Total dung ball but interested in Nos!

[sidecar]

Hi guys you can probably tell from the title of this post that I know very little about Nos other than the theory of how it works but the chap that runs a rolling road in Reading has got me interested in fitting a 75 BHP kit to my car.

My questions are what is a "wet" system?
What is this purge malarkey all about?

The plan would be to run a plate under my eddy carb along with a micro switch so that the system kicked in at full throttle.

The engine is a 4.6 with stage III heads, I run 10:1 CR, 12 degrees static, 34 all in at 2700 RPM (no vac system) It kicks out around 285 BHP at the fly.

Can anyone give me any useful tips on this laughing gas stuff?

[gelmonkey]

Hi Pete
I can help you a little with this.
The wet system is exactly what you would be using with a plate.
NOS and fuel are bunged into the mix at the same time (technical speak of course).

A micro switch system on the carb and an arming switch is a fail safe way of setting it up so that you don't fire the system accidentally.
An RPM activated switch is also a good idea.

A 75 shot would give you loads of fun in the Cobra and would not give you any hassles.

I would advise that you use a completely independant fuel delivery system with a pressure of 5psi constant when the solenoid is opened.

The purge malarky is a bit of B/S for people like us using a small amount of gas but is used to clear the nitrous delivery line of any air bubbles(just like bleeding your brakes)before your run.
If you want to run a purge you will need a separate solenoid for this.
You only really need it IMO if you are running a big hit of gas or a multistage set up.
As I say it is really B/S but it does look the danglies if you have it.

Hope this helps
Cheers

Paul PMF

[sidecar]

Hi Paul,

Thanks for the info, it does sound like fun! (Not to mention the bragging rights down the pub! )

Whilst in the bath I was thinking that I could also hook up a micro switch so that the system only fired on full throttle in fourth and fifth gear as there is no point in using it in the lower gears as the wheels "light up" already.

Cheers,

Pete

[gelmonkey]

Hi Pete
you would have to run the WOT switch and the 4/5th switch in tandem to make this work but not sure how that could be done without some clever electrickery around the gear lever.

If you are serious about a sytem please send me a pm as I may be able to help you save some money

cheers
Paul

[sidecar]

Hi Pete
you would have to run the WOT switch and the 4/5th switch in tandem to make this work but not sure how that could be done without some clever electrickery around the gear lever.

If you are serious about a sytem please send me a pm as I may be able to help you save some money

cheers
Paul

Hi Paul,

I am serious about NOS as long as it does not cost mega bucks!

PM on its way!

Cheers,

Pete

[sidecar]

Hi Everyone,

I'm still new to all this NOS stuff but the other day I was messing about with the single stage system fitted to my 4.6 Rover lump and I found something out which I think was quite interesting!
I fitted my system a while ago and along with a Summit RPM window switch, a new Edelbrock fuel pump and an adjustable fuel pressure switch. The system was armed via a dash board switch and activated by both the RPM window switch and a micro switch on the throttle pedal. (They control a relay that fires the solenoids)

I spent quite a while fiddling with jets but the system never really gave that kick up the arse feeling that I was hoping for.

The other day I was sure that it was not even working at all so I fitted an LED to the dash which would light up when the relay closed and sent the required 12 volts to the solenoids. When I tried the system out the LED was flashing like crazy, in effect the solenoids were being pulsed around 5 to 10 times a second!

To cut a long story short what was happening was that as the fuel solenoid opened there was a small drop in the fuel pressure, just enough to shut the system down. The fuel solenoid would shut so the pressure would build back up which then allowed the system to open the solenoids again. The cycle would repeat at a rate of knots!

Part of the problem is that I’ve mounted the fuel pressure switch a bit too close to the fuel solenoid but for the moment I’ve just tweaked the pressure that it trips at.

I don’t think that I actually have a fuel pressure issue because the pump runs at 7.5 PSI and can deliver around twice as much fuel per minute than the engine actually requires, I think that I just set the cut off pressure too close too the mark.

Anyway the result is that the car takes off like nobody’s business now, well it did until I ran out of gas!

I then found out something else!

