LUV94RX7

iTrader: (3)

http://auto.howstuffworks.com/framed...au/tfcalc.html

I did a test on this site. I was trying to see how bad our turbo dyno numbers can be compared to the real power we would be getting on the street. My assumption is on the dyno the IC heat soaks and the air temps are unrealistically high causing power numbers less than they would be on the street. My assumption was the intake temps on the dyno were 139 degrees and on the street they would have been 98 degrees or about 39F degrees cooler. In my test I gained from 362bhp to 404bhp or 12% more power. 12% is a BIG deal.

The parameters I used were air intercooler, bore=4, stroke=3, cylinders=6, rpm=7500, air temp 90, VE=60, boost 15, compressor=70, and intercooler=30. This got me 139 degrees intake temps and 362bhp. I changed the intercooler to 70 and got 98 degrees intake and 404bhp.

This tells me that we should do all we can to decrease intake temps, big intercooler, water injection, cold air intake, etc. Water alone is good for 40-70 degrees reduction in intake temps.

Have fun plugging in your own numbers.

Ken

tcb100

Ken as a bit of a backup to the importance of temps, one night last month I ran a 12.2 at 10:00PM on a cool evening with low humidity. 13 hours later, same car, same track, same gas, same tune, same tires, but humid and starting to get ugly hot, 3 runs at 12.6.

Water is the trick. My next mod.

setzep

Oh yeah, big difference. Durring the day I can't spin my tires in 3rd much but at night they spin a lot more. It's about 20-30 deg F difference between a hot day and a regular night from what I can see on the haltech.

KevinK2

That calculator uses deg-C, so for that 12% hp increase the temps dropped 39x1.8=70F.

Program has several significant errors in temp calculations. For your 1st case, actual intake temp would be 169 degC, not 139 degC. Power predictions assume very efficient use of fuel at the lower than reality charge temps.

Good point on reducing charge temps, bad program to correctly demo the effect. must be a better program out there.

LUV94RX7

iTrader: (3)

Good point, I missed that in my haste.

I guess I'll use this rule of thumb, about 1.7% power improvement for every 10F degrees cooler the air intake is.

Thanx,

Ken

DiaperBoy

water to air intercoolers are great for hot day's....but not for dtreet driving...get to hot. I'd go with water injection....

Carl Byck

Simpler than all that, is almost exactly 1rwhp per degree of intake air temperature drop. No formulas, just alot of hours on the dyno, with two different cars. Carl

ZeroBanger

was a hot day today, probably close to 95 F, my intake temps were 27-32C. .

I can tell you that it pulls so HARD even in the heat of day. Water Injection is for real!!!

Ok, im done with my water injection propaganda for the day

Evil Aviator

Online SAE J1349 relative horsepower calculator:
http://wahiduddin.net/calc/calc_hp_dp.htm

As for the intercooler heat soaking issue, you can reduce this by making sure that the intercooler has a strong fan on it during the dyno run. In order to get an accurate reading of your intercooler's performance on the dyno vs. the street, you need to monitor the intake air temperature during both situations. This is just one more reason to get a standalone EMS.

KevinK2

I think that sae method is for NA engines only, and would overcompensate for ambient density with turbo engines. This link suggests a correction for boosted engines ... can't verify the calcualtions but it's got the right concept.

http://home.austin.rr.com/turbolexus..._Dyno_Calc.htm