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Nah, we all are .

To check, the inj size he shows is 39 lb/hr @ 100% duty cycle. 6 x 39 = 234 lb/hr fuel, and with a 0.5 BSFC you get 468 hp, which checks.

If the hp he lists was rear wheel hp, you'd need 625 hp = 312.5 lb/hr fuel = 52 #/hr injectors @ 100% duty cycle to get enough fuel to run that number. Which doesn't seem right to me...

So, I guess the confusion in my mind is whether all these hp calculators are spitting out rear wheel hp or flywheel hp. Ideas?

[The short answer is that it is rwhp . The long answer is:]

I wasn't sure myself so a while ago I went through the derivation. If you assume constant acceleration (use s, v, a, t for distance, speed, acceleration, and time) then s = 1/2 * a * t^2 and a = 2 * s / t^2. Also, force = m * a (m is mass), work (W) is force times distance, and power (P) is work divided by time. That gives P = W / t = F * s / t = m * a * s / t or

P = m * 2 * s^2 / t^3

With m in kilograms, s in meters, and time in seconds, P will be in watts. Put in 1/4 mile and convert kg to pounds and watts to horsepower and I get:

P (hp) = 196.9 * weight (lbs) / (elapsed time (sec))^3

Note that that is the weight going down the track, with driver. Again, assuming constant acceleration then v=a * t, and using s = 1/2 * a * t^2 again and 1/4 mile we get speed (mph) = 1800 / elapsed time (sec). I took the 160 or so cars on the gnttype reader's rides page that run 13.50 or quicker and fit them to v = k / t, and got speed (mph) = 1356 / elapsed time (sec) [+/- about 2-3 mph for et's between 7 and 13.5 with no correction for tcc lockup] so the assumption of constant acceleration isn't that great here. As many people have noted, trap speed seems to be a good indicator of horsepower while et is very traction dependent, so what I do is use et=1356/speed and then use that et in the hp formula. That gives pretty consistent numbers for cars with good traction. Doing that for 118 mph and 3700 lbs gives 11.49 sec and 480 hp.

Inflating these hp's by 25% or more to get flywheel hp, and then trying to get injector sizes, is one reason I think that a typical TR bsfc is over .5 and why I think many guys are leaner than they think they are.

P.S. When I did this before I got 197.2 for the constant but I think 196.9 is more accurate (sorry, Jim Testa). My new estimate for Tim's car is 487 rwhp.

It makes perfect sense that a hp calculator would spit out rear wheel hp, since et and mph would be based on the power that one is actually putting down to the ground. I won't argue that point! If it isn't that way, it *should* be that way!

What doesn't make sense to me is stuff like Lubrant's spreadsheet. If one is to take a fuel flow and convert it to hp, then that is intuitively flywheel hp. It just has to be, the BSFC relation has got to be fuel to flywheel hp.

The problem I have is that both ways give the same hp. There is a disconnect somewhere! I wonder if Joe's spreadsheet is wrong... But it seems more likely to me though that the hp calculators can be easily fudged to include driveline losses (and therefore give flywheel hp).

Anyway, let's take a look at Dave's car. I like his since he has documented it so well.

Dave says he is moving about 180 x 2 = 360 gm/sec of air. Assuming an a/f ratio of 12:1, then he needs about 238 lb/hr of fuel. That gives an injector duty cycle of 80% with 50 lb injectors (is that about right Dave?).

If Dave sees a BSFC of 0.5 then he is making 475 hp with that 238 lb/hr of fuel. Which corresponds nicely to Lubrant's sheet for a 117 mph car. The sheet also shows that such a car needs a 50# injector @ 80% DC to run that number, which jives with the above.

That all seems nice and consistent to me. Now if Dave was really making 625 flywheel hp with that fuel flow (ie the 475 is rear wheel hp), his BSFC would be 0.38, and *that* is what does not seem realistic to me. If the above is wrong, please show me where!

