Safe rev limit??

[CliffBeer]

Wondering what may be a relatively safe rev limit to set the MSD rev limiter on my CAV. The engine is a well built crate 302 with roller cam and lifters (std rockers), mild cam, aluminum ford racing X40 heads (standard springs and retainers and push rods I believe).

Engine has 3,500 miles on it and has been nicely broken in.

The limiter is presently set at 5,500 rpm and I'm wondering if 6,000 is pushing it too far.... Any thoughts? Thanks.

 

[Ross Nicol]

My old motor was similar to what you've got. I rev limited it to 6700 and changed gear at 6500 but the torque was gone a lot earlier than that. I did bend the valves with valve float or bounce which probably happened during missed gear over revving. I reckon 6000 would be fine as long as your motor is well balanced.
Ross

 

[Jac Mac]

If you still have std springs, rockers, retainers etc, I would stick with the 5500 limit,
Comp Cams suggest an upper limit of 5600 for cams up to .550" valve lift & 275 Deg duration.

Jac Mac

 

[Ross Nicol]

yes I did have Yella Terra roller rockers in my old motor so the 5500 is probably the limit for standard rockers. I think the X303 heads valve springs only have a seat pressure of 100lb too, so valve float is possible if you take the revs too high. I did well to only have 4 bent valves in 3 years of racing that motor.
Ross

 

[Ron Earp]

If it is a crate 302 with one of the Ford Alphabet cams (E or B I'd bet) then I'd think 5500 RPM would be all she'd want. A trip to the Dynojet would show you for sure where the best place was to shift, and give you an idea of what sort of actual power you're putting down while allowing for some tweaking and tuning.

Ditto Ross's thoughts on springs. The ones I had on some FMS heads were not high quality pieces with vastly different seat pressures. They were hard pressed to make 55-5600. Ross, you did well to have only bent three on that motor if you were using the FMS springs with those heads!!!!!!

R

 

[JCoop]

Cliff, I think I have the same motor as you except for the Webers I put on. I have set the rev limiter to 6000 but rarely go there. I shift at 3800 in street driving and 5000 on spirited jaunts.

 

[DBLDREW]

Set your rev limiter a few hundred rpm past where you normally will shift. If you are shifting at 5500 then set it at 6000. You don’t want to be hitting your rev limiter during normal driving (when I say normal I mean racing). The rev limiter is there to protect your engine from over reving due to a missed shift broken parts etc.. I bet the springs on the x40 heads would be safe past 7000 with out floating the valves so setting it at 6000 or even 6500 would be fine. I have a 351W with a stock bottom end and have my msd set at 7000 and have hit that a few times (oops) with no problems, so a 302 will have no problems reving to 6000-6500 with out damaging the motor.

 

[Ron Earp]

Be careful with your rev limit.

The stock springs in GT40X heads are not that strong, and, you are running a hydraulic roller I assume. If you make a habit of visiting 7000 RPM, or even 6500 RPM, you will probably get some float and some bent valves. Experienced it first hand with the FMS heads and being aggressive on the RPM. Mine required a lot of shimming to get right and varied out of the box a huge amount. In the end they were discarded, same with the AFR stock springs when we went for a 7400-7500 RPM limit.

Both FMS crate engines with the X heads used either the E or B alphabet cam. Both cams are under 0.500" lift with the B being slightly more aggressive with around 4 degrees more duration, something like 224 at 0.050". Neither want anything over 6000 RPM and are signed off before then. While the rest of the motor might be up to high RPM, a hydraulic cam and those springs won't be. You might zing it there a lot of times with no damage, but revving it there for sustained RPM probably won't work out too well.

Besides, I think a trip to the dyno is going to show you that revving that high will largely be counter-productive for power production. It will be useful if racing the car and you need to delay a shift where an additional shift would cost time, but other than that I don't think you'll see any value. If you want another opinion call Ford Racing Parts hotline on 586-468-1356 for the lowdown in the heads and cam, they'll steer you right.

 

[Russ Noble]

Set your rev limiter a few hundred rpm past where you normally will shift. If you are shifting at 5500 then set it at 6000. You don’t want to be hitting your rev limiter during normal driving (when I say normal I mean racing). The rev limiter is there to protect your engine from over reving due to a missed shift broken parts etc.

Well, you learn something new every day. I thought it's primary purpose was to protect an expensive motor from a red misted driver!!

Cheers

 

[Jac Mac]

6000 RPM or LESS

Cliff,
I am going to repeat what I have told you already, "" KEEP YOUR RPM below 6000 "" with the combo you have at present.

