KA destroke?

[98S14SE]

So, as we all pretty much know the KA isn't made to rev, and we all know the many problems that arise due to that fact. So I was sitting around thinking to myself, why not destroke it? Say destroke it to 2.2L or 2.1L, and run a longer rod of course, and maybe even a much shorter piston. Combine that with a head that was designed to flow for a much larger engine, and the benefits become obvious. Forgetting about cost of a custom crank, rods, and pistons, is this theory flawed? If not, what is stopping us from contacting say eagle or scat or someone, and telling them we want to have them build say 10 destrokers at a reduced cost? Any thoughts?

[Thursday]

i believe you can do it with oem parts if you dig deeper into the wonderful world of nissan engines. Think outside the ka engine family.

[9sec240]

I already have a de-stroked KA project in the works... The KA rod journals are HUGE so its easy to offset grind the crank to destroke it... We are working on a bearing combo that will work well for this setup.. custom rods and pistons will be required... I plan on keeping the stock rod lenght and lowering the piston pin height to make up for the shorter stroke...

The following maximum piston speeds are from the book, Performance Tuning in Theory and Practice, by A.G.Bell. Keep in mind that this book was published almost 10 years ago and things have changed a bit since then... Materials are better and stronger so the suggested components listed are a little on the overkill end of the spectrum and the piston speeds suggested a little on the low side...

Stock Motor - 3,500 fpm (cast crank, stock rods and cast piston)

Heavy Duty Motor - 4,000 fpm (forged crank, peened rods w/ good bolts, forged piston) Drag Racing Motor - 5,000 fpm (forged crank, alum rods, lighweight pistons, etc.)

Our stock motor has forged crank, shotpeened rods... revs to 6500 puts piston speeds at about 4100 fpm.

Putting forged rods and forged pistons in your motor with good bearings and precision ballance puts your setup in the Drag Racing Motor catagory...

We often spin our stroker Evo motors to 8600 rpms which puts piston speeds at 5643 fps.... Thats quite a bit more than stated limits of a drag race motor.. Our new motor for our Drag Evo will be spinning to 10,000 rpms which will put piston speeds at 5774 fps... These piston speeds create a tremendous load on the bearings which will have to be inspected and replaced regularly.... the rod and piston combo have to be top quality and super strong to take this abuse...

With all forged components in your stock stroke KA and a good ballance, pushing it a little past 5000 fps would be quite doable... 8000 rpms puts piston speeds at 5040 which in my opinion is VERY reasonable....

OK.. back to a destroked KA.... Offset grinding the crank 3mm will produce a 90 mm stroke and a nearly square motor... This also allows for a little over 500 more rpms for the same piston speed... 8500 rpms nets 5020 fps... An added 500 rpms of revs would sure be sweet in a KA...

Of course none of this will be bennificial without a head that can flow well and an intake manifold / cam combo that are tuned for these rpms...

As always, I will be doing a lot of research and development on this project and will be posting up results....

[Florida240sx]

[deviousKA]

Ivan, your dealing with far too much weight destroking the actual 2.4l. The stroke you remove is requiring a heavier rod/piston combo than you were using originally with that deck height, and with aquired stroke and r/s ratio, it is not going to provide the greatest results. The turbo charger will help of course, but for example, in any sort of NA application, this engine would be very reluctant to rev and/or hold rpms at any reasonable level. The rotating assembly will be under less stress due to the rod angles, and you will less piston speed, but this is far from everything you need to consider when designing an engine (because thats basically what you would be doing). The rod/stroke ratio is too high, and the rod/piston combo is too heavy for 90mm stroke..

I wouldnt suggest going any shorter than 92mm in stroke on the 2.4l blocks. And for this you can use a 92mm z22 crank as a drop in to the z2.4 or in a ka24 block with turned down snout and widened thrust mains (of the block). Machined spacers with tapered head fasteners would be the best option when widening a block thrust, rather than doing any sort of welding on the block or crank.

