Using Blair to spec a Cam

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Vincenzo
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Re: Using Blair to spec a Cam

Post by Vincenzo » Mon May 21, 2018 4:56 am

Stan

should have attached these pics to my last post.
One shows computed in EngMod4T the in cylinder pressure as at the time of intake valve opening with exhaust valve size as per your opening post The negative intake wave position at intake valve opening might be queried, but running the same simulation with a change to the induction length to create a positive wave at opening resulted in a lesser computed output.

The other shows the computed exhaust valve bounce and opening delay as computed in 4StHead . The degrees shown are camshaft.
Sorry but the clarity of the line colors are difficult to determine for the valve bounce, but at least the bounce at closing is readily apparent.
This design was subsequently changed to overcome the bounce problem.

My simulation models inEngMod4T, and in 4StHead, have considerable guess work involved as I have never had access to a Pontiac engine, so I used a Ford V8 for basics. I could be far off the mark in this, but at least I hope it gives some indication of the effect of changes that will modify STA values, and the results that might be forthcoming .
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Re: Using Blair to spec a Cam

Post by Stan Weiss » Mon May 21, 2018 11:00 am

Ron,
Thank you for all of the time / work that you are putting into this. I am sure what I have come up with so far is probable not close. After I got the intake somewhat close I tried the same lobe on the exhaust. Playing with center line and rocker arm ratio I got it also close. The rocker arm ratio is not a standard one. When I get sometime I can modify the lobe so it will use the same 1.65:1 as the intake.

Stan

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Re: Using Blair to spec a Cam

Post by Stan Weiss » Mon May 21, 2018 3:28 pm

One last post to sum up where I am at, with numbers that are more understandable to some. 1.65:1 Rocker arms both .

These numbers will increase with asymmetrical lobes
LSA - 100.5
ICL - 99.5
ECL - 101.5

These numbers will decrease with asymmetrical lobes
Int Seat-to-Seat 315 - lobe - 0.050" - 273.44 - 0.200" - 196.4
Ex Seat-to-Seat 314.78 - lobe - 0.050" - 273.29 - 0.200"- 201

These numbers will stay the same with asymmetrical lobes
Int - lobe lift 0.5133
Ex - lobe lift 0.5413

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Re: Using Blair to spec a Cam

Post by pastry_chef » Mon May 21, 2018 4:25 pm

Would be interesting to see a dyno of such a cam.
A quick look at DV's BBC overlap chart says 93 degrees for 525 cubes at 7500 RPM (overlap @ .020).
Not too far off but this is not a BBC, the chart also suggests a very different 14:1 compression.
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Re: Using Blair to spec a Cam

Post by GARY C » Mon May 21, 2018 6:09 pm

pastry_chef wrote:
Mon May 21, 2018 4:25 pm
Would be interesting to see a dyno of such a cam.
A quick look at DV's BBC overlap chart says 93 degrees for 525 cubes at 7500 RPM (overlap @ .020).
Not too far off but this is not a BBC, the chart also suggests a very different 14:1 compression.
I think Pontiac is a 14 degree head? If so the BBC chart may not work.
I devised a way to use his SBC chart for high compression exotic type heads like 16,14,12 degree engines that seems to correspond with the ones I could find info on but it is only a theory I spent a cpl of hours on and I have no way to test it.
A 45* seat head would on a 110 LSA and a 52*ish seat would be on a 109 LSA, 93* overlap you would have a 313 and 311 (respectively) seat duration. But it's all a quick guess and I think you would want a little more overlap on a steeper seat angle but I could be wrong.

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Re: Using Blair to spec a Cam

Post by pastry_chef » Mon May 21, 2018 6:20 pm

Yes, Pontiac has a steeper valve angle but is limited to smaller valves than the BBC.
GARY C wrote:
Mon May 21, 2018 6:09 pm
A 45* seat head would on a 110 LSA and a 52*ish seat would be on a 109 LSA,
You lost me there, in his BBC book the suggested LSA are tight. Without valve angle adjustment here would be 103 LSA.
Not saying it is optimal, would have to test them.
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Re: Using Blair to spec a Cam

Post by GARY C » Mon May 21, 2018 6:26 pm

pastry_chef wrote:
Mon May 21, 2018 6:20 pm
Yes, Pontiac has a steeper valve angle but significantly smaller valves than the BBC.
If I recall on DV"S pump gas 525 he ran a 107/lsa and if the compression was raised to 14.1 it would have been wider. 788 hp 729 ft lbs.

