93' camshaft question

[dparkguy]

I want to replace the stock cam with one that provides better torque. I have 5 speed with 33" tires, stock 3.73 gears. I don't want to upgrade gears yet. Will a different cam make me happy?

[fastpakr]

No.

[Tee Rev]

I'll have to disagree & say not only will you be happy, you'll have a grin every time you press the go pedal.

[fastpakr]

A cam, depending on grind, may significantly change power characteristics to improve horsepower by pushing the peak torque point further out on the tach. It's not going to magically increase cylinder filling at low revs though, which is what the OP appears to want. Corrected gearing or forced air will do that.

[Tee Rev]

Originally Posted by fastpakr

A cam, depending on grind, may significantly change power characteristics to improve horsepower by pushing the peak torque point further out on the tach. It's not going to magically increase cylinder filling at low revs though, which is what the OP appears to want. Corrected gearing or forced air will do that.

This would be true if the factory cam was already allowing the maximum volumetric efficiency of said engine.

In this case the factory short duration low lift cam along with small valves hinder VE throughout the rpm range. A stock 4.0l will fall flat over 4500rpm.

Because of this, the comp 422 cam's longer duration & lift has the effect of increasing the VE of the 4.0l throughout the entire rpm band until the poor flow characteristics of the 4.0L's small valved heads come into play.

What you'll end up with, a 4.0L that has a substantial increase in torque off idle until the 5300 rpm redline.

[Bob Ayers]

Originally Posted by Tee Rev

This would be true if the factory cam was already allowing the maximum volumetric efficiency of said engine.

In this case the factory short duration low lift cam along with small valves hinder VE throughout the rpm range. A stock 4.0l will fall flat over 4500rpm.

Because of this, the comp 422 cam's longer duration & lift has the effect of increasing the VE of the 4.0l throughout the entire rpm band until the poor flow characteristics of the 4.0L's small valved heads come into play.

What you'll end up with, a 4.0L that has a substantial increase in torque off idle until the 5300 rpm redline.

WRONG!

You are going to loose low end torque with the longer duration, but pick up
high end HP. The only way to pick up both is with VVT.

[Tee Rev]

Originally Posted by Bob Ayers

WRONG!

You are going to loose low end torque with the longer duration, but pick up
high end HP. The only way to pick up both is with VVT.

Just for giggles I'll post this again. But a little bigger so you actually read it.

This would be true if the factory cam was already allowing the maximum volumetric efficiency of said engine.

[Bob Ayers]

Originally Posted by Tee Rev

Just for giggles I'll post this again. But a little bigger so you actually read it.

This would be true if the factory cam was already allowing the maximum volumetric efficiency of said engine.

Giggles is the operative word!!!

[Tee Rev]

Bob, Please don't ever PM me again. & if you have such a strong understanding of the formula for Volumetric efficiency. I challenge you to prove me wrong.

But remember one thing. I've built many engines in my career including the OHV 4.0L using the Comp 422 cam & each has exhibited the exact power increase that I've described.

As a true Ranger enthusiast I'm only trying to answer a question posted by dparkguy & I have practical knowledge on the subject.


If you feel that you have something constructive to add be my guest.

[Will]

I'm not going to recommend changing a cam to pick up low rpm torque in order to make up for incorrect gearing.

Calculating MEP at the peak torque number the 4.0 comes in at 139psi. A 305hp/335ft# LT1 Z28 comes in at 144psi--similar technologies and definately built with VE in mind I would think. A 4.3 GM comes in at 150psi. The '03 (no VVT) Dodge Hemi is at 164psi. It's possible you could install headers, clean up the ports and such and get the pushrod 4.0 up there to 250ft# with the same shape of curve. But that's only a 12% gain and the proper gears for his truck would be 4.56s and they guarentee him about 22% more torque. A VVT, 4-valve 4.0 would be up around 190psi--300ft# or so. Even then, it's not the same as having the right gears. It will still be in the 200ft# range at 1,000rpm because it doesn't matter what you have for VE at 1,000rpm. And those 33s are going to dog it out when the clutch comes up.

I've never modified a 4.0, but my instincts tell me that he's better off spending his money on gears, even if there are some gains possible at low rpm that won't move the powerband up. I guarentee with 33s on 4.56s he'll be happier than a camshaft and 3.73s with his 33s. Definately I would consider doing engine work after the gear change.

[Tee Rev]

Originally Posted by dparkguy

I want to replace the stock cam with one that provides better torque. I have 5 speed with 33" tires, stock 3.73 gears. I don't want to upgrade gears yet. Will a different cam make me happy?

When I read this, I can see that a gear change is already planned. The question is in regards to a different cam.

Having real world experience with a lightly modified 4.0L I can honestly answer the actual question.

I've run this engine combination with 3.08's, 3.55's & 4.10's, all with 26" tall tires. On the street, With the 4.10's anything more than 1/4 throttle in first results in tire smoke and a quick shift into second will keep it going. Even with the 3.55's a spirited launch has the same result. Now with the 3.08's (pretty close to 3.73's with 33's) and a soft launch there was more than enough torque to get moving quickly without even coming close to bogging the engine. (With a 4x4 in low range, not an issue.)
I can honestly say that the 4.0L should have come with this cam in the first place!!

Now, since I drag race the truck, of course I run the 4.10's & slicks for traction, and I'll admit, gears with this combo will definitely keep you smiling for as long as you own the truck!!

[AllanD]

a cam change will increase the RPM at which the torque will occour

There is No "down" to gain because the 4.0 OHV is already making
>190ftlb at 1000rpm.

NONE of the aftermarket cams increase bottom end, they move the torque
higher in the rpm band to make more power and none of that is going to
cure the fact that the OP has THE WRONG GEARS now.

He doesn't want to upgrade gears but spending easily twice as much
to install an aftermarket cam is practical? Ahhh... No.

IMO proper gearing to go with a 4.0 is as follows:
a 2wd 4.0 with 215/70-15's? 3.55
a 4x4 4.0 with 235/75-15's? 3.73
a 4x4 4.0 with 31x10.5-15? 4.10

with 33's? 4.56's would be about right...

Swapping a cam to avoid changing to the correct gears?
simply not going to do it for him.


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