destroking the ka to gain rpm's?

[Black R]

my background is high-revving 4cylinders, and one of my curent projects has turned in excess of 11k-12k in another car. I usually try to limit it to 9500, but accidents do happen..... :o That motor is still running strong.

But I digress:

I'm thinking in a tangent about how people get sr's for the turbo and the revability.

But for the $ I could piece together my own turbo kit and possibly destroke the ka to something with a more rpm friendly rod/ stroke ratio.

I'm sure this has already been done somewhere - so can you point me in that direction?

[deviousKA]

The KA24 has an extremely tall deck height, 247mm. In order to destroke and get any sort of realistic rotating assembly you will have to work with a block that has shorter deck height (unless you would like to push that heavy assembly with 1.8+ r/s). The shortest stroke i would go in a "tall" block (ka, z24) would be 92mm. With the longest rod available (ka, z24 165mm) you would have fairly decent characteristics but still have massive weight in your rod/piston combo (piston compression height would need to be 36mm to come to top deck).

So, if you want to drop the stroke down under 90mm and utilize fully counterweight crankshafts you need to start working with L and Z series components. The "medium" blocks (227mm) will offer what you need, these come in the flavor of l20, z20, and z22. Good rod/piston combos (lightweight) can be fit into these.

Both sohc and dohc ka24 heads can be adapted to these blocks, sohc is bolt on, dohc requires custom front cover and chain setup.

[s1ndicate]

So a SOHC head will drop right onto the l20, z20 or z22 block no problems? What would be the expected power/rev one could expect from this combination?

Would a KA transmission have problems bolting up to these blocks?

This is awesome, finally the KA is R&D for it.

There should be a big sticky on the different combinations and variants of hybrids and stuff that will mix match with the KA.

[deviousKA]

The sohc head will drop right on to the z20, z22 with the medium deck height head bolts. The l20 requires a few light timing cover modifications to have it mate properly, and also a passage in the deck should be plugged.

When you put sohc ka head on a z series, you can use the original z series dual row timing chain setup and timing gear. This system is much better than the original ka and has 3 posistion cam timing adjustment stock. Also available are very trick aftermarket adjustable timing gears that allow for more fine tuning than original

KA transmission, no problems, you need to run L/Z/KAtruck type starter motor with through-bolts (bolts with nuts). On the z series the bolts slide in from the starter side and thread into transmission, on the ka 240sx it is the opposite, the starter is tapped with threads. Other than that it is bolt on.

With a z series block you can use just about any flywheel/clutch you would like. From 200mm-240mm mating surface (240sx = 225). You cannot use a 240 flywheel.

Power/rev expectations, lots of factors to consider, with all of the different combinations I cannot give you an answer. You have a variety of stroke, rod length, and quality of components that can be used.

But just for reference, semi-basic setup, z22 bottom end (z22 crank, rods, custom piston) with sohc ka head made 225 hp on the dyno (many other modifications of course). This was an engine Troy Ermish made for a customer 510, runs carbs.

As far as laying out all of the combinations and such, and posting all of it publicly, probably not going to happen. I would be glad to help with the basic combinations using mostly oem parts, but I have a few secret components I would rather not share.

I would be glad to answer any questions, go do some reading on L/Z components and general rotating assembly theory to find out what you would like to do.

[Black R]

I definitely wasn't stuck on using all oem components (which I know many are because of governing bodies for certiain classes/ series).

I would definitely go with forged rods and pistons.

Even Ti rods are getting relatively affordable these days, and offer some nice midrange gains without sacrifice...

I would like to use an off the shelf crank for affordability, and availability however. Oem cranks seem to have better characteristics than the price conscious aftermarket variety.

I like the tall deck, so I can run a long rod and have a happier r/s ratio for higher rpm's...

I wouldn't mind a 2.1L to 2.2L KA that could rev sky high...

Pair that with a nice turbo+manifold and it would be a really trick (and somewhat wallet friendly) alternative to the SR20's.....

[deviousKA]

I have noticed the price drop on titanium rods as well, although most you will find are "unfinished" and require finish machining. This is good because you have some room to finish them up to your desired application, but the bad thing is most machine shops dont like to wear out their tooling. Sure, you can pay for the extra tooling cost, but most wont even take it on.

