engine and drivetrain Mostly stock 74 2002tii dyno results

[seattle2002tii]

Just posting as info, maybe useful to someone else.  Attended the local BMW club dyno day.  My mostly stock 74 2002tii dyno results are attached.  Two of the runs were in 3rd gear, last run in 4th.  Didn't make much difference.  Assuming 15% drivetrain loss and factory rating of 125hp, then expected at rear wheels would be 125 x 0.85 = 106hp.  Impossible to tell if the dyno is accurate, so 102-103hp seems in the right ballpark.

 

Car runs great overall, some info about the engine;

- I believe engine and k-fish is stock - top end done by one of the previous owners at unknown date

- Is 74tii, but has new dist. rebuilt by Adv. Distributors (no vac. retard).  Blue Beru coil (3.3ohms with resistor wire removed).  New Pertronix Ignitor II, new plugs.

- Ireland SS exhaust, stock Tii header

- Wideband O2 installed in the car, runs 12 at idle, 13.5 full throttle, but goes 14-15 at high rpm.  Also runs 15 off throttle.

[NYNick]

Sounds so ludicrous these days...103 HP. But also 2300 lbs of fun!

[RyanEsca]

Nice results :thumbsup:

I like the flat torque curve. I wonder how much the Ireland exhaust affects the tq/hp.

[Russell74Fjord]

looks like there were a few 2002's yesterday at  Carb Connection ? , I will have to try and make it next year,

 

and it that at the rear wheels ? Pretty good then,

 

vroom, vroom,,VROOM<

[jimk]

I take exception to using a 15% gearing loss.  In engineering we always used 2.5% per box.

Observing the difference between run 3 (In direct drive with no transmission power running straight thru) and runs 1 & 2, there is a 2.3% loss in 2nd and 3rd gear runs from the 4th gear run.  So it is hard to believe there is a 12.5% loss in the differential.

Using an exaggerated mechanical loss makes the engine power look better.

 

Edited July 17, 2016 by jimk

[saaron]

I put my '72 tii on a chassis dyno prior to putting the rebuilt distributor in it (I also had mine done at Advanced).  

 

My engine is 100% stock - never rebuilt, no mods other than a Crane ignition system.  Even the coil is the stock coil.  The exhaust system is stock, too.

 

It pulled exactly the same torque as yours - super flat "curve".  It pulled 90 hp.  Would it perform better with the better distributor?  Don't know - it probably wouldn't make a difference.  The car feels a lot more responsive, though.  

 

Scott

[seattle2002tii]

2 hours ago, jimk said:

I take exception to using a 15% gearing loss.  In engineering we always used 2.5% per box.

Observing the difference between run 3 (In direct drive with no transmission power running straight thru) and runs 1 & 2, there is a 2.3% loss in 2nd and 3rd gear runs from the 4th gear run.  So it is hard to believe there is a 12.5% loss in the differential.

Using an exaggerated mechanical loss makes the engine power look better.

 

The SAE J1349 standard states that 15% is be used if frictional losses aren't measured directly.  From section 3.7:

1. Alternative Method: If measured friction data are not available, it is permissible to assume 85% mechanical efficiency. When measured friction data are available, they must be used in computing mechanical efficiency. When this alternative method is used, it should be noted in the reported data that the results were corrected using an assumed mechanical efficiency of 85%. 

I have found some web sources state that diff. loss is in the range of 6 to 10%.

[TobyB]

Not that it matters much,

but I'm kinda with Jim on this-

the diff just doesn't get very hot.

For the 2002 race car, it seldom gets over 200f,

with no cooler and minimal fins.  Welded diff.

Transmissions stay even cooler.  A lot cooler...

 

On the 325, it runs about 250- 260f, and needs some fins.

When it next comes out, I should do that...  But that's with an LSD, which is

generating its own percentage of heat.

 

Now, the TIRES, all 4 of them, on both cars, get to 140 degrees on the straights,

peak at 220 in corners, and as SOON as you slow, "bloom" 40-60 degrees as they lose their

massive amounts of cooling air.  So if someone were to say "you lose 15% to your tires"

I'd tend to believe that.  The big, black- body radiators that they are...

 

Not that it matters, unless you need a big number to wave about- what you found seems to compare

pretty well to what others have seen...

 

t

 

[jimk]

Just want to add that 15% of 125hp is 15kW of energy (heat).  For those with an electric water heater at home, the heating elements are 4kW!  Go figure.

Edited July 18, 2016 by jimk

[ray_]

3 hours ago, seattle2002tii said:

The SAE J1349 standard states that 15% is be used if frictional losses aren't measured directly.  From section 3.7:

1. Alternative Method: If measured friction data are not available, it is permissible to assume 85% mechanical efficiency. When measured friction data are available, they must be used in computing mechanical efficiency. When this alternative method is used, it should be noted in the reported data that the results were corrected using an assumed mechanical efficiency of 85%. 

I have found some web sources state that diff. loss is in the range of 6 to 10%.

 

 

I'm interested to know, based on that, why a 600hp motor loses 90hp while a 100hp motor loses 15.

 

:-)

 

Cheers,

[GazM3]

It's a pretty good result for a stock.   The old owner of my 2002 had dyno sheets for 75rwhp and 83rwhp that's with an unsorted 2.3stroker with dcoe 40 carbs and 32mm chokes.  

 

Power was pretty low I thought but I can understand why.  It had a stuffed dizzy barely 8:1 comp and small chokes.  

 

The losses on chassis dynos are always a discussion point.  In % terms most people accept its about 25% for a manual rwd.  There are losses everywhere from the flywheel back , gearbox, clutch, tail shaft, diff axles, wheels, tyres, tyre pressure, etc etc.  people should use the dyno as a tuning tool but I guess it's a handy comparison figure for engines around the world.  The 25% figure comes from stock cars being dynoed eg the 507bhp v10 m5 normally dynos around 400rwhp.  Both the v8's e39 m5 and e92 m3 pull about 320bhp.  Standard e36m3's and 540i e34 pull about 230rwhp etc etc.  

[eurotrash]

It should be noted that Scott's Tii was on a DynaTech AWD dyno that is famous for coming in 10-15% under what guys expect in their pulls (as compared to a traditional machine).  So he was right in the range of 100-105HP if his car were on a Mustang or DynoJet.