KA vs. SR / Speed vs. RPM

[UNISA JECS]

Not to long ago went KA24DET and I dislike my gearing more so than I ever have on my SR20DET, and changing gears in the actual tranny is not an option to much money at this point.

I have made up my mind to do the next easiest thing and change the Final Drive to one from a 97-01 Q45 which uses a 3.69 FD vs the stock 4.08 FD.

Having owned enough SR20DE and SR20DET powered vehicles I can honestly say that they have no problems what so ever making power to redline 7,500rpm all day every day.

Having now my KA24DET it is apparent they are both really different in respect to powered band (duh) and especially torque....while the SR can and does accelerate to redline of 7,500rpm the KA24DET on the other hand has an indicated redline of like ~6,900rpm (S13).....but in my case peters out about 6,200rpm meaing doesn't really accelerate hard after this poing but for all purposes of what im about to compare will use a redline of 6400rpm.

BTW the comparison idea came up after me (S13 coupe KA24DET) and a friend (S13 coupe SR20DET) did a couple of rolling starts because I always had a theory about this and sure enough it was true ofcourse the SR has an adavantage on rolling start because its gonna be somewhere right at the start of its power band whereas the KA24DET will be somewhat into it power band already and running out of it much quicker than the SR that can rev to redline 7500rpm accelerating with ease.

Setup my car (S13 KA24DET)
225/35/18
M/T
F/D 4.08
Adjusted Redline 6,400rpm
Maximun speed per gear (based on power band and 6400rpm which if made even lower would result in less speed per gear)

1st gear = 34mph
2nd gear = 59 mph
3rd gear = 86 mph
4th gear = 113 mph
5th gear = 149 mph

-------------------------------------------------------------------------
Setup friends car (S13 SR20DET)
Dont remember exactly but it was virtually the same over rolling diameter I know that because both are speedos were dead nuts accurate.
M/T
F/D 4.08
Redline 7,500rpm
Maximun speed per gear (based on power band and 7500rpm which if made even higher would result in more speed per gear which isn;t hard to acchieve on a SR)

1st gear = 40mph
2nd gear = 70mph
3rd gear = 101mph
4th gear = 132mph
5th gear = 158mph

--------------------------------------------------------------------------
NOW my KA24DET with a 3.69 final drive everything else the same

1st gear = 38mph
2nd gear = 66mph
3rd gear = 95 mph
4th gear = 125mph
5th gear = 165mph

Much better suited as far as having a now semi comparable but still less speed per rpm than the SR. On the flip side though you wouldn;t find a SR owner really wanting to use a 3.69 final drive..

[Rnz520]

Nice thinking, I was never sure if the Q45 diff bolted up tho, I dont think it does. +1 for you for taking your time and doing this.

[UNISA JECS]

Nice thinking, I was never sure if the Q45 diff bolted up tho, I dont think it does. +1 for you for taking your time and doing this.

Yea the Q45 diff's work as follows:

Requirements:
G50 Q45 89-96 (3.53)
1) Mix and match axles from G50 Q45 and Z32 300ZX TT plus hubs from either of the two mentioned models
2) Swaping companion flange or redrilling

FGY33 Q45 97-01 (3.69)
1) JDM S13 5 bolt or J30 5 bolt axles (this is way less headache than the G50 Q45 as it doesn;t require hub and axles changes if you have 5 bolt axles already)
2) Swaping companion flange or redrilling

[WangonwWarrior]

Nice write up

[g6civcx]

You're not addressing one very critical point: effective thrust at the driving wheel(s).

Thrust is a function of torque at the driving wheels and the wheel diameter.

It doesn't matter what RPM you're turning and gear ratio and final drive, all that. All that matters is how much torque you can put to the rear wheels, and how much thrust you can transfer to the ground.

Confusing? Do you need me to explain more?


Thrust is also how you calculate your shift point in each gear. If you can make more thrust in the current gear, you don't shift. If you can make more thrust in the next gear, then you shift up. The ideal shift point is where the two thrust curves meet and the current gear drops off and the next gear picks up.