John

Originally posted by ijames

P.S. When I did this before I got 197.2 for the constant but I think 196.9 is more accurate (sorry, Jim Testa). My new estimate for Tim's car is 487 rwhp.

Carl..... you lost me at "Originally posted by Ijames!!!"

My head is still spinning!!

I need an advil now......

Originally posted by JDEstill

Hey Carl & Dave:

The problem I have is that both ways give the same hp. There is a disconnect somewhere! I wonder if Joe's spreadsheet is wrong... But it seems more likely to me though that the hp calculators can be easily fudged to include driveline losses (and therefore give flywheel hp).

Anyway, let's take a look at Dave's car. I like his since he has documented it so well.

Dave says he is moving about 180 x 2 = 360 gm/sec of air. Assuming an a/f ratio of 12:1, then he needs about 238 lb/hr of fuel. That gives an injector duty cycle of 80% with 50 lb injectors (is that about right Dave?).

If Dave sees a BSFC of 0.5 then he is making 475 hp with that 238 lb/hr of fuel. Which corresponds nicely to Lubrant's sheet for a 117 mph car. The sheet also shows that such a car needs a 50# injector @ 80% DC to run that number, which jives with the above.

That all seems nice and consistent to me. Now if Dave was really making 625 flywheel hp with that fuel flow (ie the 475 is rear wheel hp), his BSFC would be 0.38, and *that* is what does not seem realistic to me. If the above is wrong, please show me where!

John

Well, your assumptions about my car are correct. I figure it's making about 475-480HP based soley on the mph numbers I consistently turn at the track (117-117.5).

And yes I do move about 180gps of air (limited, I suspect by my stock untouched heads/block). And yes, my MSD 50 injectors do run about 80-85% duty cycle running down the track near the top of each gear.

So, Dave confirms his fuel flow is about 238 lb/hr as calculated above. And we all agree that 475 hp is needed to run his mph.

So...

238 lb/hr and 475 flywheel hp = 0.5 BSFC --> makes sense to me

238 lb/hr and 475/0.75 = 630 flywheel hp = 0.38 BSFC --> doesn't make sense to me

See my problem? Where has my understanding gone awry?

BTW, I looked at some old KB stuff relating hp and injector size and mph, and it reads the same as Lubrant's sheet, ie 118 mph = 475 hp = 50# inj @ 80% @ BSFC = 0.5. Surely these smart guys haven't been sizing injectors based on rear wheel hp instead of flywheel hp...

John

I've seen a lot of guys claim that the et-hp formula gave flywheel, not rear wheel hp, and lots others that said the reverse. That's why I cranked out the derivation to make sure it was rwhp (which it should be, as you said). It wouldn't be a huge surprise to learn that Joe used the formula thinking it was flywheel hp, or maybe to learn that they were sizing injectors using rwhp since (for the TR's, anyway), the majority use 200-4R's and similar gearing. Also, that formula gives constant hp assuming constant acceleration, which ignores the effects of gearing (I can't think that through just now, though ), friction, and wind resistance (it takes more hp to go from 100 to 110 mph in 1 second than it does to go from 0 to 10 mph in 1 second because of wind and friction).

You can fudge a little if Dave is using 45 psi fuel pressure (don't know if he is, and Tim was using 43 I think), and of course the other biggie is air-fuel ratio. If that were 12.5 instead of 12, the bsfc goes from .38 to .396, and if it were really 13.0 that gets the bsfc up to .41. Knowing the hp is rwhp, having seen where my red stripes maxed out at and where some friend's 50's are (including Tim's; his O2's were .75-ish and the injectors were static both runs), and not really believing we are getting stellar bsfc's are all what lead to my comment above about lots of people being leaner than they thought they were.

