PDA

View Full Version : Taking rpm limiter up to 7000rpms?


Josh Q
05-08-2004, 11:11 AM
I was thinking about how the aftermarket chips take the limiter up to 6900rpms. Could I have JC make a chip that took the limiter up to 7000rpms and still be safe? I don't see why not, it's only an extra 100 rpms on top of the usual raised limiter. And I would like my car to be able to go all the way to the end of the tach. I know that the M20 powerband drops off past 6700rpms but I have had times where I could have beat the sh*t out of someone if I had been able to go all the way up to 7k. What do you guys think. And Donkey is banned from posting on my posts from now on since I'm trying to get ahead of him! 8) j/k

bimmerjim®
05-08-2004, 11:44 AM
well, i dont mean to sound like a jerk, but its realy not going to do you any good to shift later. and even though its 100 rpm higher, its still 100 rpm higher. knowwhatimean?

the thing is, the m20's powerband starts to drop off at bout 5800 rpm. for the best acceleration you want to stay in your highest average tq and hp band. so, you would need to dyno your car and get a printout of the hp and tq numpers per each rpm, then sti down with a calculator and figure an average power curve. (tq+hp) then compare that with the rpm drop when shifting gears. probibly you will find that your average is lower when shifting at high rpm's vs shifting at about 6300 rpm.

Josh Q
05-08-2004, 12:10 PM
No you don't sound like a jerk. But there are times where having the lmiter raised will do you good. Like when you don't have enough time to shift before you hit the next corner, it's better to just be able to maintain the current speed and go higher in the rpms. That type of situatioin is what I'm looking at.

bimmerjim®
05-08-2004, 12:26 PM
ahhhhhhhh!! ic. okay, i have this problem of only thinking in strait lines :D

yeah, good point. my solution however would be to get longer gears... *cough* :smt077

Josh Q
05-08-2004, 12:31 PM
You mean put custom gearing in the tranny? That would cost a lot more wouldn't it? And a lot more time? And I like my gearing (except 1st which I wish was twice as long).

bimmerjim®
05-08-2004, 01:03 PM
well, no not tranny, but the diff. and yeah.. more expensive than a chip maybe.. it depends on where you find one. i traded mine so it didnt cost me a thing. but... IMO better. and this is my reasoning: becasue a longer gear box will kepp the rpms lower wheile cruzing, get beter gas milage, less ware and tare because the rpms are lower. i realy like it because i dont have to shift as often, ans my 2nd gear is just right for roll racing on the freeway, my 1st gear is just right for roll racing on the street. i have to shift less while racing and that meas there are less gears for me to miss :D heheheh.

i have a 2.79, and im shure my car would be quicker with the old 4.10 that i had, but i just hated shifting all of the time!

BUT, all of that is just my opinion. and its not the best setup for racing, its the one i like. :D

my gears used to be (with 4.10) ((about))
1st 20 mph,
2nd 40 mph
3rd 70 mph
4th 100 mph
5th 135 mph @ 6800 rpm

now they are
1st 30 mph
2nd 70 mph
3rd 115 mph
4th 162 mph
5th ???

TriFlow
05-08-2004, 02:36 PM
well, no not tranny, but the diff. and yeah.. more expensive than a chip maybe.. it depends on where you find one. i traded mine so it didnt cost me a thing. but... IMO better. and this is my reasoning: becasue a longer gear box will kepp the rpms lower wheile cruzing, get beter gas milage, less ware and tare because the rpms are lower. i realy like it because i dont have to shift as often, ans my 2nd gear is just right for roll racing on the freeway, my 1st gear is just right for roll racing on the street. i have to shift less while racing and that meas there are less gears for me to miss :D heheheh.

i have a 2.79, and im shure my car would be quicker with the old 4.10 that i had, but i just hated shifting all of the time!

BUT, all of that is just my opinion. and its not the best setup for racing, its the one i like. :D

my gears used to be (with 4.10) ((about))
1st 20 mph,
2nd 40 mph
3rd 70 mph
4th 100 mph
5th 135 mph @ 6800 rpm

now they are
1st 30 mph
2nd 70 mph
3rd 115 mph
4th 162 mph
5th ???

Your E30 does 162 mph??? :shock:

Jay Stock E30
05-08-2004, 02:47 PM
Josh, yes it is possible to rase the rev limiter to 7k. I have a chip in my car right now that raised it to 7.2k so the needle goes just about off the guage, however that is too high in my opnion. I don't know at what rpm the valves start to float, but I'm thinking mine do at 7.2krpm.

ohhh jim your second gear runs to 70mph...sweet!

Josh Q
05-08-2004, 03:11 PM
ahhhhhhhh!! ic. okay, i have this problem of only thinking in strait lines :D

yeah, good point. my solution however would be to get longer gears... *cough* :smt077

Well see here, E30s are made more for corners and fun stuff like that. You must use the force to get out of thinking in a straight line! You must Luke!

Jay Stock E30
05-08-2004, 03:59 PM
LOL

Josh Q
05-08-2004, 04:37 PM
Josh, yes it is possible to rase the rev limiter to 7k. I have a chip in my car right now that raised it to 7.2k so the needle goes just about off the guage, however that is too high in my opnion. I don't know at what rpm the valves start to float, but I'm thinking mine do at 7.2krpm.

ohhh jim your second gear runs to 70mph...sweet!

Wow, 7.2k rpms?! Did you have a custom JC chip made to do that? How much did it cost? Is there a diff that has gearing that is between the 3.73 and 2.97? I really like the 3.73 gearing but would like to be able to hit 60mph in 2nd, but the 3.73 would be able to hit 60 with a 7k rpm limiter.

