How high can the ka rev?

[DbD]

I used to own a 91 sentra that didn't have a rev limiter so you could rev that thing until it started making weird noises. I am sure that was a bad way of determining the limit of the engine.

Now with our ka's we have a rev limiter so we can't cause damage, but how high can we really go?

I was going to ask this in the ka*t section but I figured you guys would know more about this. I will be turboing my ka and want to know how high the stock internals will rev without causeing damage? I think the rods go first right?

If I bought forged rods and upgraded the valvetrain, what is the safest way to see how high I could go?

hopefully this all made sense,DbD

[deviousKA]

Stock internals the ka wouldnt be safe above 7k, (stock cam power will drop off above 6k anyway)

with forged pistons (ka already has forged rods) and very upgraded valve train you could probably bring it up to 7.5-8k safely.

Now a destroked ka (many possible variations) fully balanced and such with proper cams could push the limit over 8500+rpm. This could also be possible with custom 96mm ka race crankshaft

[daniel240]

just be safe and keep it at 6500, you dont get much more power after that anyway. if you really want it higher, 7000 is fine on stock internals but you dont want to go past that.

[apzak]

I shift at 6k rpm because according to g-tech, if i shift at redline (s14 ka24de, no nice cams like s13 ka24de) my 0-60 is actually slower. It's faster when I shift a little before redline and with a passenger to evenly distrubute weight and get traction (open diff)

[Sidewayz]

first off just because your in a higer rpm doesnt mean you have more power. Our ka's produce peak hp a around 5750-6000 after that is pretty much dead unless you rebuild your bottem end with forged rods and fatter pins, with higher compression pistions and then work on your head, with stronger valves and valve springs. Unles you intend to really send money and time i wouldnt waste your time trying to disconnect rev limiter. You will evntually blow your motor. Spend money on good tires, lsd, and tuneups. If you really need to something to your car with a limited amount of cash

[DbD]

sorry i didn't make this clear before but I will be turboing my car so the power will not drop off.

Mainly what i am wondering is how do you safely calculate the max rpm an engine can turn at? Do you just have to go until something breaks or is there some kind of formula that takes into acount the extra stiff valve springs, stronger valves, and balanced internals?

[absolute]

whenyou get your urbo get it dyno tuned and tested they should be able to safely determine the shift points or new redlines and best peak performance range when you get your work done that way you dont mess up anything in the process

[C-Kwik]

The mechanical redline of the motor is limited by many factors. The most inherent in the KA is the bottom end. According to SCC who got their info from JWT, the KA gets real rough at about 7500 RPM. I wouldn't bother getting past 7250 RPM's(leaving a small cushion) as it would start getting very expensive.

The valvetrain should be able to handle the higher revs with little to no modification. If anything, valve springs would probably be the only mechanical limit there.

Aside from this, the cams would need to be swapped to something that would allow better breathing at the higher RPM's as some have already mentioned. You'ld also have to make sure the injectors are large enough to handle the fuel requirements. The available duration get shorter with more RPM.

As far as turbos, they do not fix High RPM breathing problems. For the most part, a motor with a turbo has a similar torque curve shape as the NA version. It's just higher up. Adding a turbo does not dramatically change the volumetric efficiencies at different RPMs. So you'll find that the torque curve will still drop off at higher RPM's even with a turbo.

[C-Kwik]

first off just because your in a higer rpm doesnt mean you have more power. Our ka's produce peak hp a around 5750-6000 after that is pretty much dead unless you rebuild your bottem end with forged rods and fatter pins, with higher compression pistions and then work on your head, with stronger valves and valve springs. Unles you intend to really send money and time i wouldnt waste your time trying to disconnect rev limiter. You will evntually blow your motor. Spend money on good tires, lsd, and tuneups. If you really need to something to your car with a limited amount of cash

Strengthening the parts of the motor do absolutely nothing to create more HP. You must alter the breathing characteristics of the motor. What you are talking about is beefing up the mechanical redline. Even the higher compression won't change that. Cams will make the most significant difference.

[DbD]

I am going to be blueprinting my engine to very strick tolerances so this should fix the roughness in the bottem end correct. I will be balancing the crank/rods/pistons, knife-edging the counterweights of the crank to reduce windage, possibly cross drilling the bearing journals on the crank so i can get proper lubrication to the journals for high rpm driving.

Yes i know this is going to cost a lot of money to make everything right but I really want to build my engine right the first time, and am fine with taking my time to raise the money. I am hoping for a 9000+ redline.