The ka24 block is far to tall. Like i mentioned before shortest possible stroke to get any sort of realistic rotating assembly is 92mm. This 92mm crank is from the z22, and half-counterweighted very similar to the ka24 and z24 crankshafts. In order to get into the fully counterweighted datsun cranks you will have to work with strokes under 86mm, although these can be stroked to 90mm or so I wouldnt suggest it, the counterweights (and overall build of the crank) are to small imho. Now, one would think that 1.8+ rod to stroke ratio is a good thing, yey! more rpms. The truth is this is completely unrealistic, these r/s ratio will not come into "tune" untill very high rpm (extremely high). The components cannot handle it and you will end up with an engine that is completely reluctant to rev. This is not only due to the ratio, but also due to the sheer weight of the rod/piston combo (ever weighed a 165mm nissan rod?, how about nissan 165mm rod + 89mm bore 36-38mm tall piston, yikes). Your not going to find a lightweight titanium rod in 165mm. Trust me, you will want under 1.8 r/s, between 1.75/1.8 is where you want to be.

Look into the medium deck height blocks, not only do these have proper deck height to fit the discussed components, they require no modification to fit them.

In order to fit an L/Z crank in a ka24 the main thrust (center) bearing must be welded and narrowed, or the block main must be widened. This block widening could be accomplished with bolt on spacers (with tapered head fasteners) which would be much better than welding. I was working on this long ago before i realized I could not fit a realistic rotating assembly.

[s1ndicate]

As far as laying out all of the combinations and such, and posting all of it publicly, probably not going to happen. I would be glad to help with the basic combinations using mostly oem parts, but I have a few secret components I would rather not share.

A basic combination setup would be great. I can understand and respect the secrets you discovered and wish to keep that way. Your are a wealth of knowledge and any information you pass down is surely appreciated. I will defiently keep study and researching and posting. Searching for the setup and KA/Hybrid that fits me.

[Bigvinnie]

Z blocks are dirt cheap also, I just recieved a rebuilt for $795 with a .20 bore, works great. Then all you have to do is swap the KA head to it. I got mine from attarco, I also have quotes for used z blocks for about $300.

If you are looking for an instant turbo set up that is dirt cheap you will find z18et. The turbo mani's are direct bolt ons to the KA e and NAPSz head up to 2.4. I believe the mani uses a t3 flange. You have to order the z18et out from Japan. It isn't recomended to atempt the z18 block with KAE head though, but for the price you get all the turbo parts it's worth it.

Z18et turbo


Modified by Bigvinnie at 4:40 PM 9/29/2005

[EugeneSentraSTI]

Put in some 1-1.5mm bigger pistons, your going to save a lot of money and time!! first off your motor will be stronger and it would rev better, destroking??? ,, the parts available arn't worth it!your going to end up with a motor thats going to be unwilling to give its true potential!!!

Light weight pistons, maybe even lighter forged rods,, like wiseco'sligter flywheel to increase rotationfull engine balance

Your engine will be more willing to rev!!!

Youl not get better results!!! im talking out of experience!!

[robertwb70]

I've been thinking(mostly because I already have most of the parts) that an L-20B block (3.39" bore) with an L-16 crank (2.9" stroke) and a KA-24E head would make a real screamer,but only about 1.75 liters of displacement

but then I remember it's for my daily driven truck and the #1 rule for torque-always build the biggest motor you can -and I'll probably just use a KA-24E with a DE head...

robert

[deviousKA]

Destroking, (or short stroke properly designed engine, rather) definately has its purpose. This may not be something that would be well suited in a fully dressed s chassis (ie, heavy), but this is a KA forum not a 240sx forum. These are more suited to lighter weight chassis, as in a smaller production car or a tube race car.

Larger pistons are not going to make an engine rev better, or be stronger, in the case of the Ka24 would be quite the opposite in both respects. Larger pistons are heavier, and cylinder walls get thinner. Forged aluminum is heavier than cast aluminum, although due to the additional strength of the material forged pistons can be made with less material and still provide ample strength.

The L/Z/KA parts available are top notch components. The best steel your ever going to run across (besides 70's international harvester iron blocks ) . These parts have been and still are used for racing use worldwide. These are many of the same or similar components used in the early LZ twincam formula engines, and also the various FJ series. We are basically building an LZ/FJ, with a more modern cylinder head.

robertwb70, if your going with a KA cylinder head you may want to look into using the z series blocks. These just require a few less modifications, and offer all of the benefits of the L. Your L-16 crank will drop right into a z20 block (z20 block identical to l20 for all intents and purposes, aside from a single passage in the deck, and the timing cover design). The ka24e head will drop right on to the z20 with no modifications at all, the head mates to the cover perfectly.

