sidecar wrote:mgbv8 wrote:(Maybe the high burn rate is due to the higher cylinder pressure before the fresh charge is burnt).
The high burn rate is due to the nitrous burning quicker than the air fuel mix. So the bang happens faster. We retard the ign timing so the faster bang can happen a bit later in the cycle to make more use of the big push from the explosion. If you have too much advance the explosion can try to slow the piston down on its way up which sends cylinder pressures through the roof. I think some of the pro boys running huge amounts of nitrous run ign timing at around 16 ATDC for peak power.
You would be better off getting a bottle heater so you dont have to guess at jets sizing in different weather conditions.
Is yours the normal spray bar plate with 2 bars on on of those crossbar plates?
I'm using a 150hp spray bar plate as my 2nd stage on top of my 1st stage fogger plate. It wont hurt to run more retard while testing as its the safest way to do it.
Are you using a high power ingnition system??
Perry
Hi Perry,
I have thought about a heater but I've blown a fair bit of dosh on this system so I might have to save up my pennies first. The other thing is just how hot does the bottle have to get before the PSI gets up to 900? (To me it seems it is going to have to get bloody hot which means a shed load of current drawn from the battery!...and for how long?)
The plate under my carb has two spray bars in line with each other, one on top of the other. Is that good or bad?
The manifold is a 180 jobbie, the spray bars line up with the splitter. There is an open bore 8mm carb insulation plate between the manifold and the NOS plate.
My ignition system is just a 35DML8 with the amp on the side. I've done a few things to it such as lock the vac system because it does not work too well with the Eddy carb unless you run a really low static figure. I run more static than Rover recommend, 12 static 32 all in. I've reduced the plug gap down to 25 thou in the hope of not losing sparks when the NOS is running.
I've also modified the rotor arm to sort out a mis-alignment problem. (Not pointing directly at the HT posts when the system fires).
I'm getting more convinced that a 'retard when the NOS is running' system would be a good thing to make.
The car is only used on the road, the NOS system it's just something that I wanted to fit for the OTT factor!
Cheers,
Pete
Pete!!
Does your dissy send a signal to a normal coil??
I know zilch about these amplifier dissys so I assume its some sort of electronic trigger mechanism that gets its signal amplified to send a pulse to a dissy via a solid state relay?
If so I dont see why you could not fit an MSD coil for a better spark?
The amount of ign retard will vary between same type engines for peak power. The rule of thumb is 2 degree's of retard per 50hp shot of gas.
If you dont want to fit a bottle heater then you could always use some other method of heating the bottle before you try a run on the strip. You wil have to PM me for that info though
The bottle does not have to get very hot for the pressure to rise....
A fairly normal 250 watt bottle heater will drag about 20 amps when its on.
Heres a table of bottle temp vs pressure !!
http://www.nitroussupply.com/bottletemp.php
Your twin spray bar plate is the best for your type of manifiold as it will share its charge between the two plenums. There is a better option but its more dosh. And as you only want to use a small shot it should be fine.
Closing the plug gaps a little is a good idea if running a stock ignition system.
The main thing to check is that your fuel system can keep up with the demand + about a 50% safety margin !!
So for a 150 shot you would be hoping to have excess fuel supply of about 900 ml's per minute. 100ml of fuel per 100hp per 10 seconds is what you want to aim for.
The simple way to set your nos timing is just run the motor to 3000 rpm or whatever rpm see's max advance and move the dissy until you get the retard you need at max advance, which is where you need the retard. You may get a lumpy idle but you can just adjust the idle speed if she plays up at tickover. You can adjust this at the track for the odd day out.
Now the other info!!!
I have run my 3500 to a 100 shot with no retard. I have accidentally run my 4.6 to a 275 shot with no retard many times.
I have run my 4.6 to 10.6 seconds on gas with 4 degree's of retard and also with no retard??
But with no nretard I cracked a few pistons after about 15 passes. So I fitted Omega forged pistons and I can still run the 10's with a 275 shot on no retard??
I have now made a 2 stage nitrous system that will give me 300hp on stage 1. And another 150hp on stage 2. So I will be going back to basics and running a shed load of retard for my first test runs of 2011
You need to get yourself and your car down to the Pod for one of our days out so we can tune this thing for you mate