I am very uneducated about all of this right know, and that is why i am asking questions here and reading as many engine blueprinting/rebuilding/machining books as I can get my hands on.

As for the question that I will be asked..."why do you want a 9000+ redline?".... Well i just do! Lets just say my ego is getting the best of me, and I want to prove to certain friends, that it can be done with a ka.

thanks for everyone's patience, you are very helpfull,DbD

[deviousKA]

I am going to be blueprinting my engine to very strick tolerances so this should fix the roughness in the bottem end correct. I will be balancing the crank/rods/pistons, knife-edging the counterweights of the crank to reduce windage, possibly cross drilling the bearing journals on the crank so i can get proper lubrication to the journals for high rpm driving.

Doing this properly will raise the safe rpm that you can run continuously, not that much though.

With the 96mm stroke of the ka, at 8000 rpm, the pistons are traveling so fast that if they were to stay at this rpm long, they will explode . Piston speed at certain rpm is designated by the stroke of the crankshaft. So with say a 90mm stroke your pistons will be traveling much slower at 8000 rpm, and the limit of that factor is raised.

It is impossible to build a 9000rpm ka with basically stock internals. The nasport engines that redline at 8500rpm have custom crankshafts. They may even be destroked as i hear they are 2.2 ka24e's.

[DbD]

How far can you destroke a stock ka crankshaft? To do this they have to grind off the top part of the rod journal, then make it round again correct? Doing so would then make you go with way oversized rod bearings to compensate for the smaller journals.

Or am i way off? I haven't gotten that far in my blueprinting book yet, and i left it at work. That is the only way i can think of, right now, on how you would destroke a stock crank. The only other way i can see is to grind a new crank out of billet or something to that effect.

I will be replacing the pistons with forged ones, and i am not sure about the rods yet. Someone said they were forged so wouldn't they be able to take the same abuse as crower rods or some other aftermarket forged rod?

[deviousKA]

Usually stroke/destroke on a factory crankshaft involves welding up one side then grinding to get desired stroke. Although if different rods with smaller journals were used, welding may not be necessary as there would be enough material.

Really it is much easier to use a different crankshaft. The z22 crank is 92mm stroke, it can be used in a z block with ka head. It could be modified to work in ka block but requires lots of machine work and welding.

Slick tip- use z22 crank with z24 rods in z24 block, bore block to 91.1mm and utilize the piston kit that i sell. Because the pistons would be flat top and come directly to top deck, compression ratio would be decent. And the price of the piston kit would be $100 cheaper because the tops would not have to be modified. It would be very cheap and easy to do this.

92mm stroke x 91.1mm bore is an interesting combo

stock rods are forged but not as strong as crower or others.

[Nathan]

Are you sure you want to knife edge a crank for extended street use? I would MUCH rather bullnose it and then balance the rotating assembly. It won't make you loose any ability to hit high rpm's and will probably help your engine last longer at the expense of loosing a few horsepower (not very much). I believe crower can make custom cranks, why dont you get one of those? It'll cost you though...

[DbD]

What is this bullnosing you are talking about?

Why would knife-edging a street motor be a bad thing?

Devious...Do you have a website with information about your products?

Are there any other shorter stroke cranks that will fit into the kat with very little machining? I wouldn't mind the machine work, but not too anxious about having to web a crank to make it fit.

DbD

[Nathan]

Well, there are different words for a lot of things, I've seen bullnosing be called knife edging etc. are you talking about taking out a LOT of material over the full length of the counterweight until it is "knife edged" on the bottom? Or are you just talking about bullnosing, or cutting down the front and trailing edge of the counterweights so it doesn't drop a lot of weight but DOES cut through the oil better? I just dont like the idea of full on knife edging on a street motor because there is a reason they design cranks with such heavy counterweights...it's not so it'll rev slower either

Edit: this is what I consider to be full knife edging: http://www.tgsi.com/crank_close.jpg

[s13sr20chris]

you will never reach 9000 rpm in a ka24 with its full displacement. at least not for long. it will shake itself apart in short order. if you swapped in a ka20 crank from a jdm ka20 that would be a start. knife edging and balancing are mutually exclusive in the case of the ka24. if you knife edge it, you will NOT be balanced. a knife edged ka24 may not even be safe at stock redline. that engine has some serious balance issues. piston speed is another matter alltogether. i dont know the formula, so go to the engineering forum and ask the guys there for the rod stress formula. they are very nice and helpful fellas. rod stress is well known. i once was interested in ka24 all motor power untill i actually looked at the head on one. the valves are small but very beefy. they are nearly indestructible but so heavy. i have not flow tested one but i am convinced that it can not flow well. with a built bottom end and maybe some headwork(definitely some cams), you could have a nice turbo set up that is fun to drive and revs to 7k all day. a big laggy turbo could even give that "all at the top" feel of a maxxed out na motor.

i am not trying to rain on anyones parade. please feel free to be different. i just dont want to see someone naively waste money. helpfull, yes?

