When To Shift Stock 200

[GrantD]

Hey Folks I'm new to the forum and fairly new to the I-6. I have a 1980 mustang hatchback with the 200 I-6 and the stock 4 speed trans (3spd + OD)
I'm wondering when I should be shifting it. I think I've been shifting a little on the low side but I'm afraid to rev my motor over 3500 RPM. It is my daily driver and is bone stock. The car has 90,000 original miles on it.

For Example when driving at 35mph I'm at 3000 in 2nd, or 1500 in 3rd. Both Will work, Which would you expect to give better gas milage?

Thanks guys I've learned a lot in the couple weeks I've been reading.

 

[addo]

3rd is probably a better choice for economy.

 

[Anonymous]

I would not worry about taking it over 3500, but thats just me

 

[pedal2themetal45]

If you just driving it then the higher gear and the lower RPM would be best. No sence running the motor at high rpm just putting around..
I would even go to 4th at 35mph if your just putting. econo gear.
just my .02
tim

 

[Anonymous]

a lot depends on your rear end gearing--i could figure it out from the info you gave but why bother. If you are pulling decent in the higher gear than use it-- biggest thing is not to lug it. As long as you can still get a little acceleration without it stumbling or bucking you are okay. The 200 can easily handle 4500 rpm(and probally a lot more). The higher the gear the lower the rpm the better the mileage till you start lugging. Depending on your rear end a stock 200 isn't apt to due well at 45MPH in OD unless you are going downhill.

 

[80Stang]

That OD is 0.73 ratio, the box is a SROD. I run that same setup for some dozen thousand miles.

For the question I'd use 3rd if it doesn't seen to bother about it. I remember the stock motor with that trans and I actually never had to go over 3000 in normal everyday driving. But you can rev it to 4500-5000, the stock valve springs will surrender soon after 5K.

The question is what is your rear end ratio. I had/have 3.08.

You'll probably find your self endlessly in situations thinking about whether to use 2nd or 3rd as the gap between those is just - HUGE. Have fun with it and remember, the more you spend time in here (= start tweaking the engine up) the more obsolete comes your SROD's gearing and the more you want to do the easy T5 swap behind that SROD bellhousing.

 

[Mustangaroo]

All said above is correct, but would like to remind you that a stock cam runs out of power around 4200 to 4300 RPM and the HP drops from then on no mater how high you rev the engine!

 

[GrantD]

First of all I'd like to thank you guys for all of your responses.

When running an errand today i tried 35mph in 4th and it didn't work out to well. It kept running sure enough but it was at like 1200 and bogging down and jerking so i didn't keep that up more than like 2 seconds. That same symptom is what made me question driving at that speed in 3rd. The bogging down and the jerking is not nearly as severe in third just as long as i keep it above 1500rpm/35mph, below that and it gets pretty bad. It bogging down is what made me question 3rd gear in the first place.

Another thought I had about this topic was the powerband. Is the motor going to run more efficiently in it's power band in which case is it better to be running in a lower gear at a higher rpm between 2000-3500rpm?

80 Stang, That is some good information you have there. I imagine you are correct about eventually wanting to upgrade to the T-5. At this point and in the near future I really can't afford to do anything very drastic. The vehicle is my one and only daily driver and more importantly I just finished my freshman year of college and I've got some big bills to pay. I'm going to have to wait for some of this engineering education to start paying off.

About the rear end gearing I honestly don't know what it is. Is there an easy way to check this short of tearing it open and counting?

Again thanks for all the information, I'm sure to come back to you for some more information. Next on the list is the duraspark 2 mod.

 

[SVO42]

Check your door data sticker and see what it says under "AXLE." It's a code you can look up if you have a manual. If you don't, post it and I'll look it up for you. My money's on one of these: 2.73, 3.08, or 3.45.

Someday, once I have more cash, I'm going to build myself a nice 200-powered Fox Mustang/Capri. I think about it every day...

 

[GrantD]

the code under AX is Y i'm assuming thats axle. If you could look it up that'd be great.

I bought my I6 foxbody for 650$ with 88,000 miles on it, rust free ( impressive in minnesota), with a clean interrior. The guy was pretty cool that i bought it from.

 

[80Stang]

All said above is correct, but would like to remind you that a stock cam runs out of power around 4200 to 4300 RPM and the HP drops from then on no mater how high you rev the engine!

Very true. You can rev it but there absolutely is no more power there. Sometimes if you want to accelerate, you might want to rev 2nd gear higher to get the 3rd in and at least some rpms there. I remember it loosing 2000rpm between those gears.

Y code stands for 3.08.

Now if you want to be sure you can go under your car, find a metal tag attached to one of rear end's bolts and there should be readible 3.08. Hope the tag is still there.

 

[GrantD]

Thanks again for the info, thats interesting that the power drops off. Thanks for looking up that code for me i appreciate it. I trust that figure enough to not go crawling around looking for a tag... Maybe if i'm down there and remember .
It does lose about 1500 - 2000 Rpms when shifting to 3rd, which is kind of annoying.

 

[Anonymous]

A stock 200 doesn't like to cruise at less than 1800-2000 rpm and while there is less hp at above a certain rpm those rpm's are sometimes usefull in that they will get your speed up enough to get the next gear solidly into your power band when you shift--usually meaning you,re climbing a hill or are heavily loaded. At these times what matters is the rpm you're at when you hit the next gear. I would recommend just trying to keep your engine between 1600 and 3600 rpm. Meaning if you are cruising along and turning 1800 rpm and want to pass a car--grab a gear or two. On an older stock 200 (pre72)try 2400 and 4000. (different cam and timing set-up)

HP=torgue X RPM /5250
- theroretically, your max torgue is at 1600 and your max HP is at 3600 thus your power band is 1600-3600 with useable power a little lower but not enough for much more than level ground cruiseing.And a little higher but unnecessary unless trying to gain more speed for either more power in next gear, tarction control in turns or simply high gear top end. Hills, turns, load and need for speed, dictate real life driveing.

 

[JackFish]

Just for reference, I have a C4 with an auto, and I could drive around town all day in 2nd gear. It is perfectly flat here, though. (of course I don't!)
3.08 rear also. 2nd is your power gear, cruise in 3rd, hwy in OD. Boy I wish I had OD! :x I run about 3000rpm at 60mph. 3200 gets me 70mph.
The manual also says not to exceed 65mph in 2nd!