quick 200ci I6 question..

[SVThuh]

I recently installed a small aftermarket tach in my mustang just to see what the motor was doing while going down the road and so on. What I discovered has me puzzled.

I have noticed that this little 6 acts like a diesel motor. It shifts out of first gear at WOT at 3500rpm, then shifts to 3rd at 3000.

So, my question is: what is the normal redline of a stock 200 I6??? I know its got a tiny little carb on it, and a tiny little cam, but I can't imagine this thing only being able to spin to 3500 before nosing over like it does.

The problem with this is while driving down the hwy, Im pulling 3000rpm at 65mph. Traffic around here averages around 70-75... I dont want to zing this thing down the road at redline while just going from point "A" to point "B".

Thanks!

 

[Explorer]

Did you set the tach to 6cyl? I'm running 4:11 gears and close to those numbers, but the Mustang usually has something like 2:83 or 3:00 gears. three grand on my engine is no big deal and cruises nicely there, but it's not stock.

 

[JackFish]

How and when mine shifts depends on how hard I gas it.

I've got 3.08 gears and was cruising nicely @ 3200-3600 rpm. WOT on the stock '78 was about 4Krpm.

 

[SVThuh]

Did you set the tach to 6cyl? I'm running 4:11 gears and close to those numbers, but the Mustang usually has something like 2:83 or 3:00 gears. three grand on my engine is no big deal and cruises nicely there, but it's not stock.

The tach is set to 6cyl and as far as I can tell, the rear is stock. The tach seems to read pretty accurately as far as I can tell. Idle is right at 500 and the tach reflects that.

My grandfather was the second owner of this car if I remember correctly, so the history of the car is fairly well in tact. I don't believe the rear was ever replaced and the transmission in the car is the stock "Green-Dot" 3 speed auto.

Thanks!

ETA: If I leave the trans locked into low gear and try to pull it past 3500, it literally just falls flat on its face.

 

[Explorer]

I did forget to take into account diff. tire size. Might check for full throttle travel, it should do better than 3500rpm.

 

[SVThuh]

Tire size is 205/75-R14

Using an online gear ratio calculator, best I can figure is that this car has 3.50 gears. Does this seem right for a 6cyl car with an auto?

 

[bubba22349]

You can adjust the downshift up or down some at the carb. Old racers trick to shift all three gears on the pre 67 Ford trans take off in Low move shifter up to D (green dot) then quickly pull liver back down to L this holds it in second until you put it into D again. You can also swap in the much better 67 up select shift valve body.

 

[66 Fastback]

If you look at the data plate on the door, you can look up the axle code that came with the car.
But 3000 rpm on the highway is about right.
When you say it noses over at 3500 rpm, are you talking about losing power and running rough or is that the rpm that the tranny shifts at?

My car feels like it is about to come unglued at 4000 rpm and higher.
But that run from 75 mph to top speed took a long stretch of road, because it is running out of ponies at that point.
Doug

 

[Anlushac11]

The stock log head 170-200 inline six has a natural built in rev limiter. The engine can run up to about 5500rpm but the abysmally poor flowing log head means you run out of power usually around 4000-4500rpm.

If everything is not in good tune or working order and/or you have any vacuum leaks that could keep you from reaching 4000rpm.

When I had my 1980 Mustang with 200 L6 and C4 and 2.83 geared rear end the car would top out about 80mph. I seem to remember the rpm on factory tach would show around 4200rpm.

 

[SVThuh]

If you look at the data plate on the door, you can look up the axle code that came with the car.
But 3000 rpm on the highway is about right.
When you say it noses over at 3500 rpm, are you talking about losing power and running rough or is that the rpm that the tranny shifts at?

My car feels like it is about to come unglued at 4000 rpm and higher.
But that run from 75 mph to top speed took a long stretch of road, because it is running out of ponies at that point.
Doug

Unfortunately the door with the data plate was replaced sometime back with another door from a 65 289 car, so I no longer have the accurate info.

When I say it noses over, I mean it runs out of breath and looses power big time. The motor is still fairly new. It was rebuilt and bored .030 over maybe 1000 miles ago and at the same time it got a new rebuilt head.

I think Im just getting to the point where Im going to swap everything out to a 306 V-8 that I just put together at my shop.

Anyone want my COMPLETE 200 and auto trans???