Without you telling us what type of exhaust system you have, and if you have cats or not, the sim will be even less accurate. Also, as I recollect you have 5" runners, is this correct??
I'll see if I can get my EA Pro calculating your output this evening.
Without you telling us what type of exhaust system you have, and if you have cats or not, the sim will be even less accurate. Also, as I recollect you have 5" runners, is this correct??
I'll see if I can get my EA Pro calculating your output this evening.
Arnold
I did not realize that this was necessary but it makes perfect sense.
1-3/4" hooker headers 2151
into 3" Hooker front y-pipe,
into 3" diameter pipe
into 3" magnaflow rear y-pipe
into dual Magnaflow
Not catalytic
Also, I am considering using 1.5 rr's for the exhause valves, but I have a full set of 1.6 RR's as well.
Open headers w/6" collector:
457tq-5000rpm-5500rpm
506hp-6000rpm
All the following exhaust setups have:
25" collector, meaning a termination box would be needed at 25" off the collector, optimal would be somewhere between 18-25" I'd guess
Exhuast flow with 3" center pipe as limiting factor @ 747 CFM (Note: I don't know the proper way to put our full x (dual Y-pipe) exhausts into the program, obviously a 3" dual system flows 2x that, but since it goes into single I don't know if I should use the single value or something in between, I don't quite think these are correct though):
414tq@5000rpm
456hp@6000rpm
Exhaust flow as if dual 3" @ 1494 CFM
452tq@5500rpm
500hp@6000rpm
These have what would probably be around the full exhaust length (guessing?!) 60" collector length:
limiting center single 3" (if correct flow is 747cfm, which I don't know about):
408tq@5000-5500rpm
451hp@6000rpm
3" duals:
444tq@5000-5500rpm
481hp@6000rpm
Larry, do you have dyno results for your current motor(and cam specs)? (a graph even)
If you could give me those, the length of the primary header pipes and the total length of the exhaust system (and length when it hits the center pipe.) I might be able to get closer to your true exhaust flow right now and better predict the change.
Also, PM your e-mail address again and I'll send you all the data/graphs.
Just wanted to add, the results I obtained from my EA Pro were also SAE Conds not Std Dyno. Std Dyno results usually show about 4-5% more power output.
The headers Larry is using are the Hooker Super Comp. 2151 with 26" primary and 8" collectors. You cannot use the 8" value because you have to add 26" to the existing length of the collector. The beginning of the Y-pipe, in his case, is the actual length of the collector. So 8" + 26" make a total of 34" which is the value you have to insert when looking for the right simulation. Here is what Vizard says, "As for the secondary length-that is from about the middle of the collector to the end of the secondary (or the first large change in cross-sectional area), we find a great deal more sensitivity than is seen with the primary. By getting the collector/muffler length right, which in our case was about 40 inches, the torque at 3,500 was increased substantially."
Yes that is a great article. Thanks for the specs on the Hookers. I was guessing which is why I ran it with the 25" collector.
However I did not, and am still a little confused as to why the "collector"/secondary length changes at the single main pipe. I follow it is due to the large change in cross sectional area. So dual 3" to single 3" is 12.99sq" to 6.50sq" therefore, it is the first change in CSA and thus the length of the secondary is essentially established from midway of the collector to the end of the y-pipe, so 8" collectors + 26" =34" (or would it be 8"/2 to find midway thus 4" + 26"= 30" ???)
Also, what do you use for exhaust flow when you run this simulation?
Thanks,
Chris
P.S. When I match the intake and head port size (I don't know what Larry has so I used 1205s) and use a 34" collector with the 26" primaries and no mufflers I get:
500tq@5000
527hp@6000
Moving the intake I modeled after the HSR flow efficiency up from 80 to 95%
I get 516tq/545hp.
Last edited by USAsOnlyWay; 03-03-2009 at 01:10 PM.
Chris, I have the same Hooker headers and I used 8 + 26 for my simulation. Looking inside the collector, you can actually subtract about 2", but the pipes coming from the left and right side are actually a different length, at least mine are. So taking 8 + 26 is pretty much okay. If Larry would want to do it right he would have to measure each side and divide through 2. I really don't now if it's so important.
I have 3 different SIM programs and all show different TQ/HP. Sorry, I don't trust these programs because of this.
In about 2 months I will take mine to the dyno and I'll see which program was best.
I took 1500 CFM exhaust flow. It might be too much but I really don't know since he only has a 3" pipe going back to the rear y-pipe.
BTW, without the correct valve events, we can calculate all day long and won't get it right.
Max flywheel power: 535/6000rpm
Max flywheel torque: 507/5000rpm
I did a new simulation using SAE Dyno and changed a few things.
Ram manifold but with 2.0 runner coef.
Int. runner diameter @ head 2.3
Header runner flow coef. 2.4
Still don't know the correct valve events of the new cam
TQ 505 @ 5100
HP 539 @ 6200
Arnold
__________________
92 LT1, was auto now ZF 6 sp. 397ci, Ross pistons, heavily ported 210cc LT4 AFR heads, ported LT4 intake, 1.6 RR, SR 247/255 .664/.664 112°, 11.3:1 CR, 58mm TB, 36# injectors, Fidanza alum. fw, Hooker 1 3/4" lt headers, no cats, self made dual SS 3" exhaust sys., X-pipe, MagnaFlow mufflers, Meziere HD pump, 4.10 rear, Brembo 13.5" brakes, bigger stabs, coil overs, C6 Z06 18" wheels.
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Yes, you are right, we can only get so close. I think you also have a newer version than I do.
That is partly why I like to base these things off of dyno graphs, because I think that if you can get the sim to reproduce your real world results closely, then you actually can have a better chance of predicting real world changes.
As for the pipe with Vizards calculations of 115cfm/sqin of cross sectional area, that main 3" single pipe can only flow 747cfm. But like I said, I don't know how this really acts in this situation. I would think it would act like a muffler with 747cfm of flow dumping to the atmosphere (cooled exhaust+dual 3" and straight through perforated tube magnaflows should flow plenty from the single back.)
Then again since the exhaust pulses don't hit at the same time, maybe it still acts somewhat like a dual 3" system then it would be flowing around 1500cfm.
Yes, you are right, we can only get so close. I think you also have a newer version than I do.
That is partly why I like to base these things off of dyno graphs, because I think that if you can get the sim to reproduce your real world results closely, then you actually can have a better chance of predicting real world changes.
This is exactly what I mean, once you have it dialed in, you can use a sim for predicting real world changes. At the moment I'm using the EA Pro 3.5 version, EA 3.2 and Dyno 2003.
Larry, as you know I think your springs are not up to the task, your 3" main pipe is also a drawback. With such a huge 406 engine, big cam and heads, you can't run a single main pipe!! I would go for a dual exhaust for sure.
Thanks Chris and Arnold for your help. I don't want to trouble everyone with the SIM wackiness anymore, there is just too much info missing that I do not have yet.
But I did call Bullet this morning and they changed their opinion on the spring pressures, they now recommend 150-160 seat and 400 open pressure.
So I will upgrade the springs and also, I decided to go with this cam.
I am not looking for an all out race setup, just want to improve the numbers that I already have.
As far as the dual exhaust goes, I will likely do this eventually this summer.
One again, thank you guys very much for trying to help, I very much appreciate your efforts .
Corvette Store
Can I get a SIM?