[UNISA JECS]

You're not addressing one very critical point: effective thrust at the driving wheel(s).

Thrust is a function of torque at the driving wheels and the wheel diameter.

It doesn't matter what RPM you're turning and gear ratio and final drive, all that. All that matters is how much torque you can put to the rear wheels, and how much thrust you can transfer to the ground.

Confusing? Do you need me to explain more?


Thrust is also how you calculate your shift point in each gear. If you can make more thrust in the current gear, you don't shift. If you can make more thrust in the next gear, then you shift up. The ideal shift point is where the two thrust curves meet and the current gear drops off and the next gear picks up.

All I know is my shift point are based on on when my KA runs outta steam which is actually a tad bit lower than 6400rpm but nonetheless I still used it as an adjusted lowered rpm shift point.

The whole reason for this upgrade is to take more advantage of the KA-T powerband, moreless making it work longer in its power band (low-mid)which is more in the middle compared to a SR which is more mid-top end powered. If you have driven a KA-T you would see why a 4.08 FD sucks on a KA but is great on a SR.

[justaKAiswear]

You're not addressing one very critical point: effective thrust at the driving wheel(s).

Thrust is a function of torque at the driving wheels and the wheel diameter.

It doesn't matter what RPM you're turning and gear ratio and final drive, all that. All that matters is how much torque you can put to the rear wheels, and how much thrust you can transfer to the ground.

Confusing? Do you need me to explain more?


Thrust is also how you calculate your shift point in each gear. If you can make more thrust in the current gear, you don't shift. If you can make more thrust in the next gear, then you shift up. The ideal shift point is where the two thrust curves meet and the current gear drops off and the next gear picks up.


So what goes in to the calculation of thrust? Is it simply the point in the torque curve that, when shifting, the power at the lower RPM of the shift is equal/greater to the thrust at the higher RPM of the point at which you are shifting from?

[UNISA JECS]

KA is more like a low reving American V-8 and needs a similar FD more comparable to those found in such cars.

SR is like, well what it is a high reving JDM 4 cyl that doesn't need a taller FD because for one it can rev and two doesn;t make tons of torque (but also isn;t weak on torque neither compared to others)

[justaKAiswear]

All I know is my shift point are based on on when my KA runs outta steam which is actually a tad bit lower than 6400rpm but nonetheless I still used it as an adjusted lowered rpm shift point.

The whole reason for this upgrade is to take more advantage of the KA-T powerband, moreless making it work longer in its power band (low-mid)which is more in the middle compared to a SR which is more mid-top end powered. If you have driven a KA-T you would see why a 4.08 FD sucks on a KA but is great on a SR.

What turbo do you have on the KA-T? Wouldnt the turbo be to blame for the drop in power (and therefore speed) more so than the gearing? Seems like a larger housing could help fix the drop in power and make you a little happier with the gearset.

[UNISA JECS]

What turbo do you have on the KA-T? Wouldnt the turbo be to blame for the drop in power (and therefore speed) rather than the gearing? Seems like a larger housing could help fix the drop in power and make you a little happier with the gearset.

Well first if your a KA-T owner I think you gotta come to the realization that the KA just isn't a rev happy motor to begin with probably due to it "not" having a fully counter weighted crankshaft like the SR does for one thing, I dont think the long stroke is the issue neither as the Neon SRT-4 have been known to rev higher than 7500rpm easily but those are fullycounterweighted 2.4L engines amoungst other things.

But all is not lost you just need to fix FD to better suite the KA needs which I think is more speed per rpm because teh stock FD sucks IMHO.

[UNISA JECS]

What turbo do you have on the KA-T? Wouldnt the turbo be to blame for the drop in power (and therefore speed) more so than the gearing? Seems like a larger housing could help fix the drop in power and make you a little happier with the gearset.

Regaurdless of turbo size the characteristics remain very similar even on dynos, ofcourse you can do things to help top end breathing such as cam and what not.