If you want to drop 90mm or lower on the stroke you need to use an alternate block. You will want to concentrate on utilizing a realistic but respectable r/s ratio, and the shortest lightweight pistons you can get manufactured. Something like a mahle at 27mm compression height, or any manufacture that will get lower than 30mm.

To be satisfied with a destroked KA, you need to get very in depth and understand your complete design. Like I mentioned before, you are not modifying your current engine, you are building a whole new engine, from scratch. There is a lot of engineering to do, best thing to would be to start reading anything you can get your hands on in regards to rotating assembly/theory.

[9sec240]

Thank you for your input.... but I think your being a bit pessimistic....

The piston weight will easily be the same or less than a stock style forged piston with a good design... We are talking about moving the pin down 3mm (.118") which is not excessive... Even if the skirt needed to be lengthend by that amount the weight would not go up signifigantly.... Because the pistons will be custom, the ability to remove weight from another part of the piston is always an option.... The rod length stays the same which will not increase weight... Reducing the big end diameter for the smaller rod journal will actually reduce weight... Having aluminum rods built will produce an even lighter rod...

Rod stroke ratio goes up a slight amount from 1.719 to 1.737... refer to THIS article reguarding RS ratios in this range... NASCAR motors run a RS ratio that is almost identical to the stock KA I really dont feel the RS ratio is an issue...

Displacement will drop slightly from a stock bore stock stroke 2387cc to a .5mm over 90mm stroke of 2263cc.... .124 L is not a huge amount....

Assuming that TQ stays the same, a jump from 8000 rpms to 8500 rpms at 400 lbs tq brings HP from 609 to 647...

AMS and our engine machine shop have stroked and destroked many motors and have a lot of experience doing this... We are weighing all the options and looking for the maximum power we can get out of the KA...

[wild_maxx]

two very knowlagable people on one forum working together!

both of your post went OVER my head tho.... GOOD LUCK!

[KATwo40]

There's an old saying that has always been the best rule of thumb.

"If you want more power, you need more inches. And if you want more inches, you gotta stroke it!"

Do you know that a top fuel 6,000hp 518cid F/I engine doesn't turn more than about 7,000RPM?

Ok, sorry. I can see that my input to this conversation is slowly turning toward "No replacement for displacement" and now I'm threadjacking. I'll bow out now.

[9sec240]

F1 motors run nearly 20,000 rpms.... Whats the point?

We are dealing with a finite engine package.. We cant bore the motor much larger, we cant stroke the motor more but we CAN de-stroke the motor and get more revs out of it which equates to more HP at the same TQ....

Basically taking a motor that was built for low end TQ and re-engineering it for more top end HP...

[deviousKA]

Pessimism is valuable when devoting time to designing an engine. Mistakes are expensive.

I dont see where you are coming up with this 1.737 rod to stroke ratio. Your ratio will be 1.83:1 as described above. A 92mm stroke would put you at 1.8:1 with 2.4l rods.

Remember just how heavy forged aluminum is, yes you can probably make a lighter piston relative to the oem ka24, even with the larger dimension. The weight savings with a very well designed skirt and pin boss arrangement will be very little, not nearly as much as you would need. The piston is only the small part of the picture, as the necessary length for the rod is going to be relatively heavy no matter the material (within reason).

You will be spinning this heavy combination on a 90mm stroke with a rod to stroke ratio that works directly against your cause. The engine will not run though rpms half as fast as a lightweight 1.74-.76 r/s ratio on the same crank, it will drop out of its powerband any chance it can get.

Check your math, do some reading, I am just trying to help you out. I would rather not see a public destroked KA attempt go a flop with poor results.

[deviousKA]

And just to add,The powerband, you would rarely reach it and the strength of the available components (crank) pretty much makes it unfeasable. Within the range you can actually use the engine (9000 rpm and under, at best), it will be a pig.