There are 3 basic reasons for this:

The FORD roller hydraulic lifter is a fairly heavy item and when revved high with a marginal strength valve spring the risk of lifter pump up and further damage to the valve train is just waiting to happen. Given the chance with cold oil, a 'spit back' thru the carb, and this will happen even at low RPM.

The Ford Rocker arm with its pedastal type mount is not very tolerant of extra valve lift & if you do happen to pump up a lifter the rocker may bind on the pedastal and break the whole assy .

While high RPM sounds nice I think you will find the car is faster if you effectively ' short shift' @ 5500 and use the torque rather than the HP. Also you have been attempting to diagnose 'shaking' and other vibration issues. I would suggest that you get to the bottom of these problems before finding your upper rev limit by trial & error.

I have lost count of the number of motors that people have ruined by doing "1" more lap to see if the problem has solved itself.!!

Cheers
Jac mac

 

[Jac Mac]

Rev Limiters

This is the penalty I pay for being a slow typist.

"Dbldrew" is correct in regard to setting the Rev Limiter a few RPM above your normal shift point.

Another hint for those of you who think its OK to cruise down the Straightaway or Highway in top gear with RPM pegged by the rev limiter. ""DONT"".

With most limiters of the ' soft touch' type cut out either 2,4,or 6 cylinders at which time the air/fuel mix in those cyls is not ignited. This mix now gets pumped into your exhaust system where it will either burn off or cause an explosion in the muffler setup. It shouldnt take much to imagine what this does to the normal scavenge/extraction events that your engine builder spent lots of your $$$$$$ developing!!

Jac Mac

 

[Howard Jones]

I have learned to listen to Jac Mac. I also have a SVO X head B cam motor. It will run up to 6K but makes most go at 5500. Set shift light at 5500, put 6K chip in 6AL. Ford builds these motors for hot rods. Hot rods cruise up and down the road nice and easy with the A/C on. These motors are balanced by ford just like the 5.0 motors they put in mustangs and are not intended to be run up to 6K lap after lap .

My advice is to disassemble and rebalance the rotating assembly. If you want to push the power range up beyond 6K you will need to change the cam and upgrade the valve train. Comp cams makes a nice kit for this. If I did it I would go to studs instead of the pedestal mounts and a set of the steel roller tip rockers.

5500 is a good street motor and a nice torquey track day motor. I am guessing that mine is making about 350HP or so and is plenty for me. Any more would just spin the tires anyway without a LSD.

The real track day upgrade is another set of wheels and slicks along with a LSD in the gearbox. These together are worth a 100HP as far as lap times go.

 

[CliffBeer]

Thank you all. Very good information, and, obviously, some folks are speaking from experience....painfull and expensive experience!

I do agree that torque is probably dropping off past 5,500 (I'm not sure where peak hp is made) so there's not much point going past 5,500, particularly if valves are almost floating. The engine sounds good at 5,500 and seems to rev very, very smoothly so I was suspecting that 6,000 might not be too unreasonable. The shaking anomalies I've had recently are fore/aft due to worn engine/transaxle mounts rather than related to rotational imbalance (engine seems pretty well balanced).

Unfortunately, i don't know if the lifters are hydraulic or not.

I plan on installing roller rockers pretty soon and will have a look at the springs at that time - will leave the limiter at 5,500 for now! Thank you!

 

[DBLDREW]

Be careful with your rev limit.

The stock springs in GT40X heads are not that strong,

Well if my memory serves me right (and it usually doesn’t) the stock valves for the 5.0 out of the mustang had a seat pressure of 90lb. With that spring the redline was at 6000rpm and valve float would occur around ~6300. So if we compare that to what ford sells as the aftermarket for the gt40 heads there are 2 options. There is a single spring that has a seat pressure of 110lbs and open its 240lbs. And there is the dual spring that has a seat pressure of 135lbs and an open pressure at 395lbs.

Now I believe that the gt40x heads come with the better dual springs, but even if they don’t the singles are still better then a stock spring so it just doesn’t make sense that with better aftermarket springs you will perform worse then stock.

Cliff,
I am going to repeat what I have told you already, "" KEEP YOUR RPM below 6000 "" with the combo you have at present.

There are 3 basic reasons for this:

The FORD roller hydraulic lifter is a fairly heavy item and when revved high with a marginal strength valve spring the risk of lifter pump up and further damage to the valve train is just waiting to happen.

