How High Will It Rev, Before It Goes ?

[Doogs]

hey,

 

i was wondering to help with my selection of cams and deciding on whether i will

need the bottom end balanced to prevent damage at high revs , for my upcoming build,

how high have you guys taken your k, balanced or unbalanced, before it all went wrong ?

 

i want to get an idea on how strong the bottom end of these little motors are, i have

heard they will take a fair bit, but want to know a few peoples personal experiences,

on how high you can safely take them, without sending pistons through the block, or the like

 

so, what k are you running, with mods or not, and how high have you taken it ?

is there a particular engine that has a bad rep for failing ?

 

cheers guys

[Medicine_Man]

My 4K is a few years old now, Tighe 104 cam, Slight Head Shave, Stronger Valve Springs, Extractors, Twin Dellortos, Electronic Dizzy (Unbalanced - Should have had it done in hindsight, But will do that to my 5K when I rebuild it)..

 

I have revved it to 7000 and it doesn't seem to valve bounce (Teddy as my witness) :lolcry:

 

Basically gets raped on a daily basis and has always been reliable..

 

Suggest if you have any intentions of making power out of a K motor you get it balanced just for peace of mind..

[lappy]

I have a 3K in my speedway bored 60thou with a hot cam thats all the mods and I run it at 6600-7000 all the time for the whole race. Thats unbalanced and without a lightened flywheel or anything.

[Robert]

When i first got my KE70 the 4K valve bounced at 7200 it now valve bounces around 6700.

[Redwarf]

My race motor was balanced,, the thing hardly moved in the engine bay.

 

A k-motor won't let go. I tried destroying one a number of years ago. Involved were a 4K, a brick, and a couple of mates armed with six packs. Brick installed on throttle, valves bouncing, beers consumed. Approx two stubbies later, engine screaming, boys disappointed with lack of action. Jif introduced into engine oil. One stubbie later, toxic fumes and steam eminating from every orifice in engine. Still powering along, although at reduced revs. Finally ran out of fuel and seized solid.

 

They don't tend to let go.

[coln72]

5k, cam, extractors, twin carbs - everything else is standard. Have seen 8000rpm on occasions.

[Teddy]

TRD Brothers - TRD 5k let go at unknown RPM *looks up* - Damage = No bottom end, snapped internals hard-core, holy sump & bent steering rack.

 

:)

[old corolla bloke]

TRD Brothers - TRD 5k let go at unknown RPM *looks up* - Damage = No bottom end, snapped internals hard-core, holy sump & bent steering rack.

 

:)

 

whilst performing burnout antics years ago with a balanced 4k and heavily modified that had good valve springs...scat of all things ,twin webers etc.It broke the gear box input shaft and went bang ........lots of smoke from engine and tyres.

hole on sump and block

 

was looking at tach just as shaft broke.....8500 dialled up then big over rev.....bang

[kangaroosa]

I had a throttle linkage jam on between gear changes. My right foot 'was' pressed firmly against the floor. As i switched the ignition off, I saw my tacho needle falling from 11,500rpm. I broke 3 inner valve springs, and no damage to the bottom end.

The same engine sees 6000rpm a few times a week, and occassionally 7500rpm.

 

My engine is balanced, and has a lightened flywheel.

[Doogs]

I had a throttle linkage jam on between gear changes. My right foot 'was' pressed firmly against the floor. As i switched the ignition off, I saw my tacho needle falling from 11,500rpm. I broke 3 inner valve springs, and no damage to the bottom end.

The same engine sees 6000rpm a few times a week, and occassionally 7500rpm.

 

My engine is balanced, and has a lightened flywheel.

 

thanks guys for all the feedback, it sounds like i could get away with not getting it all balanced,

but for a few $ it is worth it, (just to be on the safe side)

 

i also figure it may be useful if i vist a few hillclimbs or circuits, for when i am at high revs then

 

one thing i have wondered for a while is, if you have a fairly lumpy cam, will lightening

the flywheel make idling more difficult at low revs ?

 

what have you found, and how much lighter is yours ?

[kangaroosa]

don't know about it not idling well with a light flywheel. Mine seemed to idle fine when i had a VERY lumpy cam in it.

 

My flywheel is only 1.4kgs lighter than standard, so its not a massive difference on the scale of things.

 

I doubt if i had two identical motors in my cars... one with and one without a lightened flywheel, that i could tell the difference. The only reason i had mine lightened was that i took it in to have the clutch face machined. I enquired about lightening it, and he quoted me about $50 extra. So I said why not, and gave him the go ahead.

[Des]

My digital tacho i had on my stock ke70 4k said 9750rpm but i don't know if it actually did it or not.

[Doogs]

don't know about it not idling well with a light flywheel. Mine seemed to idle fine when i had a VERY lumpy cam in it.

 

My flywheel is only 1.4kgs lighter than standard, so its not a massive difference on the scale of things.

 

I doubt if i had two identical motors in my cars... one with and one without a lightened flywheel, that i could tell the difference. The only reason i had mine lightened was that i took it in to have the clutch face machined. I enquired about lightening it, and he quoted me about $50 extra. So I said why not, and gave him the go ahead.

 

cool, thanks

 

do you think that just balacing the flywheel would be enough then ?

 

i am starting to get pretty excited now, after seeing how much fun you guys have had, but

i think just to be safe, i will keep it below 8 grand

 

cheers all

[Redwarf]

With the right cam, 4-7K is where it should operate. We've all revved the date out of one of these things for giggles, but thats where you should be looking. For that kind of thing, balanced is nice but not essential.

 

As far as just doing the fly wheel, if it's worth doing, it's worth doing properly. Do the whole thing.

[NoPsi]

Balancing cost sweet FA. Do it for piece of mind. My last worked 4k saw 8000rpm regularly.