tuning a crossflow 1700 approach?

[twobone]

I just don't think I'm getting all the beans out of my super sprint engine. Its running fine on the weber 40s and it revs cleanly, but it just does not pull with the power I would expect from ~100hp.

 

Should I get a colourtune and a weber tuning manual and play with the settings to see if I'm running too lean?

 

I know I should not expect too much from a crossflow, but at 525kg, she should have more go, I think.

 

Thanks

[BruceBowker]

I have the same engine with twin webers, mild cam and I am getting 140 plus hp. You should get better than 100.

[Kitcat]

Power seems to depends on the cam. When I had my X-Flow on the chassis dyno, it made 95 hp, and 93 lbs torque-this from an engine advertised as having 135 hp. And after a expensive dyno tune-up.

 

When I discussed it with BBall, who also has a Kent X-flow, he said his engine dynoed at 115 hp. But he has a hotter cam.

 

If you do a search here, you'll see that Z-tecs advertised at 210 hp have made around 145-148 hp on the dyno. Seems to depend on the dyno as much as anything.

 

One of the things discovered when I had my engine dynoed was that it was running dangerously lean. So the search for power has to balance A/F ratio as well.

 

I suspect, without knowing, that you have a normal Kent X-Flow engine-torquey, easy to drive, not all that powerful.

 

There are ways of adding power beyond the cam (wh/is not easily replaced BTW). You can beef up the internals, add rpms, etc But then longevity becomes an issue. The race tuned X-flows have a shelf life of 20-50 hours between rebuilds.

 

I am not sure how Bruce gets 140 hp from his engine, but I'd love to know his secret:)!

 

Also, if you have a 1600 cc engine, rather than 1700 cc, then you are at a slight power disadvantage to start with.

 

Mike

Edited September 15, 2010 by Kitcat

[twobone]

I guess I will just push harder on the right pedal

[JohnCh]

Have you done a tune up since you bought it? Tired air & fuel filters, distributor caps & rotors, and sparkplugs can all cost some power, as can ignition timing that is out of whack.

 

-John

[xflow7]

Mike,

 

Are the dyno numbers you put up wheel HP as recorded by the dyno, or do they incorporate correction for drivetrain/wheel losses. 20% drivetrain loss (depending on all kinds of things) is pretty typical which doesn't fully explain the delta, but explains much of it.

 

My 1700 xflow was engine dyno'd at 135HP when it was built and it pulls pretty strong.

 

Twobone,

 

The first things I'd check in addition to the items John mentioned are no intake/exhaust leaks, carb synchronization and then go through the lean best idle procedure for the DCOE's (hunt around on the 'net and you can find this). You'd be surprised how much you can change the character of the engine by getting those things right (or wrong!). You'll probably want a synchronizing meter that you can stick in the trumpets to check the sync, although you can use a length of hose and your ear in a pinch.

 

Dave

[Kitcat]

Dave:

 

No drive train loss, etc., adjustments were made. Out in the real world BBall and I ran a track day together once and he had no trouble pulling away from me on the straight, so I am inclined to believe his dyno number, relative to mine, regardless of actual hp.

 

My engine is very tractable and easy to drive. I would always like more power but enjoy being able to go flat out much of the time.

 

What is the top speed in your car, in 4th? I can do about 108 (per GPS, 113 mph on the Caterham's optimistic speedo).

 

I am hoping someone will demonstrate the balancing of carbs technique at LOG 30, which I an attending. I do have the balancing trumpet device.

 

Mike

Edited September 16, 2010 by Kitcat

[bball7754]

Mike - I think it was mostly my higher corner exit speed.

 

I'll second the impact of having the carbs in synch, and fresh plugs. Haven't changed my rotor and cap yet, although they are sitting on the shelf.

 

I do think that all the "official" HP numbers for Crossflows are at the flywheel. I have the 244 cam, which should put me in the 150 HP range, but doubt the engine is making that today at the flywheel. I think 135 to 140 is more realistic.

 

From my reading on Blatchat, the Aldon distributors that are "unleaded" also impact HP. They were built with a very conservative amount of total advance, to the point that if you set the right advance at idle (I think about 14 degrees), there isn't enough total advance to get where you need to be at WOT (35 +?). Aldon will recalibrate the distributor to the correct advance - just have to ship it to them, and provide some info about the specifics of your engine.

 

In the end, it's just a number. Sort of like one's age.

 

Steve

[Kitcat]

Steve:

 

Ouch:)! (But so true!). Hey I was running on the notorious Michelin "pileups". I never had a chance:).

 

My car was built with a Petronix distributor, not sure about its advance potential.

 

Mike

[bball7754]

Mike - Not only were you on the "pileups", but weren't they about 10 years old?

 

I had a distinct tire advantage that day.

 

Steve

[Kitcat]

Steve that's right, 10 year old tires, plus I had a cough, my socks didn't match and my helmet was too tight!