I disagree. There is no reason that he could not at least get the same performance as the 5.0 mustang that ran weaker springs.

Again I’m going to use my combo as my basis for comparison. I run a 351W that I converted to run a hydraulic roller cam (small base circle cam, and taped the block for the tray) I use standard ford oem hydraulic lifters and I typically will shift around 6500 and have my rev limiter set at 7000. Ive had no problems with this combo and it has been running strong for over 15 years.

 

[Jac Mac]

DBLDREW,

While Cliff may well be able to attain the RPM you suggest, until he is absolutely sure of which components he has in his motor and tests his actual valve spring seat/open pressure's it would be unwise to try to reach these RPM.
In his last post(#13) he indicated that he is unsure as to whether he has hyd or solid lifters, while in post(#1) he indicates a 'mild' roller cam/lifters with std rockers,springs,pushrods.
I am not doubting your components in your own motor or the RPM etc that you claim to be attaining, but in Cliff's case where none of us are absolutely sure of the exact spec's it is prudent to take a conservative approach.

cheers
Jac Mac

 

[Graham Inchley]

289 Rev's?

I have a 289 to play with. Are the above points applicable or can I rev it on a bit more due to the shorter stroke? What I am trying to say is; is it the valve train that causes problems much above 6K - generally? By default I have acquired an Edelbrock 7122 Cam that "has good power 1500 - 6500". The standard crank looks good and would like to know the minimum valve spring rate I can use. Also, can I get away with standard rockers for predominantly road use? The bottom line is minising £'s spent on the engine to spend on chassis and handling aspects.

 

[Ron Earp]

There is a single spring that has a seat pressure of 110lbs and open its 240lbs. And there is the dual spring that has a seat pressure of 135lbs and an open pressure at 395lbs.
still better then a stock spring so it just doesn’t make sense that with better aftermarket springs you will perform worse then stock.

My X heads had single springs, and, they were not measured to be at their quoted value, which is what I was trying to convey. From what I understand many other users had similar problems and folks didn't consider them worth having. My Y heads, the first set, were similar to the X's but I had them on a stock cam 5L and never tried to get past 6k as there was no point with the cam. I don't know what Cliff has in his but I think observing a limit a lot less than 7000 RPM is prudent.

Cliff do you have more info on the motor? The Ford crate motor with X heads has either the E or B cam and neither want to see more than 6k. According to FMS you've got roller rockers, aluminum ones, and, naturally, hydraluic lifters probably the stock heavy ones that FMS sells as standard replacement. At any rate, while you might get away with some blasts to 6500-7000RPM, you don't want to spend a lot of time there.

If you want to build it for some revs swap your cam for one that wants some RPM, upgrade the valve train - springs, rockers (have a look at Jesel systems and others), and make sure your intake is up to the job as well. Spend some green and you can build a motor that will out rev your Ferrari motors as covered on some other threads.

Ron

 

[Lynn Larsen]

Ron is spot on. You have to look at your engine as system with various subsystems. Just because the bottom end may be capable of spinning at 7K without flying apart, it by no means says that your hyd. rollers, rockers, springs and intake will allow it to achieve this RPM. Hyd. roller lifters/cams are meant to give virtually maintenance free, torquey performance up to about 6200 RPM and that is it. Low ETs or top speed is achieved through proper gear ratios. You can put stonger springs on the valves and maybe gain a few hundred RPM, but there is a finite limit to the spring rates as the hydraulics will fall on their faces and not be able to compress the spring. The valve float that accompanies higher RPM levels will eventuall allow the piston tops to contact the valves, especially, with higher compression ratios.

If you want reliable RPMs in the range from 7K upto Nascar revs, you have to design the whole system for it:

1) Bottom end that will hold together: shorter stroke (lower moment of inertia through reduced arm and piston velocities), lighter rotating mass (lower moment of inertia through less weight), stronger compents to be able to constrain the moment of inertia achieved, balanced assembly that minimizes not only static balance but also as many levels of harmonics as possible.

2. Valve train components that are as light as possible, to minimze inertia and are, at the same time, strong enough to minimize or eliminate distortion in any of the components and to withstand the stress imposed by springs which are strong enough to arrest the interia of the system and maintain fidelity between a properly designed cam profile and the valve faces. (Everyone usually gets this in terms of the rocker assemblies, but often forget about the lifters-- the crower high pressure pin oiling solid rollers are the best at this-- unless something equal or better has come out in the last year that I have missed.)

