Max rpm

[Gene Fiore]

For all the guys running 250 motors, what is the max rpms that you see under load? Especially if you ever run out at the drag races, what are your typical shift points? The reason I ask is my motor really struggles to get to 4000 rpm. Even not under load. Under load when it is approaching 4000 rpm it feels like it wants to...you know... It is a stock motor and maybe that's all it is capable of. Could there be something not right or maybe it's just tired?

 

[wallaka]

That RPM sounds about right. The engine is way undercarbed stock.

 

[addo]

I'd monitor two things on test drives - exhaust backpressure and manifold vaccum. Just watch what happens as the pedal goes down and stays down.

 

[Anonymous]

I know how you feel.
I have a 6000 RPM chip in my MSD 6AL and I don't know if I would hit that RPM even if I went into neutral at full boost.

 

[Bort62]

Well, When the 200 in my ranchero let go the first time, I was at 5000 RPM on the freeway

That's about all it had.

 

[CZLN6]

Howdy Gene and All:

Even for a stock 250 that is a little anemic. Assuming that your timing is set right and ignition is well serviced, your fuel system is up to par, your exhaust is not plugged, you should be able to rev to 4,500 easily.

Variations will depending on year and rear gearing. After '72 FoMoCo began to advance came timing to get a little more low end grunt at the expense of the upper rpm range. Also CR dropped from 9:1 for '71 and earlier to 8:1 for '72 and later model years.

The later your go into the EPA years the more encumbered the engine became.

So before an accurate comparison of rpms can be made we would need to know the model year, rear gearing? is the engine stock? what vehicle? What is the timing set at? what is the condition of the engine? miles, state of tune, etc.....

I can tell you that I shift my well-modified 250 at 5,000 rpms almost daily.

Tell us more about your car.

Adios, David

 

[Jamie Miles]

My stock 250 dosen't really "wake up" until after 3,000 RPM's. I will often downshift on the highway and peg it to the floor and turn a good 3,500-4,000 RPM's passing someone. Totally stock '74 250 in a '72 Maverick with Duraspark II/TFI ignition, C4 with mild shift kit and 2.79:1 rear gear. In neutral it will rev up higher then I care to rev it.

 

[Anonymous]

stock '74 250 in a '72 Maverick with Duraspark II/TFI ignition,

I don't think you really meant to include "TFI" in that sentence

 

[powerband]

Howdy Gene and All:

Even for a stock 250 that is a little anemic. Assuming that your timing is set right and ignition is well serviced, your fuel system is up to par, your exhaust is not plugged, you should be able to rev to 4,500 easily.
ngine became.
I can tell you that I shift my well-modified 250 at 5,000 rpms almost daily.
Adios, David

Good Topic!, The stock 170 pulled to @3500 with difficulty. Now pulls to 4500 easily after major head work/headers. Points dizzy and stock bottom end - anything can happen. Distinct "thumping" resonance above @ 4500 RPM. crankshaft??/ flywhl?.

The current built 250 I'm runnin' has balanced bottom end/ARP fasteners/ line bored mains etc. Upper limit RPM is a good question. Shift @5500 with no problem. I seriously start worrying about safety and expensive problems but it gladly will wind much further. I have a lightweight SFI flywheel , Centerforce clutch into a C5xx belled - toploader 3spd / 3.50 rear gears. .
Just obtained T5 to install which should help keep the RPM in the powerband.

!

.

 

[Does10s]

Man how did I miss this topic for 5 days???

Anyway, Kelly is now seeing up to 5500rpm with her 250. And from what she says it's still pulling stong up there.
With the log head I'd have her shift at 4800, I've up'd that to 5000 over the last month or so. I will probably up that to 5200-5300 soon.

Later,
Will

 

[Gene Fiore]

Thanks for all the replies. Here is what I am currently working with. 1971 Maverick 250 no a/c, no p/s, C4, 3.00 stock open rear end, aprox 150,000 miles ( I think ). Previous owner did a valve job just before I bought the car ( about 1 year ago ). I'm wondering if the head gasket that was used may be responsible for a loss in compression( factory specs say 9:1 compression). Car is in a good state of tune, timing set to 12 deg, still using original points dizzy. Stock single exhaust with some kind of "turbo" muffler...sounds like crap. That will change soon as I will be adding a Hooker 6-2 header with dual exhaust all the way back. At the track I'm only shifting at 3800 rpm, and that seems like a struggle. Still turning 17.80's at 75 mph ( car weighs 2736 lbs with me in it ). I will be doing a stout buildup on this motor at some point but that probably won't be for at least a year or so.

 

[mcmillal]

My last trip to the track showed better results shifting at 5500rpm or 5000rpm. I am running with a small log head that had a lot of work done on it. If I put it in drive and floor it, it will shift on its own at around 4000rpm.

.............Cheer, Alex

 

[mcmillal]

Sorry that should have said 5500rpm OVER 5000rpm, not 'or 5000rpm'.

.........Alex

 

[Gene Fiore]

What kind of numbers are you seeing at the track?

 

[mcmillal]

Gene, check out my other post with my numbers.

http://fordsix.com/forum/viewtopic.php?t=38618

..........Cheers, Alex

 

[Gene Fiore]

I thought you might have made a previous post but just couldn't seem to find it. Thanks for re-directing me! Those are pretty good times. Keep us posted when you change your rearend setup.

 

[Jamie Miles]

stock '74 250 in a '72 Maverick with Duraspark II/TFI ignition,

I don't think you really meant to include "TFI" in that sentence

Actually, I did. I have a TFI coil on my car fired by a Duraspark II ignition system. It has been working great for the past 25,000 miles.

 

[Anonymous]

I have a TFI coil on my car fired by a Duraspark II ignition system.

Sorry, that's where I got confused. I thought you were saying a TFI module was runnin' the show.

I also have the TFI coil on my '79 F-250....been there since 1996

 

[Jamie Miles]

Sorry, that's where I got confused. I thought you were saying a TFI module was runnin' the show.

I also have the TFI coil on my '79 F-250....been there since 1996

No problem. The one on my car is for an '89 F-350 with a 460. It works great.