k24 RPM limit

I know 7600rpm seams to be a popular rev limit for a stock k24, but I want some input from those who have had experience with a tuned K24 engine. Please vote for your preference in the poll and leave a comment explaining why...

This is for a k24 accord euro engine with all the basic I/H/E modifcations.

Thanks!

I havent had much experience with K24's in particular, but you are talking about 100rpm here sounds like you're splitting hairs

K24s vary also do they not? Are you talking about the Euro K24?

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Originally Posted by ZeForce

I havent had much experience with K24's in particular, but you are talking about 100rpm here sounds like you're splitting hairs

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I'm splitting hairs for sure... but the k24 has high piston speeds, so I'm being extra careful.

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Originally Posted by chargeR

K24s vary also do they not? Are you talking about the Euro K24?

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Yep, k24 Euro engine. Forgot to mention that.

7800 RPM here when I used to had stock internals k24a3.

We raised the rev limit now to 8300 rpm as I got Buddyclub N+ cams , valve springs , retainers.

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Originally Posted by EG5

7800 RPM here when I used to had stock internals k24a3.

We raised the rev limit now to 8300 rpm as I got Buddyclub N+ cams , valve springs , retainers.

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so no problems at 78000rpm? How long did you have the car with that RPM limit for?

Depends what model Euro motor you have. We usually turned it to safe 7400rpm (ECU cutoff). Completely stock K24 motor unopen rocker cover. From factory there about 7100-7200rpm. Im not a K-series expert. Mayb Drhonda will add his 2cents.

I believe Yonas had type R valve springs with the 7800rpm limit.

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Originally Posted by fatboyz39

Depends what model Euro motor you have. We usually turned it to safe 7400rpm (ECU cutoff). Completely stock K24 motor unopen rocker cover. From factory there about 7100-7200rpm. Im not a K-series expert. Mayb Drhonda will add his 2cents.

I believe Yonas had type R valve springs with the 7800rpm limit.

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Single valve springs k24a3 when it ran 11.82 down the 1/4 mile.
Not recomended to rev it to 7800 rpm on stock internal k24a3.
The only thing from k20a2 was crank pulley and 50 degree VTC
7400 - 7600 rpm will be the best rev limit , As power just started to drop on that RPM.


Had my K swap since July 07 , still healthy till today

thanks for the input so far guys.

At the moment I'm leaning towards a soft limit at 7500 with hard limit at 7600

edit: decided to go for 7600 soft cut and 7700 hard cut. That way it will be tuned to those RPM and I can always change the rev limiter myself at a later date :)

Any other opinions on this?

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Originally Posted by Chris_F

thanks for the input so far guys.

At the moment I'm leaning towards a soft limit at 7500 with hard limit at 7600

edit: decided to go for 7600 soft cut and 7700 hard cut. That way it will be tuned to those RPM and I can always change the rev limiter myself at a later date :)

Any other opinions on this?

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Should be no problems at all.

No point reving higher if power drops off @ 7000rpm

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Originally Posted by EG5

Should be no problems at all.

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Ok, thanks Yonas :thumbsup:

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Originally Posted by fatboyz39

No point reving higher if power drops off @ 7000rpm

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The reason for the higher rev-limit is also to do with the gear ratios of the k24a3... shifting from 1-2 with a 7000rpm limit would see you drop out of the power band and in 2nd gear you'd only be at about 4200rpm.

You can see what I mean when you look at the ratios:

Ratio 1: 3.533
Ratio 2: 1.880
Ratio 3: 1.354
Ratio 4: 1.027
Ratio 5: 0.825
Ratio 6: 0.659
Final drive ratio: 4.388

is it for circuit racing or drag racing?

Ill stick with 7400rpm rev limit

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Originally Posted by fatboyz39

No point reving higher if power drops off @ 7000rpm

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Yup No point to rev it high if power drop
Mine starting to drop at 7600 rpm on stock cams
More RPM on k24 = Engine wont last

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Originally Posted by Chris_F

The reason for the higher rev-limit is also to do with the gear ratios of the k24a3... shifting from 1-2 with a 7000rpm limit would see you drop out of the power band and in 2nd gear you'd only be at about 4200rpm.