3. Induction that will allow proper flow at the elevated RPMs to maintain high enough power that, when transmitted through the power train, the net will equal or exceed the drag. This will generally mean a trade off in where the power is in the RPM band: unless variable valve timing and/or variable runner lengths are employed, tuning for high end power usually comes at the expense of low end power. Where you want peak torque is a philosophical question and one of personal tastes.

4. However, when powertrain components provide a constraint: availability of various gear ratios wether in the transmission or final drive, maximum torque handling or others, one cannot ignore this and may have to make some hard choices that may not coincide with his/her personal preferences.

5. An area ofter overlooked is: once 1-4 have been designed in a balanced manner, one must look at the projected speeds for the vehicle and ask if that vehicle is capable of those speeds based on chassis strength, suspension design AND aerodynamics.

6. Lastly, nearly everyone of us must calculate the cost of performing steps 1-5 in such a way to achieve the desired out come. This must be done realistically and without letting one's wishful thinking overload his/her mortal ass! To ofter, the end result of making this kind of error in judgement is catastrophic and tragic.

I don't mean to be a buzz kill, but as someone said when refering to the recent and unfortunate demise of Peter Brock, motorsports is inheritantly dangerous; and, about the time you think you have is sussed, it wll jump up and bite you in the bum.

Regards,
Lynn

 

[DBLDREW]

DBLDREW,

While Cliff may well be able to attain the RPM you suggest, until he is absolutely sure of which components he has in his motor and tests his actual valve spring seat/open pressure's it would be unwise to try to reach these RPM.
In his last post(#13) he indicated that he is unsure as to whether he has hyd or solid lifters, while in post(#1) he indicates a 'mild' roller cam/lifters with std rockers,springs,pushrods.
I am not doubting your components in your own motor or the RPM etc that you claim to be attaining, but in Cliff's case where none of us are absolutely sure of the exact spec's it is prudent to take a conservative approach.

cheers
Jac Mac

Again there is nothing wrong with taking a conservative approach. But we have to apply a little common sense to his problem as well. I just think you guys are being a little too cautious.

Look at it this way. How many 5.0 mustangs were built? They all can rev past 6000 rpm. So it just seem a little odd that you guys think that with aftermarket parts and better springs then stock, that he will not be able to rev it as high. That just seems illogical.

My guess with those heads they probably wont provide the flow to make power past 6000rpm anyway. So my suggestion is pull off the valve cover and check the springs. If they are dual springs there would be no problem setting the rev limiter at 6500- 7000rpm if it is the single spring then set it at 6200 rpm. Most likely you will be shifting between 5500-6000 anyway…

 

[CliffBeer]

My X heads had single springs, and, they were not measured to be at their quoted value, which is what I was trying to convey. From what I understand many other users had similar problems and folks didn't consider them worth having. My Y heads, the first set, were similar to the X's but I had them on a stock cam 5L and never tried to get past 6k as there was no point with the cam. I don't know what Cliff has in his but I think observing a limit a lot less than 7000 RPM is prudent.

Cliff do you have more info on the motor? The Ford crate motor with X heads has either the E or B cam and neither want to see more than 6k. According to FMS you've got roller rockers, aluminum ones, and, naturally, hydraluic lifters probably the stock heavy ones that FMS sells as standard replacement. At any rate, while you might get away with some blasts to 6500-7000RPM, you don't want to spend a lot of time there.

If you want to build it for some revs swap your cam for one that wants some RPM, upgrade the valve train - springs, rockers (have a look at Jesel systems and others), and make sure your intake is up to the job as well. Spend some green and you can build a motor that will out rev your Ferrari motors as covered on some other threads.

Ron

Ron, I think you've got some good solid advice here. As you say, until I have a real clue as to what the cam and lifters and springs are comprised of then going all out on the rpm isn't prudent. On the other hand, the devil in me says "what the hell, these aren't expensive engines" but then destroying perfectly good running machinery isn't something to be proud of in my book.

Ultimately, I'll be moving towards a stroker with webers built on an aluminum block with some really good heads and valve train - going to be a longer term project with current time constrainst (prego wife, moving house, new job). And, yeah, it might rev up like the ferrari but oh boy that Italian exhaust note is going to be tough to top. One thing I'll say is that mucking around with GT40 stuff is a lot more fun than is had with the Modena crowd...mainly because it's simple, less expensive and the forum compadres are way more into really doing something with their cars instead of wine tours and discussing who makes the best wax/polish, etc.

So, for now I'll be keeping her under 5,500.....

Thanks!