367 hp lwfw and charles exhaust with 80 lbs off back of car best mod

 

Nice, agree that its not really relevant to compare numbers from different dynos. The point of my post is to let those who may be interested know that on my car and with my supporting mods, the IPD and tb mod has shown big gains. Not trying to say it's the "best" mod...glad to hear you are one of many happy Dundon clients. His exhaust is a work of art.

Will talk to Cheyne about the different gearing between my old and new 4th gears. I'll get back on the dyno soon after my cat deletes are fabricated and installed.

 

So from your dyno chart, if we use the 5000rpm tq peak as a constant, the difference from the 2 runs is 5.1%. If you use the 6% additional gear reduction that should equate to 5.1% less power, which from 361.8whp x .949 = 343.5whp. Assuming that is the change in gearing

 

I have the IPD with 997 TB (plus M&M exhaust). Car hauls like a freight train. Makes similar numbers to 997.2 RS on the same dyno. 365 rwhp is my number but not really relevant.

 

Thx Ian. May have to try it. Thx! Do you have to drop engine up change plenum?

Mk

 

Un bolt and lower the engine down a bit or all the way, that extra 1-2" is priceless when doing something like this.

 

I didn't have to lower the engine. I did need to remove the oil filter housing. It wasn't difficult.

Thanks Charles, I spoke to Cheyne this am. He confirmed that he did change the gear ratio on the dynapack to account for the different gearing. He says any additional uncompensated difference due to mechanical advantage is very small.

 

According to the dynapak screen shot the gearing is the same. They both show 4.488

The gearing isn't the problem as that doesn't matter. The issue is that the dynapak reads the RPM readings based on the gear reduction.

If you have a 5:1 total gear reduction and you REV to 8000rpm the hub speed is 1600rpm. The dynapak takes this 1600 x 5.0 to get 8000rpm and that's how it calculates HP

If you take that 5:1 and change it to 6:1 gearing but don't change the gearing in the software it will still try to allow acceleration to 1600rpm at the hubs. This would be 1600 x 6.0 which is 9600rpm. This means the tq peak at 6600 would show up on the dyno sheet at 5500rpm and the 5250 tq peak would show up at 4374rpm earlier than they actually do. Also when the rev limiter kicks in at 8200 the dynapak would actually show 6833rpms

Remember the dynapak doesn't know anything about the engine. It gets its "rpm signal" from the hub speed x gear ratio.

 

Ok, thanks for all the info. On pg 1 of this thread you'll see from my 2012 dyno runs that the ratio number was 4.208. You will see that the 2016 dyno run plot used a ratio of 4.488.

 

actually i did not see that, i only saw on the comparison sheet that the one ratio was listed, thanks for pointing that out.

I m still curious about the difference in the resonance peaks being so far off. I have seen them off before by intake air temp because the SOS changes as air temp does. as it gets hotter the sound waves move faster, but i've only seen it move 100rpms or so tops.

I am no in any way disagreeing with your dyno or data, just curious as to those peaks being so far off.... Maing me want to give one of those a try again

 

If your goal is to go around a track more quickly, your modifications need not any further validation. Mission accomplished.

 

For a noob - as u said that it's far off. Why would it happen? Are u saying numbers are being manipulated? Anyway there's an archive of adventures with IPD mod by 911 slow and results show less than stellar results. Anyway nice that people are experimenting and see what results happen. I'm siding on 911slow on this though. Mike

 

Lol! I hope you're joking about number manipulation. There are no "sides" to be taken. I don't care if anyone runs out to buy one of these, just posting my results.

 

I have no reason to believe anything was manipulated. Just was curious about a few things. But after asking a few questions everything makes more sense now.

Other than a few things i'm still scratching my head over, i am actually going to order one of these to try out on my next 996 GT3 exhaust victim. Stock before and after the exhaust.

Does seem like you have the best and most valid results that i have seen with this piece compared to everyone else.

 

The old thread about John's car (911SLOW) seems to have disappeared which stinks because it had alot of great info in it.

He did back to back testing of the IPD unit on a dyno. The graph showed torque gains through about 5500 rpm but otherwise power and torque were lower than the OEM setup at the top of the curve.

I'd love to see another independent test. A fried of mine installed one of these a year or so ago and swears the mid range pull is much improved on his car. He never dyno tested though.

Numerous times I looked at machining the OEM plenum and adding an 82mm throttle body to see if it'd add any power on my car but I haven't found enough compelling evidence that it's worth it to go down that road.