Cams- Flat tappet & Roller-- Are lift and Duration figured the same? - Hot Rod Forum : Hotrodders Bulletin Board
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Old 12-31-2007, 09:50 AM
Farmer Buck
 
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Cams- Flat tappet & Roller-- Are lift and Duration figured the same?

I finally ordered my cam for my flat tappet engine project. As I studied lots of cam specs, I'm a bit confused about "duration and Lift". --Point in question: I settled on a Crane came with 210 duration and .469 lift for my 74 Ford truck engine. (Flat Tappet) --I was just thinking that if this works really well I might want to also change cams in my 91 Ford truck. (Roller Cam) --Would a roller cam with this same duration and lift produce the same effect as the flat tappet? (I realize it would be a different cam, but am wondering about reading the specks, if this duration and lift would bring me the same low end power.)

Thanks!

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Old 12-31-2007, 10:16 AM
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roller cam

the roller cam should not only give the same results but should be slightly better. because of the less friction of the roller cam.
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Old 12-31-2007, 10:30 AM
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Might just be me but the ramping of the lobe profile of a roller cam will make it act all together different from a flat tappet cam... Even with the same overall spec`s (lift & duration) besides the less friction...

I know one thing for sure that they sound alot different...
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Old 12-31-2007, 12:11 PM
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I doubt the 91 truck motor has a roller cam in it. The blocks are compatable and everything can be installed from a roller car motor.( spider, dog bones, and pushrods) You may need to tap the 2 spider retaining stud bosses.

Also be aware that the aftermarket roller cams are a different firing order than the non HO cams.
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Old 12-31-2007, 04:11 PM
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Scottford351---Yes, the 91 does have a roller cam set up. Ford went to rollers in the latter part of the 80's. ---Your statement that "aftermarket cams are a different firing order". Are you saying that Roller cams are different, or that AFTER MARKET cams are different firing order? I've never heard that before. Could you explain that a bit more? Thanks!
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Old 12-31-2007, 05:30 PM
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The HO motors and aftermarket stuff is 13726548
Non HO is 15426378

Im not sure if the 91 truck has sequencial (sp) or not, but using the wrong firing order on a sequential fuel injection screws it up.

Car motors got roller cams in 86, 85 for the HO mustang motors
I rebuilt a truck motor in our company 91 pickup and it was flat tappet.



Edited: I can't type

Last edited by scottford351; 12-31-2007 at 08:47 PM.
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Old 12-31-2007, 05:42 PM
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To take what Bumpstick said a little further: You'll probably notice when comparing non-roller to roller cams that, given the same amount of duration, the roller cam will usually have more lift. Since the roller follower can "roll" up a much steeper ramp without binding than a flat tappet lifter can, the cam lobe can open the valve faster. This allows the valve more time to open a bit higher, or to keep the valve open at a given point of lift for a bit longer (a rounder lobe tip as compared to a pointier lobe tip).

In a street engine, when you are trying to balance performance with driveability by avoiding huge duration and overlap numbers, a roller cam can help you out - it will allow you to use a stronger cam while still maintaining streetability. This is the main reason I am attracted to rollers and not the reduction in friction (though that is definitely not a bad thing).

Basically, yes, the roller will produce, at the very least, the same results and likely better results.
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Old 12-31-2007, 06:35 PM
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Quote:
Originally Posted by scottford351
The HO motors and aftermarket stuff is 13726548
Non HO is 1546278

Im not sure if the 91 truck has sequencial (sp) or not, but using the wrong firing order on a sequential fuel injection screws it up.

Car motors got roller cams in 86, 85 for the HO mustang motors
I rebuilt a truck motor in our company 91 pickup and it was flat tappet.
so let me get this right--a non HO motor only has 7 cylinders???

just kidding and everybody have a happy new year!!

to answer the OP, lift and duration are measured the same, but can't be compared directly because the roller will have more area under the curve.
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Old 12-31-2007, 08:45 PM
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Dang!
You got me good on that one!

Thats why they have less power
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Old 01-01-2008, 07:36 AM
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[QUOTE=scottford351]The HO motors and aftermarket stuff is 13726548
Non HO is 15426378

Im not sure if the 91 truck has sequencial (sp) or not, but using the wrong firing order on a sequential fuel injection screws it up.

Car motors got roller cams in 86, 85 for the HO mustang motors
I rebuilt a truck motor in our company 91 pickup and it was flat tappet.
++++++++

Scottfford:: Thanks. That sends me back to the drawing board on my 91. You may be right that the trucks stayed with the flat tappets longer than the car engines. There were a number of differences between the two, though I never thought that was one of them. I'll have to do some more checking on that one!

Last edited by Lloyd1wv; 01-01-2008 at 07:42 AM.
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