[blownmotor]

Swapping the final drive only band aids up your problem. Possible problem is not that your KA is running out of breath, maybe your turbo is too small. The only way and engine truly "runs out f breath" is due to the design of the head itself by not flowing enough. You might just need a bigger turbo and/or cams to help the engine breath at higher revolutions.

[UNISA JECS]

Swapping the final drive only band aids up your problem. Possible problem is not that your KA is running out of breath, maybe your turbo is too small. The only way and engine truly "runs out f breath" is due to the design of the head itself by not flowing enough. You might just need a bigger turbo and/or cams to help the engine breath at higher revolutions.

lol....a band aid.....yea your right about head design and what not about teh turbo being small and stuff but all that said and done even at 6400rpm look how weak your speed vs rpm is on the KA compared to a 7500rpm redlineing SR. These cars characteristic are nowhere near the same. Knowing that tells you you need to do something about the gearing to gain more speed per rpm, instead of having to shift much more rapidlt then you would have to in a SR.

[UNISA JECS]

Just because of this one fact alone the KA has a lower rev range than the SR should tell you the gearing may become an issue specially for a turbo'd KA, the KA need to able cover more ground in a shorter rpm band then the SR to be more comparable.

Look at the V8 powered Fords, Chevys "low reving" and the like with ~6000rpm redlines give or take a few hundred rpms and look at the final drives, ofcource the overall rolling diameter of there wheels is a factor also but you see mainly 3.5 and less final drives used.

[g6civcx]

Look at the Chevys "low reving" with ~6000rpm redlines give or take a few hundred rpms and look at the final drives


Looks under hood. Chevys "low reving" - check.

Looks at diff. Stock 4.083 - check.

What's your point? :)

[UNISA JECS]

Looks under hood. Chevys "low reving" - check.

Looks at diff. Stock 4.083 - check.

What's your point? :)


1999 Mustang GT one source shows ~3.27 and ~3.55 final drive with a redline of ~5700rpm

Like I said above somewhere to, the overall rolling diameter is also part of the math, just as important since im talking about other vehicles with different transmission, there respective tranny ratios are equaly important which I believe you will also find some taller than the stock SR and KA ratios.

[UNISA JECS]

Better yets let compare and see what MPH these "low reving" american cars get at there respective redline, something tells me its much higher than that of a stock KA24DE with a 4.08 being rev to 6400rpm gear per gear....It just not that easy to get all there tranny specs, tire specs, and final drive without searching then you can easily calulate the difference for comparison sake.

[Skeeg]

i can tell you my stock ka pulls hard till 7k... all i have done is an intake, hotter plugs, and s13 cams in a 95 s14 de.

im guessing there is something either wrong with your car or you just dont have the right parts to get what u want out of it.

[Koopa Troopa]

You know what makes the RPM's go up faster? More boost.

You're the only one to blame if you can't take a KA24DET to 7k rpms and make power.

[GSXRJJordan]

When I first saw this, I thought "omg, he's putting taller gearing into his S-chassis? WTF?"

g6 hit the nail on the head - it's not about speed in each gear, it's about thrust. You're going to feel like you've got even less power now, because you'll effectively be trading torque for top speed.

Good luck, and remember, you can always change back and get cams :)

[UNISA JECS]

I can hit the rev limiter no problem, theres no problem there it just doesn't seem worth it at this point to do that, I diffenantly will invest in cams in the future and Nistune so I can tune my own ECU real soon.

I dunno if you look at alot of dyno's of KA-T's you'll see quite a few KA-T's droping power by a fast amount around the 6k give or take 500rpm.

[S14DB]

Do you have stock cams?

[UNISA JECS]

Do you have stock cams?

Yea I have stock cams, I know there is a noticeable diff between the 91 cams and the 98 cams, im using those as a refference because I owned both engines and both turbo'd and the 91 pulled better.

[oskars14kat]

My KA-T pulled hard untill 7k RPMs what size is your turbo???

