Rev Limiter ???

[Xtremeracing]

I was just wondering how hard it is on motor to be on the rev limiter?. Would only be for a second or so.
I have an MSD HEI with built in rev limiter that I have been running for years. I got it because I had trouble throwing driveshafts and got so when or if this happened as a safety precaution so wouldnt turn motor 10 grand and blow it when lost drive shaft.

I am thinking of changing gears so have more coming off, but dont want to turn this motor as hard at end of straight aways

[dylchris]

The "chip" type MSD rev limiters do not protect on a free unloaded rev. If you spit the diriveshaft, it will over rev anyway. I am not sure if it will be the same with the HEI type. Someone else may know but the limiter is electrical so it will only limit under power and if the engine is unloaded and overrevved, I am thinking it will free turn past the limiter.

[dirttrackrocker]

The "chip" type MSD rev limiters do not protect on a free unloaded rev. If you spit the diriveshaft, it will over rev anyway. I am not sure if it will be the same with the HEI type. Someone else may know but the limiter is electrical so it will only limit under power and if the engine is unloaded and overrevved, I am thinking it will free turn past the limiter.

Then why does it work when I put a 3000 chip in it and rev it to check to make sure it is working??

To answer the original question, I don't think it will be a problem. I hear crate guys leaning on the chip at the end of the straight quite a bit.

[rubbinsracin]

The "chip" type MSD rev limiters do not protect on a free unloaded rev. If you spit the diriveshaft, it will over rev anyway. I am not sure if it will be the same with the HEI type. Someone else may know but the limiter is electrical so it will only limit under power and if the engine is unloaded and overrevved, I am thinking it will free turn past the limiter.

im going to go with dirttrackrocker on this one and say you are fine. the rev limiter has nothing to do with if you are under load or not. it will stop at wherever you put the limit at. most boxes are within 150rpm give or take where you set the limiter at from what we have found. we had a previous box that with at 6500 chip would let us go to 6600ish, but the new box we have only goes to just shy of our 6500 chip. i guess there are some people out there that can open up the MSD boxes and "tighten up" the variation to get it so it gets you right to the chip you have in and maybe just a hair more but we have never done it. we just go with the luck of the MSD draw lol.

[dylchris]

this was our experience; under load the engine was pulling and within a 100 or so rpm;s of the limiteer, it would cut the electrical circuit. We stripped a set of gears at full throttle one evening, the MSD cut the electrical circuit but the engine overreved past the chip; there is no mechanical brake or anything on these so if you are ramping up and at the highest point, the load is removed while the throttle is still open, I think the engine would have to over rev. IMO; I would love to hear from others, if not then our problem must have been two fold the night we lost the gear?

[rubbinsracin]

it should not do that. there would be less stress on the motor after the driveshaft/load was lost, but the limiter should not have let the ignition go past the set amount of revs.

[ask0329]

on dry slick I might hit the rev limiter going into the corner. More often than not I wont. Last week was super tacky and I hit the limiter about half way down the straights. I'd let off, drop the rpms and get on it again. (yes this sucks for racing I know) The only thing I noticed was that the car ran about 10 degrees hotter than normal banging the chip. 9 times out of 10 the track is dry/slick so I'm not too concerned about it at this point unless a new trend of tackieness developes.

[Egoracing]

Your rotating engine will NOT gain momentum during rotation if something breaks, compression and friction see that it will not happen.

[Team11D]

We run a 6al box with a 8400 chip. We broke the lower shaft in the quick change at full throttle half way down the straight.The engine went way past and i mean way past the chip so it will happen. We ussually run up to and or on the chip all the time. Unfortunately for us a few nights later we pulled a wrist pin out of a piston im sure the over rev contibuted to it .

[stock car driver]

on dry slick I might hit the rev limiter going into the corner. More often than not I wont. Last week was super tacky and I hit the limiter about half way down the straights. I'd let off, drop the rpms and get on it again. (yes this sucks for racing I know) The only thing I noticed was that the car ran about 10 degrees hotter than normal banging the chip. 9 times out of 10 the track is dry/slick so I'm not too concerned about it at this point unless a new trend of tackieness developes.

I always run a little warmer on tacky tracks, the reason is your not breathing the motor letting it rest or re fill with air etc. Your temp has nothing to do with the chip and hitting it on tacky tracks.

[Egoracing]

I've lost the driveshaft and transmision on our drag cars with a playback tach (Not a memory but an MSD tach with a full aftermarket data recorder to show engine RPM, oil pressure, trans temp, oil temp, water temp and air temp and recorded a full 9 second run) and when they broke the rev limiter stopped the engine from killing itself. If you are not getting the proper operation the wiring or something is keeping it from operating properly.

