Rev limit ? - The Unofficial BMW M5 Messageboard (m5board.com)

Carrera2RS · 30th July 2004, 10:38

I would like some assistance with the view of the safe rev limit for the stock M5 Engine ?

I understand the M5 runs with hydraulic lifters which can often compromise the safe limit from the valve train's point of view, ditto valve springs and assembly. Reading the reviews of Nowack's mods, they replace con-rods. Are these marginal on the M5 ?

The 'advice' given or read is as follows :

Dinan say 7300 max limit (Conversation)
Superchips seem to have no problems re-mapping to 7,500 rpm
Superchips graphs show the dyno plot running nearer 7,900 rpm
Another M5 UK tuning house says 7,900 is safe and 8,000 would be ok

I am not sure where the limiter is on the M5 I am picking up (7,500+ I think) and the engine has :

Remap (superchips)
Velocity stacks
Gruppe M carbon air boxes
Plasma coils
supersprint crossover pipe
Kelleners race back boxes (Look luvly and sound awesome, but a touch 'race' for a street car...... I will pick up help on how to tone them down on another thread)

The car seemed to be pulling hard at 7+ so the reason to aks the question is to make sure I don't become blasey about the shift point and end up with a crippling bill !

Tks

PS If anyone wants help with rev limits on E30M3's or 964 C2RS's I can give chapeter and verse

PPS I will dyno the car when I pick it up to see what these mods give

CSBM5 · 30th July 2004, 14:31

I can't help with the rev limit question, but if the velocity stacks are similar to the ones another board member had on his car, you may want to consider taking the stock stacks with you to the dyno. Swap in the stockers after you run once as is. His experience was that the car made much more total power (area under the HP vs. rpm curve) and actually even more peak power with the stock velocity stacks. The short stacks were more tuned to resonate at a higher rpm, which without a cam/breathing change, they simply caused him to lose power everywhere.

There's a long thread on this subject here on the board not too long ago.

TexasM5 · 30th July 2004, 20:44

Well, my personal view is that the stock rev limiter is just fine. I am happy to play with an E30's engine, but when you look at the costs of a replacement engine on our M5s, I would leave well enough alone

A few hundred more rpms may be just fine, but I do not want to be the one at the BMW dealer with a crippled M5 explaining that I "only" raised the limiter 200rpm. Call me conservative, but if my engine blows, I want to be able to roll into my local dealer and have them replace it.

TexasM5

4ocious · 30th July 2004, 22:21

Quote:

Originally Posted by TexasM5

Well, my personal view is that the stock rev limiter is just fine. I am happy to play with an E30's engine, but when you look at the costs of a replacement engine on our M5s, I would leave well enough alone

A few hundred more rpms may be just fine, but I do not want to be the one at the BMW dealer with a crippled M5 explaining that I "only" raised the limiter 200rpm. Call me conservative, but if my engine blows, I want to be able to roll into my local dealer and have them replace it.

TexasM5

Powerchips recommends 7250. My 03 seems to run fine at that limit.

Carrera2RS · 31st July 2004, 21:06

Quote:

Originally Posted by CSBM5

I can't help with the rev limit question, but if the velocity stacks are similar to the ones another board member had on his car, you may want to consider taking the stock stacks with you to the dyno. Swap in the stockers after you run once as is. His experience was that the car made much more total power (area under the HP vs. rpm curve) and actually even more peak power with the stock velocity stacks. The short stacks were more tuned to resonate at a higher rpm, which without a cam/breathing change, they simply caused him to lose power everywhere.

There's a long thread on this subject here on the board not too long ago.

Thanks for the info, I read the post with great interest. I also haven't got the original velocity stacks !

I would be surprised if it hadn't picked up a little at the top end, the performance was rather dissapointing. I have done a lot of work with inlet systems understand the maths and used to build F1 engines in the 80's. Given the reduction in length and the fact that they are straight it really must be a restiction above. I might have some notes somewhere, I ran a heavily modded 911 engine with a variety of ram pipes different lengths, roll etc. Ounce the final decision was made the air boxes were no more than 1" from the top of the stacks and the power runs were no different lid or lid off.

Has anyone dynod the car with the top box off box off ? , is it possible to do that I wonder, that would resolve that issue.

I will get my car dynod when I pick it up next week

mottati · 31st July 2004, 21:19

Quote:

Originally Posted by Carrera2RS

Has anyone dynod the car with the top box off box off ? , is it possible to do that I wonder, that would resolve that issue.

