6800 vs 7100 rev limit

[mwood]

I'm about to order a rev limiting rotor for my Bosch points type distibutor. 6800 rpm or 7100 rpm?

Thoughts?

Thanks

[Purple Frog]

I think you should tell us what engine you have...

[Pop Chevy]

Depends how long you want your engine to last and how it's built. And you didn't even say what it is.

[Don Elzinga]

I assume this is for a Kent motor. Now that we have lightened flywheels I run a 7k limit, but I rarely hit it. I tend to shift by around 6800. I never had any luck with the centrifugal rotors. After a couple months, the engine started breaking up at higher RPM and load (but well below the set point). Swapping the plain rotor back in cured it. I now run a Pertronix rev limiter box.

Don

[mwood]

Yes, Kent motor...sorry, no information makes it hard to help.

edit: Pertronix on amazon.com was $125 w/free shipping, so that's what I bought. Heck, cost wise, that's like three of those rotors vs a permanent solution, right?

[mwizard]

Yes, Kent motor...sorry, no information makes it hard to help.

edit: Pertronix on amazon.com was $125 w/free shipping, so that's what I bought. Heck, cost wise, that's like three of those rotors vs a permanent solution, right?

I have the Pertronix unit. 6800 is the standard for Kent motor unless you have s SCAT crank and a good build.
Mark

[Modo]

with 4 forward gears you may want to stay in gear and overrev for a second instead of cutting out, also if you go to a higher gear just to accomodate your engine limiter, u may lose pickup and there they go, bye bye, call it lug city .....anyway just a consideration

second round - these guys will tell you the Kent flattens out between 6800 and 6900 so it has it's own rev limiter, then for missed shifts would set it high for save, 7300 at least.....

[KevinFirlein]

no rev limiters period. A good driver wont need it and I dont want aything on my car limiting what I can do with it. I can read a tach and I am a bog boy. I know what it means to run to 7200 but there may be a point on a course, particualry autocross, where running higher RPM is faster then shifting then having to come back down.

Having said that I did run them on my rental cars when I rented CF and FA

[Jim Garry]

I can read a tach ...

There are no opportunities to read a tach during an autocross run other than before starting and after finishing.

[rickb99]

no rev limiters period. A good driver wont need it and I dont want aything on my car limiting what I can do with it....

I understand what you're saying BUT, every machine has its 'maximum limit' of operation. Considering the vast experience with the Pinto engine as we have them tuned in FC, 6,800 to 7,100 is pretty close to the maximum able to survive point.

If you know how to change gears in the MK8/9 then you shouldn't be running out of RPM's any place critical on the track. We used both an MSD limiter and an IVEY Reve limiting rotor. Both worked fine.

Last summer, a friend of ours missed an up shift. The engine hit about 8,000 RPM and broke a cam follower. I saw him in the paddock and somebody was helping him replace it (almost done). I ALMOST said to him "gosh Steve, you should let Ivey take a look at that before running it again", but, I didn't. Next session out, second lap, the number 3 rod came out the side of the block.

[Charles Warner]

Listen to Kevin. You can learn to shift by sound and be within 50 rpm every time. Save your money and the addition of one ( or more) thing to break and ruin your day. Besides, a rev limiter will not do any good on a missed shift.

[mwood]

Thanks for the comments, gives me more to consider, for sure. I'm still thinking, for autocross, the idea of a soft limiter makes sense. I know with my former cars, being able to hang right at peak rpm for an extra second or two without concern for damaging internals was helpful at times. If I was road racing, I'd still shift by ear and feel.

[Neil_Roberts]

Last summer, a friend of ours missed an up shift. The engine hit about 8,000 RPM ... the number 3 rod came out the side of the block.

Been there and done that as well, with no rev limiter. It sounded like "Gzzzzrk", then it got real quiet so I could hear the locked rear tires sliding through the grass.

Whatever you do, don't put an adjustable rev limiter within reach of the driver. Human nature leads to holes in the block.