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the rev limit question your asking is really irrelevant to gaining quicker times out of ur stock k24.

im fairly sure u'll find more torque clawing at the road in any given higher gear at 4200rpm than u will any where above 7000rpm on the lower gear on a stock k24.i think your misinterpreting where your powerband actually is.

most stock honda motors ive seen have a rev limit 500rpm higher than where u should be shifting at,its just for a bit of headroom so your not bouncing the limiter all the time while trying to get the most out of what the motor will provide.
it would be terribly painful if u had 100rpm of limiter above your useful powerband,especially in first gear, u would be bumping the limiter all the time.
i dont know how fast your needle is moving at the top of first gear,but i know mine is moving too fast to differentiate 100 rpm,or maybe im just slow......

go out the quater mile & shift at 7krpm & then try shift at 7500rpm,im sure u'll get better times at 7krpm.

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Originally Posted by CRXer

the rev limit question your asking is really irrelevant to gaining quicker times out of ur stock k24.

im fairly sure u'll find more torque clawing at the road in any given higher gear at 4200rpm than u will any where above 7000rpm on the lower gear on a stock k24.i think your misinterpreting where your powerband actually is.

most stock honda motors ive seen have a rev limit 500rpm higher than where u should be shifting at,its just for a bit of headroom so your not bouncing the limiter all the time while trying to get the most out of what the motor will provide.
it would be terribly painful if u had 100rpm of limiter above your useful powerband,especially in first gear, u would be bumping the limiter all the time.
i dont know how fast your needle is moving at the top of first gear,but i know mine is moving too fast to differentiate 100 rpm,or maybe im just slow......

go out the quater mile & shift at 7krpm & then try shift at 7500rpm,im sure u'll get better times at 7krpm.

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You've really got to drive the Euro to understand how stupidly large 2nd gear is compared to 1st. He's not talking about having more torque up high, but shifting at a higher km/h as to land higher in the revs in 2nd.

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Originally Posted by integral90

You've really got to drive the Euro to understand how stupidly large 2nd gear is compared to 1st. He's not talking about having more torque up high, but shifting at a higher km/h as to land higher in the revs in 2nd.

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uve pro got a slightly better second gear than my DC2 second,but ur right theres a large discrepancy between 1st & 2nd on the euro box posted above.

the point is liam,what does the torque curve look like after 7krpm?
ive never seen anybody dyno a k24 past 7krpm,its prob cos the torque curve is headed off into the abyss by then.
if what described above is correct about u landing at 4200 from 7000 then ure landing right into the meat of the torque curve on the stock k24,whereas at 7500 in first gear,ur prob making like very little more,if not less, than u would be in 4200 second,which is a big statement for 1st -2nd gear comparisons. once u get up to 2nd-3rd,4th-5th,game over.

k24 has a fairly long stroke on it,id hate to think how fast those pistons are moving at 7500rpm.

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Originally Posted by CRXer

k24 has a fairly long stroke on it,id hate to think how fast those pistons are moving at 7500rpm.

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I remembered @7500rpm on k24 is like 9000rpm on a F20c, piston speeds i.e.

Why not get k20a internal and fit it into the euro box? Or use a smaller tyre wheel combo.

thanks for the input everyone

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Originally Posted by tinkerbell

is it for circuit racing or drag racing?

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circuit

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Originally Posted by CRXer

the rev limit question your asking is really irrelevant to gaining quicker times out of ur stock k24.

im fairly sure u'll find more torque clawing at the road in any given higher gear at 4200rpm than u will any where above 7000rpm on the lower gear on a stock k24.i think your misinterpreting where your powerband actually is.

most stock honda motors ive seen have a rev limit 500rpm higher than where u should be shifting at,its just for a bit of headroom so your not bouncing the limiter all the time while trying to get the most out of what the motor will provide.
it would be terribly painful if u had 100rpm of limiter above your useful powerband,especially in first gear, u would be bumping the limiter all the time.
i dont know how fast your needle is moving at the top of first gear,but i know mine is moving too fast to differentiate 100 rpm,or maybe im just slow......

go out the quater mile & shift at 7krpm & then try shift at 7500rpm,im sure u'll get better times at 7krpm.

