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Old 12-17-2010, 07:37 AM
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Dynosim BMEP's seem out of line...

I finally got my copy of Dynosim 5 and decided to start looking at hydraulic roller camshafts for a pump gas, street/strip 496 BBC "torque monster" kind of engine.

AFR 305's (the 290's gave almost identical numbers, but cost quite a bit more for some reason).
Dual Plane Max Torque Intake (not really sure this is possible with a rectangle-port head)
18cc dome
10.02:1 SCR
8.10 DCR

I set the optimize function for max torque under the curve between 1500 and 4000. I ended up with a Comp Cams 11-420-8. (0.566/0.566, 110 LSA, IVC @ 49 ABDC (0.050))

The numbers were not quite what I expected.
Basically 700+ lb-ft of torque from 1500-3500 rpm. Peak HP was about 490 @ 5000 rpm.

However, the BMEP's were from 200-227 throughout the same range.
This seems very extreme, especially given the reasonably low DCR of 8.10:1.

Any thoughts? Is this just an example of an unbuildable sim result?

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Old 12-17-2010, 10:56 PM
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I have noticed this also on some torque builds. I think it has to do with the excellent intake components and exact cam match. If you put an intake on the motor that will not flow as well, the BMEP will come down. I think it's a matter of ramming air into the motor. I got a BMEP of 253 on a 352 Chevy small block (4.155" X 3.250") using the right cam (chased through about two dozen cams to find the right one), two 650's and a max flow tunnel ram through Brodix -10 heads at 12.50:1 SCR on E85 fuel. This motor will be in a retro gasser '57 Chevy with a 4-speed.
RPM HP TQ
3000 237 414
3500 299 448
4000 380 499
4500 466 544
5000 546 573
5500 621 593
6000 663 580
6500 698 564
7000 700 526
7500 688 482
8000 671 440
Peak volumetric efficiency 119.2% @6500
Peak BMEP 253.7 @5500
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Old 12-17-2010, 11:23 PM
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So a BMEP of 227 doesn't worry you on a torque build?

Given that a F1 car runs a peak BMEP of 212 (given, it's at 19,000 rpm ).

By the way, tech...are you just typing those numbers in manually, or are you cutting and pasting them from somewhere? I'd love to share more detail if I don't have to transcribe numbers all afternoon LOL.
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Old 12-18-2010, 06:03 PM
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Quote:
Originally Posted by nofearengineer
So a BMEP of 227 doesn't worry you on a torque build?

Given that a F1 car runs a peak BMEP of 212 (given, it's at 19,000 rpm ).

By the way, tech...are you just typing those numbers in manually, or are you cutting and pasting them from somewhere? I'd love to share more detail if I don't have to transcribe numbers all afternoon LOL.
Nawwww, I bite the bullet and type them in custom every time. I also look up cylinder head flow and factor it down by .95 on some of the Sims that I do, if they are of enough interest to me. I spend quite a lot of time on some of these fellows.

The reason for factoring the flow is, for instance, RHS flows their small block heads on a 4.200" fixture. Now I ask you, when's the last time you saw a Ricky Racer type guy with a small block Chevy that was anything but 4.030" or maybe 4.155" in the case of a 400 block. So, I cut the flow back a little to make it more real world.
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