low lift flow on all out drag engines

[cgarb]

Well, I assume dyno results...how much did the extra flow net?

[travis]

Another way to look at this.

Increasing high-lift flow at the detriment of low-lift flow means you need a cam that spends more time at high lifts. This is OK for two reasons:
1. Its an all-out race engine so idle quality, vacuum and low rpm performance are less important.
2. Reduced low-lift flow probably also means less flow in the reverse direction (which only happens at the "ends" of the duration ie low-lift and unfavourable revs)

Wouldn’t that mean improved idle quality, vacuum, and low rpm performance, due to reduced low speed reversion?

[Carnut1]

The part that bothers me with back to back tests like this is the lobe centerline angle is right for one valve angle and off a bit for the other. With more low lift flow the engine sees a larger overlap triangle so the Lca needs to be spread. The problem with that is if every other cam point is right for the combo you would change those points. I totally see on this combo how the steep seats would help. My question is if it makes more power now is it worth a lca change worth the trouble looking for more? Thanks, Charlie

[289nate]

I believe valvetrain improvements have allowed shorter duration intake lobes, with quicker ramps, much more lift, and much more time that the valve spends at lifts where there is actually meaningful air flowing for the duration. In that case low lift flow becomes less important on things such as daily drivers that are overhead valve two valve headed. So the cylinder heads have changed because of valvetrain advancements.

LSx engines come with what where considered "race heads" when I first started trying to learn how to make my '66 Mustang faster as a kid. Now those "700+ hp race heads" come from the factory on my SUV and have pulled my Mustang on the car trailer very well.

All out, I figure a loss in low lift flow for a gain in high lift flow is a win. For the simple fact that was mentioned earlier. More lobe area with hopefully less reversion.

[289nate]

Charlie, I would think the person designing the cam would want to be in control of the aspects of the engine regarding intake and exhaust sides for the specified displacement, budget, and rpm range in an all out effort. Otherwise, they are designing a cam around what you have and not based on what they can do.

[RevTheory]

I think it's application-dependent and in Joe's case, it's definitely a good move. I'm sure the overlap window is insane with an aggressive roller that's near 280/290* at .050 on a 109.

[mag2555]

In a all out race motor set up to run in a 1800 rpm power band or less,I think that added low lift flow will only add more peak hp if the Intakes systems port area is not already hitting the velocity ceiling, otherwise all you will see is that the motor holds onto peak hp numbers a little longer.

[Carnut1]

Another factor that I don't believe has been discussed but is an interesting point would be the steeper valve seat is better at self centering at high rpm. Since there is more of a wedge, this also reduces the tendency for the valve to bounce. Any wear on the guides could amplify these issues. So the changes have been redo the guides, steeper seat angles, Change valves to ti from Stainless. I can see how each of these changes added power to this high speed combo. Thanks, Charlie

[CGT]

Did I miss something? I don't believe Joe has tested the results with the new head work yet.

[steve316]

Mag2555 do you have any Dyno data that shows where adding low flow did add more peak hp; if so would you share?

[CGT]

Mag2555 do you have any Dyno data that shows where adding low flow did add more peak hp; if so would you share?

Good luck with that.

[289nate]

In a all out race motor set up to run in a 1800 rpm power band or less,I think that added low lift flow will only add more peak hp if the Intakes systems port area is not already hitting the velocity ceiling, otherwise all you will see is that the motor holds onto peak hp numbers a little longer.

I thought this was about adding low lift flow at the expense of higher lift flow?

[randy331]

With more low lift flow the engine sees a larger overlap triangle so the Lca needs to be spread. The problem with that is if every other cam point is right for the combo you would change those points.

RIGHT !!
EXACTLY !!

That's why I'm so glad that's what you guys did in your cylinder head tests !!

I don't remember now, but how many different LSA/CAMS did you guys test with the BIG difference in flowZ ?

Randy

[MadBill]

With more low lift flow the engine sees a larger overlap triangle so the Lca needs to be spread. The problem with that is if every other cam point is right for the combo you would change those points.

Since the increased LLF would likely also be a factor re optimum IVC timing, perhaps the intake lobe should be say 4-6°shorter but on the same CL.

[68corvette]

Did not see this yet linked, but its informative article:
http://www.hotrod.com/articles/1203phr- ... e-job/amp/