Hey there everyone,
I'm finally getting around to asking this, on my 84, while doing about 70, the rpms are at 4k, and this seems very high for a pushrod 4 to be doing. I dont dare do over 70 unless I have to. This however is becoming an issue as on I-696, the average speed is 75-80, is this high of rpms this normal? or is my tach off?

Your tach may be off but I'd recommend checking your RPO codes to find out what transmission you have...

quote some related RPO codes: LR8 Engine, 2.5L L4 L44 Engine, 2.8L V6 (Hi Output) MD9 3-speed automatic transmission (THM125C) MG2 Transmission, manual, 5-speed (Muncie) 3.61 ratio MG3 Transmission, manual, 5-speed (Muncie) MM4 Transmission, manual, 4-speed, provisions (84-86) MM5 Transmission, manual, 5-speed, provisions (85-88) MT2 5-speed manual transmission (Isuzu) 3.35 ratio MV9 3 speed automatic transmission (THM200C) MX1 3 speed automatic transmission MY7 4-speed manual transmission (Isuzu) MY8 4-speed manual transmission (Muncie) 3.32 ratio M17 4-speed manual transmission (Muncie) 3.65 ratio M19 4-speed manual transmission (Muncie) 4.10 ratio

If you have the performance transmission setup (highly likely), you will be turning some high RPMs at highway speeds... Hope it helps.

quote Originally posted by CL_Fiero: Hey there everyone, I'm finally getting around to asking this, on my 84, while doing about 70, the rpms are at 4k, and this seems very high for a pushrod 4 to be doing. I dont dare do over 70 unless I have to. This however is becoming an issue as on I-696, the average speed is 75-80, is this high of rpms this normal? or is my tach off?

I have the 4.10:1 final gearing on my 84 Duke and I turn 3400rpm at 70 mph. I have 215/60/14 tires which are the factory size. If you are running smaller tires (smaller in circumference) then you will turn higher rpms.

I know when I was looking at it, it had the performance gearbox, but it just seems so high of rpms, I don't wanna blow a rod going down the freeway lol

yup. the 4.10 gearset run mighty high RPMs on the freeway. Gotta remember the tranny was made back in the days of 55 max speed limits.

I got the 4.10 gears as well. and, for me - 50mph = 2500 RPMs, 60 = 3000 RPMs, 70 = 3500 RPMs and so on.

so - yes - if you are running smaller tires - 4000 RPMs @ 70 does not sound to far off. tho - it may also be a Tach not quite reading right - but close.

I put in the 4.10 gears with the intention of having larger rear wheels by now.....but - always seems to be something else I gotta do first.....

Thanks guys, I think my tach must be off, cuz I'm running 195/70/14's (not my choice, came with it, im not a fan of skinny tires), the tach at times will also go a little goofy for a few seconds while accelerating, and reads 1300rpms at idle when warm, but the engine does not sound like it's revving that high at all.

Here's a google spreadsheet that has all the fiero transmissions:

Just input your tire size in the blue boxes, and speed, and it will do the rest. I've made it editable, so you can play online, but please feel free to save a copy as excel and play away.

For the rest of you, have at it, just ask that you only change the blue fields.

Link

edit: I only made this for the stick's, that's all I'm going to use.... sorry to all the auto guys.
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Currently in the middle of my 88 + 3800NA swap

[This message has been edited by aaronkoch (edited 05-19-2010).]

WOW.. thank you so much.. im suprised the fact that I have 195's make such a difference. Looks like I might go looking for some 225's, and maybe some 16 inch rims

My calc says you should be doing a true 3160 rpm at a true 70.0 mph, and switching to 225/70R14s would cut that to 2955 rpm. 225/60R16s would be 2935 rpm at 70.

[This message has been edited by Isolde (edited 05-21-2010).]