Hodaka Rider Posted February 12, 2005 Share Posted February 12, 2005 I was just wondering what you are basing your drivetrain loss on, to estimate your crank HP at 230 when the road HP is 161? I've read everywhere from 25% to 37% factor for AWD in general (and it varies by Dyno, too). Have you done a 1/4 yet? I think you can figure crank HP pretty accurate from that, too. In any case, I think what you've done with it is really great, but have trouble understanding how it could really be 230 at the crank? If the same conversion factor were applied to a STi, that would mean close to 370 crank! I'm NOT slamming you. 161 whp, 206 wtq is AWESOME! Just wanting to know where the conversion factor came from. Quote Link to comment Share on other sites More sharing options...
WJM Posted February 13, 2005 Share Posted February 13, 2005 I am basing it as the same drivetrain loss as a WRX....which is about 30%. It does between 158~163 to the wheels on any average WRX in bone stock condition.....and the factory statement is 227 at the crank...so thats about 70% of crank power making it to the wheels. Since mine is an older style 5spd like the WRX...and the previous number we ran worked out right for an RX thats been posted a few times in near stock condition...I went with that number. STi's however...are NOT the same. Their 6spd is a COMPLETELY redesigned transmission...its very un-similar to alot of things SUBARU has done in the past and is VERY efficient. STi's put down about 258~265 to the ground...300 at the crank as stated, thats about a 13.3% loss.....86.7% efficiency. PLUS....the numebers as compared to running with a near stock 2.5RS on the street matches the dyno numbers in various boost levels, as well as what Kevin has done at stock boost with his TWE stuff is within 1% of my numbers at stock boost with the TWE stuff. Quote Link to comment Share on other sites More sharing options...
Hodaka Rider Posted February 13, 2005 Author Share Posted February 13, 2005 Wait. 161 X 1.3 (30%) = 209. I think that's more reasonable than the 43% loss your 230 crank estimate comes out to (230/161=1.42857). How much are you outrunning a stock WRX by in a straight line? You have about a 600lb weight advantage, right? Quote Link to comment Share on other sites More sharing options...
WJM Posted February 13, 2005 Share Posted February 13, 2005 430lb over WRX, and 630 over STi. We used the 0.7. 161/0.7=230 and 206.5/0.7=295 An 88 RX with bottomless intake box and 10 psi did 88 to the wheels...thats about 118 CHP. My wagon did 99.2/141. WRX=~160=~227. Kevins on stock boost on cone intake did like 75 or so...thats 107 which is about 100% correct for a higher mileage/older turbo engine. Quote Link to comment Share on other sites More sharing options...
Hodaka Rider Posted February 13, 2005 Author Share Posted February 13, 2005 We used the 0.7. 161/0.7=230 and 206.5/0.7=295 Hmmm. I've always seen the equation as multiplying the whp by the loss factor (X1.3 as opposed to /.07) Which way is correct? The numbers end up way different!! Quote Link to comment Share on other sites More sharing options...
WJM Posted February 13, 2005 Share Posted February 13, 2005 Well....if we do 160x1.3 thats 208 CHP for the WRX. :-\ Do 160/0.7=228.57142857142857142857142857143. Close enough. Quote Link to comment Share on other sites More sharing options...
Myxalplyx Posted February 13, 2005 Share Posted February 13, 2005 I started going by the 30% drivetrain loss like Will mentioned. When my car was stock, I had gotten about 78hp/95lb-ft of torque to the wheels on the dyno. http://www.ultimatesubaru.org/forum/showthread.php?t=24534&highlight=dyno A stock RX turbo makes about 115hp and 134lb-ft of torque to the crank stock. http://www.ultimatesubaru.org/80s/specs/general/specyears.html If you were to take away 30% of each of the stock hp/torque numbers to represent hp/torque loss through the drivetrain, you'd get 80.5hp and 94.5lb-ft of torque supposedly getting to the wheels. Those numbers are pretty close to the dyno numbers. Seems like a pretty good guesstimate. Just remember every car that rolls off the factory line aren't exactly 115hp/134lbs-ft of torque, especially being turbo'd. Also, more variables come in to play because our cars are so old. Despite all of this, the numbers are still pretty close which is good. Hmmm. I've always seen the equation as multiplying the whp by the loss factor (X1.3 as opposed to /.07) Which way is correct? The numbers end up way different!! Let's see! You know that if you had 100hp and you had 30% loss of hp through your drivetrain, you should have 70hp to the wheels. Now, if you took 70hp/.70, it would equal 100hp. If you take 70hpX1.3, it would equal 91hp. Makes sense now? Quote Link to comment Share on other sites More sharing options...