[deviousKA]

problem is you will never find let alone get a ka20 crank at a decent price and who knows if it is even fully counterweighted. It is much easier/cheaper to modify a l20b crank to fit. The crank will always have to be balanced after any kind of modification (knife edge, bullnose, etc..). The reason the ka cranks counterweights are so large is because they have half the counterweights to do the job.

It is a waste of time and money to do any of that kind of work on the ka crank because the gains will be very minimal

[Nathan]

Which is why my rotating assembly is just getting the journals polished and everything fully balanced It's just incredible overkill to do that stuff.

[SSS]

You also have the option of having the crank undercut to reduce weight, this will also allow it to be fully balanced at a later stage as well as bull nosing.It's the option i'm taking, i would be happy to drop even 1kg from the static mass of the crank; i'm sure it will end up being more.Also, if anyone familiar with the process of undercutting a crank is concerned about it weakening, i am having the crank cryogenically treated.

[s13sr20chris]

undercut? where exactly is the cut? what area of the cranks do they remove material from? any weight you lose from the counter weights you need to lose relatively from the piston. the rod does not count as much towards the counterweight as it is only half reciprocating.

[Nathan]

Believe it or not you loose material from the sides of the journals if I'm understanding this right....it doesn't make it significantly weaker since you dont loose compression strength and there aren't significant enough tensile forces on a crank along the length of it to make a difference. In theory, it makes it stronger.

[s13sr20chris]

huh. i will have to research that. maybe if you could remove the material at the base of the journals it would have less effect on the balancing. it would also have less effect on the inertia though.

[deviousKA]

you could take lots off material off using that method. The only journal that you could not touch would be the middle(thrust). You could make the crank lighter but like s13sr20chris said you wouldnt loose much rotational weight

[SSS]

Here's what i'm talking about:

[DbD]

Well, there are different words for a lot of things, I've seen bullnosing be called knife edging etc. are you talking about taking out a LOT of material over the full length of the counterweight until it is "knife edged" on the bottom? Or are you just talking about bullnosing, or cutting down the front and trailing edge of the counterweights so it doesn't drop a lot of weight but DOES cut through the oil better? I just dont like the idea of full on knife edging on a street motor because there is a reason they design cranks with such heavy counterweights...it's not so it'll rev slower either

Edit: this is what I consider to be full knife edging: http://www.tgsi.com/crank_close.jpg

From what i have read knife-edging is only sharpening the front of the counter weight so that it will cut through the oil better than a round or flat surface. What you posted looks like a UFO or something. Does anyon ehave a picture of what they would call bullnosing?????????

[sikass13]

might not mean much to you guys. but my personal opinion is to keep the knife edging so that there is less windage and lighten up the rotating mass as much as possible before rebalancing for optimal rpm range with the longest rod possible domestic guys have been doing this for quite a while and it's not anything new to the automotive performance world. i'm a firm believer in more cubes. the most ideal place to lose weight is the rod itself because the loss in rotating mass becomes moer exponential rather than taking it all off the ends

[sikass13]

if you don't mind me asking why do you guys prefer high rpm vs. low en torque?

[groundhogday1976]

if you don't mind me asking why do you guys prefer high rpm vs. low en torque?

Because we have SR envy. Just kidding. If you look at most of the all-motor import drag cars, they're running high rpms. If you look at the production NA 4-cylinders with high specific outputs, they all rev really high. I'd be perfectly happy w/ my 6900 rpm redline if I can get my KA to pull all the way to it. Although it'd be pretty cool to see what a KA w/ one of deviousKA's modified cranks, some head and valve work, cams, and a better intake manifold could do.

[s13sr20chris]

high rpms with requisite power at said rpms means a faster car. of course you can think of a fast car with low rpms, but that only proves that that car could be faster. all things being equal, the same torque curve moved up in the rpms range means faster car. see this thread for infohttp://www.nissaninfiniticlub....ement