i have a cam for my 4ac, i got it a while back but I'm a little unsure what its like as i havnt had that much to do with single cam motors. i have not yet put it in (was waiting for a bigger carb so it would make a driffrence).

 

the guy who i brought it from siad it was 290degree with an extra .6mm or .8mm of lift, its rated between 3500-7500. is this considered a big cam..? i know this is about the biggest you would want to go with a 4ag in a street car. i did a seach on you tube but i found conflicting clips with claimed 282degree cams, i sounded stock on idel and the other ideled like a stock one with the choke on.

 

also because it has extra lift does that mean that it will valve bounce earlyer or cause more stress on the valve train making failure more likely?

 

when i build a new motor i intend on revving it to 7500, in most peoples opinion would new standard valve springs (more tention than the shagged 20od year old ones) be enough for this rpm reliably? or does someone know where slightly stiffer one can be brought from? or taken from other engines?

 

 

thanks for any light that can be shead.

i have a cam for my 4ac, i got it a while back but I'm a little unsure what its like as i havnt had that much to do with single cam motors. i have not yet put it in (was waiting for a bigger carb so it would make a driffrence).

 

the guy who i brought it from siad it was 290degree with an extra .6mm or .8mm of lift, its rated between 3500-7500. is this considered a big cam..? i know this is about the biggest you would want to go with a 4ag in a street car. i did a seach on you tube but i found conflicting clips with claimed 282degree cams, i sounded stock on idel and the other ideled like a stock one with the choke on.

 

also because it has extra lift does that mean that it will valve bounce earlyer or cause more stress on the valve train making failure more likely?

 

when i build a new motor i intend on revving it to 7500, in most peoples opinion would new standard valve springs (more tention than the shagged 20od year old ones) be enough for this rpm reliably? or does someone know where slightly stiffer one can be brought from? or taken from other engines?

thanks for any light that can be shead.

 

gee that will be fun on the street :), that is huge, i think you might have a bit of trouble in traffic idling, or your everyday driving rev range

 

it will sound cool, and will go like hell when you are up in the high revs, but from the small amount i know, that seems pretty big !

 

i am not sure what your increased lift will do for valve bouncing, but i know even a small increase in lift can really increase your flow

its a pretty big cam :)

 

definately get new stronger springs, a much bigger lobe is more prone to problems at higher rpm.

 

try performance springs they ship aus wide and have a large range of springs, see if you can find out

the seat and nose spring pressure for the cam to find a suitable set of springs.

 

also check and replace cam timing gear if needed and spend some time dialing it in properly :)

I had a 290degree cam with 0.480"Lift in my old 4K with standard springs. No Idle issues at all. It was mistaken for a rotary a heap of times. All of my K motors have always had similar cams to this......I guess its just the rotary wannabe in me. :)

That engine used to love the high revs (4000-7500rpm). Anything under 3500rpm and it was just a standard 4K.

All that meant is that I cruised in 3rd gear instead of 4th. Or 4th instead of 5th.

 

I realise you have a 4ac, but I assume the principles would be similar.

Edited July 11, 200719 yr by kangaroosa

Did she say it was big???

I had a 290degree cam with 0.480"Lift in my old 4K with standard springs. No Idle issues at all. It was mistaken for a rotary a heap of times. All of my K motors have always had similar cams to this......I guess its just the rotary wannabe in me. :)

That engine used to love the high revs (4000-7500rpm). Anything under 3500rpm and it was just a standard 4K.

All that meant is that I cruised in 3rd gear instead of 4th. Or 4th instead of 5th.

 

I realise you have a 4ac, but I assume the principles would be similar.

 

thats awesome that they still will idle, with a big cam like that !

what does it usually idle at for a stock 4k ?, i spose seeing it is such a small engine it

doesnt mind the high revs as much

Edited July 13, 200719 yr by Rad Rolla

definately get new stronger springs, a much bigger lobe is more prone to problems at higher rpm.

 

try performance springs they ship aus wide and have a large range of springs, see if you can find out

the seat and nose spring pressure for the cam to find a suitable set of springs.

i know a standard motor can do that sort of rpm, but i want it to have some sort of reliability. i e-maild them, have to wait and see if i get a reply.

 

gee that will be fun on the street , that is huge, i think you might have a bit of trouble in traffic idling, or your everyday driving rev range

 

i had troble with my standard carby in traffic... i will just turn the idel up if need be..

 

 

I guess its just the rotary wannabe in me.

 

your not the only one.

Edited July 11, 200719 yr by tas_ae71

i know a standard motor can do that sort of rpm, but i want it to have some sort of reliability. i e-maild them, have to wait and see if i get a reply.

i had troble with my standard carby in traffic... i will just turn the idel up if need be..

your not the only one.

 

It doesn't sound like much extra lift, although you'd have to measure it to be sure. 290 is a lot duration wise though. To be quite honest, you'll just have to try it and see. It should be reasonably drivable with it having lower lift, and you could probably get away with only stock springs as it's not running much more lift. But if you're going to spend the money, you'll probably find upgraded springs are a similar price anyway. Just make sure there is no binding and you should be good.

 

If I had the time and ability to jet the cam properly, I'd try it out and see if it's any good. If it's OK I'd grab new springs and do it all properly.

It doesn't sound like much extra lift, although you'd have to measure it to be sure. 290 is a lot duration wise though. To be quite honest, you'll just have to try it and see. It should be reasonably drivable with it having lower lift, and you could probably get away with only stock springs as it's not running much more lift. But if you're going to spend the money, you'll probably find upgraded springs are a similar price anyway. Just make sure there is no binding and you should be good.

 

If I had the time and ability to jet the cam properly, I'd try it out and see if it's any good. If it's OK I'd grab new springs and do it all properly.

 

as i said thats what the guy who i brought it off of said, it was either 6.mm or.8mm extra lift. I'm trying to spend as little as possible :)

 

what do you mean by 'binding'?

 

does anyone have a cam with a simerla profile that they could take a vidio clip of..? how do you find them to drive?

what do you mean by 'binding'?

 

does anyone have a cam with a simerla profile that they could take a vidio clip of..? how do you find them to drive?

 

Coil bind is where the valve spring fully compresses, thus limiting the movement of the valve. Its a bad thing :)

 

I have a movie of my old 4k kicking around somewhere. I'll look for it now.

 

*EDIT* Found it, and here is the very very short version of it.

CLICK

Edited July 13, 200719 yr by kangaroosa

kangaroo, any idea what sort of duration that cam was?

 

was that how it always ideled because mine used to idel llike that when it was cold witht he stock carb..

 

edit* just saw the heading... 290

Edited July 14, 200719 yr by tas_ae71

Thats how it idled when it was warm. I could drop the rpms a touch and get it sounding better, but the oil pressure suffered and the alternator wasnt charging properly.

I had twin 1.5" SU's on it at the time.

Coil bind is where the valve spring fully compresses, thus limiting the movement of the valve. Its a bad thing :)

 

I have a movie of my old 4k kicking around somewhere. I'll look for it now.

 

*EDIT* Found it, and here is the very very short version of it.

CLICK

 

man thats cool !!!! :)

that sounds sweet as, any idea of what rpm it was idling at ?

About 900rpm, maybe a touch under.

I'm awaiting Xany's post in here as his 5K sounds very rotor-like with the cam he has in that.