turbo cams?

[TCIC 300ci superbeast]

i was told that isky had good cams for turboed 300. the only one i could find was only for 7psi.

compcams 66-236-4 has 32* of over lap
crane cam503905 has 42* of over lap
isky 331-TA has 28* of over lap
........what else is there?

 

[80broncoman]

i was told that isky had good cams for turboed 300. the only one i could find was only for 7psi.

compcams 66-236-4 has 32* of over lap
crane cam503905 has 42* of over lap
isky 331-TA has 28* of over lap
........what else is there?

At what cam lift are measuring the overlap?
Advertised duration nubers are just that.... advertising.

 

[wallaka]

You need to call Isky or Comp or whoever and let them design a cam for you. They should recommend you a good cam.

 

[TCIC 300ci superbeast]

ok. has any one done this? how much does it cost to get a custom grind?

 

[addo]

It's often pretty affordable, if a regrind off your own core. If you went to billet, then cost would go up.

 

[XPC66]

i was told that isky had good cams for turboed 300. the only one i could find was only for 7psi.

compcams 66-236-4 has 32* of over lap
crane cam503905 has 42* of over lap
isky 331-TA has 28* of over lap
........what else is there?

At what cam lift are measuring the overlap?
Advertised duration nubers are just that.... advertising.

How do you mean advertising? I find advertised far more accurate than guesstimating the 0.006" figure and the 0.050" is nothing more than a standardised reference point too.

Try doing a leakdown test at various valve events and I think you'll find the advertised is fairly handy.

 

[Thad]

I read somewhere long ago that the best turbo cam was the basic torque type profile because of low overlap.

Don't want much overlap for turbo because during overlap it blows through wasting fuel and pressure.

 

[XPC66]

That's what the internet mechanics would have you believe. If you look hard enough you'll even find "experts" who advocate negative overlap and inlet openings of 20 -30° ATDC.

Blow through doesn't seem to have been a problem with turbo cams that have the inlet centreline advanced a degree or two, which contradicts the notion.

The FE 300 appears to have a rod/stroke ratio of about 1.71 ish; that would put the default centrelines around 106°. The ER of the turbo is going to be a major determinant whether that should increase to say 109° to inhibit reversion, especially if the intake centreline is advanced for even earlier peak torque.

The 331-TA isky cam is advertised at 112° and 262/250, which means it's 19/63 57/13. That gives a 32° overlap, which is nothing to write home about. My guess is they've probably kept a decent overlap because of constraints on flat tappet lift, requiring increased duration to get the inflow. By increasing the duration they are lowering the effective compression and by coincidence reducing the opportunity of det. Retarding the centrelines to 112° will also move peak pressures later, also reducing insidious knock..... not the best for efficiency, but less strain on stock internals.

 

[Anonymous]

I like Isky stuff, but their turbo six cams SUCK. I ran them when they first came out and the stock cam made more power throughout the range at any boost than the Iskys.
I talked to Ak Miller and he said to use low overlap, and the exhaust should be about 10* bigger than the exhaust, somewhere around 190 intake and 200 exhaust at .050" lifter rise and lobe spread of 114-116*.
Had Isky make one and it was FIERCE.
If you don't know Ak Miller, Google him!!!!

 

[80broncoman]

At what cam lift are measuring the overlap?
Advertised duration nubers are just that.... advertising.

How do you mean advertising? I find advertised far more accurate than guesstimating the 0.006" figure and the 0.050" is nothing more than a standardised reference point too.

Try doing a leakdown test at various valve events and I think you'll find the advertised is fairly handy.

Advertised numbers are not always at .006 Some companys like .004 and it may even vary in a single companys line of cams. I have seen it as low as .001 to make a cam seem lager than it should be.
And besides all that an awful lot can happen between the .001-.006 and the .050 lift. once you get to the .050 area of the lobe you are commited to the curve.
Ever look at a inverted roller profile? That one will make you think if you haven't studyed up on the subject.

 

[XPC66]

Well if I were believe the nonsense of some, the cam would have no effect until it reached the much misunderstood 0.050".

You have basically agreed with my position, by throwing in the bogey of roller profiles. The reason advertised is more indicative of cam events, is because of the variance in flat tappet, roller and bucket followers. The cam ramp does have a noticeable effect and shouldn't be discounted in favour of the flanks.

 

[80broncoman]

Well if I were believe the nonsense of some, the cam would have no effect until it reached the much misunderstood 0.050".

You have basically agreed with my position, by throwing in the bogey of roller profiles. The reason advertised is more indicative of cam events, is because of the variance in flat tappet, roller and bucket followers. The cam ramp does have a noticeable effect and shouldn't be discounted in favour of the flanks.

I never stated that cams of different profiles have no effect till .050 tappet lift. Its just common knowledge that at .009-.010 valve lift there really isn't much air flow. hardly enough to make much power with. Of course the less the lift the less of an effect on air flow.
Doing a leakdown is not really that bad of idea except that air does not go out the intake ports, I'd think the better test would be to pressureise the intake and measue how much air comes out the exh side.

Food for thought:
All tappet have round (Raduis) bottoms, some are just bigger that others.