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There were a few reasons why I came up with the rough 7600rpm figure

• That's where hondata sets the redline for their ECU reflash.
• By looking at the gear ratios and engines power curve taking into account the torque multiplication factor of lower gears. See:http://www.datsuns.com/Tech/whentoshift.htm

This all lead me to believe three things:

• the ideal shift point isn't what will land you at the engines peak torque
• the ideal shift point isn't at the engines peak power
• the ideal shift point is achieved when "firstgeartorque is equal (or close to) secondgeartorque" (accounting for the torque multiplying factor of gear ratios)

edit:
for comparison:
dc2r 1st gear = 3.23, 2nd = 2.105
euro 1st gear = 3.533,2nd = 1.880

but thats what im saying,what is the torque figures like at 7500rpm?
i could imagine theyd be pretty grim,cosidering it looks like the k24 is rolling off the top of the cams at 7000rpm.

is that so jimmy,luckilyy the F20 was built for those type of speeds

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Originally Posted by CRXer

but thats what im saying,what is the torque figures like at 7500rpm?
i could imagine theyd be pretty grim,cosidering it looks like the k24 is rolling off the top of the cams at 7000rpm.

is that so jimmy,luckilyy the F20 was built for those type of speeds

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I'm still waiting for the car to be tuned properly, so I won't know for certain untill that happens. Torque will definitely have dropped by 7500rpm though. But accounting for the 1st gear torque multiplyer it will still be higher than the available torque in 2nd had I shifted at 7000rpm.

The cars stock rev limit is set at 7300. see: http://www.hondata.com/reflash_tsx.html you'll notice that with the reflash/intake and header peak torque occurs at 6000rpm

Ok for circuit. Then changing from 1st to 2nd wont be a problem. When we had the k24, it had the usual stuff, Intake, RBC, 62mm t/b 3' exhaust, headers. Power dropped off around 7100rpm.

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Originally Posted by fatboyz39

Ok for circuit. Then changing from 1st to 2nd wont be a problem. When we had the k24, it had the usual stuff, Intake, RBC, 62mm t/b 3' exhaust, headers. Power dropped off around 7100rpm.

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Good point... the 1-2 shift really only matters on the drag strip. Maybe 7400-7500 is more sensible after all.

hahaaahaa,i missed that post yonas.......8300rpm???....."stock" bottom end......

were gonna have to alert air traffic control to divert the planes next time your running out the creek in case one gets shot down by a k24 piston,imagine how fast those little babies are running,honda would be proud

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Originally Posted by CRXer

the point is liam,what does the torque curve look like after 7krpm?
ive never seen anybody dyno a k24 past 7krpm,its prob cos the torque curve is headed off into the abyss by then.

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http://img206.imageshack.us/img206/3609/dsc0408t.jpg

That's with stock ECU and cams, all the runs it hit the 7200rpm redline while still climbing hard. With the right breathing mods I think the stock cams could make power to 7500rpm or so.

My point about the shift isn't so much about where you land in the torque, but just how big the gear is. It would be like redlining 2nd then going into 4th and flooring it. You'll fall back into the torque sweet spot but it doesn't matter because the gear is so damn long.

I'm sure you could get away with the longer 2nd of the K24 in a lighter car, but the Euro doesn't build momentum as quick as lighter cars obviously, the gear really kills it. After discussion with people I reckon on the 1/4 mile there's .2 or .3 in the 2nd gear.

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Originally Posted by fatboyz39

Ok for circuit. Then changing from 1st to 2nd wont be a problem.