[S14DB]

Get some 264's then talk to us about top end.

[UNISA JECS]

Get some 264's then talk to us about top end.

I'll be happy to get some soon after I get my Nistune shit..:)

[S14DB]

Seeing Dyno's of KAT guys breaking in their turbo motors NA. The KA seems to choke NA up top on the stock cams. Turbo it just gets worse.

[Koopa Troopa]

I can hit the rev limiter no problem, theres no problem there it just doesn't seem worth it at this point to do that, I diffenantly will invest in cams in the future and Nistune so I can tune my own ECU real soon.

I dunno if you look at alot of dyno's of KA-T's you'll see quite a few KA-T's droping power by a fast amount around the 6k give or take 500rpm.


Post more of your set up.

I can go well past the 9K RPM rev limiter in my Alto but it doesn't mean I'm making any power...

[UNISA JECS]

Seeing Dyno's of KAT guys breaking in their turbo motors NA. The KA seems to choke NA up top on the stock cams. Turbo it just gets worse.

I agree with that, its easily seen just by looking at alot of stock cam'd KA dyno's.

[projectRDM]

Not that it matters, but those 18" wheels effectively change the gearing also. Stick a pair of 15" wheels with 50 series tires and drive it again.

[UNISA JECS]

Ok just for fun;

KA24DE
Q45 3.69 FD
6875 rpm (stock S13 redline)

1st gear = 40 mph (same as SR)
2nd gear = 70 mph (same as SR)
3rd gear = 101 mph (same as SR)
4th gear = 133 mph (+1 mph over SR)
5th gear = 175 mph (+17 mph over SR) highway cruising saver gear :)

It takes a 3.69 final drive to match speeds with the SR at redline just by having a 700rpm lower redline.

[UNISA JECS]

Not that it matters, but those 18" wheels effectively change the gearing also. Stick a pair of 15" wheels with 50 series tires and drive it again.

Not in my case because im within factory specs (I did the math :) I'd even be fine with 40 series as far a rolling diameter is concerned which is what also changes the gear ratio) even though I run 18's as far as rolling diameter is concerned which is the ultimate determing factor here anyways. Plus 15" cramps my steelo...haha

[g6civcx]

I'm going to post a writeup some time this week that I've been putting off for a long time.

I think it's going to dispel a lot of myths about gearing and shifting and power and torque, etc.

It's all about maximizing thrust to the drive wheel.

When I get off my lazy azz you'll see what I'm talking about :D

[UNISA JECS]

I'm going to post a writeup some time this week that I've been putting off for a long time.

I think it's going to dispel a lot of myths about gearing and shifting and power and torque, etc.

It's all about maximizing thrust to the drive wheel.

When I get off my lazy azz you'll see what I'm talking about :D

I understand your point about the whole thrust thing, I also couldn;t help but see civcx (thinking that some way shows affilation with HONDA could be wrong though..lol) in your name so i assume a conenction, and I know the thrust things really helps the HONDA guys in that department of acceleration because its known they dont make gobs of torque like like the KA24DE....so they use numerically higher final drive to help them accelerate quicker to make up for a lack in torque.....My reasoning and thinking is since the KA24DE makes alot of torque down low you can afford to give some of this advantage up in inchange for greater speed and a more usualble 1st and 2nd gear anways that even at 7psi can overwhelm the tires, im not pulling dirt in the back of my pick up engine anymore, what the KA was meant to do anyways haha jk.

Im sure theres a way to calulate how much torque the KA and SR with the 4.08 and then calulate how much advantage it looses by going to a 3.69. Im not talking about the dyno torque numbers but the large numbers that include calculations using the gear ratio and multiplication or what not.

[chituntang]

With a given engine, you change the gear to match the power.
With a given transmission, you change the power to match the gear.

I thought it is simple math, why do people keep saying changing the cams when he can actually change the gear and make the powerband more useful?

[Koopa Troopa]

I thought it is simple math, why do people keep saying changing the cams when he can actually change the gear and make the powerband more useful?


