Milwaukee Midget

[Sumner]

That close to the end of the pipe can lead to reversion sucking fresh air into the pipe in between exhaust gas pulses and giving erratic readings.
One of the tricks used at emissions stations to get a border line car to pass emission tests is to pull the wide band probe out of the pipe a few inchs (the probe is about 18 inches long). Just those few inches closer to the end of the pipe can let enough fresh air to back flow and mix with the exhaust gases to give readings that are a bit leaner than the real values.

http://www.innovatemotorsports.com/resources/news3.php

I agree that could be the issue.  Is it worse at low rpm or higher?

It would be interested in seeing the difference in HP required to run at one density level vs. another to deal with the difference in drag and the HP the more dense air has to offer.  Our na motors or just air pumps and rely pretty much on the atmospheric air pressure to move air into the cylinders.

The only advantage I've ever seen talked about running in thinner air aero wise is if you can make the HP up with boost such as a turbo and then they talk about air densities of 12,000 feet or more.  With the blower you can have the HP and the less dense air to run through at the same time.  My calculations might not be exact but I see about a 6-7 hp advantage of running in 4600 foot air vs. 7000 foot air with a 100 HP engine. 

I'm a firm believer in seeing what the air/fuel ratio is and a number of people now use that way more than egt to tune.  I'd figure out your gauge problem, it might be as simple as moving the O2 sensor up the pipe.  Good luck and I'll bet you get that record,

Sum

[Milwaukee Midget]

This was the recommended placement after a phone call to the tech folks. 

It may well be operator error of some sort, but the exhaust column is better than 25 cubic inches after the sensor.  At 7,600 rpm, a reversion of catastrophic proportions would need to occur in order to draw sufficient air from the end of the tail pipe to give the kind of erratic reading I'm seeing - at all rev ranges.

It just never stops bouncing.

No, there's something else screwed up on this.

[Andy Cooke]

I'd try to get the LC1 working on the daily, just make a tailpipe extension for it.  It'll be wrong at idle but should be OK under way.  That being said, don't be too surprised if the LC1 is duff, we had a massive failure rate on them (might just have been a batch, but I wouldn't take the chance again).

I was reading about your running a total loss battery, you might want to consider adding a 2V Cyclon cell in series for anything voltage sensitive.

If you build a plenum would it be possible to choke it down on the dyno so that it's at Bonneville pressure, or would you need to do something with the exhaust too?  I think your carb references to the airbox? 

Andy

[Crackerman]

When i installed and ran my lc-1,
it was installed about 22" after the turbo outlet, on top of the pipe, and the only time i ever had issues was when i had an exhaust leak, or when leaded gas killed the sensor. it would bounce around like crazy during idle surge or "bounce" during a poor idle tune up. other than that, rock solid under way.

Even a small leak at the head flange, collector flange or any other slip joint can make things go erratic.
Wire grounds are also very important to accuracy.
Also, the wire from sensor to unit, and unit to gauge cannot be near or draped over any ignition cables or coils. that will throw it into observed "freak out" mode.
These are just observations i have found in my failures through the 5 years i owned and ran the same unit. but never had any failure of the unit itsself.

[Sumner]

I'd try to get the LC1 working on the daily, just make a tailpipe extension for it.  It'll be wrong at idle but should be OK under way.  That being said, don't be too surprised if the LC1 is duff, we had a massive failure rate on them (might just have been a batch, but I wouldn't take the chance again).

I was reading about your running a total loss battery, you might want to consider adding a 2V Cyclon cell in series for anything voltage sensitive.

If you build a plenum would it be possible to choke it down on the dyno so that it's at Bonneville pressure, or would you need to do something with the exhaust too?  I think your carb references to the airbox? 

Andy

The 2v battery in series is an interesting idea.  We run a separate battery for all our data logging as we don't have an alternator at the moment on the engine and the Innovate stuff can have problems if it drops out during cranking (the air/fuel will go back into the O2 sensor heater cycle),

I think the idea above about moving the LC-1 to a different vehicle is a good one to see if there is a problem with the unit or the exhaust system in the car that is making it run erratic,

Sum

[Milwaukee Midget]

Sum, I like that idea, too.  I'm thinking I'll take it a step further and compare it with a stand-alone A/F meter I know to be correct.

Been thinking as to how to wire in the extra 2 volt battery.  It wouldn't need to go to the starter, so a separate circuit for the ignition would incorporate it in series with the 12 volt, and could be taken out of the circuit with a single throw, double pole switch or relay.  I'm thinking a separate 2V charger could also be incorporated - build that and the guts of a standard Century battery charger into a separate chassis, bolt it to the floor of the trunk and plug it all in with an EIC cable.

