Building a 542 stroker motor, need cam specs

[Go Fast For Life]

I am building a 542 stroker motor for my car. Here are the engine specs.
4.031 bore,
4.25 stroke,
10.5 CR,
GTS-R heads cnc ported,

I need to select a hydraulic roller cam and want a peak HP at about 5600rpm and still good drivability characteristics . I am shooting for 700-725HP (crank) or about 625-650RWHP.

I am thinking about a cam with 243 intake and 246 exhaust duration at .050 and a total lift of .560.

Can any of you builders/tuners tell me if this will give me the HP and driveability I want?

 

[Fast Freddy]

the more displacement an engine has the more u can upsize your cam and still retain the stock characteristics. that being said i would use the new jesel 1.7 ratio roller rockers and go for a cam that would give me at least .600 lift seeing how u are gonna have 10.5:1 compression ratio. as far as the duration is concerned i would look for a cam that gives u about 5-10 degrees more duration than stock since u still want your horsepower peak to be in the 5600 rpm range. good luck

 

[jp]

I would step up closer to 0.600 in lift, but not over. If you want good driveability...no more the 235 in duration, lobe sep 110-116 depending on if your going use any more power adders.
But you need to know the head characteristics to make a good camshaft design.
I'm myself using a +250 duration camshaft in my Viper, it's way lumpy...

 

[Daniel Cragin/DC Performance Inc]

That 242 duration cam will make power but will require some tuning to run right. Anything over 235 degrees will not work with the cats.

 

[XLR8]

How much lift will the heads take without getting coil bind? I was told anything over a 580 lift is pushing it. 1.7 Ratio rockers will bring the lift of the cam up so a smaller cam is needed with them. Right? So what is the max cam lift with 1.7 rockers and stock springs?

 

[Daniel Cragin/DC Performance Inc]

You wont want to run the stock springs with a .600 lift cam.
On large camshaft profiles we find it better to run a .100 longer valve, this keeps the spring pressure reasonable at full lift and no chance of coil bind. You are limited on spring pressure with the production lifters and have to be careful to draw the line between valve float and acceptable spring pressure. To much spring pressure and the lifters bleed down and make a racket on start up and the rollers wear out prematurely. To little spring pressure and the valves float at high rpm causing other valvetrain problems.

 

[joe117]

My question would be,

Why go to 1.7 rockers?

Wouldn't that put extra pressure on the lifters/rollers?

Why not get the extra lift from the cam grind if you are changing the cam anyway?

What am I missing?

 

[Go Fast For Life]

JP,
Fast Freddy
Dan Cragin
XLR8
and Joe117

Thanks for all the comments. I will keep you all posted as the project progresses.

Go Fast

 

[proracer1]

call Jeff Morys 248-576-9204 He's the man

 

[GRAPE]

When you use the rocker ratio you ease the strain on the lifter bores. Most big buck pushrod stuff....aka nascar, uses rocker ratios in the 2.somthings.

 

[joe117]

Grape,
I must be missing something here. I don't understand why lifter bore stain would be less. Do you mean the lifter would move less distance?

The 1.7 ratio rocker moves the valve more distance than a 1.5 rocker, that means everything on the cam side of the rocker is under more pressure when lifting against the same spring.

I think,
More pressure on the cam side means more wear.
If the lobe on the cam is larger, you get the same lift without the increased pressure caused by the mechanical lever disadvantage of a 1.7 rocker.

Perhaps some engines are limited in cam lobe height due to the limits of the bearing surface circle diameter and the shaft thickness required.

 

[Torquemonster]

Joe - going too fast on the lobe puts more strain on the lifters. Hydraulic roller lifters are really not ideal and are pushed to their limits by this kind of application. personally I'd throw them away and go solid roller - but there are trade offs and most prefer the convenience of stock type.

The higher ratio rockers allow for a faster ramp and more lift - providing a little more power and area under the curve - but without stressing the lifters AS MUSH AS SPEEDING UP THE CAM LOBE WOULD. Does that make more sense? You are right - more ratio will still put more stress on the lifter but it is LESS than using the same lift and ramp via a more agressive lobe.

 

[joe117]

I don't know about that Barry. I'd have to devote some thinking time to be sure, but that will not stop me from talking off the top of my head. ;-)

The acceleration of the lifter might be the limiting factor. I don't know about that.

Do we know for sure that the distance between the cam shaft itself and the peak of the cam lobe isn't the limiting factor.
What I mean is, the lobes can't stick out past the cam bearing surface circle. You wouldn't be able to get the cam into the engine if the peaks were sticking out too far.

If the lobes were out as far as they could go, then more lift would require a larger rocker ratio.
Coould that be the reason for going to a 1.7 rocker?

 

[George Bryce]

I know that a Pro Stock Dodge with a 2 to 1 rocker ratio and 1000# of open spring psi transfers 2000 psi to the lifter, cam and etc.....WOW!!! I think more lobe lift and less ratio would be the way. GB3

 

[joe117]

Right, but what is the limit on the lift that you can get from the cam?
In other words, what is the difference between the shaft diameter and the bearing circle diameter?

That difference is the max lobe lift.