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yep! :thumbsup:

if you are 'worried' about pushing too hard, then be conservative with upper limit

it is always better to make it home, than be 0.1 faster...

plus driver ability > than engine power

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Originally Posted by tinkerbell

yep! :thumbsup:

if you are 'worried' about pushing too hard, then be conservative with upper limit

it is always better to make it home, than be 0.1 faster...

plus driver ability > than engine power

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totally agree, thanks for the input..

I'm thinking 7400-7500 should be totally fine for circuit work. 1/4 times mean very little to me so there's no point pushing it too hard :thumbsup:

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Originally Posted by integral90

That's with stock ECU and cams, all the runs it hit the 7200rpm redline while still climbing hard. With the right breathing mods I think the stock cams could make power to 7500rpm or so.

My point about the shift isn't so much about where you land in the torque, but just how big the gear is. It would be like redlining 2nd then going into 4th and flooring it. You'll fall back into the torque sweet spot but it doesn't matter because the gear is so damn long.

I'm sure you could get away with the longer 2nd of the K24 in a lighter car, but the Euro doesn't build momentum as quick as lighter cars obviously, the gear really kills it. After discussion with people I reckon on the 1/4 mile there's .2 or .3 in the 2nd gear.

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sorry liam,i wasnt trying to compare my second gear to yours,i was just sending out some sympathy cos i know what its like competing with a tall second gear in my little shitbox 1000kg class.

the point is how much torque at 7500rpm,"stock" k24 cams?
even with as much as 50% torque conversion between 1st & 2nd gear,u might find your car making 50% less torque at 7500rpm.

u cant compare different cams,cos as soon as u change the cam profile uve just lifted the mechanical limit imposed by the stock cams.
it doesnt matter what breathing mods,how much u fiddle your vtc,or what other NA tricks u try to introduce more mix into the motor,u r still stuck with the fact that the stock valves will only open for so far & for so long,with the stock cams & u just cant supply what the motor is demanding at higher rpms.
500rpm is along way relative to running out of cam efficiency.

the only way your gonna get more mix in the motor,short of changing the cams is to pull the head & hack away at the valves & ports or cheat with forced induction or different gas other than atmospheric air.
honda would of already given u a head start on getting the most out of the stock cams from the factory,so your window of improving their efficiency would be even smaller still.

when u use terms liking "climbing hard" it just leads to people assuming your misinterpreting the power band.
if uve got no torque curve present on the graph,just hold your power curve graph at 45deg clockwise & then look at it. It will give u a better understanding of where & how fast the powerband is dropping away.
dont forget power is just torque proportional to rpm.

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Originally Posted by CRXer

sorry liam,i wasnt trying to compare my second gear to yours,i was just sending out some sympathy cos i know what its like competing with a tall second gear in my little shitbox 1000kg class.

the point is how much torque at 7500rpm,"stock" k24 cams?
even with as much as 50% torque conversion between 1st & 2nd gear,u might find your car making 50% less torque at 7500rpm.

u cant compare different cams,cos as soon as u change the cam profile uve just lifted the mechanical limit imposed by the stock cams.
it doesnt matter what breathing mods,how much u fiddle your vtc,or what other NA tricks u try to introduce more mix into the motor,u r still stuck with the fact that the stock valves will only open for so far & for so long,with the stock cams & u just cant supply what the motor is demanding at higher rpms.
500rpm is along way relative to running out of cam efficiency.

the only way your gonna get more mix in the motor,short of changing the cams is to pull the head & hack away at the valves & ports or cheat with forced induction or different gas other than atmospheric air.
honda would of already given u a head start on getting the most out of the stock cams from the factory,so your window of improving their efficiency would be even smaller still.

when u use terms liking "climbing hard" it just leads to people assuming your misinterpreting the power band.
if uve got no torque curve present on the graph,just hold your power curve graph at 45deg clockwise & then look at it. It will give u a better understanding of where & how fast the powerband is dropping away.
dont forget power is just torque proportional to rpm.

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You're exactly right, and I accidentally posted the dyno graph with the AFR instead of torque :o

Here's the torque graph:

http://img35.imageshack.us/img35/3484/dsc0409s.jpg