Hodaka Rider Posted February 13, 2005 Author Share Posted February 13, 2005 Good points. While I agree that seems to be the correct way of doing the equation, I am somewhat intrigued by the fact that in about an hour of searching the 'net, I found only one site that said to do it that way. It seems that most insist to add the correction to the whp number (the equation I used), while the seemingly correct way (the way you both have done it) is not often used (?). PS: I made an error in my calculation in one post: 230c vs 161w is not 43%. My bad. In any case, putting the same amount (or more) to the ground as a WRX is SWEET! Quote Link to comment Share on other sites More sharing options...
WJM Posted February 13, 2005 Share Posted February 13, 2005 The internet is not always 100% correct. HOWEVER...when you get ppl that know what they are doing and ahve others that know as well...and they back each other up with results and numbers that are real....then you know its true. Quote Link to comment Share on other sites More sharing options...
Hodaka Rider Posted February 13, 2005 Author Share Posted February 13, 2005 That's the confusing part. Some of the people using the "other" calculation WERE supposed to know what they were talking about!! Quote Link to comment Share on other sites More sharing options...
WJM Posted February 13, 2005 Share Posted February 13, 2005 That's the confusing part. Some of the people using the "other" calculation WERE supposed to know what they were talking about!! ROFL!!!! Quote Link to comment Share on other sites More sharing options...
PoorManzImpreza Posted February 14, 2005 Share Posted February 14, 2005 ok guys 30% loss....this means that crank hp =100% and wheel hp=30% less than crank or 70% so 70% of the crank HP is getting to the ground..or (wheelhp)/(crankhp)=70/100 or whp/chp=0.7 thus we get Will's equation of chp=whp/.7 or chp=whp*1.429 is correct (to 3 decimal places) assuming 30% loss..chp=whp*1.3 assumes approx 23% loss which doesn't correspond to the loss in a typical subaru AWD/full-time 4wd train...LOL isn't math FUN! Quote Link to comment Share on other sites More sharing options...
WJM Posted February 14, 2005 Share Posted February 14, 2005 What HE said. Looks like I might get the RX on a mustang dyno this comming weekend. Not sure yet tho. Quote Link to comment Share on other sites More sharing options...
mattyg41383 Posted February 14, 2005 Share Posted February 14, 2005 The other way being discussed, (not WJMs, hes right), is adding on 30% of the Wheel HP, which isnt the same as 30% of the Crank HP... ya see. lol Therefore by doing WHP/0.7 is indeed correct. Also, anyone have a ballpark # for what the loss is through the 3AT 2WD tranny. I was thinking 25% Quote Link to comment Share on other sites More sharing options...
PoorManzImpreza Posted February 14, 2005 Share Posted February 14, 2005 LOL auto?? at least 60% loss get thee a 5 speed! Quote Link to comment Share on other sites More sharing options...
mattyg41383 Posted February 14, 2005 Share Posted February 14, 2005 hmm, 60% loss = 350hp to the crank in my little beast, lol... seriously, anyone know a reasonable # for the loss through the slush box??? I know that a stock 5spd clutch wont hold because we have the same setup in another car that had a brand new one, and it slips a lot. So a conversion would mean $$, which i dont have. Quote Link to comment Share on other sites More sharing options...
WJM Posted February 14, 2005 Share Posted February 14, 2005 40% for 2WD me thinks. Quote Link to comment Share on other sites More sharing options...
mattyg41383 Posted February 14, 2005 Share Posted February 14, 2005 WOW, if thats the case (40% loss) then I'm getting 233HP at the crank. (35%=215 ; 30%=200) 14.9sec @ 93mph, 2360lbs = 140HP to the ground 140HP / 0.6 = 233HP. **The 5spd conversion looks nice right now, but one off the ea82 line wont hold, cause my Bro's car just slips it unmercifully... I cannot wait till the track opens up in spring, April 3 to be exact. Quote Link to comment Share on other sites More sharing options...
Recommended Posts
Join the conversation
You can post now and register later. If you have an account, sign in now to post with your account.