Techie Question (2)
Discussion
Can't help noticing while watching NHRA TF dragster and funny car racing on TV, the amount of attention the cars receive from the crew chiefs after they have burnt out and are waiting to go in pre-stage. They appear to make several different adjustments even at that late stage.
They appear to make fuel adjustments, and I'm sure I've seen one or two crew chiefs reach into the cockpit of TF dragsters and make an adjustment. My question is what can/do the crew chiefs do just seconds before going into pre-stage?
They appear to make fuel adjustments, and I'm sure I've seen one or two crew chiefs reach into the cockpit of TF dragsters and make an adjustment. My question is what can/do the crew chiefs do just seconds before going into pre-stage?
You can raise or lower the RPM, by adjusting the amount of air going into the injector, which in turn affects how much the clutch drags when the car is staging. This can be done with plugs, or just with good old fashioned racer tape. Just a guess, but with electronic timers, it may be possible to preload a number of timer settings (one aggressive, one conservative, and one somewhere in the middle, for example), and have the crew chief decide which one to use on the line, once they've seen what the track's like. I don't know if any of them are actually doing this or not, but it might explain why they'd be leaning into the cockpit. Without having seen the footage myself (I can't receive Channel 5), it's hard to say what they might be changing.
hornet said:
Here's a question, and excuse my ignorance...
What does "nose over" actually mean? For example, John Spuffard saying he felt the engine nose over but stayed in it. I always assumed it meant the engine starting to go away or something?
What does "nose over" actually mean? For example, John Spuffard saying he felt the engine nose over but stayed in it. I always assumed it meant the engine starting to go away or something?
As far as I understand it, it's performance going away at the top end, for any number of reasons..
nose over means the motors starting to lean out! big time lean out usually ends in a big bang and melt down, leaning out is where you have more air than fuel going into the motor and temprature starts to rocket because there isnt ehough fuel going into the motor richer fuel settings usually help keep the motor cooler on the burn , and help the motor from melting down and detonating !
noggin the nog said:
nose over means the motors starting to lean out! big time lean out usually ends in a big bang and melt down, leaning out is where you have more air than fuel going into the motor and temprature starts to rocket because there isnt ehough fuel going into the motor richer fuel settings usually help keep the motor cooler on the burn , and help the motor from melting down and detonating !
Its not just a lean condition, a motor will nose over if too fat (rich) too, with a roots design blower it will basically run out of steam and reach a peak but the fuel with continue, so its rich.
It can also be caused by timing. ie retarded.
mr nog, that depends on cylinder size ,shape ,fuel type,fuel mixture,ignition type
being used,blown or not.
with blown methanol,because you do not run an ignition cruve.
and it becomes more of a problem.
if you run under around 20degrees static ignition or getting greedy backing the six shooter off on the run.
the motor will start fine ,idle fine,
get to around 5-7000 rpm under load ,then the car will fall on its face.
this sort of thing normally happens when the timing is set wrongly or no timing light to check it.
being used,blown or not.
with blown methanol,because you do not run an ignition cruve.
and it becomes more of a problem.
if you run under around 20degrees static ignition or getting greedy backing the six shooter off on the run.
the motor will start fine ,idle fine,
get to around 5-7000 rpm under load ,then the car will fall on its face.
this sort of thing normally happens when the timing is set wrongly or no timing light to check it.
Nitro-Besty said:
the normal routine of datalogger switch on is I assume carried out
Depends on the datalogger. The old racepaks used to have a very limited record time, so you had to switch them on after the burnout. I'd hope the newer ones don't have the same restriction. Certainly we now just switch ours on when we fire the car up, and leave it running to capture both the burnout and the run.
mr bennett with the amount of ignition advance that you dial into a fuel motor i cant see myself how you could have a retarded timing problem ? can you time a fuel motor too retarded ? i suppose anyone trying to time up a fuel or alkie motor up without a timing light were really running on a shoe string! does anyone do this ?
Tet said:
Depends on the datalogger. The old racepaks used to have a very limited record time, so you had to switch them on after the burnout. I'd hope the newer ones don't have the same restriction. Certainly we now just switch ours on when we fire the car up, and leave it running to capture both the burnout and the run.
We have a Race Technology DL1 (www.race-technology.co.uk/dl1_4_617.html) which I won in a Motorsports Now competition and that can record for ages as it was designed for circuit racing and use a compact flash card so if you want more time just get a bigger one. At present it is only set up to work with RPM and accelerometers but there are all sorts of sensors we could wire into it. I tested it in my road car once and the results looked promising, hopefully when we get the car sorted I'll have some really data to look at.
