Worlds Fastest Comanche LSR build EAPro sims

[1bolt]

Okay Pete I got some more runs for you including the more meaty data that's not included in the simple dyno plot. For the uninitiated this is a Dyno sim using Engine Analyzer Pro of Pete's 5.0 land speed record build he intends to run Bonneville (this fall still Pete?). This is based off every bit of data we can accurately put in in except Valve train weights. So it should be fairly accurate. Highlights include a HESCO Aluminum head with full flow bench numbers, a seriously agressive roller cam, custom header, and an intake that's to be decided. Part of the purpose of this will be to optimize the tuning (the lengths of intake and exhaust) with the cam for maximum volumetric efficiency, in the range where a LSR engine will need it most... I.e. at max sustained RPM in top gear...

The basic short block stats:


In addition we have 38" 1.625" exhaust primaries with open headers (nothing from the collector back) and 6.5" intake runner lengths, a carb (not being simulated) a custom solid roller cam, and a 12.3 Compression ratio running off race fuel.

Assumed are very optimal spark timing (in other words a very accurate ignition system curved/programed optimally), a single plane Carburetor intake and also valve train mass and spring rates.

The current baseline run:


Following are the in depth simulated data from the base run. Obviously this data is potentially a hell of a lot more useful, than the dyno plots... Among other things, your "mach" numbers suggest that you could use bigger higher flowing intake ports and manifold (which is why I suggested porting the crap out of that HESCO head).

there's more of this data than I can fit in a single screen shot (EAP wont let me adjust the bottom of the window to show more of the data in pace of the notes)

or two screen shots for that matter here's the last couple bits of data:


The A/F ratio being poor suggests that exhaust reversion is high, possibly we can look at a little less valve overlap and see what that does. Unfortunately you can't do much to the combustion chamber to lower reversion, current heart shaped chambers have a ridge between the exhaust and intake valve seats with a sharp edge at the top. This makes the flow coefficient much worse in between the valves so reversion is lowered and air/fuel mix has a better tendency to not get sucked out the exhaust as much (in other words the mixture has to do a 180 over the ridge instead of a comparatively smooth 90 across a smooth chamber roof.

Currently we're making peak power 500 RPM's short of Pete's stated goal of 6500 RPM, shortening the intake runnners and exhaust a tad could help this. Making peak torque later in the RPM range translates into more HP. The way to do this is simple, move the torque peak higher in the RPM range. sacrifice it lower...

Comparing the first cam specs with a Clifford Cam that Pete wanted to look at:

The Clifford is making peak torque lower than the base spec (custom grind) cam. Which IMO makes it a downgrade, but we're not talking a lot here.... 9 hp less for about 11 ft-lbs more around 3500 RPM's. Still lowering the RPM of peak torque is not a step in the right direction. Unless you change your mind about what RPM you want to make your best power at.
Three pages of data to compare to the base run data:




Next time: subing in an individual runner intake for the single plane carby. and 300cfm "hypothetical" porting job.

[Plechtan]

Thanks for the work! The first cam is something that came out of Desktop Dyno, and probably could not even be made. It has a 126 intake centerline which does not really open the intake valve until around TDC. The second cam is more reasonable. I played with the numbers on DD, it seem to like a Cam with 112 intake centerline 112 exhaust centerline, and 112 deg lobe separation. Still a dual pattern cam with the exhaust duration ( @.050) 10-12 deg longer then the intake duration.

I finally decided to go with a IR setup, but with a common plenum http://extrudabody.com/ I will be using a Clifford Weber DCOE intake, with 6 throttle bodies. I should receive the manifold this week, but i think my total runner length will be closer 7-8" The 6 throttle bodies will be attached to a common air box, which i am hoping will act as a plenum. My thought is that at WOT the throttle plates become irelivnet, and the system will function as a normal intake.

[TurboTom]

The extrudabody stuff looks nice. Interesting concept.

