Rev limits, how much abuse...

[Jezz_s13]

Hi,

Can i ask what rev limits you are running and more importanly what you regularly use?

If you are not using a stock crank, rods or pistons please say so.

Cheers,Jezz.

[Notchbackca]

no point in raising it unless you are running extreme cams and a very large turbo

[Jezz_s13]

I am.

950cc injectors, SC-52 turbo 600bhp (550 reality), JE pistons, Pauter rods...

What i want to know is what experience NICO CA owners have with running high revs, 7800-8500.

IE will my stock crank cope with 8200 without flex etc.

[Def]

I imagine the crank will be able to handle it as long as you don't go too high since loads increase with the square of your RPMs. I'd worry about the valvetrain though. I can't imagine the stock valvetrain being that happy anywhere north of 8000-8200RPM frequently.

It will probably do it for a while, but eventually something runs the risk of snapping.

Reinforcing the valvetrain would be a smart idea for these kind of revs.

[Jezz_s13]

Valve train is being sorted, springs, light weight retainers.

I'm a bit undecided whether to go for solid lifters or not though.I have a brand new set of Stock lifters, but I'm not sure what to do.

I've jsut done some maths, i have lightweight rods and pistons (12% lighter) and the maths show that at just over 8200 with the light stuff, the kinetic energy possessed by the rod/piston mass is the same as stockers at 7700.Whether I've done my maths right I'm not sure.

Basically i calculated the maximum piston velocity for various rev limits using a spreadsheet I found on the WWW, then put the velocity figures into the std equation for Kinetic Energy, KE = 1/2 * M * V * V.

Do you know if this is the right way to go about it?

Oh, I've had about 0.25kg shaved off each of the crank balances to which will help a bit.

[boost_boy]

Max rev limit is about 8700rpm, but I've seen the rpm needle touch 9k. I programmed my active rpm/fuel cut at 8200rpm which is where most of my useable power was at. The motor is totally stock bottom end-wise with the addition of the HKS (now Tomei) camshafts. The bottom is up to the task of high revving hp, but the valve train will need to be upgraded.

Dee

[Def]

You don't want to look at kinetic energy at all in this case. You want to find what forces your bottom end components will be having to withstand, and that means acceleration.

IC engines are hard to examine thoroughly in this area because they have a non-constant acceleration of the piston. For instance, at 10 degrees ATDC, the piston will be accelerating much slower than 90* ATDC.

But that's only necesssarily to do a quantitative analysis. To do a qualitative analysis, you can just compare your figures to a known "good" rev limit. Say 7800 RPM as a very safe figure.

Since your components are 12% lighter than stock, I'd say maybe 10% of that mass reduction will be above the rod neck which has to withstand all these loads. Assuming max acceleration will increase exponentially with RPM(2nd order), since mean piston velocity increases linearly, you can take the square root of this 10% figure(F=MA) to get an approximate increase in RPM for the same force level due to mass reduction. This turns out to be ~3.2% higher, or only 8050 RPM to match the same force level as the stock components will experience at 7800 RPM.

Now, I'm sure the stock bottom end can withstand more than 7800 RPM, but this exercise gives you a good idea of just how quickly forces can increase with higher RPMs. I'd say with a good balancing and lighter weight components, you can most likely go 5% more RPMs over what people consider "safe" for a stock engine. Don't expect the engine to last forever though, as the forces will be absolutely tremendous approaching 9k RPM.

The valvetrain will most likely not hold up to those RPMs though, with the stock lifters at least...

[Jezz_s13]

thanks for the reply Def, I'll have a better (clearer) look at it in the morning as I'm rather drunk at the minute.

Yeah IC engines are terribly difficult to work out for, it would be so nice is some kind person had created a java web site that I could plug numbers into.

I'm not sure what you mean by rod neck?The rod istelf shouldn't be a problem, Pauter rods are by all accounts very good, it's the effect of the rod/piston mass on the crank that is my concern so surely the entire rods/piston mass is applicable? Or am I missing something?

I don't intend to run to 9k, 8.2k will be just dandy, 8.5K would be awesome.

I've been given this link which looks pretty good, I've not had a decent look at it yet but i shall do tomorrow.http://www.seas.upenn.edu/~mea...s.pdf

[Jezz_s13]

Right I've been doing some digging. LOL

I found a web based calculator that lets you enter rod lenght, stroke and revs and gives you the accelaration in g.I've done this for a range of revs 7200-8500 then converted g into m/s/s.

