Fico

iTrader: (1)

So this summer I got all my engine mods on (Takada long intakes, M370 Intake manifold, and OBX Arc Style Cat Back) and got a tune to the effect of 276awhp.

My friend has about the same mods (Stillen Long Intake, M370, and Ark Exhaust) he was tuned at 293rwhp.

Few things in consideration....
G37x Coupe weighs 3840lbs
G37s Coupe weighs 3640lbs
6mt vs 7at

We did a couple of pulls from 2 and 3rd gear and every time I would start to inch away.
The only thing I can come up with is this....
on the dyno it was running 50/50 split front to rear in order to find awhp, so if my front tires weren't "slipping" i.e. engaging AWD then am I putting more hp to the rear wheels?
does this make sense?

JSolo

iTrader: (14)

Aside from the weight difference, you need to consider gear ratios. Both have different gear and rear end ratios. If they don't equate to the same final ratio, then that would be your difference.

Combined = product of trans gear * final drive ratio

awd
2nd gear: 3.193 : combined = 10.718
3rd gear: 2.042 : combined = 6.855
6th gear: .862 : combined = 2.893734
final drive: 3.357

rwd 6mt
2nd gear: 2.324 : combined = 8.580
3rd gear: 1.624 : combined = 5.996
6th gear: .794 : combined = 2.931
final drive: 3.692

As you can see, for any given speed in those gears, the awd has the engine spinning at a higher rpm. Do the test in 6th gear and you should get nearly identical results.

Edit: Crunching the numbers for all the gears shows that 6th in both would be the closest in terms of final gear ratio. 4th in both would be the 2nd closest.

Fico

iTrader: (1)

That was my other thought ill have to get him to come back this way again and give that a try

Varjo

Gear ratio doesn't affect horsepower (theoretically at least, in practice it doesn't affect it much). The difference is likely mostly due to two factors.

1) He has a 6MT, torque converters (so conventional automatics like the g37), even fully locking ones, have a fair bit of parasitic power loss due to oil friction and turbulence (see here). While there is no set rule for how much power is lost, a fairly efficient torque converter might be a tad above 5 percent. This would account for most of the difference.

2) A much lesser factor than the torque converter, but you have AWD. Even when running with only power to the rear wheels, there are still half shafts rotating adding friction (and rotational inertia while accelerating). Again, this is likely small compared to the above effect, and tends to have more of an effect on acceleration than actual horsepower.

G35xsSC

How exactly do you know it was running 50/50 on the dyno? I am very curious because every time I have had to dyno my car the disabled the AWD via the glove box because it was shifting power back to front past a certain RPM. And if anyone is wondering this didn't fully disable the AWD there was still some power going to the front.

gsm026

If I understand the OP correctly, the AWD auto was pulling away from the RWD 6MT. All else equal, there is 200 lb more weight and a slight amount of extra friction in the AWD system. But the overall effect is almost negligible with ATTESA. Neighbor has a 2WD 7AT, I have an XS with the 7AT. We have never raced, but we can't tell any difference in acceleration by driving the two cars.

As Jsolo points out, specific gear ratios at the point he was pulling away are the likely culprit.

Here is what we should expect based on engineering factors and published quarter mile times: the fastest off the line is the AWD 7AT. Very low first gear, and it takes off with almost no wheel spin. Mine typically chirps the tires going into 2nd, but that is about it. Over the course of a quarter mile, the lighter weight and reduced friction of a RWD 7AT will catch up and the RWD should be slightly ahead (maybe .05 sec) at the finish line. The 6MT and 7AT RWD quarter mile times are almost identical - the favorable gear ratios of the 7AT making up for the greater efficiency of the 6MT. At that point it becomes individual car to car variation.

gsm026

One other thought - I have only driven one 6MT, but (after spending a lot of time with the 7AT) I have the impression that the gear ratios on the 6 speed are too close. It's almost like the old Trans-Am cars (early Z28, Boss 302, etc). Those were peaky engines and the close ratio boxes allowed you to keep the engine in it's power band during Trans-Am style racing. The cost was poor off the line acceleration. But in our case we have a flat enough torque curve with the 3.7 that that I'm thinking performance would improve with wider ratios in the 6 speed.

RISKY GUY

iTrader: (9)

As far as any car in general. It's all about the gearing.
If both cars have approximately the same power levels, the one with the more aggressive gearing will win.

The evo I have has a 4:16 ratio bone stock, although its a dual clutch without a torque converter.

I see how it cracks the sub 5 second 0-60 it's all a out the gearing.

If it had less aggressive gearing, it would just fall flat on its face.

Varjo

Ah, miss-read his post. Yes, it's likely down to gearing.

SAL9000

IME it's unlikely ATTESSA was pushing power to the front at dyno speeds, even if it was slipping. Having driven my G37x in the snow a lot IME you'd hit VSC nannies if you were getting rear wheel slip at 70+ mph (which would be obvious).

The answer is chassis dynos have colossal suckage for accuracy. If it's better than 5% (+/- 15 hp) at ~300 hp I'd be absolutely shocked - it's probably approaching 10% (+/- 30 hp).

awais

iTrader: (4)

Were both cars tuned on the same dyno? If yes, even the same car will put different numbers on different days due to temperature variations and stuff.

The X would launch better but then the rwd should catch up. Looks like your car is putting down more power.

Fico

iTrader: (1)

I was able to take down a RX7 FD TT last weekend by a couple cars from 60-120....
I use to curse the auto-tragic, now....im loving it
RX7 2800lbs....225whp
G37X 3840lbs....276whp

daonlyillwiz

iTrader: (2)

Wait how do you disable AWD via glove box ?

Fico

iTrader: (1)

I didn't.....never heard of that

daonlyillwiz

iTrader: (2)

apparently if you remove the AWD fuse the car will not engage AWD at all and be fulltime RWD...meh, good for those that like to ruin their car drifting :|