As far back as the early '90s, Ilmor's Indycar engines had an intelligent rev limiter. If the limit was being approached rapidly, as in a missed shift or curb hopping, the limiter would start dropping cylinders about 2500 RPM lower than the set value. If the rev limit was being approached very slowly, as in the end of a straight in top gear, you could get to within 10 RPM of the limit and nothing would happen. The other clever thing that it did was drop only as many cylinders as neccessary, working backward through the firing order. Doing that distributed the unload equally among all of the cylinders.

For a brief moment in 1992, we got to play with traction control. That was implemented by active control of the rev limiter set value. Tuning it was great fun for the engineers, but it was banned at the end of the season.

[Barry Ott]

Personally, I always ran a rev limiter on my Kent powered autocrosser. There's plenty of times when I accelerated through the gears that I didn't need it. I almost never touched it in 1st, and I never touched it at a situation where I knew I was going to use third. But, there are lots of times, lots and lots of times, when I was at the top of second gear, and *busy*, where a limiter was essential to keep me from reving a little too high. I usually ran my MSD with a 6800 pill. Every now and then, after a run or two, I knew I'd be on the limiter for a relatively long time, but shifting wasn't prudent, so I'd put in my 7k pill, just to get a *little* more. I never had any problems with my MSD soft touch limiter.

Best of luck!
Barry

[Dick R.]

Track racers please keep in mind that every event is a new "track" for autocrossers and we have no practice and no time before or between runs to optimize gearing after we walk the course to learn it visually. As a result we frequently either end up short shifting (by ear), lifting, over revving, or "sitting" on a rev limiter for a few car lengths. Even a Kent engine revs rather quickly in a 60 or 80 mph gear near redline. A soft cut rev limiter is "probably" better than a rotor type for "sitting" on the limiter afaik.

Edit to add: Ditto to what Barry posted!!!

Dick
CM 85

[TedV]

Mine has an MSD with a 6800 pill in it.

at 60- 70 mph a Kent will keep pulling the car till it goes POP! BANG! PUKE!
I don't have the $$$$ for that. Do you?

[mwizard]

There are no opportunities to read a tach during an autocross run other than before starting and after finishing.

+1
Us autocrossers have the gear ratios closer together, so less chance of falling below the power band.
Mark

[ahowe]

I ran 6800 all year except at Lincoln on the East Course where I wanted a little extra in one spot on the course. Then I set it for 7200... and didn't hit it (would have hit a 6800 limit).

My point is, most of the time there is no reason for more than 6800. But once in a while, when it really counts, you'll want a little more.

Andy

[bill gillespie]

Listen to Kevin. You can learn to shift by sound and be within 50 rpm every time. Save your money and the addition of one ( or more) thing to break and ruin your day. Besides, a rev limiter will not do any good on a missed shift.

Ummmmm, sorry Charlie,

I'll have to raise the BS flag on that. The adjustable rev limit options with the Motec series ECU's are definitely able to cope with a missed upshift.......you just don't want to stay on the limiter, and nothing will cope with a downshift at too high of a road speed.

Regards,
Bill

[Charles Warner]

Maybe the new fancy-pants versions will stop a missed upshift from zinging the motor . . . none of the ones I've seen were that quick.

[DougW]

Bringing this thread back up from the dead. I am deciding between the Microdynamics RL-3 and the MSD soft touch rev limiters for my Kent powered Formula Ford. I have a Bosch distributer and Pertronix ignition.

It appears that they serve the same function in the same way. The MSD uses plug in modules to control the rpm and is cheaper. The RL-3 varies the rev limit with an adjuster.

Anybody know a reason to pick one or the other?

For RL-3 users how easy is it to get the rpm adjusted?

For MSD users I assume right part number is MSD -8728 (for use with OEM/non CD ignition).

Happy New Year everybody.

[DanW]

Bringing this thread back up from the dead. I am deciding between the Microdynamics RL-3 and the MSD soft touch rev limiters for my Kent powered Formula Ford. I have a Bosch distributer and Pertronix ignition.

It appears that they serve the same function in the same way. The MSD uses plug in modules to control the rpm and is cheaper. The RL-3 varies the rev limit with an adjuster.