Because he'll still have a motor running out of breath at 6500 RPM's.

[UNISA JECS]

Its like buying a pick up truck you usually get options on the final drive depending what your intended duty is gonna be i.e. heavy pulling (numerically higher final drive) or mixed driving i.e. some towing and alot of highway communting so some people make a compromise and choose a numerically lower number for better highway gas milage with a little bit less ability for payload.

Know anyone with a KA-T can tell you they have no problem what so ever getting outta the whole from a stand still with the stock 4.08 thats for sure, its a big difference between SR and KA down low. Know you put a 3.69 on a SR its a different story its probably gonna feel alot more slugish than the KA off the line and probably everywhere else.

[UNISA JECS]

Again my reasoning for not taking my car always to redline was stated eariler in here, the KA is not rev happy and has nasty engine harmonics at higher revs, again this is due in part to its only half counter weighted crankshaft, the higher it is rev'd the more apparent or worse the problem will become.

Being an owner of more than a handful of SR20DE(T) powered vehicles and then going KA24DE(T) its one of the very first things I said to myself, "this thing does not rev like and SR one bit!" but its still got some balls :).

An SR feels smooth all the time and maybe this can be contributed to its fully counterweighted crankshaft, even at long distance sustaned 4500rpm driving the SR feels right at home, but the KA doesn't not feel the same way thats for sure. And this was apparent to my on both KA24DE N/A and Turboed doesn;t matter becase the engien characteristics are still there just amplified by the turbo...

I love both engines I just want the KA to use more of its power band to its advantage because it seems like its not taken advantage of it high points down low....

[UNISA JECS]

Lets try this since different gearing then would have obvious affects on your torque output:

1st gear
Stock NA SR20DE ~140hp ~132tq
3.321*4.08*132 = 1788 lbs-ft

1st gear
Stock NA KA24DE ~150hp ~155tq
3.321*4.08*155 = 2100 lbs-ft
-------------------------------------------------------------------------
NOW with a Q45 3.69 FD
1st gear
Stock NA KA24DE ~150hp ~155tq
3.321*3.69*155 = 1899 lbs-ft (still makes more lbs-ft than an SR with a 4.08)

[chituntang]

Because he'll still have a motor running out of breath at 6500 RPM's.

Maybe he wants more low end power?

[UNISA JECS]

Maybe he wants more low end power?

The KA already has gobes off low end power, thats not what im trying to gain, rather you can look at it as borrowing some torque for higher top speed per gear and a side benefit is even a better 5th gear cruising rpm. The more and more its sounding like adjustable cam gears...haha

[Koopa Troopa]

Again my reasoning for not taking my car always to redline was stated eariler in here, the KA is not rev happy and has nasty engine harmonics at higher revs, again this is due in part to its only half counter weighted crankshaft, the higher it is rev'd the more apparent or worse the problem will become.

Being an owner of more than a handful of SR20DE(T) powered vehicles and then going KA24DE(T) its one of the very first things I said to myself, "this thing does not rev like and SR one bit!" but its still got some balls :).

An SR feels smooth all the time and maybe this can be contributed to its fully counterweighted crankshaft, even at long distance sustaned 4500rpm driving the SR feels right at home, but the KA doesn't not feel the same way thats for sure. And this was apparent to my on both KA24DE N/A and Turboed doesn;t matter becase the engien characteristics are still there just amplified by the turbo...

I love both engines I just want the KA to use more of its power band to its advantage because it seems like its not taken advantage of it high points down low....

You can't compare a KA24 to an SR considering the massive ammount of stroke the KA has. It also has giant exhaust ports limited by it's tiny ass cams, another Nissan blunder... Let that bitch breath!

[S14DB]

Again my reasoning for not taking my car always to redline was stated eariler in here, the KA is not rev happy and has nasty engine harmonics at higher revs, again this is due in part to its only half counter weighted crankshaft, the higher it is rev'd the more apparent or worse the problem will become.