Full custom rotating assembly to spin 11k+ and those dimensions may be usable. By then you would be coming into the range where the engine is efficiently spinning its own weight, with a few thousand rpms to go.

Trust me, you want 2.1-2.2L displacement you need a shorter block.

[9sec240]

You are correct.. my math was off for a 90mm stroke... I cant figure out what I did to come to that RS ratio...

[Edub1]

I hate to be a wet blanket but assuming this would work, would it be at all practical? If you're prepaired to do all that custome fab work, why not spend the time putting a better motor in your car?

[TheOne]

I hate to be a wet blanket but assuming this would work, would it be at all practical? If you're prepaired to do all that custome fab work, why not spend the time putting a better motor in your car?

because.......they like their KA's, and i like my KA too, its somehow a unique engine overall.

i mean yeah you can put in another engine and blabalbla, but most good swaps have allready been done and so they want to be unique by having better parts and better knowledge about this particular engine.

[PapaSmurf2k3]

because if ivan can re-design a motor, he can do just about anything, and sell it, and people will buy it. Besides, its just cool.ivan gets my vote.P.S. Ivan- i talked to you the other day on the phone about that oil line fitting. I think im going to try to make my own. Sorry I took up your time, foster made me do it

[Florida240sx]

Once he completes the engine.If it has strong gains then it will be a new market that he owns. He will have the respect of doing it.Just like he has with the twins car. Look at his current engine.........enough said. He builds and people buy it. It adds to list of new parts for the KA motor. Why drop in a 305 when you can destroke the motor and have equal if not greater power. Until #'s are produced and you can compare, keep your mouth shut abotu jsut swap to bigger motor. This isn't a "What motor to get thread" it's a thread about exploring the capabilities of the ka.

[98S14SE]

Good info all. For clarification, I am speaking of a forced inducted application. I first thought of the idea while trying to match various compressors to the engine. I kept running into problems with maximum rpm. I hate to say it, but I am a little lax in the physics department. If someone is seriously interested in building a custom crank, I think it would be feasable to have one mass produced. For the record, I know for a fact that scat and eagle claim to be able to make custom cranks for anything, and at basically any stroke. If someone has the dough, and can convince them that it can be a profitable endeavor I am sure one could be mass produced. Getting the first one right, though, is the key. If 9sec240 gets it right the first time, if provided the specs, I think I could convince scat or eagle to produce it, if given permission. Oh, I work in parts for a massive WD, and for some reason these companies take our imput pretty seriously, despite how inept some of my coworkers may be

[KATwo40]

I hate to be a wet blanket but assuming this would work, would it be at all practical? If you're prepaired to do all that custome fab work, why not spend the time putting a better motor in your car?

[KATwo40]

Why drop in a 305 when you can destroke the motor and have equal if not greater power.

For the record: No 146cid engine will EVER have the power output potential of a 305cid engine, mod for mod. Otherwise, all racing vehicles would run 4cyl. engines.

I still think fabbing up a kit to destroke the KA is moot. Even if the parts are mass produced, the cost will outweigh that of purchasing an SR20DET already capable of handling the revs and power. Sure, might be just a tad down on torque, in terms of peak numbers, but it will still be within a useable rpm range. I'm with DeviousKA on this one. If you want a smaller engine, build a smaller engine. Heck, if you want to rev 10k or more, swap in a B18B or a Wankel...they like to rev...and both would certainly be "different."

[C-Kwik]

While HP does increase with RPM for a given amount of torque, decreasing displacement will tend towards decreasing torque. So to keep torque levels higher at those higher RPM's, you'ld really be having to stretch VE or the strength of the components. I'd probably not compromise the components so increasing VE would be the better option, but I think you'll end up with a narrow powerband that might prove less effective overall. If your purpose is to challenge yourself or build a dyno queen, go for it. But if you're looking for a better way to do things, I'd probably take a more realistic look at what results you may be ending up with.

