Too much cruise rpm? Ford 2.3L again

[ap72]

I just ordered some tires for my Ranger I'm building. Nothing too crazy, just 30" all terrains.

This truck is powered by a ford 2.3l that I'm modifying. I'm working on figuring out how to wire in microsquirt. I also have a cam I ordered (230/230 110lsa .540" lift), will be porting a head (may step up to 1.84/1.6 valves) and will eventually see a turbo with mild boost (10-15psi) and e85.

With all that being said, should I go with 4.10 gears or 4.56? This truck is driven to work fairly regularly and will see some mild trail use (yes it's 2wd).

I was leaning to the 4.10s but with the cam will that be enough gear? It puts my cruise rpm at about 2500, it's at 2800 with 4.56's. This is at 70mph. At 80 it's 2900 vs 3200. My concern with 4.56's is that it's not uncommon to cruise close to 80mph on my longer road trips which puts the engine at a somewhat high rpm when you are talking hours on end.

This car will not be drag raced, so max acceleration is not the primary concern- I just want what will be easiest on the engine which means balancing the load vs rpm.


If this question isn't appropriate for engine discussion please feel free to move it. The heart of the question is regarding engine durability so I thought it may be best here?

[Truckedup]

30 inch tire with 4.56's is close to 3000 rpm at 60 mph.. So the truck has an OD top gear? 3200 pound truck with a modified 2.3 engines is going to need some rpm at cruise so it's responsive to the throttle

[ap72]

30 inch tire with 4.56's is close to 3000 rpm at 60 mph.. So the truck has an OD top gear? 3200 pound truck with a modified 2.3 engines is going to need some rpm at cruise so it's responsive to the throttle

2900lbs and .79 OD gear.

And yes, I know I'll need some rpm I just don't know if it'll be 4.10s or 4.56s.

[DCal]

I'd seriously be considering a 3:73 gear if you're going highway. My car has 31.5 Hoosiers and 3:73 gears and at 55mph it's turning 2500 and it drones something awful. When the turbo is working I don't think you need a lower gear ratio.

[ap72]

I'd seriously be considering a 3:73 gear if you're going highway. My car has 31.5 Hoosiers and 3:73 gears and at 55mph it's turning 2500 and it drones something awful. When the turbo is working I don't think you need a lower gear ratio.

3.73s put me at about 2300 rpm at cruise. Which probably won't have much of any throttle response and be cruising under boost on anything with an incline.

Keep in mind this is just 2.3L. I don't think 2300rpm will be enough for this small 4 banger?

[peejay]

My 2.2l VW/Audi engine, as delivered from VW, cruised at 4000rpm at about 75mph. 0-60 runs needed three upshifts at WOT/max RPM

It has a 3.39" stroke and it also has just shy of 400,000mi on an unopened engine.

Don't sweat a thing.

[Brian P]

Your wheels will be doing 672 revs per mile; at 60 mph with 4.10 and 0.79 OD it will be at 2756 rpm in direct (presumably 4th) and 2177 in overdrive (presumably 5th).

The engine will probably be off the cam at that rpm, but the cam isn't too wild, so it shouldn't be horrendously down on torque. Let's say you have somewhere near 140 lb.ft of torque at that rpm. Means you have about 58 horsepower available = 43 kW

Drag coefficient is probably near 0.55 (pretty bad)
Ruff-estimate frontal area is probably near about 85% of overall height x overall width not including mirrors. I don't know what sort of suspension you have planned. But let's say the truck is 1.9 m wide (75") and 1.7 m tall (67"). If you have better numbers, go ahead and substitute.
Effective frontal area is 85% x 1.9 x 1.7 = 2.74 sq m
Cd x A = 1.51 sq m

Speed in metres per second (sorry, I gotta do this stuff in metric) at 60 mph = 26.8 m/s

Drag force = 0.5 x density x Cd x A x V^2 = 0.5 x 1.2 x 1.51 x 26.8^2 = 652 N

Friction force - let's take an estimate of 1% of the mass (1400 kg) = 14 kg x 9.81 (gravitational constant) = 137 N

Force at the tire contact patches to get the truck down the road at 60 mph = 789 N

Power = force x velocity = 789 x 26.8 = 21 kW

At the engine, assume 85% efficiency of the driveline, it will see about 25 kW of load. It has 43 kW available. This should be OK.

If you were to use 3.73 it would be about 10% lower revs and it will be even further off the cam ... probably pushing your luck and I doubt if it would actually be better for the engine.

If you re-crunch the numbers for 80 mph you have about 57 kW available and the power demand is about 54 kW with the 4.10 gears. In other words, you will top out around 80 mph in 5th with the 4.10 gears (but only doing around 3000 rpm ... it will have more power available in 4th and won't be out of revs). With the 3.73 it will not pull that gear at 80 mph unless we have guessed way wrong on the drag or frontal area.

Verdict is ... 4.10, in my opinion, based on the above.

[novadude]

With no OD and 3.08-3.336 typical gears, almost every car built in the 1960s cruised at 3000 rpm going down the road at 70 mph. I wouldn't worry about it.

[PackardV8]

Am I the only one who thinks for the intended use, the 230 degree cam is too much with the 2.3l turbo?

[roc]

Your wheels will be doing 672 revs per mile; at 60 mph with 4.10 and 0.79 OD it will be at 2756 rpm in direct (presumably 4th) and 2177 in overdrive (presumably 5th).