I then put these acceleration figures into F=MA along with the weight of a stock rod/piston assembly (1.178Kg) to work out the max force at each of the rev values.

I then reversed then recalculated the force using F=(0.88*M) * A to give the force with the lighter rods etc.I did this all in excel then looked at the force generated at 7700 for the stock stuff and looked it up in the column for the light stuff to see at what revs the force is the same.It actually works out exactly the same a using Kinetic Energy.

The force at 7700 with stock is the same as at just over 8200 with the light stuff.

accelaration calculator...http://www.slowgt.com/Calc2.htm

Really useful site...http://www.epi-eng.com/ET_TOC.htm particularly sections 6&7 but it's all pretty good.

Here's my results...

Using KE...

If you assume the revs on the left are safe, then the revs in the far right are the light equivalent.

revs speed stock ke stock ke light speed light revs light 7200 29.880 525.868 462.764 31.852 7675.226 7300 30.295 540.577 475.707 32.295 7781.826 7400 30.710 555.488 488.830 32.737 7888.427 7500 31.125 570.603 502.131 33.179 7995.027 7600 31.540 585.920 515.610 33.622 8101.627 7700 31.955 601.441 529.268 34.064 8208.228 7800 32.370 617.164 543.104 34.507 8314.828 7900 32.785 633.090 557.119 34.949 8421.428 8000 33.200 649.219 571.313 35.391 8528.029 8100 33.615 665.551 585.685 35.834 8634.629 8200 34.030 682.086 600.236 36.276 8741.229 8300 34.445 698.824 614.965 36.718 8847.830 8400 34.860 715.764 629.873 37.161 8954.430 8500 35.275 732.908 644.959 37.603 9061.030 8600 35.690 750.254 660.224 38.046 9167.631 8700 36.105 767.803 675.667 38.488 9274.231 8800 36.520 785.555 691.289 38.930 9380.832 8900 36.935 803.510 707.089 39.373 9487.432 9000 37.350 821.668 723.068 39.815 9594.032 9100 37.765 840.029 739.226 40.258 9700.633 9200 38.180 858.593 755.561 40.700 9807.233 9300 38.595 877.359 772.076 41.142 9913.833

Using Acceleration and F=MA...You look in the last but one column for force value for the revs you feel are safe, then look that up in the last column then read back across to see what revs the force is associated to.

revs acc (g) acc ft/s/s acc m/s/s Force std Force lgt7200 3186.000 102506.519 31243.987 36805.417 32388.7677300 3275.000 105370.009 32116.779 37833.565 33293.5387400 3365.000 108265.674 32999.377 38873.266 34208.4747500 3456.000 111193.512 33891.782 39924.520 35133.5777600 3549.000 114185.698 34803.801 40998.877 36079.0127700 3643.000 117210.059 35725.626 42084.787 37034.6137800 3739.000 120298.768 36667.064 43193.802 38010.5467900 3835.000 123387.476 37608.503 44302.816 38986.4788000 3933.000 126540.533 38569.554 45434.935 39982.7438100 4032.000 129725.764 39540.413 46578.606 40989.1748200 4132.000 132943.169 40521.078 47733.830 42005.7708300 4233.000 136192.748 41511.549 48900.605 43032.5338400 4336.000 139506.675 42521.634 50090.485 44079.6278500 4440.000 142852.776 43541.526 51291.918 45136.888

[Def]

I wouldn't be very worried about the crank. The cross sectional area of the crank is absolutely huge compared to even the "beefiest" rods around.

The usual failure mode due to high RPMs is for the rod to shear off just below the wrist pin. This happens on the end of the exhaust stroke, as the intake stroke starts since there is not much pressure on the piston face pressing back down, and can even go into vacuum abruptly due to cam timing.

Regardless of all this, I still think the stock lifters in the head are your weak point by far. Go with a solid lifter conversion before you even think of stressing the bottom end to the max.

[Jezz_s13]

Cheers.

I have revved (by accident) the stock rods with stock pistons hanging off them to 10k before, they didn't snap but it bent the crank though. so the pauter rods will deffo cope with it.

Yeah, I'm pretty much convinced that solid lifters is the way to go.