 

[addo]

Not all! Renault motors through the sixties, seventies and much of the eighties, have a dead flat tappet base. A frequent cause of grief, is cam regrinders putting that angle on the lobes.

 

[80broncoman]

Not all! Renault motors through the sixties, seventies and much of the eighties, have a dead flat tappet base. A frequent cause of grief, is cam regrinders putting that angle on the lobes.

Leave it to addo to bring in the french!

However you are right IIRC there was a BMW engine from the 20s or 30s that had a lifter of entirely right angles. I left that one out too.

 

[XPC66]

Well if I were believe the nonsense of some, the cam would have no effect until it reached the much misunderstood 0.050".

You have basically agreed with my position, by throwing in the bogey of roller profiles. The reason advertised is more indicative of cam events, is because of the variance in flat tappet, roller and bucket followers. The cam ramp does have a noticeable effect and shouldn't be discounted in favour of the flanks.

I never stated that cams of different profiles have no effect till .050 tappet lift. Its just common knowledge that at .009-.010 valve lift there really isn't much air flow. hardly enough to make much power with. Of course the less the lift the less of an effect on air flow.
Doing a leakdown is not really that bad of idea except that air does not go out the intake ports, I'd think the better test would be to pressureise the intake and measue how much air comes out the exh side.

Food for thought:
All tappet have round (Raduis) bottoms, some are just bigger that others.

Apologies if you thought I directed the 0.05" at you.

I don't quite follow what you are trying to say about the tappets having radiused bottoms?

Advertised is 0.006 at valve.

 

[80broncoman]

All the cam company here in the us I guess have thier own idea about what advertised duration is. Over here they are usally at around .004 at the lifter. I have seen as low as .001 :roll: and as high as .006 at the lifter.
If you really want an example of where advertizes number are moot just look at the solid lift cams. The lobe designer must put in a ramp to take up the lash smoothly before ever getting the work of opening the valves.

As a side note solid lif cam and hys can't be compaied and at ANY amount of lift without deducting some duration from the soilid lift cams because of the lash involved.

A common flat tappet (hyd or solid) actully has a radius. They are really not flat. The raduis is some where around 17 inchs. This happesn to be the dia of the grinding wheels used to grind most cams. It is the.002-.003 crown on the bottom of the lifter that is the radius. This is to reduce contact area and promote lifter rotatation which gives it a much, much longer life. If you have ever looks down in a lifter bore with the cam installed you have probibily seen the cam lobe is not centered in the bore. The cam lobes have a taper ground into them also all for the lifter rotataion ( and in the case of the SBC to keep the cam in the block!)
The outside dia also dictates thow radical the profile of the cam can be. If the profile get out of hand and the lobe contacts the edge along the bottom of the lifter it will stop spinning and wipe out the lobes in a hurry.
This why a ford with a dia of .875 can use quicker ramps than a GM lifter of .842 dia.
This is also whay a Chrysler/AMC with a dia of .904 can use a quicker....

Then the roller ,REALLY opens up how fast the cam can open and close the valve. Instead of the lifter size liminting you you run into the limit of what the springs and vlaves can handle without breaking.

Clear as a chunk of coal, Yes?

 

[XPC66]

The reason you see different figures for the cam durations is because the "advertised" is actually a translated valve duration. So say you have a rocker with a 1.5:1 ratio, the 0.006" valve event would translate to 0.006/1.5 = 0.004" cam event. The radius of the pad would also skew that value. A roller would be different again and a bucket would be 0.006", but with buckets the 0.006" becomes redundant, which is why that figure is occassionaly omitted on the spec sheet.

For a cam grinder the advertised specification would be a nightmare, because he would actually have to do some calcs, so the 0.05" is his benchmark in copying a profile. But for determining the actual performance, which is what we as users are generally interested in, we need to look at valve events, gross, net or otherwise.


My objection is to the parroting of myths and conjecture which seems to have sprung up amongst auto enthuisists since the advent of the internet. Before cyberspace we had to work things out. The simple task of throwing in a 0.05" specified cam and playing with rocker ratios required some maths and guess what.... the result was valve duration ~= "advertised".


Truth is that when you go to a cam grinder with your 250 camshaft and ask for 290/290 cam, he'll probably use a rule of thumb and knock 60° off to get the 0.05" figure anyway. Then you'll be pissed when you realise you forgot to tell him your rockers are actually 1.6:1.... so much for the 0.05" spec.

 

[tjnavyblue]

Comp Cams will grind you a custom cam for $200. It pays to download their (now) free software to check out flow specs

 

[351wF-250]

I like Isky stuff, but their turbo six cams SUCK. I ran them when they first came out and the stock cam made more power throughout the range at any boost than the Iskys.
I talked to Ak Miller and he said to use low overlap, and the exhaust should be about 10* bigger than the exhaust, somewhere around 190 intake and 200 exhaust at .050" lifter rise and lobe spread of 114-116*.
Had Isky make one and it was FIERCE.
If you don't know Ak Miller, Google him!!!!

Do you have the cam card for this cam. I am trying to select a good cam. I have desktop dyno and would love to know how well that cam really is on there. What were the lift values and the intake and exhaust opening and closing points. And on turbo cams someone told me that lift doesn't matter as long as the duration is right. So could I have a similar cam made and increase the lift and be fine or is this a bad thing.