The Dodge Challenger Message Board

Hi,
I need some info, I would to know something about Rhoads Lifters.... These are special lifters for big cams that reduce the duration and lift at idle and low rpm, so the engine can idle well and have good mid rpm with a big cam....
Thanks for any help
Ciampone

What is it about them you want to know?

I only would to know if these lifters really work good like they say or no from someone who has that in his engine....

I can't think how to do this without one of my long winded explainations so prepare to be bored!!

As far as I remember (I looked into this some years ago) there are two types of 'variable duration lifters', as they are called, on the market.

The oldest design (about 30 years?) is the Rhoads lifter but about 15 years ago Crane started making their own version called the 'Hi Intensity' lifter.

I don't know if you know how a normal hydraulic lifter works but without any load on it oil can flow through it keeping a small internal chamber full of oil. As soon as the pushrod starts to push down on the lifter a valve inside closes - trapping the oil so the lifter starts to push open the valve.

Any normal lifter like this will slowly collapse (leak-down) if the pressure is kept on it as oil will always bleed past the internal parts. However as the valve is only open for a short time the effect of this is not noticed.

The Rhoads lifter has a groove that allows oil to escape more quickly. A normal lifter will leak-down in about a minute but a Rhoads lifter will only take a second!

The Crane lifters use a greater plunger-to-lifter body clearance to achieve the same thing but the rate of leakage is slower. Leak-down in this case would take about 5 seconds.

This makes the cam act 'smaller' at low rpm but still work OK at high rpm.

The advantage of these lifters is that when used with very long duration camshafts they can give you more torque at lower rpm. In fact tests have shown the Crane lifters in particular increase horsepower and torque over the whole range. But the increase is really very small (about 6-9 bhp) and I am not sure you would notice it.

However the amout of vacuum you get at idle increases about 2-3 inches which can be a big plus if you use power brakes etc.

The big disadvantage with the Rhoads lifters is that they are very noisy and 'clatter' at idle.

The Crane lifters are no more noisier than a standard lifter.

So the breakdown is this:

The most power gains are from the Crane lifters but it is only about 1%.

The best vacuum is from the Rhoads lifters (2-3") but the Crane lifters are not far behind (about 2").

The Rhoads are noisy but the Crane are quiet.

Now before you go and buy a set of either just remember that these are for LONG duration cams. Cylinder pressure with a stock or mild cam could be too high with these and cause 'pinking'. In fact if your engine is close to detonation with stock lifters it might detonate with these. Don't use the Crane lifters unless you have a very low static compression ratio or unless your can is bigger than 220 degrees @ 0.050" lift.

Another point is that the Rhoads lifter is better suited to the very old style cam designs like Chrysler Performance grinds that have not changed since the 1960s. The Crane lifter is better suited to cams with a faster rate of lift.

I hope this helped you.

Thank you very much Dave for all the infos! Don't worry, I'm not bored and now I know many more tech!!
I'm not bored at all and I have another question....
I read that the crane Hi Intensity cams can produce detonation at low rpm with high compression ratio, in fact these are for use with low comp ratio... why????
Thanks
Fabiano "ciampone"

Greeting from Italy

It's always me....
Dave, I can read my mind, the trouble that starts all my question about is an old MP cam with too much intake for a 383 4v..... So torque at low rpm is very low....

Thanks again

Last message of the day,
I hope, the question of the previous message is: why crane lifters can produce detonation and the Rhoads no??
Thanks again
Good night

I read that the crane Hi Intensity cams can produce detonation at low rpm with high compression ratio, in fact these are for use with low comp ratio... why????

Not quite right. Use them with low comp ratio or long duration camshaft.

It is to do with actual cylinder pressure and not theoretical compression ratios.

With everything else equal as duration is shortened the cylinder pressure will increase.

A big duration cam needs a high comp ratio otherwise the actual cylinder pressure will be low. These lifters will increase cylinder pressure a bit with cams like this.

However a milder cam with these lifters will produce lots more pressure.

Rhoads claim their lifters can be used with any cam in any engine. But that is only their claim. Both companies have done tests of their own but these are biased to say the least. The only independant test I know of was in Car Craft some years ago. I kept a clipping.

The test was done by Rick Roberts at Air Flow Research.

He found that even though the overall average pressure rise was equal with both makes of lifter the rates were very different.

The Rhoads lifters produce a lower but wider pressure rise during crank rotation but the Crane produced a shorter but higher pressure curve.

The cam you have is out-dated. If you have to keep it then the lifter you use depends on the amount of duration you have. Do you know the duration of your cam??

Hi,
thanks again for the explanation, very clearly! very good! You're my professor!!
I hope to not bore you with my questions
The cam is an MP 4452993 280°adv. duration and .474 lift

OK. You can use the Rhoads lifters no problem with this cam and expect a 1% power increase and 2-3" more vacuum at idle. But you will get the noise at idle and low rpm.

You can also use the Crane lifters as your cam is just big enough and have the quite operation with about 2" more vacuum than now and slightly more power than the Rhoads but if your engine already detonates easily stay with the Rhoads or standard lifters.

