Harold Brookshire lobes and intake centerline.

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Re: Harold Brookshire lobes and intake centerline.

Post by steve cowan »

Where I dyno my engines the guys are not big on moving cam timing around on the dyno, my last one has a belt drive and I said I want to test but they are very adamant it only rocks the curve back and forth.
It has to be tested on the track.
Now on a couple of my 383 combos I have backed cam timing up 4 degrees to straight up 109 - 109 as an example and picked up 2 mph in the eighth and 4 mph in the quarter.
Now whether you agree or not is personal preference but I found it interesting.
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Re: Harold Brookshire lobes and intake centerline.

Post by Tom68 »

steve cowan wrote: Tue Nov 29, 2022 2:00 am Where I dyno my engines the guys are not big on moving cam timing around on the dyno, my last one has a belt drive and I said I want to test but they are very adamant it only rocks the curve back and forth.
It has to be tested on the track.
Now on a couple of my 383 combos I have backed cam timing up 4 degrees to straight up 109 - 109 as an example and picked up 2 mph in the eighth and 4 mph in the quarter.
Now whether you agree or not is personal preference but I found it interesting.
Then you need to do it on the Dyno to see if it upped average horsepower, or dropped a bit of power that would have otherwise gone up in wheelspin etc.

i.e..You might as well see the effect of the change as it may help you dial the chassis in as well.
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Re: Harold Brookshire lobes and intake centerline.

Post by juuhanaa »

I'm just thinking out loud that if for some reason we have to use different parts on the dyno vs. the track, the torque can drop too early and we compensate for the acceleration losses by changing parts..

If someone is driving where the engine is happy and making torq, does he need to change the carb to go faster?



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Re: Harold Brookshire lobes and intake centerline.

Post by steve cowan »

Tom68 wrote: Tue Nov 29, 2022 3:17 am
steve cowan wrote: Tue Nov 29, 2022 2:00 am Where I dyno my engines the guys are not big on moving cam timing around on the dyno, my last one has a belt drive and I said I want to test but they are very adamant it only rocks the curve back and forth.
It has to be tested on the track.
Now on a couple of my 383 combos I have backed cam timing up 4 degrees to straight up 109 - 109 as an example and picked up 2 mph in the eighth and 4 mph in the quarter.
Now whether you agree or not is personal preference but I found it interesting.
Then you need to do it on the Dyno to see if it upped average horsepower, or dropped a bit of power that would have otherwise gone up in wheelspin etc.

i.e..You might as well see the effect of the change as it may help you dial the chassis in as well.
When I changed ICL from 105 to 109 ICL - 109 LSA no other changes, the car was a different animal.
At 105 it felt like it was out of legs at 6500rpm but on dyno it peaked at 568 hp @ 6600rpm and only down 5hp at 7000rpm.
Car ran consistently 121 mph which I was a little disappointed.
Backed up cam to 109 ICL with no other changes ran close to 125mph.
This is one week later so weather was not a huge influence.
It was quicker and faster across the 1/4 mile and engine turned clean to 7500rpm on the gearshift and 7000rpm at the stripe. It definitely would of been interesting to see the curve on the dyno,I had no idea changing centreline would be a night and day difference.
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Re: Harold Brookshire lobes and intake centerline.

Post by Tom68 »

steve cowan wrote: Tue Nov 29, 2022 5:41 am I had no idea changing centreline would be a night and day difference.
It was a tuning aid for US Speedway in the 50's and Quick Change Diffs were already old school by then.

There's so much more going on than the few things most people focus on.

Back to old school basics, making power higher in the rev range is more total power
PLAN
https://www.f1technical.net/features/16900

But that forgets limited gears racing, Speedway for example in most cases runs in one gear. If you make all your power under 6000 and gear it to suit you can get away with a narrow powerband.

If you make your power up around 9000, you need a broader power band to cover the minimum to maximum mph.

This is why old school lugger engines carry on past their prime in many classes of racing, they do eventually get overtaken of course.
Ignorance leads to confidence more often than knowledge does.
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Re: Harold Brookshire lobes and intake centerline.