 

I'm thinking this is doable.

Could actually be kind of slick. 

[Interested Observer]

Midget/Fordboy, a few thoughts--

Ground clearance - I’m not sure if FB was serious about the zero-clearance statement, but it would be wise to maintain at least 1/2-3/4” clearance.  You’re not always on a groomed course, and even that can have holes, ruts, ridges, etc.  It can also make trailer loading/unloading a challenge or, at least, a more ticklish operation.  Do you use alternate, larger diameter “transport” tires and wheels?  To avoid excessive aero pitch-up, just strap the front suspension.

Brakes - I’m with you--keep them until they are demonstrated to be a significant issue.  Check it out before the discs rust up.

Tow bars - generally result in a lot of salt being thrown onto the racer.  A decent length tow strap is pretty simple and effective.

Air/fuel - It is sometimes good to remember that these things are based on an oxygen sensor, and that they simply infer the mixture rate from the remaining oxygen.  Also, as I recall, they need to be pre-heated (electrically) to work properly, especially with leaded gas.  They can also cease to work well, or at all.  This may be at the root of your wildly varying readings.  Rather than a gauge, consider a data logging system to gather this info (as well as other useful information, revs, oil pressure, etc.) since there is nothing you are going to do about it during the run anyway.  With your wheelbase, you need to be looking down the road, not trying to read and remember gauge readings.

Body seams - While taping up the gaps is an easy thing to do to clean up the surface, that can’t be done, and at 120 mph one might question the effectiveness anyway.  Reworking the bodywork to neaten up the still existing gaps seems like a lot of work and expense for debatable benefit unless you have some really grievous misfits, or you just want to do it for aesthetic reasons.  See if you can get “Blue” to render an opinion.

Density altitude - Since aero drag is proportional to the air density, and presumably the power output is also proportional, academically, performance shouldn’t vary with DA.  I would suspect that the increased temperature may be producing better vaporization and/or a more advantageous inlet and exhaust “tuning” condition.

2V battery - are you saying that the 12V battery dips below 2V?  If not, and 2V is sufficient to avoid the problem, what is the problem?  A second (motorcycle?) battery would seem a lot simpler for data and instrumentation stability.

[Tman]

Our AEM A/F meter works like a charm. Plus I can bitch at Nate if I have an issue (not that I ever would!)

[aut0m4tic]

MM:
  Most of the problems I have had with the LC-1 were ground reference issues. Are your sensor/controller grounded to a common point with the gauge?  I run a megasquirt ecu on my daily driver and see lots of these issues resolved on their forums by proper grounding.  Just a thought.  I've run mine for several years on my turbo honda accord.  Might try a new sensor or updating/downgrading the firmware.  I have used 2 different firmware in mine and am ready to downgrade as the older seems to be more reliable.

Cory

[Stan Back]

Interested --

Usually agree with you --- but we run "whiskers" on the back bumper of our tow vehicle with tow bar.  Don't get any salt on the race car except on sharp turns -- it comes from the open front wheels on the roadster.

400 miles with a tow strap is not safe.  And a time-killer.  At a safe 10 MPH, that's 40 hours!

[Tman]

Interested --

Usually agree with you --- but we run "whiskers" on the back bumper of our tow vehicle with tow bar.  Don't get any salt on the race car except on sharp turns -- it comes from the open front wheels on the roadster.

400 miles with a tow strap is not safe.  And a time-killer.  At a safe 10 MPH, that's 40 hours!

We needed whiskers this year or a full width mudflap.

[Sumner]

We run a bar with full width mud type flaps on the tow vehicle and it works great.

The 2 volt battery is interesting, but a second motorcycle battery is much easier to put in and recharge between runs.  We have a small charger on ours and a larger charger on the main battery.  Works very well.

Are you data logging the LC-1 along with a gauge?  I'd for sure data log it.  The MTX-L have large readable numbers and green, yellow and red lights around the perimeter that you can program to come on at different air/fuel ratios, but at speed you don't have enough time to always look at those or remember them.  I had no problem watching them on the D license run and some of the C but later not really.

You are probably WOT most of the time, but for cars that get in and out of the throttle during the run and can't run full throttle in the lower gears data logging the TPS to correlate with the air/fuel is pretty much a given and if the car is blown then the boost is also real important to make decisions on which way to go with the fuel.  You can't count of the driver to give you accurate info on any of those at speed,

Sum

[fordboy628]

Midget, Marcello:
You’re so close--only need about 10% more.
Some ideas in addition to what has been suggested above.