I do not use either as the Rhoads lifters are not suitable for the fast-rate-of-lift type cam I have and also I am close to (and still sometimes get) detonation so the Crane are out too.

The only difference with my lifters is that they have a heavy circlip in the top holding everything together rather than the stock type which has only a thin wire.

In case you were wondering I took your 280 advertised duration and multiplied it by 80% to get an idea of what the duration at 0.050inch lift would be. It works out at about 224 degrees but this is just an aproximation. If you remember I said that Crane specify a cam bigger than 220 at 0.050" lift so you are just in there.

not 80%. it's 85%. so it will be 238 at 0,050"

All the Mopar cams are 85% cams

Mmm. I was always told the old mopar cams you used 80%. Unless I lost a few more brain cells this christmas (very possible) and remember it wrong.

If what you say is right Tore then he is well into Crane lifter territory. Thanks for that.

Hang on a minute Tore. 238 @ 50thou is a pretty serious cam. You are talking the same sort of size as my 440 cam. 500hp+ type of area. 3000+ stall, huge induction and headers etc.

I have fitted a MP 284 duration cam to a 440 before and it was a LOT milder than that although it did loose a bit of vacuum at idle. The 284 is considered a street/strip cam.

I must have been right.

(work keeps getting in the way)

So what I was saying Tore is that this old MP street/strip 284 cam works out as 241 duration with your method but if you look up the spec of cams like that you are talking one serious cam! It could still be streetable but only just! You would need 3500 stall and huge compression ratios etc.

Using my 80% method the same cam works out as 227 degrees @ 50thou and that gets us in the real street/strip area.

So I am pretty certain I am right to use 80%.

Ok Dave,
Thank you again for your help.
I know that 280° is only the advertised
duration, when the valve starts to open
the lift is so little that the flow is nothing...
I write to you this time to know if I undestand
the problem or no.
I promise to you that these are the last
questions, yes-or-no replay can be sufficient :
1) Compression ratio is 9.5:1 and I use 95
octane unleaded fuel, now I have no detonation
problem, I can use both.(?)
2) If I understand well, You say that with C. or
R. lifters, the engine idles better but there is
just a little bit of more torque at low rpm.(?)
3) "A big duration cam needs a high comp ratio
otherwise the pressure will be low. These will
increase cylinder pressure a bit with cams
like this" Ok, but all this happened only at
low rpm.(?) Or at any rpm ?
4) You say "the Rhoads lifters are not suitable
for the fast-rate-of-lift type"
It's because the Rhoads are non-roller lifters?
I have 2 pics about cams, standart (hydraulic)
in red and roller in yellow..
Yuor fast-rate-cam is like the yellow?

Thanks and great burnouts for this new year!
Thanks to Stefan Hill (Germany) for to show
me your site and message board.
Ciampone

HELP!
how I can put the images??

Full instructions on posting images in the test messages area and under formatting in the left frame.

Answers to questions.

1/ Yes both but I think the Rhoads will work better in your case if you can put up with the noise.

2/Yes. in fact they also give a little more torque over the whole rpm range because of the increase in cylinder pressure.

3/Over whole rpm I think.

4/I am only talking about normal hydraulic lifters here and not solids or rollers.
The fast rate of lift cams I refere to are the more modern designs but some that are made only for chryslers have an even faster rate of lift because chryslers have wider lifters that allow this. Look at the Hughes Engines web site for a full explanation.

here are the pics
d:/roller.jpg

don't work...
I'll send to you e-mail Dave...

d:
roller.jpg

YaaaahoOO!!!

Ciampone.
Go to the test messages area and read Henrys/Christers instructions as well as the instructions under 'formatting' on the left. They are very clear. You were not even close with that attempt! Also you should experiment in the test area and only try to post here when you have it figured out.

Go on. Try again!

Excuse me Dave,
Do you can see the pics or no? My pc do!
These are the pics (roller and Hydraulic) I told you in the previous long message...

That's funny. I can see them on this machine at work but not on mine at home! Strange!

Welcome to the PC-world!

Funny. I can see them at home now to. Very strange.

Anyway. You can see how fast a roller lifter must rise on that first profile. The faster a valve opens - the longer it can be open enough to flow the max amount of air through the intake ports. Effectivly giving a longer duration before damaging idle quality. You have to watch how fast you close a valve though because you don't want it smacking the valve seat too hard.

The other profile is a more typical cam lobe for a more normal tappet.

The wider the base of the tappet - the more steep you can make the sides of the cam lobe. Chryslers have wider tappets than Fords or Chevys but as Chrysler performance parts are only about 3% of the market most cams you buy are designed around the ••••• and •••• limitations.

Make sure the cam you buy is a modern fast rate of lift design made ONLY for Chrysler engines.

The cams offered by Chrysler themselves are not fast opening and closing and were designed in the 1960s so although they will work they will not work as well as a modern cam.

Ooops! I forgot I added F0rd and chuvvy to the swear word list!