Post by In-Tech »

Hiya,
This is a much bigger conversation than ICL. I have picked up 90hp at 7600rpm due to ICL, IGN timing and Fuel curve on a limited carb 4412 360cu in. Not 90hp peak, nor the average added up.

This conversation isn't talking about reality when you don't know the lobes nor have a baseline of that :)
Heat is energy, energy is horsepower...but you gotta control the heat.
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Re: Harold Brookshire lobes and intake centerline.

Post by hoffman900 »

I don't understand how CL's / LSA all became this thing to argue about. It's like drawing a line in the sand over ignition timing. People have been moving cams around forever, and builders with DOHC engines move it around all the time. It is what makes the best power for your application. This isn't rocket science :lol:

The centerline for any given application "depends". It depends on the entire engine system which is dictated by architecture, rules, use, etc. Then on top of it, for comparison sake, you can have non-symmetrical cams (Harold called his "un-symmetrical" as opposed to "assymetrical", which is probably a better way to describe them). If you look at Harold's lobes and with the quick opening side, that means for IVO to be the same as a symmetrical cam, peak lift is going to be advanced relative. I think the "why's" also need to be thought of. Harold has stated here he really thought of the engine not working until after TDC and that "overlap area is what it is", and that's how he ended up where he did with those designs. Basically was looking to keep IVC the same and minimize the bad parts of the overlap cycle. This is all on here in old posts by Harold himself.

But really, the engine needs what it wants, and there are so many factors in it, and moving it around on the dyno will help tell you and tell your cam guy what the engine needs going forward.
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Re: Harold Brookshire lobes and intake centerline.

Post by hoffman900 »

CamKing wrote: Mon Nov 28, 2022 12:59 pm
Stan Weiss wrote: Mon Nov 28, 2022 8:36 am
CAM_______Lift______Opens___Closes__Duration
_________________Deg_BTDC__Deg_ABDC_____________Area____ICL
_________0.00600____58.55_|__98.51_|_337.06_|__49.93_|_109.98
_________0.01000____55.54_|__94.96_|_330.50_|__49.90_|_109.71
_________0.02000____49.91_|__88.28_|_318.19_|__49.81_|_109.19
_________0.04000____41.66_|__78.54_|_300.20_|__49.56_|_108.44
_________0.05000____38.25_|__74.49_|_292.74_|__49.38_|_108.12
_________0.10000____24.20_|__57.88_|_262.09_|__48.24_|_106.84
_________0.15000____12.59_|__44.14_|_236.73_|__46.61_|_105.78
_________0.20000_____2.05_|__31.68_|_213.73_|__44.69_|_104.81
_________0.25000____-7.97_|__19.82_|_191.84_|__42.22_|_103.90
_________0.30000___-17.84_|___8.15_|_170.31_|__39.19_|_102.99
_________0.35000___-27.83_|__-3.67_|_148.50_|__35.60_|_102.08
_________0.40000___-38.30_|_-16.05_|_125.65_|__31.47_|_101.12
_________0.45000___-49.77_|_-29.62_|_100.61_|__25.94_|_100.07
_________0.50000___-63.45_|_-45.80_|__70.75_|__18.78_|__98.82
_________0.55000___-86.25_|_-72.77_|__20.98_|___5.81_|__96.74
Above is a true asymmetrical profile, and nothing like what Harold called an asymmetrical.
Harold's "Asymmetrical" profiles are completely symmetrical above .050" lift. The only difference, is he would put a slow lash ramp on the closing side, and no lash ramp on the opening side. They would just accelerate quickly, right off the base circle. This would make for a much later intake opening point, so you would need to advance them more to get the intake opening point closer to where it would be with a profile that had an opening lash ramp.
You can see that here:
Image

viewtopic.php?t=11713&start=15
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Re: Harold Brookshire lobes and intake centerline.

Post by Stan Weiss »

I may have been given the wrong data but this is the only difference I see in one of Harold's designs.

Stan
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Re: Harold Brookshire lobes and intake centerline.

Post by CamKing »

Stan Weiss wrote: Tue Nov 29, 2022 11:15 am I may have been given the wrong data but this is the only difference I see in one of Harold's designs.

Stan

Lunati_704_UD_PC_AS.gif
That's coorect.
Blue is the opening curve.
Green is the closing curve.
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