Don't get me wrong, I'd love to see it accomplished, but to make this work as effectively as you'ld like, I think you have some huge challenges to overcome. It just seems like you'll be to a large extent, working against yourself. If you're up to the challenge though, I wish you luck on it...

[KATwo40]

While HP does increase with RPM for a given amount of torque, decreasing displacement will tend towards decreasing torque. So to keep torque levels higher at those higher RPM's, you'ld really be having to stretch VE or the strength of the components. I'd probably not compromise the components so increasing VE would be the better option, but I think you'll end up with a narrow powerband that might prove less effective overall. If your purpose is to challenge yourself or build a dyno queen, go for it. But if you're looking for a better way to do things, I'd probably take a more realistic look at what results you may be ending up with.

Don't get me wrong, I'd love to see it accomplished, but to make this work as effectively as you'ld like, I think you have some huge challenges to overcome. It just seems like you'll be to a large extent, working against yourself. If you're up to the challenge though, I wish you luck on it...

FWIW, most engines designed for N/A application, in terms of head design, actually LOSE VE when you add the turbocharger, since the resonant effects are negated by the giant restriction in the exhaust stream. Currently, it's common to see N/A engines with 115% VE, while adding the turbocharger tends to knock it down a bit. Few turbocharged engines see more than 100% VE and most that do exceed this have extensive headwork.

[Iamjohnhayes]

explain to me how something can be more than pefectly , 100%, efficient. i think its more like new na motors are in the range of about 93-97% (damn those hondas) and someone explain how adding a turbo lowers your ve. i can see how the added heat produced could mabe do it or just something im not thinking of.

[KATwo40]

Using engineered resonance and perfect valve overlap to achieve optimum scavenging, the engine can acutally consume more air (in terms of displacement, not lb/min.) than the mathematical displacement of that engine. Therefore, it's common to see 100%+ VE on late model N/A engines.

Once you add the turbocharger, you negate the resonating effects that were designed to achieve the high VE. All head scavenging has ended because the exhaust manifold pressure is greater than the intake manifold pressure, so you've reversed the delta P across the head.

When highly engineered setups achieve exhaust manifold pressures equal to or lower than the intake manifold pressures, but still spool the turbocharger (this would be an example warranting the use of the VATN tubocharger, heavy N2O use to spool a large turbine, etc.), the resonance can occur that promotes scavenging, thus increasing the engine's VE.

Hope that helps.

[jollygreen]

Wouldn't it be possible to have the block machined downed a couple mm to lower the deck hight??? This probably isn't possible due to oil and water passages but I just thought i'd throw it out there. Couldn't material be welded to the cylinder head to make it almost flat in the combustion chamber and have the majority of the flame front characteristics and quench zone be handled by the pison domes?
Modified by jollygreen at 8:54 PM 4/18/2006

[PapaSmurf2k3]

i beleive if you do something like that, it will severely screw with your compression ratio. so in a short answer.. No, you cant do that.

[C-Kwik]

FWIW, most engines designed for N/A application, in terms of head design, actually LOSE VE when you add the turbocharger, since the resonant effects are negated by the giant restriction in the exhaust stream. Currently, it's common to see N/A engines with 115% VE, while adding the turbocharger tends to knock it down a bit. Few turbocharged engines see more than 100% VE and most that do exceed this have extensive headwork.

What production NA motor is putting out 115% VE? Getting over 100% VE out of a N/A motor requires certain conditions to exist. And even in a race motor, it occurs for only a relatively short range of RPM's. And asking it of a production engine? Without tuned intakes and headers, it's unlikely that you'll accomplish such a feat. Even with the variable lift and timing systems currently available, it's difficult if they are going to rey and balance it with drivability, smog and fuel economy standards that manufacturers need to keep an eye on.