[1bolt]

Here's Pete's latest Cam, it's better by a good deal than the previous Clifford profile, note the loss of 30 ft lbs of low torque... If you want an excellent illustration of just why putting a wicked agressive race cam in your junk (or porting the crap out of your street heads) then just imagine 30 to 50 less foot pounds of torque between 1000 and 4000 RPM's...


I drummed up a fictitious "max effort" porting of the HESCO head about 300CFM intake and 170 CFM exhaust, It wont be the most accurate curve because in reality the port cross section will change considerably with that much porting, and without ACTUALLY doing the porting I can only guess at how much it will really increase in size.

Next Pete has mentioned wanting to get something close to 200 CFM exhaust, so I simulated some porting of the 300 CFM (intake) theoretical HESCO head (remember these are fictional "what-if" numbers he hasn't actually had the head ported yet) to compare the 170-ish CFM exhaust port (as it is in the above graph) to a 200 CFM exhaust port...

The difference says to me that just cleaning up the exhaust and trying for the easy gains should be sufficient, the "max effort" intake porting is money better spent.

The flow table for exhaust are cut and pasted as insets (I wish EAP did stuff like that) one of the things to look at is the flow "coefficient" this is an interesting number that the performance industry really SHOULD be using as the metric to compare head flows etc.,,, CFM doesn't tell you nearly as much as flow coefficient. Basically the higher the number the better the port is at a given lift, it's like a 1-10 scale of how good a port is. 4 is bad 5-6 is normal to good 7-8 is outstanding and the numbers will usually be best at low lifts where the port is little to no restriction and the valve job is king, worse in the middle as valve shrouding happens, and then better again at high lift when the valve being further away from the chamber wall reduces shrouding.

We still don't have the peak HP RPM at 6500... But now knocking on 500hp's door I don't guess you really need it Pete... 6000 will keep the engine alive longer, but you may need to re-gear if you've already got your rear end done.

[Plechtan]

Maybe you should run one with forced induction.

I have not set up the rear axle yet, so i can put the correct gears in. I am going to have 2 or 3 different size tires to enable me to change gearing. I am goinf with a 25" dia to start, and have a 23" and 26" waiting in the wings.

Even with the fictional head, the engine is runnng out of air. I had done some desktop dyno runs with a smaller displacment engine, but similar flow nunbers. HP did not change that much, but moved up in the RPM range.

[1bolt]

Heheh everything runs out of air, the trick is to optimize whats physically possible with whats sanely affordable... By definition an engine is going to reach a point where it's no longer getting optimal air, and the work to suck it in starts to defeat the gains from getting more.

The size and CFM flow of the intake and exhaust tracts are simply tools to place the peak efficiency where you want it.

You can super charge it but it's a whole other engine can o' worms.

Besides aren't we well past what you need to see even though we don't have the peak at the specific RPM range.... In my mind getting near your target power 500RPM sooner is a good thing in many ways. for a old school straight six engine, that things a monster "on paper"

[Plechtan]

The class i am running in you cannot use a turbo or supercharger. I just thought it might be interisting to see what kind of HP was avaiable at 7.500 or so if enough air was available.

The Indy motor with twin turbos produced around 650 hp and tha was only 188cid.

[John]

650 with 30lbs boost.. twin turbo, likely sequential.

John

[1bolt]

Okay as promised a comparison between intakes. Now Pete I don't think was seriously contemplating a single plane carb intake but when we first started this it was on the table, and was the easiest default intake to choose.

Since an IR (Individual Runner) intake has been solidified and details of what he's going with have emerged (6x45mm throttle bodies and EFI) and he's contemplating putting a plenum at the end of the IR runners, I thought it would be fun to look at those options.
The best simulation of a EFI tunnel ram is a single plenum Race manifold AKA a Sheet metal intake. These are near "black magic" status in some circles, but they are basically a Tunnel Ram with a couple small distinctions that only EFI allows (like a perfect bellmouth radius at the end of the runner, stood off from the plenum floor.