The engine will probably be off the cam at that rpm, but the cam isn't too wild, so it shouldn't be horrendously down on torque. Let's say you have somewhere near 140 lb.ft of torque at that rpm. Means you have about 58 horsepower available = 43 kW

Drag coefficient is probably near 0.55 (pretty bad)
Ruff-estimate frontal area is probably near about 85% of overall height x overall width not including mirrors. I don't know what sort of suspension you have planned. But let's say the truck is 1.9 m wide (75") and 1.7 m tall (67"). If you have better numbers, go ahead and substitute.
Effective frontal area is 85% x 1.9 x 1.7 = 2.74 sq m
Cd x A = 1.51 sq m

Speed in metres per second (sorry, I gotta do this stuff in metric) at 60 mph = 26.8 m/s

Drag force = 0.5 x density x Cd x A x V^2 = 0.5 x 1.2 x 1.51 x 26.8^2 = 652 N

Friction force - let's take an estimate of 1% of the mass (1400 kg) = 14 kg x 9.81 (gravitational constant) = 137 N

Force at the tire contact patches to get the truck down the road at 60 mph = 789 N

Power = force x velocity = 789 x 26.8 = 21 kW

At the engine, assume 85% efficiency of the driveline, it will see about 25 kW of load. It has 43 kW available. This should be OK.

If you were to use 3.73 it would be about 10% lower revs and it will be even further off the cam ... probably pushing your luck and I doubt if it would actually be better for the engine.

If you re-crunch the numbers for 80 mph you have about 57 kW available and the power demand is about 54 kW with the 4.10 gears. In other words, you will top out around 80 mph in 5th with the 4.10 gears (but only doing around 3000 rpm ... it will have more power available in 4th and won't be out of revs). With the 3.73 it will not pull that gear at 80 mph unless we have guessed way wrong on the drag or frontal area.

Verdict is ... 4.10, in my opinion, based on the above.

Superb work!

[adam728]

With no OD and 3.08-3.336 typical gears, almost every car built in the 1960s cruised at 3000 rpm going down the road at 70 mph. I wouldn't worry about it.

1960's? My 2001 Jeep TJ came with 29" tires, 3.73 gears, and a 3 speed auto. Just a bit over 3000 rpm at 70 mph, with a straight 6 not known for it's revving abilities.


I would not be afraid of making the little engine rev a bit, especially since moving the power band up in rpm with the cam.

[DCal]

I'd seriously be considering a 3:73 gear if you're going highway. My car has 31.5 Hoosiers and 3:73 gears and at 55mph it's turning 2500 and it drones something awful. When the turbo is working I don't think you need a lower gear ratio.

I have 689 ft/lbs of torque available so maybe I'm not the right person to comment on your 4 cyl.

[ap72]

Your wheels will be doing 672 revs per mile; at 60 mph with 4.10 and 0.79 OD it will be at 2756 rpm in direct (presumably 4th) and 2177 in overdrive (presumably 5th).

The engine will probably be off the cam at that rpm, but the cam isn't too wild, so it shouldn't be horrendously down on torque. Let's say you have somewhere near 140 lb.ft of torque at that rpm. Means you have about 58 horsepower available = 43 kW

Drag coefficient is probably near 0.55 (pretty bad)
Ruff-estimate frontal area is probably near about 85% of overall height x overall width not including mirrors. I don't know what sort of suspension you have planned. But let's say the truck is 1.9 m wide (75") and 1.7 m tall (67"). If you have better numbers, go ahead and substitute.
Effective frontal area is 85% x 1.9 x 1.7 = 2.74 sq m
Cd x A = 1.51 sq m

Speed in metres per second (sorry, I gotta do this stuff in metric) at 60 mph = 26.8 m/s

Drag force = 0.5 x density x Cd x A x V^2 = 0.5 x 1.2 x 1.51 x 26.8^2 = 652 N

Friction force - let's take an estimate of 1% of the mass (1400 kg) = 14 kg x 9.81 (gravitational constant) = 137 N

Force at the tire contact patches to get the truck down the road at 60 mph = 789 N

Power = force x velocity = 789 x 26.8 = 21 kW

At the engine, assume 85% efficiency of the driveline, it will see about 25 kW of load. It has 43 kW available. This should be OK.

If you were to use 3.73 it would be about 10% lower revs and it will be even further off the cam ... probably pushing your luck and I doubt if it would actually be better for the engine.

If you re-crunch the numbers for 80 mph you have about 57 kW available and the power demand is about 54 kW with the 4.10 gears. In other words, you will top out around 80 mph in 5th with the 4.10 gears (but only doing around 3000 rpm ... it will have more power available in 4th and won't be out of revs). With the 3.73 it will not pull that gear at 80 mph unless we have guessed way wrong on the drag or frontal area.

Verdict is ... 4.10, in my opinion, based on the above.

Thank you for this. As an engineer in a little embarrassed I didn't do this work for myself already.

4.10 does look like it will work, and as a bonus I can scour the junk yards for this gear set. Wouldn't have been able to get a 4.56 set at the junk yard.

Thank you for all your time and help.

[IDT-572]

Am I the only one who thinks for the intended use, the 230 degree cam is too much with the 2.3l turbo?

No I think it will be a snotty no torque deva and not come on power till around 3500+ and that's with out the turbo.

[ap72]

Am I the only one who thinks for the intended use, the 230 degree cam is too much with the 2.3l turbo?

No I think it will be a snotty no torque deva and not come on power till around 3500+ and that's with out the turbo.

That's what I think too.