However, my reference to VE still stands as it would be necessary to increase it to make up for the lower displacement. Since power output is very closely related to how much air is going through an engine, an engine with a smaller displacement will need to have a higher VE to make up for the airflow.

[C-Kwik]

When highly engineered setups achieve exhaust manifold pressures equal to or lower than the intake manifold pressures, but still spool the turbocharger (this would be an example warranting the use of the VATN tubocharger, heavy N2O use to spool a large turbine, etc.), the resonance can occur that promotes scavenging, thus increasing the engine's VE.

It doesn't take a highly engineered component. Just good turbo choice. Even in a well chosen turbo, the low exhaust pressure to intake pressure ratios exist only a certain range of the turbo's map. This is why making sure the compressor is matched well to the turbine as far as where the peak efficiencies occur can be very beneficial.

As far as a VATN turbo, it, in that of itself, does not create this type of effect. Even with a VATN turbo, sizing the turbine and compressor wheels appropriately is necessary. VATN (Variable Area Turbine Nozzle), simply, is a variable A/R ratio on the turbine. At lower RPM's and boost, it can apply a low A/R allowing the higher velocity needed to spool the turbo and then open up the A/R as RPM's and airflow rise and becoming less of a restriction in the exhaust stream.

[KATwo40]

I know how a VATN system works, otherwise I wouldn't even mention it. I don't throw references I don't understand. A VATN setup could allow for a vastly oversized turbine housing, which would provide the proper delta P across the head to achieve scavenging.

And yes, some production engines have been recently documented to achieve over 100% VE. While only for a short time, it's still happening. And if it's happening for a short time in the RPM range, then it's obvious that the overall VE % is higher than what the industry accepts as "standard."

If you wish, I'll cite my source. This is a thread from the EFIUniversity forum. There are some of the best tuners in the world found here.

http://www.efi101.com/forum/viewtopic.php?t=1354

[C-Kwik]

I know how a VATN system works, otherwise I wouldn't even mention it. I don't throw references I don't understand. A VATN setup could allow for a vastly oversized turbine housing, which would provide the proper delta P across the head to achieve scavenging.

But here's my point. It doesn't require a VATN turbo to achieve this result. Your post implies otherwise.

And yes, some production engines have been recently documented to achieve over 100% VE. While only for a short time, it's still happening. And if it's happening for a short time in the RPM range, then it's obvious that the overall VE % is higher than what the industry accepts as "standard."

If you wish, I'll cite my source. This is a thread from the EFIUniversity forum. There are some of the best tuners in the world found here.

http://www.efi101.com/forum/viewtopic.php?t=1354

But how is it common? To be fair, maybe you should clarify what you consider common as well. But I speculate that the effort to build motors that can do this would be reserved for specific applications. Common cars tend to be people movers and don't need that kind of attention. I don't question the possibility. But given all the things manufacturers need to keep an eye on as they design, build and tune their motors, it would not be a cost effective option to be seeking extremely high VE's out of cars that will rarely see the RPM range where these high VE's are likely to be tuned to occur. I think that we are more likely to see a relative "handful" of motors that can achieve this from the OEM.

As far as your source, it mentions only one specific example. I'd love to see an actual list. Even better would be to know when the event occurs(RPM range) and perhaps what VE these motors run at other RPM's.

[KATwo40]

You should log in over at EFIU and ask in that thread. I'm sure you'd get your list, and it would make for some good reading. I'm inclined to believe those guys when they say "most of the engines produced today" when it comes to which one's achieve 100%+ VE. These guys are some of the top tuners in the world. They tune for a living, on a daily basis.

Also, to clarify something...the Enthalpy on that forum is NOT the Enthalpy that tunes Nissan ECU's. I asked.

Also, I never said that a VATN would be the only way to achieve the ideal pressure differential across the head. I was just stating that it would be a very good way to do so. It's not like the VATN is a BAD thing, right?
Modified by KATwo40 at 1:58 PM 4/19/2006