Anybody know a reason to pick one or the other?

For RL-3 users how easy is it to get the rpm adjusted?

For MSD users I assume right part number is MSD -8728 (for use with OEM/non CD ignition).

Happy New Year everybody.

I used the MSD for 1-1/2 weekends. It failed during qualifying for the second race of the weekend. Ignition started to cut out at 5000 rpm. Pulling the module did not help, so I lifted the ground and removed the wire from the coil. That solved the problem. Rev limiter came out and went in the trash the following week.

I still have a complete set of modules from 6000 to 7000. Yours if you want them.

Neither device will save you from a mechanical over-rev, such as a mis-selected downshift. As Neil Roberts would say "If its not on the car, it can't break."

Regards,
Dan Wise

[reidhazelton]

I used the MSD for 1-1/2 weekends. It failed during qualifying for the second race of the weekend. Ignition started to cut out at 5000 rpm. Pulling the module did not help, so I lifted the ground and removed the wire from the coil. That solved the problem. Rev limiter came out and went in the trash the following week.

I still have a complete set of modules from 6000 to 7000. Yours if you want them.

Neither device will save you from a mechanical over-rev, such as a mis-selected downshift. As Neil Roberts would say "If its not on the car, it can't break."

Regards,
Dan Wise

I had the exact same issue with it failing, mine just lasted about 5 weekends.

I would rather go with a rev limiting rotor and change it regularly and put a standard one in for a race.

[Dick R.]

For RL-3 users how easy is it to get the rpm adjusted?

Doug, Assuming you mean the DRL-3 that Pegasus sells, adjusting the rev limit is EASY. Just hold the button while reving the engine to one half the desired revs. Then release the button. As I recall there is a light to indicate status.

I used the MSD limiter for many years and was one of the apparently lucky users since it did not fail. I also had their selector switch with a 6.0 to 8.2K range . I covered the switch knob to minimize the setting being changed "by accident".

http://www.msdignition.com/Products/...6_0K-8_2K.aspx

I changed to the DRL-3 in 2011 to save space under the engine cover and because I was concerned that my good luck with the MSD was about to run out.

Be sure to protect the units and wiring from excessive heat.

I use quick connects at the coil terminals so that it is very easy to disconnect the rev limiter if the car isn't running properly. Unfortunately at Nationals this year the rev limiter wasn't the problem . . . (plugged primary main jet).

Dick

[chrisw52]

Doug, Assuming you mean the DRL-3 that Pegasus sells, adjusting the rev limit is EASY. Just hold the button while reving the engine to one half the desired revs. Then release the button. As I recall there is a light to indicate status.

I used the MSD limiter for many years and was one of the apparently lucky users since it did not fail. I also had their selector switch with a 6.0 to 8.2K range . I covered the switch knob to minimize the setting being changed "by accident".

http://www.msdignition.com/Products/...6_0K-8_2K.aspx

I changed to the DRL-3 in 2011 to save space under the engine cover and because I was concerned that my good luck with the MSD was about to run out.

Be sure to protect the units and wiring from excessive heat.

I use quick connects at the coil terminals so that it is very easy to disconnect the rev limiter if the car isn't running properly. Unfortunately at Nationals this year the rev limiter wasn't the problem . . . (plugged primary main jet).

Dick

I have DRL-3 installed in my car. It works pretty good, easy to setup. It also has a clutch switch that you can hook up for rudimentary launch control which could help.

[stephen wilson]

Ditto what Dick said, But I put my disconnect in the dash, so I can disconnect it while driving. My next version will probably have a toggle switch bypass in the dash. I've run the DRL-3 for several seasons with no issues.

[Jerry Kehoe]

I would learn to read the tach, much cheaper & teaches discipline!

[Dick R.]

I would learn to read the tach, much cheaper & teaches discipline!

Have you ever autocrossed a FF?

Dick

[Jerry Kehoe]

Have ever driven a FA or F1 car? Have you got your answer?

[chrisw52]

I would learn to read the tach, much cheaper & teaches discipline!

