14 replies to this topic

[Military84]

I was looking into getting a tachometer for my mini, but I was wondering what the rev limit or suggested RPM redline is for the engine. It's a 998cc, carbed. Thanks.

[Madmax]

on my last 998 (reasonably tuned) i had a redline of 6500 before valve bounce

[mini90]

Valve Bounce HEHE
Seriously depends on your build standard 998 6k ish
The rally mini with a breathed on 1293 revs to 7k waste of time above 6 in top
The 998 will go to 7.5

[Military84]

thanks for the replies...at least I have some place to start to normalize this engine. So many people have messed with the carb adjustments (most not knowing what they're doing) it runs a little funny. I only just recently got the throttle cable to stop sticking.

[BruteSound]

When you have double valve springs, and SW5 cam, is it possible that you could pull towards 7.5k?

I know with the SW5 cam it makes no sense. But sometimes I pull him in the high revs, only for the kick.

[mini_mad69]

I never had valve bounce on my 2 standard stage 1 998 engines, took them up too 8k a few times, realy realy screams then, no point as there is little power. But my messed around 998 engine just wouldn't go past 6.5-7k.

[Marky Tizz]

mine is a standard 998 with a poorly tuned and OLD hs4 and stage one kit. not been rolling roaded. But I have had it to 8k but there is no real power after around 6k, although for some reason I get a sudden surge at around 7k so if I'm really battering it that's where I'll shift especially from 2nd as then it drops 3rd right into the power, massive whack of speed and good for getting over 60 in a reasonable time.
I'm rambling sorry.

[mini7boy]

there's a big difference between what an engine will grudgingly rev to and what it will willingly and enthusiastically rev to. It's generally not much fun to rev an engine beyond the RPM where it really wants to go because the progress of getting there will be slow enough as to make it boring. However, if an engine is tuned properly so that it can pull high RPMs in a hurry, then that's a whole different matter. Engines also have torque curves that are RPM sensitive and revving an engine too far beyond its torque peak will also prove useless. Cams definitely have RPM ranges for which they were designed and trying to force an engine to rev beyond its designed maximum RPM will induce sleep.

And then the issue of gearing makes the whole deal a bit more interesting. Who hasn't driven a car on the motorway with gearing that was so low that it caused the engine to run at higher RPM than was comfortable for passengers? The noise and vibrations at high RPMs can make for a really uncomfortable driving experience. On the other hand, low gearing is a substitute for torque, and thusly horsepower, so that a less powerful engine running on B-road gearing with a close ratio box and low final drive(diff) setup might embarrass a more powerful car which has motorway gearing with large RPM drops when shifting and a high final drive ratio meant more for quiet cruising than red mist B-road flying on the ground. Horses for courses, as they say.

As mentioned previously, the valve springs may impose a redline because the valves will bounce and not allow the engine to rev beyond a certain RPM. Since bouncing valves can also contact pistons, it's not wise to force an engine to reach the RPM where valve bounce causes misfiring and uneven running.

Bottom line: an engine will let you know just how fast it is comfortable running and you would do well to avoid revving over that RPM. Exceeding the RPM at which an engine is comfortable will result in increased engine wear, or failure, and will do nothing to enhance the driving experience.

[Dan]

I'll add to the above that a standard 998 run at very much above 7000 rpm for any reasonable length of time is pretty much guaranteed to break a piston ring. It's not all about valves.

[mini7boy]

I'll add to the above that a standard 998 run at very much above 7000 rpm for any reasonable length of time is pretty much guaranteed to break a piston ring. It's not all about valves.

Don't tell that to any of the guys racing in Mini7 where their 998s often hit 9000 or more. Their engines aren't standard, but the rings are close enough to standard that the statement I made still applies.

Rings are some of the strongest parts on engines. Assuming an engine was machined and assembled correctly, rings usually only break due to piston trauma caused by detonation, pre-ignition and other abnormal engine conditions. Even absolutely standard rings should have no trouble revving over 7000 without ring breakage. I'm sure that road engines often are revved past 7000 without ring failure. Ring failure can sometimes go undetected, but it should show up eventually if leakdown tests are performed or oil consumption increases.

Edited by mini7boy, 19 April 2009 - 10:57 AM.

[Dan]

a standard 998

Rings are strong but by no means infallible. I speak from experience in this respect, rings on 998s do break when pushed beyond the design red line. I've done it and several of our members have complained of similar problems in similar circumstances. A broken ring rarely goes un-noticed, unless you never look in your mirrors to see the huge column of white smoke I suppose.

Edited by Dan, 19 April 2009 - 11:08 AM.

[Ouster]

I'd be afraid to push a standard 998 past 6k to be honest - certainly no point as there's no power up in that range!

[monster_mini]

so, long story short its best to rev to no more thank 6k but it will do this all day long (not literally) but you know what i mean

nick

[Madmax]

holy thread revival!

i answered that first post in 2004

[Ouster]

Didn't notice the OP date!