Continuing the first paragraph, maybe people are lean in 1st and 2nd but can get away with it because everything is cold to start with and the load is lighter, and then in 3rd the boost gets turned down some so the afr is more reasonable. I think that so long as you aren't detonating the bsfc should fall as the afr rises from say 11 to 13:1; we just have to run richer than 13 to keep the egt under control. So we make more hp than the formula shows in 1st and 2nd where we can run lean, and less in 3rd, and I think that means we can use a smaller injector than the formula says? Does that make any sense? I have to get back to work so can't think this through any further just now.

The chart's injector ratings have always seemed to be way on the aggressive side to me too, and I couldn't ever resolve the discrepancy other than that. For example, it says you can run 140 mph in a full weight GN with 72 lb inj at only 90% duty. Now I know mine is tuned very conservatively, but 90% duty with 72's got me into the low 130's mph I also know of at least one other GN, probably not as conservatively tuned and with a 274" mill running low 140's mph that was running out fuel with 84's, so that's pretty consistent IMO with what I saw. Just FWIW. YMMV.

TurboTR

Todd, that does make sense if in fact Joe has made a mistake in his chart. 130 mph = ~55 lb/hr injector based on the hp he shows, but if the injectors should be sized based on his hp/0.75 then you get a 72 lb/hr injector required to run that fast. Which jives with what you see.

BTW, Dave, ever had your car on a dyno? Some rear wheel hp numbers from you would be the icing on the cake. Or anyone that had dyno numbers, et's, good translator/extender air flows, and injectors that weren't maxed out.

John

That's what SHE said ;-) ;-)

I was at a new 1200 hp dyno facility today, where some of the 7-800 hp Supra's dyno. Nice. When the new mill comes in maybe we'll go hook up and see if we can out pull the Hoopty's on their own turf ;-) I'd like to see if the fuel flow results and all can be made to jive though.

Interesting, in the stang Race Pages there's a new product, a "HP Computer" that I assume looks at inj duty, MAF signals, Speed density signals, whatever. It retails for over $400 though. I certainly don't feel the need for one

PS John, maybe you can throw some of the FAST ecu numbers into your spreadsheet and see if it calculates matching air for 72's at 88-90% duty and about 11.6:1 a/f? I think we had about 85% VE, 28 psi boost, air temp about 130 deg, RPM about 6300.

Todd

Originally posted by TurboTR

PS John, maybe you can throw some of the FAST ecu numbers into your spreadsheet and see if it calculates matching air for 72's at 88-90% duty and about 11.6:1 a/f? I think we had about 85% VE, 28 psi boost, air temp about 130 deg, RPM about 6300.

Lessee, your rpm/cid/VE/MAT give an air flow of 525 gm/sec. If you had Translator/Extender, you'd start pegging it around 6100 rpm or so. 231 cid, Champion heads, bigger cam, 28 psi, pretty decent volumetric efficiency, and my calcs say you would just be hitting the limit of the translator. That's why I find it hard to believe that Tim could peg it at 20 psi...

Anyway, 525 gm/sec = 4166.7 lb/hr air flow

4166.7/11.6 = 359.2 lb/hr fuel flow

359.2 / (6 inj x 72 lb/hr) = 0.83, or 83% duty cycle. Which assumes that 83% duty cycle delivers 83% of the rated flow, which may not be quite accurate. But close enough for me.

Looks like we match up pretty well Todd, even if my calc is a tad optimistic.

So, how much power does that make? 359.2 lb/hr fuel @ BSFC = 0.5 --> 718 hp, @ 0.6 BSFC --> 599 hp. So I'd guess flywheel hp to be in the 600 to 700 range. According to Lubrant's sheet, 700 hp would put you around 135 mph in the quarter.

If we assume 20-25% driveline loss, then rear wheel hp --> 525-560 hp, and you'd be closer to 123-124 mph. Which I know is low for you.

If you are putting down 700 hp to the ground, you'd need 875-925 hp at the flywheel. 360 lb/hr fuel / 900 hp --> BSFC = 0.4

I may be wrong, but I though BSFC's that good were unusual for production type turbo motors?