Being an owner of more than a handful of SR20DE(T) powered vehicles and then going KA24DE(T) its one of the very first things I said to myself, "this thing does not rev like and SR one bit!" but its still got some balls :).

An SR feels smooth all the time and maybe this can be contributed to its fully counterweighted crankshaft, even at long distance sustaned 4500rpm driving the SR feels right at home, but the KA doesn't not feel the same way thats for sure. And this was apparent to my on both KA24DE N/A and Turboed doesn;t matter becase the engien characteristics are still there just amplified by the turbo...

I love both engines I just want the KA to use more of its power band to its advantage because it seems like its not taken advantage of it high points down low....
I didn't see anyone say to raise the rev limit. I know I didn't. We an't asking you to raise it up to 9k.

The KA has a hard time breathing at the stock limit with stock cams. Many NA 264 dynos I have seen see major gains at the top end with minimal low end loss.

Try the 264 at stock limit and see the difference.

You should play GT4 on the test track with a adjustable transmission. Then play with gear ratios. You'll learn a lot.

[UNISA JECS]

Well I finally installed the 3.69 final on my KA24DET and I LOVE IT!!! Feels like home, the hell with stock 4.08 final drive on a boosted KA24DET even at only 7 psi on a T25, i'll take the 3.69 anyday.

[chituntang]

The problem is you are running T25 on a KA...

But anyways, it is about what you wanted: Higher speed vs. faster pickup. If you set a speed (within your rev limit) and compare it for a SR20DET and your KADET, given the same/about the same gear ratio, you will reach it faster, since you are making more power.

It's like driving a turbo'ed civic/teg. Yes, it makes a lot of power, but it still tops out at like 120 where as my SR is still going way pass 140 until fuel or rpm cut.

[Marcus]

this thread is awesome.

[S13 curtis]

The problem is you are running T25 on a KA...

But anyways, it is about what you wanted: Higher speed vs. faster pickup. If you set a speed (within your rev limit) and compare it for a SR20DET and your KADET, given the same/about the same gear ratio, you will reach it faster, since you are making more power.

It's like driving a turbo'ed civic/teg. Yes, it makes a lot of power, but it still tops out at like 120 where as my SR is still going way pass 140 until fuel or rpm cut.
jus cut the speed sensor wire on the ecu problem solved.

and a t25 on a KA= Ghey.

[SilviaSR20DET]

how is a t25 on a KA ghey... Id rather have a boosted KA rather then a all motor KA. 130 rwhp vs 230 whp what would you rather pick. Plus im running a t25 right now so im biased.

[fuk240sx]

You should play GT4 on the test track with a adjustable transmission. Then play with gear ratios. You'll learn a lot.

LOL...your so right....I learned alot from that game about final drive ratio's and gear ratio's in general....GT4 FTW

[S13 curtis]

how is a t25 on a KA ghey... Id rather have a boosted KA rather then a all motor KA. 130 rwhp vs 230 whp what would you rather pick. Plus im running a t25 right now so im biased.


because a t25 is a pos and it makes not much power.
its too small for a ka. a s14/s15 t28 would be nice.

[SilviaSR20DET]

some people like autox so response is crucial hence why the t25 can be good in different situations. Not everything is about raw power..

[s14driftNA]

In the end, there are way too many variables of how fast the car get's to redline or what mph you are at at that redline. Someone with the exact same setup can go either faster or slower. And duh, the KA was not a factory engineered turbo engine, so it's not going to have the internals for forced induction, PERIOD. Get new pistons to lower the Compression Ratio to somewhere around 8.0:1, then get the valve train stengthened, then get a balanced crankshaft and eat your own words. The KA will not compare to a ENGINEERED turbo engine (SR) just because you slapped a turbo on it. The KA is better in my opinion, cast iron = no need for sleeves, more displacement = LOADS of torque, but crappy ports = restricted power and redline. A t28 or T3 would be great for it. A smaller turbo (T25) will spool fast but hit it's limit early, so balance it out with a bigger turbo.