Jerry, during a typical autox run, you might have a slight chance to quickly scan the gauges once during your run.

listening to the engine speed is easier than reading the tach while auto crossing. Until I am familar with how these kent engines sound at 7000 rpm, I will leave the DRL-3 installed. I will most likely leave it in anyway as an extra measure of safety. It is far to easy to over-rev the engine while autocrossing.

[Neil_Roberts]

Have ever driven a FA or F1 car? Have you got your answer?

Have you ever missed a shift?

[Dick R.]

Have ever driven a FA or F1 car? Have you got your answer?

No.

Happy New Year!

[mwizard]

I have over a year of experience autocrossing my FF. I found that my Stacks dash has a shift light. I hooked it up and left it set for 6500. I seldom see it go on as I shift to 2nd soon after starting. I may have seen the shift light in 2nd once on my way to 60mph max. I have shifted to 3rd on occasion(Mike Wood shifts a lot more than I do) and back to 2nd. All this as my power band is 80% at 4200 and maxes out at 5720 on way to 85% at 6800. This is a broad power band to play with so I think I don't need to worry about getting near redline very often, 3rd gear more often would work well to avoid any need for a rev limiter.
IMHO of course.
Mark

[Jerry Kehoe]

Everyone has but you are dreaming if you think a full throttle missed shift is saved by a rev limiter which is why most people level the foot when making a shift. I'd worry more about downshifting which is controlled by the mechanical and therefore you could have the worlds most expensive rev limiter and it won't do you a damn bit of good if the wheels are turning the motor faster. By the way in 35 plus sucessful years with pretty high revving motors I have never poppped one with an over rev from a shift, and by the way I have won more than my share!

[DougW]

Thanks for the advice everyone. I think Barry O. said it best (for me). At the top of second gear when things are very busy, I want the extra safety net if I stay in the throttle and don't shift to third.

On a recent course I upshifted early into third vs winding it up in second and holding it in just a few places. The clock said leaving it in second was better, way better. No time to read the tach while looking through a series of transients. The shift light is easy to spot when my eyes are forward....but I am not always looking forward. After the event the data logger showed I was shifting or lifting and at 6400 to 6500 rpm. Nicely done but frankly I was slower while worrying about rev limit as opposed to trying to see far enough ahead. There may come a day when I am so in tune with the car that I wont need the rev limiter. But...

When autocrossing, sometimes my bucket is just full. Too much going on, and I don't completely trust myself (or my various codrivers) to lift rather than stay in it when the red mist descends and a trophy is on the line.

Anyway, I appreciate all the advice and the vast experience here at Apexspeed. I wish each of you a happy, and prosperous New Year. May it be filled with victory.

[PCalhoun]

Doug,
I previously used both an MSD and Pertronix rev limiters in the car. MSD soft-touch I never had any issue w/ in my old Reynard and it lasted for a while in the DB-1, the Pertonix wouldn't make it through two w/e. They would vibrate apart inside upon post failure inspection at Pertronix.

The DB-1 engine bay just seems very suspect to heat and vibration and making one of them live. Though I always liked having the safety net of them when they operated properly.

[Neil_Roberts]

I got a glimpse of the future while driving a VW Polo. Instead of an ignition cut rev limiter, the Polo just rolled the drive-by-wire throttle closed at its redline. It was very smooth, and a nice surprise.

[Dick R.]

The DB-1 engine bay just seems very suspect to heat and vibration and making one of them live. Though I always liked having the safety net of them when they operated properly.

Doug,

Since the DRL3 is so small you will have far more options for "less hot" mounting locations than with the "huge" MSD unit. Maybe even outside the engine compartment (with rain protection in mind, of course).

Also, its small size and low weight make "soft mounting" easy.

Dick

[stephen wilson]

Yeah, I mounted mine on the dash with rubber mounts.

[mwood]

As an update, the Pertronix I bought off Amazon still works fine, after a year. I mounted to the bulkhead, but interior, not engine bay, side.

Now that I'm used to the shifting required on my 4 gear autocross set up it is less important, but once in awhile having it to bounce off of comes in handy.