Rolling Road Results

[Mknight702]

That's more like it. Troy at Northampton Motorsport has just rolling roaded the car, result 99.9 Bhp at about 6,500. He has uncovered a problem with the Weber though, the accelerator pump jets don't work!

[erictharg]

That sounds more like it! Sounding like a healthy A Series. Fix the acc pumps and you'll be flying. How was the service at Northampton Motorsport?

[Westfield 129]

While I have found that rolling roads (Chassis Dynos here in the 'States) are useful for many tuning duties, they are not so great for finding actual HP.

I use trap speed at the drag strip. It takes so much HP to accelerate a weight to a specific speed in the quarter mile. What is interesting about this is that the launch is not that important. You can just roll away in second gear, and not make 3 mph difference. The quality of your launch really has effect on the elapsed time, not the trap speed. That is only a function of HP. So, you don't have to drop the clutch, smoke the tires ( or the clutch) or speed shift (shifting with the throttle floored, fanning the clutch), or abuse the machine in any way.

There are numerous websites to compute your HP using trap speed, and your launch weight. The weight is important in this equation.

My XI launches at about 1230 lbs, and does 103mph in the quarter mile. That works out to around 105 HP. A bit less than the 120 estimate given by a local chassis dyno. I will go with the calculated HP. Since then, I have added a new, 6" manifold of a far better design. I am hoping for 106 mph, maybe more.

I have a couple of straight roads available, and a friend with a Vbox, an extraordinarily accurate GPS based device used by many magazines for testing. This greatly simplifies the testing, as I don't have to go to the races and wait around all day to do a 14.5 second lap... I also have the opportunity to test with the magazine cars, if I have my XI along.

What I have found in my days hanging around drag strips during my misspent youth, is that often, the incredible HP claims are not rewarded with the expected performance.

All it takes for a Dyno tuner to impress a client is to just bump up the temperature factor on the computer a few degrees, and the HP just comes right along...

Anyway, 100 to 110 HP in an XI is pretty exciting, and if you are not careful, axle snapping.

[Mknight702]

The pump jet is a bit problematical. They did dismantle the Weber and tried various ways to clear the blockage, but it seems as though the casting is not drilled correctly. To fix it I would have to drill out some gallery plugs, redrill the bore, tap and replug the gallery. Not impossible certainly, but not straightforward. The fuel seems to get from the pump to the ball valve, but not from the ball valve to the jet very well, so the fuel just dribbles out the accelerator jet but is being forced up and around the brass pump.

[erictharg]

Agree with you on HP dyno numbers. It's also pretty easy to gauge what an A Series of a given spec will make, assuming its been screwed together OK and run in OK. 110HP is about as much as you can make and still have it road driveable (without going for big capacity via offset boring / stroking - something I'm not in favour of).
If someone claims their 1300 Mini is making 130 HP and it's used on the road they're smoking dope!
Matt - I have heard that some of the newer Weber castings can have problems with casting quality. May be worth contacting Webcon and seeing if they have a fix. If you can HP die cast a passage for the accelerator pump, you can probably get to it with a drill to clear it.

[Westfield 129]

I have been running a 1380 for a few years, with no problems. There are quite a few advantages to be had, like having 100~110 HP without turning the engine past 6500 RPM, and being able to use a hotter cam with fewer compromises.

The really important part is the cylinder head. The real power comes from there, and with some additional compression. I use 10.6:1, which seems high for our 91 pump fuel, but it works just fine, even on hot days. I favor Longman cylinder heads. I have used 5 of them over the years. Each worked quite well in making HP.

There have been no problems with the crank, rods, or the block itself. No additional wear that I have seen so far. My engine prep includes line boring the block, resurfacing the block deck, truing and inspecting the crank, resizing the rods, and making sure that all the clearances are at optimum.

The engine has over 16,000 miles on it now (three lifetimes for most of the XIs that I have seen), and oil consumption remains at a pint/1000 miles when run hard.

My plans to rebuild this engine to a 1400 when the time comes. However, it is doing extraordinarily well for a race engine on the road. I expect it to last a few more years.

[Mknight702]

Well, I emailed Webcon to ask if they had any views whether redrilling the gallery was possible and they actually phoned me and asked me to send the carb back to them to look at. I'll have to do that after the trackday in September though as I am away for the last 2 weeks of August and don't want to miss the trackday!

[erictharg]

Sounds promising. Let's hope they can sort it out. That big squirt of fuel is one of the things that gives the Weber the edge over SU on response, so shame to miss it. Where's the track day?

[Mknight702]

It's the WSCC handling day at Alconbury airfield. I did it last year and lunched a wheel bearing after 10 minutes, hence the thread on correcting it for this year!