Aero
Since closing the grill and/or radiator seem to be against the rules, fit a radiator with exceedingly close fin spacing or maybe some damaged fins.  Close off any other internal flow paths from behind the grille except maybe a “cold” air duct inlet for the engine airbox.     Some of this has been done.   More attention will be devoted here.
Lower the car, maybe a bit of rake, too.   This has already been done, the max that was easily achieved.   More needs to be done.   MAY require shorter front tires to improve the rake . . . . .   Talking about lowering the front to the point where it's on the ground at launch, because of the high speed lift.
Tire pressures?    Probably should have been running the higher pressures all along . . . . .    Well, you learn as you go . . . . . .
Were the windows rolled up?    Yes.   Probably going to check if there is any lexan window deformation at speed.

Power
In the dyno session I seem to recall that you just chose the better of the inlet and exhaust configurations that were at hand.  Both of these may respond to refinement and tuning for the generally hotter conditions at Bonneville.   Undoubtedly true.   Have to get more experience with jetting the carb for the severe Density Altitude differences @ B'ville.   What are the inlet and exhaust tract geometries at present?    It's a non-standard combination for the engine's displacement, based on what is currently accepted as gospel for BMC's.   None of which I care about.   We made tuning choices based on dyno results . . . . .   Do they work together?    Yes and no, er, it's complicated.   I picked the inlet length for one peak torque rpm and the header primary length for another, slightly lower peak torque rpm.   I did this to flatten the torque curve and give a wider usable bhp curve.    Now that Midget has gotten a year with a bunch of good runs, and the car and concept have proven competitive, probably going to do a couple of things to raise the bhp output and narrow the useable power range.    One will be to tune the inlet and exhaust tracts to the rpm at top speed.   Probably narrow the working range from 2200/2000 rpm to 1700/1500 rpm.    With the close ratio gearbox he has, and the narrowed powerband, probably looking at a push start . . . . . .
Icewater intercooler?   Definitely, on both fuel and inlet air, if legal in GT.
Front end toe minimized.   At factory minimum now, probably going to try less.    
Slow down the water pump.  It’s probably cavitating at 8k anyway.    Already done.   His original setup, (and what most Spridget racers use), spun the water pump at 13,000+ rpm at 8000 crank rpm.   As I'm sure you will agree, that's crazy.   Back in the build diary are photos of the gilmer belt setup I designed and machined to fit this application.    It uses a 3/8 pitch toothed belt with a 15/28 under drive ratio for a .5375 w/pump to crankshaft speed.    At 8000 crank rpm, 4286 water pump rpm.    I wanted to get it a bit lower, but 32.96% of the original water pump rpm is way better.    It also uses a wider than needed water pump pulley, so that an additional accessory drive can be fitted.    Say, uhmm, a dry sump oil pump . . . . . . .

Interested Observer,

All great ideas, some/most of which have been partially used.

Going to come up with a strategy for reducing potential brake drag.   Also going to reduce trans/diff losses by going to lighter synthetic lubricants coupled with lowered fluid levels.

I am confident that the Grenade's output can be raised to about 103/105 bhp reliably.   Since the 1310cc F/Prod SCCA engines are making 106/114 bhp/litre (depending on whose dyno numbers you believe . . .) we might be able to achieve that level.   Since the 999cc has better breathing capability coupled with lower flow demand, we might even do slightly better.    I want to remain realistic though, no Nascar or F/1 budget here . . . . .

As always, thanks for your thoughts.
 
Back to Fordboy

Midget/Fordboy, a few thoughts--

Ground clearance - I’m not sure if FB was serious about the zero-clearance statement, but it would be wise to maintain at least 1/2-3/4” clearance.  You’re not always on a groomed course, and even that can have holes, ruts, ridges, etc.  It can also make trailer loading/unloading a challenge or, at least, a more ticklish operation.  Do you use alternate, larger diameter “transport” tires and wheels?  To avoid excessive aero pitch-up, just strap the front suspension.

Brakes - I’m with you--keep them until they are demonstrated to be a significant issue.  Check it out before the discs rust up.

Tow bars - generally result in a lot of salt being thrown onto the racer.  A decent length tow strap is pretty simple and effective.

