higher revving question

[racemonkey11]

Ok I was just sitting down thinking one day about our problem with not being able to make much power na due to our half weighted crank. So I know bc crower makes a stroker kit with a fully balanced crank so theoretically wouldn't that mean we could rev a lot higher unlocking more power potential? The only reason I ask is cuz I haven't seen anyone comment on revving higher with it. I just wanna see what yal think cuz its something I have pondered.

[compactfean]

In a sense, yes you can rev higher with a fully counter weighted crank, but because the stroke changes it will cause more friction and more heat ....especially at high rpm. However, they do make a crank that is stock stroke and fully counterweighted that would be more suitable for higher rpm's.

[moso]

You will need to address more than just the crank, sooner or later (more likely sooner) you will encounter valve float.

[asoomal]

BC also makes a fully counter weight crank for the stock stroke.

Retails for under $2000.

[idahotuner]

yeah alot of things affect revs besides the crank

[liquid_cool]

why not just have your rotating assembly fully balanced at a machine shop insted..rods..pistons..crank..rings..and just buy some BC duel springs...my NA.block reved to 9k and was stable for 2 years "stock rod gave out"...thats the route id go...its cheep and fun!

[idahotuner]

light weight parts too, my pistons and rods were noticeably lighter just holding them, and then add a light weight flywheel.

[moso]

why not just have your rotating assembly fully balanced at a machine shop insted..rods..pistons..crank..rings..and just buy some BC duel springs...my NA.block reved to 9k and was stable for 2 years "stock rod gave out"...thats the route id go...its cheep and fun!

there is definitely a difference between having your motor balanced by a machine shop and getting a counterweighted crank. when a machine shop balances a motor they weigh every like part and then grind down on the machining tabs untill they all weigh the same. counterweighted crank has large balances to offset the weight of the pistons and rods so when spun it wont try to walk or wobble. most machine shops wont just counterweight a crank, they have to be specially ground and then matched to your internals. beyond all that tho is the question "Why spin the motor faster?". The ka series motors were never designed to spin at high rpms and dont make power beyond 6500rpm or so. originally the motor was designed to be a truck engine and as such makes more torque and horsepower at low to mid range rpms. This design makes the motor quite reliable and great for drifting and draging where your motor demands are inline with a high torque low rpm setup. boosting the ka motors only exaggerates this condition, rasing both horsepower and torque in the mid rpm range, and falling off quite drastically as it approaches redline. To really appreciate the gains made by spinning your motor faster you will need to greatly shorten the intake runner length; increase the valve diameter, duration, and lift; increase the port area on both the intake and exhaust side; and setup some kind of forced induction ( aka turbo/supercharger). In other words its just not worth the money spent, unless you have a serious hard on for the ka motor.

[asoomal]

Don't forget the awesome 1.71:1 Rod to stroke ratio, perfect for high revving applications.

[liquid_cool]

why not just have your rotating assembly fully balanced at a machine shop insted..rods..pistons..crank..rings..and just buy some BC duel springs...my NA.block reved to 9k and was stable for 2 years "stock rod gave out"...thats the route id go...its cheep and fun!

there is definitely a difference between having your motor balanced by a machine shop and getting a counterweighted crank. when a machine shop balances a motor they weigh every like part and then grind down on the machining tabs untill they all weigh the same. counterweighted crank has large balances to offset the weight of the pistons and rods so when spun it wont try to walk or wobble. most machine shops wont just counterweight a crank, they have to be specially ground and then matched to your internals. beyond all that tho is the question "Why spin the motor faster?". The ka series motors were never designed to spin at high rpms and dont make power beyond 6500rpm or so. originally the motor was designed to be a truck engine and as such makes more torque and horsepower at low to mid range rpms. This design makes the motor quite reliable and great for drifting and draging where your motor demands are inline with a high torque low rpm setup. boosting the ka motors only exaggerates this condition, rasing both horsepower and torque in the mid rpm range, and falling off quite drastically as it approaches redline. To really appreciate the gains made by spinning your motor faster you will need to greatly shorten the intake runner length; increase the valve diameter, duration, and lift; increase the port area on both the intake and exhaust side; and setup some kind of forced induction ( aka turbo/supercharger). In other words its just not worth the money spent, unless you have a serious hard on for the ka motor.

you CAN have a crank balanced to handle high revs without spending wads of cash, and it can be counter balanced ither by welding in the wieght or adding tungston or even removing weight...what sets your power band mainly on the ka is the cams...with a bc 272 cam its all mid and high end power..ect ect...if someone plans there build properly its easy to build to a goal reliably..as for the intake ports on the head..there big enough..i agree the ext side leaves something to be desired thou, it's a little anemic and cannot be ported large enough without risk of penetrating the water jacket.....with machine work and a little tuning..you CAN make a ka a happy revmonster with 225whp...

[asoomal]

Top end is fine. It's the bottom end that has problems with high revving.

At around 7200~ RPMs, the harmonics will cause the crank to eat the bearings.

Anyways, about the "why spin the motor faster"

There's more potential to create more power when the engine is spinning faster. More cycles in a minute, more power can be made. Also, you'll have a wider powerband with more revs, instead of having 4500-6500, you'll have 5000-8000 RPMs worth of power.

[moso]

I don't mean to offend but I am not sure I would call a motor that pitched a rod in 2 years a "happy revmonster", and increasing the revs of a motor will not increase the powerband. The only way to increase the powerband is to change the valveing and intake ( aka valves, cams, cam timing). I am not saying it cannot or should not be done, I just dont believe in its cost effectiveness.

[compactfean]

Isn't the stock stroke on the ka like 90mm? Far from ideal stroke for high revs in my opinion.

[asoomal]

96mm.

However, it has 165mm rods, less side loading and wear on the bores.

[liquid_cool]

I don't mean to offend but I am not sure I would call a motor that pitched a rod in 2 years a "happy revmonster", and increasing the revs of a motor will not increase the powerband. The only way to increase the powerband is to change the valveing and intake ( aka valves, cams, cam timing). I am not saying it cannot or should not be done, I just dont believe in its cost effectiveness.

i allso had a 14: to 1 cr man..i pushed it to the limit...and it laste3d 2 years..thats awsome for a motor you drift with and hang in the redline on...some racers will be satisfyed with 1 season on a motor...while others will be happy with just 1 race.

[moso]

I totally hear that liquid..... Race motors, Fun until BOOM!