The plenum in this case does not fulfill the same purpose as a carb intake (which is a ready surplus volume of air/fuel mixture to keep up with instantaneous demands that may be more than the Carburetor can supply in a given instant). In this case a plenum is simply a tuning aid, it allows the reflected waves created by air backing up against closing valves to be bounced back down a runner that has an open vavle. This effect is called helmholtz tuning, and along with tuning the length/cross section of the runner allows two distinct "free" super charging effects, called inertia raming

An IR intake alone will only benefit from the straight momentum aspect of inertial raming... air starts speeding down the runner and as the intake valve starts closing the air at the valve gets restricted, but the air "behind" it wants to push it past the closing vavle... This is why volumetric efficiency can be above 100%... This effect happens in ever intake manifold ever devised, it happens "better" the better you tune the length.

This is most easily thought of as just like a siphon effect with a hose....

Now slam the valve closed and that air that slams to a halt doesn't stand there at the valve and take a smoke break. It bounces back up the runner.

Now put a plenum on top and it can bounce around inside, HOPEFULLY into an opening intake valve. In an IR intake it vents out to atmosphere uselessly. How well and when the reflected waves add to power is mostly a function of runner length/cross section and plenum size. What RPM you'd like to make peak power at has a lot to do with how big you make the plenum.

Here's the sim of all three, the base single plane carb is obviously the clear loser, it gives up torque and peak power.


The next thing to do is figure out what the ideal plenum volum is... 151cc just happens to be the size of a 99+ intake plenum, and was left there without tweaking.

[Plechtan]

It is interisting to see the torque actually going up around 3200 rpm, Can you do a plot from 1500 or 2000?

The Plenum will be about 4" diameter and 20" long (4.0L?) The smallest i could probably go would be around 1.25L

[1bolt]

With the cam you have I'm not sure your engine will even run that low. I do the plots from 3000 RPM's to keep thing neat and detailed in the RPM range that matters. But I'll be happy to do one up later that shows the lower RPM's for curiosities sake.

[1bolt]

Okay as requested here's a simulated pull from 1500 RPM's I put a stock 4.0 pull in there just for frame of reference.

I ran different plenum sizes for an hour or so, it seems either EAP does not simulate the reflecting wave for plenum volumes or the manifold I've selected doesn't. Larger plenum improved power ever so slightly. Make it as big as you can seems to be EAP's verdict, I distrust that, if that were the case then IR intakes with no plenum would make more power than the EFI sheet metal intake or tunnel rams.

Also anywhere I've stated 150cc's for plenum volume substitute cubic inches. Man I'm bad with stuff like that.

Anyway this is kind of anti climactic and makes me wonder how much better the 99+ OEM intake would do in the 4.0 simulation, supposedly that intake was designed to reinforce the power peak around 5000 RPM's due to the size of the plenum being "acoustically" tuned (for lack of a better term) for that RPM.

I'm Asking the makers of EAP about this...

[1bolt]

One other thing, Pete when you get a chance can you measure the new cross sectional area of the intake and exhaust ports now that HESCO has opened them up? I checked and with the "max effort port job" simulated head if I open up the cross section of the port from 1.75 ish to 1.9 ish the engine losses a fair chunk of power. (yeah I know that's a fair chunk of cross section too, but I'm just guessing).

[Plechtan]

Gee, this looks crazy, I would expect the torque below 3,000 rpm to be in the sewer, but it seems to have over 300 ft lbs down to 2,000 rpm. If this is true, i guess i will not need a push start.

[yuppiexj]

Looking at the graph(s) this looks like it could be almost street-able.

I would imagine that around 3300 RPM it would feel like a turbo spooling up.

C'mon mega millions, that would a great engine in an old Metropolitan (if you could keep traction, that is)

end thread hijack

That's sick power out of a NA i-6.