I set my Eddy 500 carb up to run the AFR at around 13.5:1 at WOT, The other day whilst running at about 5K in fourth gear I flicked the NOS switch even though the NOS bottle valve was shut so the system could only dump fuel into the carb. When I flicked the switch the revs rose up to 5800 RPM and I could feel that the engine liked the richer mixture. I’ve now upped the secondary jets to 83 and the result is that the engine pulls much harder above 5K. I don’t know what the AFR is yet but I guess it’s around 12-12.5:1. The engine was putting out 285 BHP, I reckon that it must be bunging out a fair bit more for me to be able to notice it!

(300-310 BHP without the NOS....maybe, or maybe I'm dreaming!)

[mgbv8]

Pete!
How much gas do you want to use??

Perry

[sidecar]

Pete!
How much gas do you want to use??

Perry

Hi Perry,

I guess my cylinder head gaskets have determined the amount of NOS that I can use. I was running a jet combo that according to the formulas on the web would have been adding about 115 BHP. I've rebuilt the top end of my engine and made a few changes along the way so that it will hopefully hold together. I'm now running a 75 BHP shot. (41 NOS jet 39 fuel jet). My MSD box retards the ignition back from 30 to 26 when the NOS is running.

A chap on the Cobra forum has turbo'd a few 4.6 lumps, he reckons that the huge chamfer that Rover machine into the top of the liner is a problem because around half of the fire ring of the head gasket ends up floating about in mid air not being compressed. This does seem a bit daft of Rover, the chamfer could have been 1/4 of the size that it is now.

Regards,

Pete

[DEVONMAN]

Pete!
How much gas do you want to use??

Perry

Hi Perry,

I guess my cylinder head gaskets have determined the amount of NOS that I can use. I was running a jet combo that according to the formulas on the web would have been adding about 115 BHP. I've rebuilt the top end of my engine and made a few changes along the way so that it will hopefully hold together. I'm now running a 75 BHP shot. (41 NOS jet 39 fuel jet). My MSD box retards the ignition back from 30 to 26 when the NOS is running.

A chap on the Cobra forum has turbo'd a few 4.6 lumps, he reckons that the huge chamfer that Rover machine into the top of the liner is a problem because around half of the fire ring of the head gasket ends up floating about in mid air not being compressed. This does seem a bit daft of Rover, the chamfer could have been 1/4 of the size that it is now.

Regards,

Pete

Hi Pete,
Maybe the gaskets should be a sniffter bigger. I believe that 96mm gaskets are available to suit the big bore guys but that may be too big in your case.
Regards Denis

[mgbv8]

Pete!
How much gas do you want to use??

Perry

Hi Perry,

I guess my cylinder head gaskets have determined the amount of NOS that I can use. I was running a jet combo that according to the formulas on the web would have been adding about 115 BHP. I've rebuilt the top end of my engine and made a few changes along the way so that it will hopefully hold together. I'm now running a 75 BHP shot. (41 NOS jet 39 fuel jet). My MSD box retards the ignition back from 30 to 26 when the NOS is running.

A chap on the Cobra forum has turbo'd a few 4.6 lumps, he reckons that the huge chamfer that Rover machine into the top of the liner is a problem because around half of the fire ring of the head gasket ends up floating about in mid air not being compressed. This does seem a bit daft of Rover, the chamfer could have been 1/4 of the size that it is now.

Regards,

Pete

Pete!
I've been running a 300 shot of gas for ages via my custom made fogger plate. This was the setup that saw me running regular 10.6's back in 2009. It was only when I changed to the spider plate with the same amount of gas that I damaged the block when the head gaskets blew out.
This spider plate issue is a whole new debate that I wont go into on here at any length as its a very sensitive issue for me..

All of 2010 was just havng fun runs in the low 11's and high 10's to see how the jb weld repairs held out on the block face while I waited to build another engine.

I'll make the following statement based on my own personal experiences!!
The 4.6's I have built all perform well on a max advance of 28 degree's.
Over this and they lose power with my own build settings and carb etc.
For the 300 shot I retarded to 22 btdc. This worked fine with no problems.
I used normal comp gaskets with no adhesive but I set my ARP head nuts down to 72ft/lbs instead of the expected 68 ft/lbs.
And I used C55 spark plugs. Even with these super cold plugs she started ok from cold with no choke (as I dont have one) Just 3 pumps on the pedal + a 10 second wait and then turn the key.