John

BUT the new angle here is, maybe the drivetrain loss doesn't scale directly as a % of engine hp. In other words let's say the drivetrain takes about 100 hp to run in my case above, and let's think dyno queen only for a second and ignore aerodynamic loss. Then let's say we attach Murillo's 1700 hp turbo SBF to the same drivetrain. Poor 200r4 But does that mean that all of a sudden that same drivetrain now takes 20% of 1700 hp = 340 hp to drive? I say no, and the assumption of a flat percentage loss may be part of what's throwing off our "paper napkin" numbers here

TurboTR

Tim, have you found out anything with your setup yet?

John

Also I hooked up my TL boost sensing cable to a 3 bar map. So now I have boost sensing for Directscan. Has anyone else done this? I'de like to swap some info in relation to the boost/temp readings at certain levels.

Thanks

Originally posted by TRDirks

Also I hooked up my TL boost sensing cable to a 3 bar map. So now I have boost sensing for Directscan. Has anyone else done this? I'de like to swap some info in relation to the boost/temp readings at certain levels.

Thanks

Ya, but keep in mind, your engine, heads, intake combo are COMPLETELY different than mine. My engine is completely bone stock, nothing touched to aid breathing, so yours is going to need far less boost to get the same flow that mine does at very high boost levels. Since I have nothing done to aid in flow through the engine, I have to compensate as best I can with increased boost.

Originally posted by TRDirks

I am running pump gas now so I cant reference this to the 20psi run at the track but my initial post/readings were at 16-17 psi so thats what I did today. The numbers I am getting now are lower than before with a max of 184 compared to prior settings when it was 213. So it is about 16% lower than it was before meaning my 20 psi run should bring MAF #'s in the 219 range with the switches set as they are now.

If you can give me some more data, I can give a ballpark idea of what is realistic.

For example, you say 17 psi and 184 x 2 = 368 gm/sec. Right off the bat this sounds high, but I'll assume some things to check:

Assuming:

rpm = 5500

intercooler outlet temp = 130 deg F

engine size = 231 cid

Using those assumptions I calculate a volumetric efficiency of 91%.

That seems high to me for a turbo car. Not saying it isn't possible. If this is what you really have, then congratulate yourself for a job well done!

In comparison, Todd's car (big cam, great heads, big turbine) is around 85%, which we know is a good number since it comes from his FAST system.

TurboDave's car, using some estimates similar to yours (but with 26 psi and 360 gm/sec air flow), comes in at 70%. Some ported heads and a cam would really get the air moving for Dave (would probably need a bigger turbo too!); at the same boost level and a VE = 80% (and holding the other assumptions constant) he would see air flow go up to 415 gm/sec, which ought to get him up into the low/mid 120's in the quarter. And 85% VE would get him up to 440 gm/sec, enough to get over the 125 mph hump I would think.

Tim, let me know about the assumptions. If you are running more rpm, have more displacement, or think your intercooler works better than what I guessed at, then any of those would serve to move the VE I calculate down some, maybe to a more typical (and realistic?) level. A lower air flow reading would of course do the same thing, once you get that dialed in.

John

The CID is slightly more due to 20 over JE pistons, so my calculations make it 235.6

As far as the intercooler out let temp I have no idea. The intercooler itself is an Eastern Performance front mount and the outside temps last night were @50 degrees and Ihave a 14 inch K+N mounted on the end of the MAF under the hood.

Flow wise I dont think the Translator is causing a higher reading anymore. With the switch settings I am currently running (base settign "5" being lean, WOT "0") I am pulling 3% out throughout the range. So if I understand it right it is now reading lower than actual incomparison to before when it was set to base lean and WOT "5" which is 10% rich.

Any chance we can get inj duty cycle readings from Tim's test passes?

Interesting that if Tim's hdw and all was sized to be able to keep the VE good up to about 6400 that he could gain 6400/5400 => another 18% of airflow and hp potential by taking it to that rpm. Food for thought. 'Course he'd probably want a solid cam and a good block or bottom end setup for that though ;-)

TurboTR

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