[deviousKA]

Heres some reference photos.

Fully counterweighted vs. half-weighted datsun/nissan crank

Fully counterweighted:L20Z20L16 < not allL18 < not all

Half weighted:KA24Z24Z22

Heres a knifed, polished, and prepped L crank, looks pretty but to light for 1.8L + displacement. Lots of work into this little bugger.

Heres a NISMO FJ24 racing crankshaft (yes, it really is a nismo fj24 crank, non production race only)

Heres a LZ twincam, 2.0l, same block and crank as l20/Z20 (its actually L20 but for sake of discussion)

[Bigvinnie]

Fully counterweighted:L20Z20L16 < not allL18 < not all

When you are speaking in refrence that not all L16 and L18 were fully counter weighted I am under the assumption that it is in refrence to the L series blocks that came in the datsun trucks (510 trucks during the late 60's and early 70's). Truck style cranks that were half counter weighed.

[deviousKA]

I am not sure what designates the l16/l18 crank as fully counterweighted (as far as what the engine came out of, and casting numbers). Most of the production l16 datsun car cranks are half weighted, and the fully counterweighted ones used for race use are mainly nissan motorsports versions (which are also a low volume production crank). L18 is much more rare, I havent inspected enough of these to give you a valid answer on that one either.

The datsun 510 guys would know, I would ask over at the510realm.com if you would like to know for sure what casting numbers had the fully counterweighted cranks.

[EugeneSentraSTI]

Well you could go with what others think??

Why do you think you get something like a stroke ratio?????Why do you think do the smaller engines rev easy???

look on the market most high revving motors all have big pistons!!!

The longer the rod the more torque but slower rotation?The bigger piston gives you better revving motor!!So it would balance the lazyness out of the motor, and with a couple of light weight applications and balancing will do wonders and be cost effective!!

u dont have to try my mod? try what you think will work, if your done let me know if it was worth the effort!

[SonyPete]

Why do you think do the smaller engines rev easy???

Because they have a small stroke!

look on the market most high revving motors all have big pistons!!!

Because to keep that revving ability they have to kepe the stroke small and the only other way to get more displacment is with a bigger bore.

The longer the rod the more torque but slower rotation?The bigger piston gives you better revving motor!!So it would balance the lazyness out of the motor

The rod length has nothing to do with the size of the stroke or slower rotation. Its the actual size of the stroke that limits the RPMS and gives more torque. Remeber stroke dimensions affect engine displacement quite a bit more then an bore size does. "Balance the Lazyness out" isn't a very scientific way of thinking or very valid way of evalutiing how cars work. Please do some more reading about engines before spewing stuff out. No offense but only open your mouth when you know exactly what your talking about. Hey I had to learn this same lesson that I speak of now.

[EugeneSentraSTI]

yes well your right in the way you look at it but alas,, yeas smaller engines rev eaasyier because of theure smallness,, but what your saying is that all bigger motors cant rev fast ,,,??? well im thinking of ferraris and m3 now!yeas that is what your saying and chaging a motors stroke ans does affect

Yeas shure a short stroke is nice but on small capacity motors youl want torque aswell otherwise its just going to go in 1srt and 2nd,, thats what happens with hondas shure they rev fast but tou lose more than you gain,,

Like i stated before if you change your stroke and bore youll get diffrent types of results!

maybe you should think into the bigers picture and let guys with experience handle it! no offence

[elgarvo616]

the size of the motor has nothing to do with the how fast it revs. top fuel dragsters(500cc's) can rev faster than my car(stock KA).

[SonyPete]

Quote »yes well your right in the way you look at it but alas,, yeas smaller engines rev eaasyier because of theure smallness,, but what your saying is that all bigger motors cant rev fast ,,,??? [/quote]No I never once stated that big engines can't rev fast. Cause you can have an engine that big in displacment but still have a smaller stroke and rev very well, its all bsaed upon many factors. I was only speaking in terms of basic run of the mill engines that you normally see on the road. Definantly not drag cars of any sort. There is allot of research put into those engines and allot of things done to get them like that but my previous comments had no correlation with those types of engines.

Quote »well im thinking of ferraris and m3 now![/quote]Umm first of all ferraris are known for having a huge bore sizes and very short strokes. The only reason they have such a big engine is because they have more cylinders than the average engine. LOL. And even the V8 ferrari engines are decent sized because they do have 8 cylinders still and they make up some displacment with bigger bore sizes.