DO you mean with the plenum cover removed? You'd need some other type of engine management system, because without the plenum cover, the MAFS would not be supplying any info on airflow into the engine. There have been suggestions about a larger plenum cover, or a spacer to increase the plenum volume, but no dyno data (that i know of) to back it up. I see no mention of the plenum spacer on the dinan web site anymore, either, i wonder if they abandoned it?
Mike

Carrera2RS · 31st July 2004, 21:27

Quote:

Originally Posted by mottati

DO you mean with the plenum cover removed? You'd need some other type of engine management system, because without the plenum cover, the MAFS would not be supplying any info on airflow into the engine. There have been suggestions about a larger plenum cover, or a spacer to increase the plenum volume, but no dyno data (that i know of) to back it up. I see no mention of the plenum spacer on the dinan web site anymore, either, i wonder if they abandoned it?
Mike

Got ya, I forget with Roadies they are mapped on airflow / mass flow meters and not throttle angle !

When I pick the M5 up I will have a look at clearance for the stacks and have a ponder...... If the stacks need to be built even shorter I might be able to get some fabricated. These tuning guys are on a different planet spun alloy ram pipes $1000 for 8 !!!!! I had a whole inlet system made in carbon, taper throttle bodies to my spec, ram pipes in carbon to my spec and all carbon airboxes, linkeages etc for about £1,200 a couple of years ago ! (Ok it was 6 cyl not 8, but jeez someone's making some money !)

shadowman · 31st July 2004, 22:55

The various commnets made with regards to what is a safe maximum RPM........... to many opinions by to many tuners and unfortunately very few if any that are based on much more than "seat of the pants" tuning.

BMW spent alot of time and $$ stress testing this motor and as such decided upon a extremely safe point that would insure a reasonable life span based on anticipated usage. Having shared this I doubt that anybody including myself has invested the time and $$ to reverse engineer the motor for the purpose of undertanding exactly how much stress and what RPM can be maintained for a given period of time.

Having shared this I agree with PowerChips and that 7250 should be considered a safe maximum. I typically use 7200 RPM and I do so based on an opinion developed over time after I gather data from a variety of sources, including first hand. Certainly the motors can be spun faster, in fact I have experienced this, however at what point in their life cycle. As the motor gather miles and hours of operation valve train pieces such valve as springs show there wear unfortutely this wear is not visible without opening the motor. The springs are a key factor that will determine at what point the valve is no longer controlled by the cam cycle and float is developed.........because the piston to valve clearances in a stock motor are relatively close the results with this scenerio is contact between these pieces afterwhich it is simply a matter for the AMEX card because there is no easy or inexpensive fix.

I have one such example sitting on my desk as I write this.

Besides, how many times do you truly need to twist her any higher than 7250....... max horsepower and torque were felt several hundred RPM's earlier so shift and place her back in the power band and keep on accelerating under power ........ not simply accelerating.

Have fun

shadowman · 31st July 2004, 23:14

Quote:

Originally Posted by Carrera2RS

Thanks for the info, I read the post with great interest. I also haven't got the original velocity stacks !

I would be surprised if it hadn't picked up a little at the top end, the performance was rather dissapointing. I have done a lot of work with inlet systems understand the maths and used to build F1 engines in the 80's. Given the reduction in length and the fact that they are straight it really must be a restiction above. I might have some notes somewhere, I ran a heavily modded 911 engine with a variety of ram pipes different lengths, roll etc. Ounce the final decision was made the air boxes were no more than 1" from the top of the stacks and the power runs were no different lid or lid off.

Has anyone dynod the car with the top box off box off ? , is it possible to do that I wonder, that would resolve that issue.

I will get my car dynod when I pick it up next week

You are correct.

With sufficient space within the plenum, particularly the area above the air horns increased top end is experienced however there was a measurable (minimal nonetheless measurable) loss with low end torque. This is only one of the reasons that the bubbles were incorporated into the carbon fiber covers. However given the ideal situation the physical length of the air horns/stacks pay a key role too. The data we have collected to date indicates that most being used are simply to long, to tall for normally aspirated motors and that no re-mapping of the DME to support such a change is being solicited. At the moment additional testing is being completed to see if a compromise in air horn/stack length supported by additional plenum space supported by re-mapping within the DME can produce the desired results. The present goal is zero loss.......... moderate gains will the goal once zero loss can be established and then further tuning can commence. The results thus far have been interesting with the pendulum now swinging towards good.

Have fun

greg · 1st August 2004, 04:30

Quote:

Originally Posted by shadowman

Besides, how many times do you truly need to twist her any higher than 7250....... max horsepower and torque were felt several hundred RPM's earlier so shift and place her back in the power band and keep on accelerating under power ........ not simply accelerating.

Shadowman - I agree with you on most of this - but the statement above isn't fact without more data. The reduction of torque past the peak RPM in our cars is more than offset by the increased torque at the rear wheels while remaining in the lower gear. This is definitely true past the factory redline. There IS a point where the engine torque has fallen enough that more torque would be available in the next higher gear, at the associated lower (but higher torque) RPM. However without knowing the torque curve of the engine up to the max RPM being considered we can't tell what the "optimum" shift points are.