KA head, good or bad?

[Swedish Mike]

Hi guys!

We never got the KA here but some guys import them so we got a few.Heard a while ago that the KA got a bad head (when we talk flow and shape), is this true? From the beginning a low powered truck engine.Is the CA18 or SR20 heads better?

The KA block is probably the strongest we can use right? Do you know if the SR or CA head would match the KA block?

Many hard questions but I know some of you are good!

/Mike

[corn322]

Apparently they're not as bad as everyone thought, there was a thread on here a while ago this guy started 'cause he cut one in half...

zerothread?id=162991

Some flow numbers in there too.

[Swedish Mike]

Apparently they're not as bad as everyone thought, there was a thread on here a while ago this guy started 'cause he cut one in half...

zerothread?id=162991

Some flow numbers in there too.

Yeah, saw that when I searched. Do you know about the rest? Can exhaust valves and stuff handle the heat?

/Mike

[david200095367]

i think it can handle the heat. we have a few guys with over 500hp redlining at 7200 rpm on stock heads.

[ShionS14]

Most people say the KA head is crap because it cant rev to oblivion but psi to psi with a SR20 motor the ka will be more powerfull because of the displacement. Now like any motor the internals have their limitations but parts can easily be sourced to build a "bullet proof" motor, including exhaust valves made with inconel material

[Chezedik]

And in fact, it can rev better than SR since it is cam on bucket. You don't get rocker arm float like you do on SR.

[sunnys14]

theres no point of revving that high because u dont make power up there. the thing you would want to worry about isnt the head (if u want to rev to 7200). you should be more worried about throwing a rod if u rev to 7200...

[Chezedik]

Perhaps more true in a turbo (I am getting very close to getting mine ready to blow up, lol), in my previous NA 240, it was a very common practice to take it to 7.5. Although, I know now that it was worthless to do (as it put me beyond peak TQ, making me slower), I also know the engine is more than capable of taking it.

[sunnys14]

how did u rev to 7.5k on a KA? did u have an ecu reflash??!

[S14tat]

its not wise to rev a KA that high anyways, the piston speed would be waaaay to fast to be reliable. thats the problem with having a longer stroke, i personaly think that's what kills us, we have the same gear ratio's as a SR, but they can make power waay past our redline. if a SR revs to 9K it can hit like 170 and change in 4th with a different rear end and larger wheels, when can barely hit that in 5th with a 7K redline and larger wheels. so when we have the advantage off the line with the low end tq, once the engines already at full boil and you shift and stays on boost, it appears that the SR has a broader power band up top for roll on races.

[Chezedik]

It was a long time ago, and it may have been a little lower, but I know it was well into red. And I never once hit a rev limiter. It was a 92 S13. I killed the speed govenor, but I would doubt that affects the rev limiter. It was worthless and stupid little kid stuff, but the point stands that it is a very strong motor, that will not have the valve float problem that an SR will.

[KATwo40]

My KA24DE-T has approx. 180k miles on it, and I've been boosting for the past 20k+ miles.

Before and after adding the turbo, it has ACCIDENTALLY seen 7400rpm (no limiter was hit...'93 5spd, stock ECU).

After getting the SAFC2 and playing around with the monitors, I realized that the stock tach is off by as much as 350rpm around 4-5k rpm. So, I'd imagine that when it says 7400, it's really more like 7100rpm.

I don't make it a habit to rev that high...sometimes while autocrossing I need about 30 more feet before lifting and hit the red. I really gotta quit that. Not sure how long this 180k mile engine is gonna take 8psi @ redline from a T04E. LOL

[Nismo_Freak]

It was a long time ago, and it may have been a little lower, but I know it was well into red. And I never once hit a rev limiter. It was a 92 S13. I killed the speed govenor, but I would doubt that affects the rev limiter. It was worthless and stupid little kid stuff, but the point stands that it is a very strong motor, that will not have the valve float problem that an SR will.

You will run into more valve float problems on the KA than the SR, due to the fact that the valve is considerably larger. The rocker arm setup is not as bad as everyone puts it out to be, in fact rocker arm failure as a result of the arm coming off is rare if you keep it under 8000 RPM.

[Swedish Mike]

Thanks guys! That´s really good info.

I just hate rockers and you say the KA got the same valve mech as CA18? Nice...I still think about what engine to use, done the CA and SR before but KA is new.I´ll build a forged botton but need a solid head and this sounds good.

You got 2 KA´s right? One 155 hp and one low powered? Difference?

/Mike

[Thursday]

Thanks guys! That´s really good info.

I just hate rockers and you say the KA got the same valve mech as CA18? Nice...I still think about what engine to use, done the CA and SR before but KA is new.I´ll build a forged botton but need a solid head and this sounds good.

You got 2 KA´s right? One 155 hp and one low powered? Difference?

/Mike

SOHC KAand DOHC KA

to the wheels there is about a 9 whp difference

[Chezedik]

Good point, the only one I was making is that by having the extra part in the mix (rocker) that you would have a longer recoil time, but certainly our valves would be heavier too. Hmmm, this hasn't turned out to be a bad thread after all.

[Nismo_Freak]

Good point, the only one I was making is that by having the extra part in the mix (rocker) that you would have a longer recoil time, but certainly our valves would be heavier too. Hmmm, this hasn't turned out to be a bad thread after all.

The rocker is loose and only about 1/6th of the weight of the rocker arm rests on the valve. The best cylinder heads ever to come out of Japan run rocker arms, keep that in mind.

My hypothesis on the rocker arm debate is that the HVLA's are incapable (read, not designed) to solve lash conditions at high RPM's. The lash then opens and the impact loading from the rocker and cam cause either the rocker to shatter, or for the rocker to dislodge.

Then again the KA's issue isn't the valvetrain design, it's the bottom end when it comes to sustaining high RPM. On the SR, you run into both a valvetrain and bottom end grey area when you are sustaining RPM above 8000 RPM. There are people running SR's to 9000 RPM on stock HVLA's, but I don't exactly want to put up with the mess when things go wrong. At those RPM's the OEM bearings and rod bolts aren't up to the task IMO.

[Swedish Mike]

The rocker is loose and only about 1/6th of the weight of the rocker arm rests on the valve. The best cylinder heads ever to come out of Japan run rocker arms, keep that in mind.

My hypothesis on the rocker arm debate is that the HVLA's are incapable (read, not designed) to solve lash conditions at high RPM's. The lash then opens and the impact loading from the rocker and cam cause either the rocker to shatter, or for the rocker to dislodge.

Then again the KA's issue isn't the valvetrain design, it's the bottom end when it comes to sustaining high RPM. On the SR, you run into both a valvetrain and bottom end grey area when you are sustaining RPM above 8000 RPM. There are people running SR's to 9000 RPM on stock HVLA's, but I don't exactly want to put up with the mess when things go wrong. At those RPM's the OEM bearings and rod bolts aren't up to the task IMO.

That´s very true, most jap cars got rockers but only one got good reasons I think. Honda need it for the V-tec soo that´s ok with me.

The bad thing with rockers is not weight, reaction time or noise IMO.The problem is this, they brake. With every new moving part you put in an engine you increase the risk of problems.

Many high hp cars here have rocker problems, you buy stiffer springs and high lifting cams, the rocker brakes even easier after this.My friends SR20 got problems even after buying CNC made rockers.

Just hate rockers, if I can I would live a rocker free life.

/Mike