[rubbinsracin]

well we had a driveshaft problem this week guys. had the u-joint fail coming out of the corner and the engine went right up to the limiter and banged the chip for about 2 seconds or so before i figured out what was happening and never went over. if your limiter lets it go past the chip you have in it under any circumstance you have a wiring/chip/something problem.

the chip should kill any further acceleration past whatever chip you have in it. otherwise when they come around each week to check our chip by putting a 3000 chip in our box and revving it in the pits it should continue to go past 3000.....but it doesnt. well one guys did...but he lost his points and money.

[Egoracing]

well we had a driveshaft problem this week guys. had the u-joint fail coming out of the corner and the engine went right up to the limiter and banged the chip for about 2 seconds or so before i figured out what was happening and never went over. if your limiter lets it go past the chip you have in it under any circumstance you have a wiring/chip/something problem.

the chip should kill any further acceleration past whatever chip you have in it. otherwise when they come around each week to check our chip by putting a 3000 chip in our box and revving it in the pits it should continue to go past 3000.....but it doesnt. well one guys did...but he lost his points and money.

A friend bought a car once that DOMINATED and when the new owner got it he only was a 5-8th place at BEST! After about a month the original owner came to the track and came buy and told him once the race starts to flip a switch on the dash marked "cooler" and push the radio button during the race. He did and the car went about 700 RPM over the chip that was sealed into the box. He had it wired to bypass the box with the switch and button. You had to have them both set or it would not go past the limiter.

[rubbinsracin]

A friend bought a car once that DOMINATED and when the new owner got it he only was a 5-8th place at BEST! After about a month the original owner came to the track and came buy and told him once the race starts to flip a switch on the dash marked "cooler" and push the radio button during the race. He did and the car went about 700 RPM over the chip that was sealed into the box. He had it wired to bypass the box with the switch and button. You had to have them both set or it would not go past the limiter.

That would be neat. however, they check our ignition pretty thoroughly so its pretty hard to get away with junk like that.

[charcoal01]

i shot the pinion out the front of a set of gears in the middle of the straight one night, got my foot out of it as soon as i heard the bang. motor never hit the chip (had an incar cam running and could hear everything happening) and reved 2-300 rpm past the chip. ran at a different track two weeks later, was down on power and found two bent push rods and every exhaust valve was bent after the race. talked to my engine builder and he told me its common when the motor has heavy load on it and something like that breaks, the rpms come up so fast that the rev limiter can't catch it in time and the motor can over rev. so it does happen.

to answer the guys original question, if you're driving around the track, full throttle, on the chip the whole way around it might cause some problems. if you're only hitting the chip for a second or so at the end of the straight away, you should be fine.

[dylchris]

I am going to call MSD and ask the question; I do not see how interrupting the ignition circuit will stop the revolutions in motion other than what egoracing said, I have used sevearl of his offerings and they were always spot on. I understand the physics of weight and friction and it makes perfect sense.

Thanks and I will learn from your input.

[Egoracing]

i shot the pinion out the front of a set of gears in the middle of the straight one night, got my foot out of it as soon as i heard the bang. motor never hit the chip (had an incar cam running and could hear everything happening) and reved 2-300 rpm past the chip. ran at a different track two weeks later, was down on power and found two bent push rods and every exhaust valve was bent after the race. talked to my engine builder and he told me its common when the motor has heavy load on it and something like that breaks, the rpms come up so fast that the rev limiter can't catch it in time and the motor can over rev. so it does happen.

to answer the guys original question, if you're driving around the track, full throttle, on the chip the whole way around it might cause some problems. if you're only hitting the chip for a second or so at the end of the straight away, you should be fine.

I would havbe the chip checked. A truck sereis that used them would find differences in chips when they were tested and 2-300 would fit into the 400 rmp window they found. Some were less than labled and some were more.

[mbaker76]

Don’t take for granted that your recall on the tach is correct either. Our tach recall reads about 3-400 rpm faster than the actual peak rpm. I thought we were blowing way past the chip but when I put in a low chip or just simply rev and hold at a given rpm, then hit the recall it always showed faster. I have also heard it the other way, the tach is slow and recall will be lower than the chip. Might be something to check.....

[cheaterleaddog]

A friend bought a car once that DOMINATED and when the new owner got it he only was a 5-8th place at BEST! After about a month the original owner came to the track and came buy and told him once the race starts to flip a switch on the dash marked "cooler" and push the radio button during the race. He did and the car went about 700 RPM over the chip that was sealed into the box. He had it wired to bypass the box with the switch and button. You had to have them both set or it would not go past the limiter.

I have the capabilities to do things like this for as little as $100.00 for more money can make it remote control from pits.

[ep33510]

Xtremeracing

The HEI module rev limiter should cut things out if its loaded or unloaded. I have seen the MSD boxes with the Chips have their sockets loosen up and add resistance to the soft touch circuit. That added resistance will cause the limit to be moved Up or allow the box to free wheel if one side the chip does not make contact.

Yes, the MSD boxes can be Blueprinted to eliminate the common 150 rpm low issue with the chips. We have three versions ( 1% rule, 400rpm, Racer choice) depending what direction you would like to go. If you questions please feel free to contact me.