Twin Cam Dyno Results

[Pfreen]

Attached are the chassis dyno results for my Lotus Europa Special.  It has a five speed 365 transaxle.  The engine has been blueprinted, balanced, cc'd, compression ratio raised to 10.3:1, extensive porting, headers, standard size big vales, and it has a Dave Bean sprint cam.  It also has two Hitachi SU carbs (Stromberg head).  The ignition system is an Electromotive HPV-1.  The advance curve is set as a straight line interpolation of between 1000 RPM, 3000 RPM, and 7000 RPM.  The 98 BHP run was in third gear and all the other runs are in 4th gear.  Since the air fuel ratio was fairly at high load, I leaned the carbs out by screwing the jets, which gave the highest 115 BHP reading.  However, it would not idle at this setting so I richened it up a little.  I then advance the timing 3 degrees (every reading advanced from what is in the graph).  This did not measurable change any torque reading throughout the RPM range.  From this, I believe the timing curve is fairly close to ideal.

The timing curve shows what I dialed in and all the curves in Miles Wilkins book. If indeed anyone set their timing as shown in 41225A Stromberg, the timing would be very retarded.

I have now installed an oxygen sensor in the exhaust to monitor the air fuel ratio and dial in the carb needles so it does not go so lean at low load and so rich at high load.

I hope others post their dyno results.  There are very few results posted online.

Enjoy!

[Grumblebuns]

Thanks for posting your dyno results. I'm wondering what an optimized stock Stromberg setup would produce.

Joji Tokumoto

 

[Clifton]

I love looking at dyno curves. It pulls really good up top. "Most" cars fall off by 6500.  Your afr is good for turbo but killing your hp and torque, especially down low where you need it most. When you get your needles dialed in it will be really screaming.

[BDA]

I don't have a Twin Cam and I don't have a fancy computer plotted dyno sheet but for those who are interested, here is the dyno sheets Dave Bean drew up for me when he built my motor back in the old days of pen and paper (1981).

[Pfreen]

So what engine is it BDA? Stock, modified, engine dyno? 

[BDA]

Yes, it's a BDA, it has a warm cam, it's been balanced, blueprinted, ported, etc. and yes, the dyno run was an engine dyno - so it's not a direct comparison to your dyno results.

Dave said, and it's pretty obvious from the graph, that there's more power above 7500 rpm, but because I opted for a cast crank, 7500 is my red line. Dave offered a steel crank for $500 and unfortunately I demurred, but on the other hand, I figured I didn't really need to go above 7500 on a street car and at another 10% more for the motor it seemed pretty expensive.

[jbcollier]

Remember, you are comparing apples and oranges. Pfreen is using a rolling road dyno and Bean an engine brake dyno -- nevermind differences in altitude, humidity, temp, etc.  115 hp at the rear wheels is pretty fine.  Typically wheel HP is 15% less than engine hp.  That would give Mr. Pfreen roughly 132 hp at the flywheel.  Do even better if you binned those SU clones and fit modern motorcycle carbs.

[literarymadness]

I have been trying to document the horsepower changes in my Early Twin Cam Special.  An optimized Fed Spec Big Valve gets about 83 horsepower at the rear wheels and about 97-98 horsepower at the flywheel.  My plan is to keep it as stock looking as possible but to maximize the stromberg setup with the factory airbox.  My TCS already had the emissions removed when I got it.  I wanted to document the horsepower changes on a dyno after each change to see how much of an increase each mod did. The first change I did was switch to a Borla high performance exhaust.  The car dynoed about 89-90 horsepower at the wheels which seemed about right for a 46 year old motor.  I switched to electronic ignition (Pertronix Ignitor III and Flame thrower III coil.  This surprisingly added about six horsepower on my next Dyno run.  The next change was to add headers (from R&D mild steel).  I was hoping for more but the headers only added three horsepower.  My last run showed 99 horsepower.  All dyno runs were done at the same place and approximately same time of day (10 a.m.).  I just had the Strombergs rebuilt and the needles switched out to B1DTs and the cams reground to a slightly hotter than factory "E" spec.  My car had the original Federal "C" spec cams.  I am hoping to get another 10 hp on my next dyno run. 

[literarymadness]

Here is the first dyno run. 

[jbcollier]

That's a much better way of evaluating things, good work.  Fitting modern flat-slide, smooth-bore motorcycle carbs will make a huge difference.  It wouldn't look that out-of-place either.

Spot on about the headers.  Hard to beat a nice 4-2 manifold for the street.  Mostly headers are just noisier and more fragile.

Did you change the ignition settings when you switched to electronic?  Bigger plug gap even?  As long as it wasn't missing, it shouldn't make that big a difference.

[Sherman Kaplan]

What needles are you using?  I'm thinking of switching to SU's for my 73 TCS.

Sherman

[Pfreen]

The carbs are four screw round top Hitachi SU’s off of an early Datsun 240z.  They came with the car when I bought it in 1986. The needles are SU  SM.  I just had the throttle shafts rebushed by Z therapy in Oregon.  They have been very reliable and the car runs great.  I did not even realize it ran rich at full load.

[jbcollier]

Better that than lean.

[Sherman Kaplan]

Thanks.  There is an article on switching from strombergs to SU's and in the article it suggest OA8 for the needles.  It looks like when I'm ready I may have some experimenting to do.

Sherman

[Pfreen]

Where did you find the article?