I went ahead and put the GAB (gutted airbox, how ‘bout another acronym :o )--with stock air filter--on the modded L67 TB and re-did the VE tune…



This is a significant increase over the previously reported numbers in this thread, and it is clear the bigger TB needs a less restrictive intake (heck, previous mod levels may have benefitted from this, I don't know). Calculations now put the car at:
Peak crank torque: ~305-310 ft lb at ~4200 rpm
Peak crank hp: ~260-265 hp at ~5200 rpm

IPW'* are telling me that, at WOT with PE on in the 5000-5500 rpm range, I'm now at about 97% of injector duty cycle…luckily, I’ve got L67 injectors on the way from BillBoost37, so I can continue modding.


I can see there have been requests for how I’m coming up with these hp and torque estimates:
The “quick and easy” method for hp estimation is to analyze Brake Specific Fuel Consumption (BSFC), expressed in lb/(hr-hp), which is related to thermal efficiency:
http://www.epi-eng.com/ET-ThermEff.htm
http://www.answers.com/topic/brake-*...el-consumption

BSFC = observed fuel consumption (lb/hr) / horsepower

Lower BSFC is more efficient, with a typical n/a liquid-cooled engine coming in around 0.44 to 0.45; 0.53 is pretty bad, and 0.4 is really good.
(Note: air-cooled engines, power-adders such as turbo or */c, high intake air temperatures, knock, etc. tend to decrease efficiency and increase BSFC, while cold air temperatures, optimized timing, intercooler, aluminum heads and blocks, CAI’*, reducing underhood temps, multi-valve configurations, headers, reduced ECT’*, etc. tend to do the opposite.)

So what is the BSFC on my car? In stock configuration (assuming the published 5200 rpm peak hp number of 205):
100% injector duty cycle at 5200 rpm = 21.2 msec
Measured IPW: 15.8 msec
Calc Injector duty cycle = 15.8 / 21.2 = 0.74 (or 74%)
Max injector flow rate: 22.4 lb/hr
Calc fuel consumption @5200 rpm = 0.74* 22.4 lb/(hr-injector) * 6 injectors = 99.9 lb/hr
BSFC = 99.9 lb/hr / 205 hp = 0.487 (or 48.7%)

This seems pretty reasonable for an n/a car with cast iron heads and block, and nothing done to enhance engine cooling beyond an auxiliary tranny cooler, 180 T-stat and some fan settings in the PCM.

Now, on the (admittedly large) assumptions that:
1. The factory torque/hp curves were done under conditions that would derive similar thermal efficiencies to the engine mounted in my car; and,
2. My thermal efficiency hasn’t changed throughout my mods

Hp should be directly proportional to observed fuel consumption (more specifically, IPW), as follows:

Hp (@5200rpm) = IPW (in msec) / 21.2 msec * 22.4 lb/(hr-inj) * 6 inj / 0.487 lb/(hr-hp);

Which reduces to:

Hp (@5200rpm) = IPW (in msec) * 13.0 (hp/msec)

I haven't changed timing since the PEM. Also, all my testing has been done with the same cooling system, the same fuel brand, over the same "road course", and in a very narrow range of outdoor temps (70-75 F)...so I've done all I can to ensure no change in thermal efficiency.

Charting it out:

Mod level......Meas avg IPW(@5200 rpm).....Calc bhp
Stock..............15.8........................... ...................205
Plus PLIM......16.6.................................... ..........216
Plus PEM.......17.3.................................... ..........225
Plus L67TB...19.3...................................... ........251
Plus GAB.......20.6.................................... ..........268


I have another method that relates VE to torque and hp, but it will take me a while to explain that one. :P

Of course, my estimates need verification with a real dyno...I'm working on that

First off, the factory probably generated their hp and torque data on an engine stand in a controlled temperature room, rather than in a car; this likely would improve thermal efficiency on the order of 10-15%, which would translate directly to a good 10-15% drop in actual bhp versus my estimates. If I could somehow do a brake dyno on this car today, I would expect to see results somewhere around 265-270 ft-lb torque at ~4200rpm, and 225-230 bhp at ~5200rpm (compared with stock numbers I would expect to have been 200-205 ft-lb @4200rpm / 170-175 bhp @5200 rpm).

Second, of course, I expect a 20-25% drivetrain loss. So if I were to wheel dyno this car today, I would expect to see results somewhere around 205-210 ft-lb torque at ~4200rpm, and 175-180 whp at ~5200rpm (compared with stock numbers I would expect to have been 155-160 ft-lb @4200rpm / 130-135 whp @5200 rpm).

Yeah, those numbers ain't so flashy; but then again, I haven't moved on to the "big money" mods yet

i need to subscribe to this thread.. the results are outstanding

I am very interestd in seeing a set of ER Rockers on your setup. I know that it would take care of that drop off. And you would make power til 6000

I've got the rockers in a box in the garage. After I put on the L67 injectors, they're next.

You are going to love the rockers, well atleast i know i did. I can not wait to be able to do some more engine mods to my car. As soon as the trans is in and tuned, and i get some solid track numbers of where i am at with the new trans, then let the engine mods begin Thank you for all these info, it has been awesome.

Agra, if your car is making 260hp at the crank I will be astounded. Not saying it'* impossible, but I don't think we've ever seen a car with such minimal mods making that much power. I truly hope you get numbers that high. You need to get that car on a dyno ASAP, because if you can back up your VE graphs with numbers it will change the focus of many L36 modders in the future.

I don't know if I've been this excited about a car since I put in my cam! I'm intrigued by the estimations so far, but I really want to see hard numbers.

Like I said, I really expect more like 230 bhp (180 whp) max...but a man can dream

Even so, this would represent somewhere north of 25 added hp over stock for around $150 in modded stock parts. Aside from a few ideas I have for the UIM, mods start to get relatively expensive from here on out (modded stock rockers, modded heads, 105# springs).

I'm hoping to get some dynos sometime in July or August...best price I've found around here is $90 for two pulls

If you make 180WHP on stock valvetrain then you have my most respect. I truely hope so. I cant wait to see some real numbers. My ultimate goal would be to break 200whp on rockers. I hope it happens. Congrats on everything so far, and thank you for all the data and ideas.