Jay Stock E30
05-08-2004, 05:21 PM
yes there are plenty of diffs between 3.73 and 2.97, the e36 uses a 3.25 or somthing, also I think the e28m5 uses a 3.43 or somthing like that.

I got the chip off of ebay (aprox $50), I'm sure somebody ripped of a JC chip and then figured out how to change the redline, atleast thats my guess...

Josh Q
05-08-2004, 05:25 PM
Do the E36 diffs fit our cars? I know some of the E28 diffs fit but I thought that was it.

Jay Stock E30
05-08-2004, 05:41 PM
I'm pretty sure that they do, people with m50 swapps use them because the gearing in the m50 trany is different than in the e30 trany's. You might have to swap the back diff plate, but I'm not sure. I know the e28 diff plates are different, but the m roady ones will mount in an e30.

Chris
05-08-2004, 05:47 PM
What does it mean when your valves begin to float.

modifiede30
05-08-2004, 06:03 PM
What does it mean when your valves begin to float.


Its when the rocker arms lose contact with the cam lobes because the valve springs aren't strong enough, or aren't responding as fast as the rest of the valvetrain. The valves therefore don't pull back into their normal closed position as fast as they should, which results in lost compression.

Chris
05-08-2004, 06:06 PM
Thanks.

Is this something that is avoidable with some aftermarket internals?

modifiede30
05-08-2004, 06:12 PM
You can buy performance springs, titanium valve retainers, and other components to make the head more sturdy, but to be honest, taking an M20 beyond a certain point really doesn't gain you much except saved time from shifting. Once you're around 7000rpm, shifting into the next gear should put you in a pretty good power band. I can see why it would be undesirable to shift in drag racing, or if you're stuck in the middle of a turn though. I've experienced this at Lime Rock and NHIS but that's all a part of learning to drive in a specific power band, and learning to keep your momentum. M3's are known to be momentum cars, and the 325's aren't much different, just a has a different range of torqure.

Josh Q
05-08-2004, 06:12 PM
Yes it's very easy to fix. Companies make stiffer springs and a very common thing (which I'm going to do) is put in double valve springs to help prevent this.

modifiede30
05-08-2004, 06:14 PM
double valve springs


Even the 325is will experience valve float, and they came stock with dual springs. You really need schrick or another aftermarket type of spring to be safe beyond 7000. I'd also recommend going all the way as far as internals - retainers, rockers (if you can find them), etc.

Josh Q
05-08-2004, 06:39 PM
In my dreams, I wish I could buy titanium everything in the head. Can you imagine how light it would all be? And then buy titanium rods, a crank, and....

Giga Shadow
05-08-2004, 07:37 PM
Titanium engine oil..

modifiede30
05-08-2004, 08:11 PM
I'm not sure they make a lot of parts in titanium, except maybe keepers and the little retainers. Not sure they're even worth it. But if I was going to take my m20 to over 7000, I'd want to be damn sure it can handle it. Might be fine on the street, but on a race track, anything that goes wrong internally can become a major risk to yourself and others. Since that's about the only place I push my car, I guess I'm a bit more cautious.

Jay Stock E30
05-08-2004, 09:40 PM
modifiede30...do you know what rpm the m20 i motor starts to get valve float?

Also I'd imigen with valve float the pistons could come incontact with the valves right?

Josh Q
05-08-2004, 10:16 PM
Yes I do believe if the floating is bad enough that the valves can hit the pistons. At that point with the rpms that high I think things would be toast if they hit each other. I just thought about this, someone higher in the thread said that the "is" engines came stock with double valve springs, does this mean the "is" and "i" engines are different? I've never heard that before (not to say it isn't true at all).

modifiede30
05-08-2004, 11:16 PM
The "i" and "is" both had dual valve springs. All of the eta's had single springs. Not sure when valve float starts, but I'd think somewhere over 7000 depending on the condition of the head. And yes, you can have piston contact but I've never heard of anyone completely blowing the engine from this since the overlap is so minor. Would likely bend a valve but that's bad enough.

Josh Q
05-08-2004, 11:58 PM
Well in general if the pistons hit the valves bad enough you can put holes in the pistons.

Chris
05-09-2004, 11:35 AM
Well in general if the pistons hit the valves bad enough you can put holes in the pistons.

Sounds like you could bend the valves too, no?

Josh Q
05-09-2004, 12:29 PM
Yeah, the first thing that will happen if they hit is the valve(s) will bend. And you will more than likely get a indentation on the piston where the valve hit. If they hit hard enough then you will get a hole in the piston. This last time my t-belt broke only 8 valves bent from hitting the pistons and there were no marks on the pistons but I did break the head in two spots. Last time at about 80mph all the valves bent bad and every piston had marks in it where the valves hit but the head itself was fine.

Chris
05-09-2004, 01:10 PM
What's going on with your car right now. I know you are looking for a head, but what is it doing in the meantime?

Josh Q
05-09-2004, 03:02 PM
Gathering dirt. That's it. Just sitting at my old house waiting for new engine or head.

modifiede30
05-09-2004, 07:53 PM
Josh, what have you done to your car to make it break 2 timing belts? Is your car turbo charged?

bimmerjim®
05-10-2004, 11:17 AM
i think its just a run of bad luck... :(

bimmerjim®
05-10-2004, 11:26 AM
ohhh jim your second gear runs to 70mph...sweet! yeah, i took some videos yesterday. zip tyed the camera to the passenger seat headrest :D youll get to see first hand what its like in my car. you can see how i run the 1/4 mile in 3 gears..

iv got to get acess to my servder again. ill be moving the end of this week so my home interent is shut off for the moment. and who knows how soon untill i can get cable hooked back up. :roll:

Your E30 does 162 mph??? :shock:

yes, in 4th. :D dont get me wrong, it takes a while, but it gets there. it takes about 40 seconds from a stop to get there.