Well I can only answer from alky experience, if you think of the shear amount of fuel that goes into a motor especially a fuel motor then timing is critical, I no the fuel motors run very advanced as nitro is slow burning and is why you see header flames cos the engine simply cant burn all the fuel. Which is why if the motor loses timing the all that fuel is not burnt and it will hydraulic.
As for alky, I tune our motor by ear in pits and by checking timing with timing gun and by reading the motor after a run, by that I mean read the parts, plugs and bearings, and also the biggest tuning aid is feedback from driver, which is where im lucky as my old man gives perfect feedback.
As for alky, I tune our motor by ear in pits and by checking timing with timing gun and by reading the motor after a run, by that I mean read the parts, plugs and bearings, and also the biggest tuning aid is feedback from driver, which is where im lucky as my old man gives perfect feedback.
nitro besty im curious, you say a cam driven pump will have a fuel curve that can alter? what do you mean ? are you saying the faster the cam spins the more fuel will be pumped!which it will obviously or the more psi it will produce ?which i cant imagine happens , if thats the case why does a normal fuel pump say like a small block ford or chevy for instance which have a lever that is activated by a cam maintain the same psi at idle and max revs so you have a flat fuel curve and does not have avariable curve if you get my drift. is there some sort of device fitted to a nitro pump then that can make it pump differing psi during the run as dialled in by the mechanics while doing their tune up.
nitro besty what do you mean by "ignition in a rich state"? im aware of the term weak spark that is when the spark is not very good due to malfunctioning or worn ignition components but i have never heard of a rich spark ? as far as im aware a spark from example a 44 amp mag it will produce the same spark all the time i dont think you can dial in or have a tuning condition where you can have a rich spark ?your never going to have a spark thats too rich !the more spark the better is the way to go surely ,adjusting the timing gives you the same spark where ever you set, the only diffrence when adjusting the timing is it makes the plugs actually fire in a diffrent place in relationship to where the pistons is !ie 60,40, 30 ,ect ,ect btdc .(before piston reaches top dead center)thats basic mechanics .
mr noggin,
the old oem diapham pumps you speak of can only phyisically pump so much .
as a holley or carter carb can only take around 7 psi before it over comes the floats and floods .once it has got to its designed psi range.the positive side of the fuel system ie,from the pump to the float needle.stops it from pushing anymore into the system ,as the pressure is too high. ,if the demand is not there.
however, on a constant flow injection system ,you basically throw everything the pump has at the motor .
then bleed off with check valves or air timers and jets what the engine needs at diff rpm ranges.
or if the blower is going away .
or diff engine loads.
hope this has started to answer your question.
i will try to explain the fuel pump and roots blower curves to you.
if you drew an arse on a bit of paper , i bit like an m .
the first curve would be the blower psi and the second would be the fuel pump psi.
as you see the blower curve is there first but drops away first.
from left to right is time or rpm.south to north psi.
this is why you would use a check valve or timer to take more fuel away when the blower psi falls away.to keep the mixture correct.
or it will drop off power or nose over.
this is only a rich condition.
or as at the race last week hakan saw a lean condition ,with nastier results.
the fuel pump started to fail and you have a lean condition.
in his case ,the clutch locked up and leaned it some more .
a lean mixture burns slowly ,so it was still burning when the inlet valve opened.
an inlet manifold full of nitro.
bang.
cliff
the old oem diapham pumps you speak of can only phyisically pump so much .
as a holley or carter carb can only take around 7 psi before it over comes the floats and floods .once it has got to its designed psi range.the positive side of the fuel system ie,from the pump to the float needle.stops it from pushing anymore into the system ,as the pressure is too high. ,if the demand is not there.
however, on a constant flow injection system ,you basically throw everything the pump has at the motor .
then bleed off with check valves or air timers and jets what the engine needs at diff rpm ranges.
or if the blower is going away .
or diff engine loads.
hope this has started to answer your question.
i will try to explain the fuel pump and roots blower curves to you.
if you drew an arse on a bit of paper , i bit like an m .
the first curve would be the blower psi and the second would be the fuel pump psi.
as you see the blower curve is there first but drops away first.
from left to right is time or rpm.south to north psi.
this is why you would use a check valve or timer to take more fuel away when the blower psi falls away.to keep the mixture correct.
or it will drop off power or nose over.
this is only a rich condition.
or as at the race last week hakan saw a lean condition ,with nastier results.
the fuel pump started to fail and you have a lean condition.
in his case ,the clutch locked up and leaned it some more .
a lean mixture burns slowly ,so it was still burning when the inlet valve opened.
an inlet manifold full of nitro.
bang.
cliff
Edited by blownalky on Wednesday 18th April 00:11
Edited by blownalky on Wednesday 18th April 00:24
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