Quote »maybe you should think into the bigers picture and let guys with experience handle it! no offence[/quote]EugeneSentraSTI from what I can tell your the one with very little experience, as you can't even differentiate what affects an engines displacement. Please like I said before go read up

[EugeneSentraSTI]

i knew this befor you told me (amazing) but think a little futher why big pistons and short stroke??

short stroke isnt the only reason the rev, the big bore attends alot more to that than you think?

Thats why if you want a torque motor then you go for stroke which like you said aswell is a slower revving motor!but by adding a set of bigger pistons you get a better balance between torque power and revs? dont you think?

look at a honda? they rev but they dont torque, which leads to them only beeing fast revving in 1st and 2nd in standard form or mildly tuned.but put the same car on the highway let it race past the 400m mark and where is the honda then,thats why a sr20 is so good on performance cause theyre a mix between a hp and torque motor and not bad revving capability,,thats why they lie to react so well to small tuning, dont you agree?

[UK-SRi]

I would suggest you try sr20forum and search for "desaxe" that will get you to a thread I contributed on, the reply from a west Indian racer by the screen name of "BigToe" will give you in one paragraph a rebuttal of why that is only part of the story. He takes his SR20's to 9K on the track and rebuilds them regularly, a word of caution the http://www.sr20forum is quite harsh on people who dont search.

Mike

[HashiriyaS14]

the size of the motor has nothing to do with the how fast it revs. top fuel dragsters(500cc's) can rev faster than my car(stock KA).

Not that this invalidates your point, as you are still conceptually correct, but last time I checked, Top Fuel Dragsters have 500 Cubic INCH engines, not 500cc.

Not even those things can make 10,000hp on 500cc, lol.

[EugeneSentraSTI]

ok well i was partly wrong, but bigger pistons does help make your car rev faster? weve experienced it with the sr20'sif theyre nt heavyier than stocks!

[pregmantis]

The sr20det is known for its power because of its turbo. dont make it about its stroke and bore.

[UK-SRi]

Look to bigtoes description of the engine about half way down:http://www.sr20forum.com/showthread.php?t=126570

And another description of nissan engines from the same guy about half way down:

http://www.sr20forum.com/showthread.php?t=129275

and again about half way down:http://www.sr20forum.com/showt...age=2

about 3/4 down for this one:http://www.sr20forum.com/showthread.php?t=105540

Anyway the point of all those is to show some of what is needed to make a revhappy engine.

Mike
Modified by UK-SRi at 11:10 AM 10/8/2005

[SimpleEnigma]

Wow....that dude really knows his stuff. i will definately have to go to do a little more research on have the vocabulary words he used and reread what he has posted, but that is a great deal of highly valuable info.

i wonder if anyone makes a fully counterweighted crank for the KA block or if it is possible to dynamically balance a half-counterweighted crankshaft found the KA motors.

personally, i wonder what the CORR guys use.

[UK-SRi]

Well there was another one of his long posts where he discusses the range of bore/stroke and rod stroke ratios that was really useful but I couldnt find it easily. I wish I understood engines as well as him. One of his posts discusses understroking an SR20, overbore to 92 to keep the cc's then sort out the valvetrain to make a 9K screamer out of the SR20. but the same principles apply to any engine. We have to look at which part of the configuration is preventing us from getting what we want out of the engine.

Mike

[EugeneSentraSTI]

if you think a sr20 is only fast with a turbo!!!

then if got abig surprise,the sr20 is one of the best 4 cyl motors available today,, even if you dont turbo it,, it is possible to get a sr20de to get 250hp n\a obviously at the loss of drivability but you can very well go higher!!!

even if you consider the fact that the hp and torque is all up there!!!

if you considera honda will be able to make the horses shure? (i think)but it would be able to torque in the same effect as the nissan!

this we have all seen time and time,, look at the 400m times?shure the honda's goes,, but look at the speeds? strange hey?

[zero_gripS13]

question.. u guys are tlaking about using the ka24e head.. i didnt think it had potential for high rpms due to its rocker arm setup... or am i missing something... thanks guys

[UK-SRi]

I thought the KA24 had a better valve arrangement than the SR20. In the SR20 it is one lobe feeding two valves and that can get tangled trying to follow at high RPM. But I figured the question was about the bottom end limits and that the top end changes might be something that the original poster knew what to fix??

Mike