93' camshaft question

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?

No.

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

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.

fastpakr said:

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.

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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.

Tee Rev said:

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.

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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.

Bob Ayers said:

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.

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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.

Tee Rev said:

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.

Click to expand...

Giggles is the operative word!!!

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.

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.

dparkguy said:

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?

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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!!

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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Alright Tee Rev, I made sure not to attack you while differing with your opinion. I consider your bolds and italics somewhat pointed and insulting. And they definately are not evidence--just word enhancements.

3.08s with 26" tires is the same as 33" tires with 3.90s. 26" tires with 4.10s is 5.20 gears and yes, my stock 4.0 would destroy tires with 5.20 gears on it. The 4.0 is a good engine without doing anything to it.

Competition Cams uses a 350 chevy to designs cams and then grinds them on blanks for everything else. They didn't put a 4.0 on the dyno and make a magic cam. Ford did though. They didn't do what CC did and pull a grind out of a generic box and slap it on the blank. They had that engine on the dyno for a year trying differnet things so it would pass the EPA sniffer and mileage requirements while also keeping an eye out for competitive power figures and drivability. All engines from the factory are tunes to make low end power. That's where people drive. The VE of a factory engine is maximized where you actually use it. They do studies to see where people drive and then maximize it right there.

You have a truck you are claiming low 14s without enhancements. A stock 4.0 from 1991 was rated at 155hp, net. A 3,000# Ranger would require 275hp net to acheive that. If you are using the CC 270HR grind in that motor, and those heavy lifters aren't jumping off the lobes by 5,500rpm, you have a BMEP of 162psi. The 207hp SOHC 4.0 is at 127psi (why did they bother, they should have called you!) and I'm trying to find something close to your 4.0 and can't do it. You are competitive with the 1995 Saab 900 turbo and the 2000 Porsche 911 non-turbo is a little higher.

All from the iron headed 2-valve (smaller valves than the 2.9--you should work with that engine, probably be ruuning it at Indy) Ford 4.0--which Ford erroneously replaced with cammer heads trying to get power out of it to compete with everyone else.

While I can appreciate both school's of thought, more power vs. more gear the OP has said he doesn't want to do gears at this time. I have known Tee Rev (not a newbie) for several years and can say his truck flat out moves. I have seen dynograph's for his engine, and if I could link them I would, but here's the results (intake porting and headers as well)

The engine produced 198 ft/lbs @ 1700 rpm and gradually climbed to a peak of 219 @ 3510 rpm. Torque does not fall below 200 ft/lbs till 4700 rpm

Peak horspower was 181 @ 4760 rpm, and the engine exceeded 170 hp from 4300 rpm to 5340 rpm. And at 5560 rpm (end of the test) the engine was still at 161 hp.

Will the cam make a difference? YES

Will gears make a difference? YES

I say let him decide what he wants to do. He might be happy with 4.56's and 33's now, but decide to go 35" or bigger later and want more gear. The cam will help in the mean time, and it'll help later as well.....

Those numbers sound remarkably like a typical OHV 4.0 with peak airflow point moved up 500-1000rpm, as Will, AllanD, and myself suggested. Quite the opposite of what the OP appears to need. Not that a cam is a bad change, but it does nothing to improve low RPM airflow.