 

[Fast Freddy]

put in a .575 lift cam with a 1.7 ratio rocker and u will have a little over .600 lift. also, have your cam ground with 7.5 degrees more duration. coupled with the increased rocker ratio this will give you a total of about 10 degrees more duration for your cam. in my opinion this would be the perfect amount of lift and duration for your 542 stroker engine. seeing how u want everything to run and perform like a stock motor concerning idle characteristics and peak power band output, etc.

when increasing the displacement of an engine u can upsize your cam profiles and still retain stock characeristics.

 

[joe117]

I'd say a .575 cam lift coupled with a 1.7:1 rocker, would give .977 valve lift. Am I missing something?

 

[Fast Freddy]

a .575 lift cam is based on a 1.6 rocker ratio. duh!

 

[joe117]

Well, since we were talking about cam lobe lift and rocker ratio, I figured that when you said "put in a .575 lift cam". I figured you were talking about lobe lift.
I don't think that's "duh".

 

[George Bryce]

Joe, you are right. The biggest lobe that will fit is the key....then put in the ratio you need to get the lift you want. GB3

 

[George Bryce]

Freddy the cam is not based on any ratio unless you base it on one. Like Pro Stock....a .500 cam with a 2 to 1 ratio gives you 1.00 lift. GB3

 

[Dr Roof]

George Bryce

when you gonna bring your Fast LPE ALl Motor car to the
V-10 Nationals? WOuld be great to see you and sw AND nORM gO HEAD TO HEAD!

Bring your car out of retirement and come on down to Florida Feb 6-8

 

[Torquemonster]

What the Dr said - it would be nice to see that LPE car run at the Nationals events.

re cam lobe lifts - right Joe - the lobe cannot go higher than the base circle, but the lift limits of the lobe are not that - they are the spring pressures required, mechanical ramp limit before scuffing, and hyd roller lifter capabilities that limit the lift at streetable durations. The base circle would probably allow a 0.500" lobe lift - more than any street engine is likely to want by the time you multiply the rocker ratio.

The 2000lb loading referred to above is a static load - a race cam will regularly exceed 160,000 lb per square inch on the lifter face - enough to exceed the OEM oiling ability to prevent wear and enough to break the Viper hyd lifters instantly.... which is why serious engines run solid roller

 

[George Bryce]

Hi, Doc. I would love to come out and play with you all. My race and testing schedule is so full, on purpose, it is almost un human. I am very lucky to get to race for a job. Our S&S Vtwin race engines do not have the same cam bore limits as the Viper engine. We run big lobe lift hyd. rollers and mild ratio rockers to make more lift with less wear and tear. In the next few years we will all see this unfold in the big auto iron. Our old v10/ v8 stuff is built with small cam bores. All world class race engines are stepping up on bigger base circles.....if they are not...they just don't know about it yet. GB3

 

[TX WHOS YOUR DADDY]

GB3,TRY TO MAKE THE V-10 RACE IN BOWLING GREEN,KY APRIL 16TH-17TH.WE DONT WANT OUR BROTHER S.W. TO BE ALONE WITH THE SOON TO BE 2ND FASTEST MOTOR ONLY SNAKE. REGARDS-NORM K

 

[THEMASH]

The cam i have in my car is not too bad, call Heffner for the specs.

 

[Fast Freddy]

.359 lift cam X 1.6 rocker ratio = .575 lift cam. duh!!!!!!!

have your cam ground with a .359 lift and use a 1.7 rocker ratio and u will get .610 lift.

also have your cam ground with 250 duration @ .050 lift (based on a 1.6 rocker ratio) and u will see approximately 252 degrees of duration with a 1.7 ratio rocker.

this would be the ideal cam for a 542 stroker motor that u want to retain stock characteristics with in my opinion. the gts-r heads from caldwell feature 2.02 intake valves and 1.60 exhaust valves.

the compression ratio that u are going to use of 10.5:1 should be fine for pump gas with a octane booster since your displacement has been increased.

 

[joe117]

"spring pressures required, mechanical ramp limit before scuffing, and hyd roller lifter capabilities that limit the lift"
Barry,
I still don't understand why one would want to use a higher ratio rocker than needed for the lift required.

In other words, if the cam is going to be a custom grind anyway, then have it ground so that all the lift possible comes from the lobe lift. Any profile can be created, just normalize the lift numbers to get the most possible lift out of the cam.
Any more lift required would come from rocker ratio.

Reducing rocker ratio would reduce strain of all kinds on the cam side of the rocker.
The lower the ratio the better as long as the valve sees the lift at angle profile required.
Right?

 

[George Bryce]

YES! Thats it. GB3

 

[SW]

GB3,TRY TO MAKE THE V-10 RACE IN BOWLING GREEN,KY APRIL 16TH-17TH.WE DONT WANT OUR BROTHER S.W. TO BE ALONE WITH THE SOON TO BE 2ND FASTEST MOTOR ONLY SNAKE. REGARDS-NORM K

Yes George, please go to Bowling Green, KY. I'm tired of me putting Norm on the trailer over and over again, it's time for someonelse to do it. Norm and his boy have tried and tried to beat my old 510ci, but now they are going to a 542ci. and are going to try again. I might just take my wife's new Viper and let her car do it this time...

SW