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Re: Using Blair to spec a Cam

Post by pastry_chef » Mon May 21, 2018 6:30 pm

GARY C wrote:
Mon May 21, 2018 6:26 pm
If I recall on DV"S pump gas 525 he ran a 107/lsa and if the compression was raised to 14.1 it would have been wider. 788 hp 729 ft lbs.
OK.. this Pontiac 535 will be pump gas.
Do you recall what the durations were for that BBC 525 ?
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Re: Using Blair to spec a Cam

Post by GARY C » Mon May 21, 2018 6:31 pm

pastry_chef wrote:
Mon May 21, 2018 6:20 pm
Yes, Pontiac has a steeper valve angle but is limited to smaller valves than the BBC.
GARY C wrote:
Mon May 21, 2018 6:09 pm
A 45* seat head would on a 110 LSA and a 52*ish seat would be on a 109 LSA,
You lost me there, in his BBC book the suggested LSA are tight. Without valve angle adjustment here would be 103 LSA.
Not saying it is optimal, would have to test them.
Thats off of something I came up with comparing to different known engines. but if you read his stuff a higher compression would be a wider LSA

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Re: Using Blair to spec a Cam

Post by GARY C » Mon May 21, 2018 6:32 pm

pastry_chef wrote:
Mon May 21, 2018 6:30 pm
GARY C wrote:
Mon May 21, 2018 6:26 pm
If I recall on DV"S pump gas 525 he ran a 107/lsa and if the compression was raised to 14.1 it would have been wider. 788 hp 729 ft lbs.
OK.. this Pontiac 535 will be pump gas.
No, DV's BBC 525. this one https://www.youtube.com/watch?v=diaKgpqzoA8

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Re: Using Blair to spec a Cam

Post by pastry_chef » Mon May 21, 2018 6:37 pm

DV's BBC 525 - 4.5 inch stroke.
Peaked around 6150 RPM, with a 107 LSA I would suspect it had some duration in the cam.
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Re: Using Blair to spec a Cam

Post by GARY C » Mon May 21, 2018 6:42 pm

pastry_chef wrote:
Mon May 21, 2018 6:37 pm
DV's BBC 525 - 4.5 inch stroke.
Peaked around 6150 RPM, with a 107 LSA I would suspect it had some duration in the cam.
I think it was in the 240's a .050, it was a 10.5 to 11.0 compression pump gas engine.

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Re: Using Blair to spec a Cam

Post by Scotthatch » Mon May 21, 2018 6:59 pm

Stan wanted 900 HP
He said the airflow would be 432 cfm @ .800
To make 900 he would need 438 cfm or 101% of the flow
With the camshaft he designed which is 273.44 duration @ .050 on a 99.5 degree lobe center the closing point of the intake is 56.22 degrees ..... that puts the Z factor at 36.22 degrees or just past the 1 line ....
15238124921820.jpg

I find it interesting that it came out to the same number
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Re: Using Blair to spec a Cam

Post by hoffman900 » Mon May 21, 2018 7:23 pm

How much of that 107* LSA was driven by available cam cores? I can't imagine there are any available cast cam cores that could handle that.

An oldie but a goodie: Vizard on 106* LSA vs 112* LSA in a BBC http://www.speedtalk.com/forum/viewtopi ... =1&t=16186

The late Harold Brookshire mentioned grinding 107* LSA BBC cams, but that they were anything but streetable.

I'm not sure where this cam is installed, but no doubt it's tight. 358ci, 7000rpm peak, 9:1 compression. https://www.youtube.com/watch?v=Ne6nsVVykWw

I've been around a lot of cams in the 104-106 centerline area, and they're very lopey and not happy from a dead stop. Make a ton of power in the 5000-7200rpm range (which is what the engines were designed to do).
-Bob

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Re: Using Blair to spec a Cam

Post by hoffman900 » Mon May 21, 2018 8:15 pm

Gary,

Hope this helps:
Since Blair uses metric 177.645 = 12.2482 Bars

► BMEP_BARS = 12.2482
► (5.02 * BMEP_BARS + 57.78 ) / 10000 = 0.0119265964s/m (intake pumping)
► (1.7775 * BMEP_BARS + 74.822) / 10000 = 0.009659317549999999s/m (exhaust pumping)
► (4.1185 * BMEP_BARS - 17.985) / 10000 = 0.00324592117s/m (intake overlap)
► (3.0296 * BMEP_BARS - 11.363) / 10000 = 0.002574414672s/m (exhaust overlap)
► (1.6329 * BMEP_BARS - 7.1871) / 10000 = 0.001281298578s/m (exhaust blowndown)
► (2.4022 * BMEP_BARS - 14.57) / 10000 = 0.001485262604s/m (intake ramming)
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Vincenzo,

So 4stHead can export a cam file to show the bounce to be run in a sim program? I like that feature a lot.
-Bob

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