Air/fuel - It is sometimes good to remember that these things are based on an oxygen sensor, and that they simply infer the mixture rate from the remaining oxygen.  Also, as I recall, they need to be pre-heated (electrically) to work properly, especially with leaded gas.  They can also cease to work well, or at all.  This may be at the root of your wildly varying readings.  Rather than a gauge, consider a data logging system to gather this info (as well as other useful information, revs, oil pressure, etc.) since there is nothing you are going to do about it during the run anyway.  With your wheelbase, you need to be looking down the road, not trying to read and remember gauge readings.

Body seams - While taping up the gaps is an easy thing to do to clean up the surface, that can’t be done, and at 120 mph one might question the effectiveness anyway.  Reworking the bodywork to neaten up the still existing gaps seems like a lot of work and expense for debatable benefit unless you have some really grievous misfits, or you just want to do it for aesthetic reasons.  See if you can get “Blue” to render an opinion.

Density altitude - Since aero drag is proportional to the air density, and presumably the power output is also proportional, academically, performance shouldn’t vary with DA.  I would suspect that the increased temperature may be producing better vaporization and/or a more advantageous inlet and exhaust “tuning” condition.

2V battery - are you saying that the 12V battery dips below 2V?  If not, and 2V is sufficient to avoid the problem, what is the problem?  A second (motorcycle?) battery would seem a lot simpler for data and instrumentation stability.

Interested Observer,

Just talking about launching from the deck.    I like your idea of 1/2" to 3/4" of front ground clearance, coupled with limiter "straps/cables/chains" better.   Trailer loading/unloading is already a "pita", just as it is.   Probably going to have to go the "transport" wheel & tire route . . . .

I'm also with you on keeping the brakes, but definitely want to eliminate any "drag", with a system of some sort to push the pads/pistons back a smidge.   Currently thinking about Tony's (Maguromic) simple s/s spring setup.

Tow strap, tow bar, whatever gets the job done.   But, I wasn't there to brush the salt off, either.   Salt with my frozen Margarita?  Why yes, thank you!!    Salt with my suds?  Ahh, not so much . . . . .

I favor data logging, but I'm not the one popping for it.   IMHO, drivers have too much to do at speed, and my pro racing experience is that they can't provide enough accurate data for analysis and preserve their behinds.    I'm a disciple of Norbert Singer, I want to keep the driver's job humanly possible.

Unsure at this point what is going on with A/F ratio.   Good sensors and data logging would help to solve that problem, but, from experience, I am reluctant to tune for A/F, based on only an oxygen sensor.    I would like to collect some of the other data you have suggested, (as well as a couple of other things), and the data logging is the best way to accomplish this.

Some of the body fit could use a bit of help.   After all, it's a Brit kit car.

I agree with you on the density altitude and thought the car would be faster in the cool of the morning.    However, it's undeniably faster in the heat of the afternoon, (approx. 3 mph!) so we are missing something important here.    Could be any one of a number of things.

I favor a second small 12V battery as well.  I am devoted to the KISS principle . . . . . .     besides, it's an LSR car, not the Space Shuttle.    I think the suggestion to add a 2V
battery in series to the existing system, is to keep B+ voltage for the ignition from falling below 12.0 volts.     Some electronic ignitions don't work reliably below 12.0 volts, as I am sure you are aware.

Thanks for your thoughts.
 
Fordboy

[hotrod]

I agree with you on the density altitude and thought the car would be faster in the cool of the morning.    However, it's undeniably faster in the heat of the afternoon, (approx. 3 mph!) so we are missing something important here.    Could be any one of a number of things.

In theory engine power should change at about 1/(the square root of the absolute inlet air temperature change)
Air drag drops with the air density

Power required goes up at the cube of the speed change. This implies that in hot temps you are likely making more power along with the lower aero drag from air density as power required to go faster increases faster than power drops due to inlet temp changes.


Intake tuning will change with intake air temp change, the tuning will move toward higher rpms as air temp increases. Perhaps your intake is moving the torque peak up the rpm range slightly in the heat giving higher average power.

Fuel density will change slightly with ambient temp if the fuel has time to stabilize at the new temp (and is not some how controlled for temp like running through an ice bath).

Rolling resistance on the tires and wheel bearings should also drop with increasing temps.

If you have the data, see if your shift points change (time in each gear) between the cold and warm runs, you might be getting into better gears earlier on the hot runs or something so you have more time to pull the long gears.

Interesting puzzle will be fun to see what the key variable turns out to be.

[Captthundarr]

Chris, I don't mean to beat a dead horse on the A/F thing but how far is 8" form the end of the tail pipe from the head pipes collector? My experience has been to have the sensor with in 12" of the collector to keepthe sensor heat up.