I'm around 18-1900 rpm, still under 2k. Even with 2:73's my first gear is still useless even second can get hairy. The gear/rpm calculators are they way to go they're fun and pretty acurate.

You could add some good drag springs and shocks to the list.

Thanks good idea on the shocks... I think im a little more rpm's at 80 i think im over 2000 in 5th....

 

[NIKwoaC]

Most people will say that 185s are too large for a 302-306-308 engine, unless you are running a supercharger or turbo. Use 165s unless you plan on adding forced induction later on down the road or stroking the motor. 185s would be great for a 347ci stroker.