The only way to actually know how much nitrous you are flowing is to do a proper timed flow test. Before I damaged the block surface when I was running strong 10's all day long I had my controller set to give me a 100 shot off the line with the other 200 coming in over 1.5 seconds in 1st gear. This would give me 60 foots of 1.5 to 1.6 seconds if the slicks hooked up ok.

If you blew gaskets on a 4.6 with a 100 shot then you may have problems with the mating of the heads to block. Or you are running way too much advance which is giving you very high cylinder pressures.

Have you actually measured the advance with a strobe so you can see exactly what advance you are getting??
And how much retard the MSD is giving on activation??

How do you activate the ign retard ??

I must add that I use Omega forged pistons as the stock Rover pistons crumbled after about 7 passes with a 225 shot of gas. And I set my ring gaps to 40 thou.

Perry

[sidecar]

Hi Perry,

Thanks very much for your detailed reply, lots of useful stuff in there!

V8Dev also reckon that all the bigger RV8 lumps only need 28 to 30 degrees total advance, I was running 32 so this probably was pushing the peak pressure up too high, or at least too early in the power stroke.

Really I'm not looking for mega high BHP figures from my NOS system, my car is just a road going Cob replica rather than a drag monster! The lump is stage III anyway so the car goes quite well even without the NOS.

With regards to the ignition timing I've spent a long time setting it all up. The pointer really does point to zero at TDC. The damper has marks every 2 degrees up to 40 BTDC.

The dizzy is locked, the bob weights have been removed. I then made a new base plate and fitted an MSD pickup coil. (A 5hit load of work!).
I also worked out when the unit needed to trigger the MSD unit in order to reduce rotor mis-alignment to a minimum. This is quite tricky because the MSD supplies 6 sparks over 20 crank degrees (10 dizzy degrees) below 3000 RPM. I've managed to set it up so that either the leading edge or the trailing edge of the rotor arm is never more than 5 dizzy degrees away from the correct HT post.

The MSD unit is the fully programmable jobbie. It always works on a retard curve that you can plot into the unit via some MSD software.

http://www.msdignition.com/Products/Ign ... 6AL-2.aspx


The dizzy is actually set to 36 degrees BTDC when the engine is static. The MSD then retards this to 11 degrees from 0-700 RPM which gives the starter motor an easy time. From 700-1000 RPM the ignition is set to 18 degrees BTDC. The MSD then advances the ignition to 30 degrees at 2700 RPM. (I don't run a vac advance system). The MSD never stops 'adding' some retard so even though the dizzy is set to 36 degrees this figure is never 'seen' by the engine.

I know that 18 degrees at idle is quite a lot but I've read Des Hammils book on dizzy based ignition systems, it gives lots of advice on finding the best idle setting. It does seem that my lump likes at least 16 degrees whilst ticking over. Alot of my mates with small block chevy lumps seem to run similar idle figures. V8 Dev only run 8 at idle but I bet that's because they are using standard Lucas dizzies and are more concerned with the total advance figure

The MSD unit has a pink wire that can 'add' extra retard as soon as 12 volts is applied to it. At the moment it 'adds' 4 degrees retard with a 0.5 second delay before it is applied. (I added the 0.5 second delay to allow a bit of time to the NOS line to purge). When the 12 volts is removed the 4 degrees retard is removed without a delay. The pink wire is connected to the wire that triggers the NOS and fuel solenoid.

I think that I may knock the timing back to 28 in total, it only takes 2 minutes using the software. I have checked all of this with a strobe, I also fed 12v to the pink wire and observed that the timing did back off 4 degrees.

My plugs are only one grade colder than standard, BP6 from memory, My Arp studs are now torqued up to 75 ftlbs. The pistons are standard cast jobbies so I'd better not get too greedy with the NOS!


Cheers,

Pete

[mgbv8]

I guess you are running a manual tranny ??

What does all the elctronic stuff do to your nitrous and ign systems during a gearshift?

ie, how does it know to shut down and restart etc??

Pel

[sidecar]

I guess you are running a manual tranny ??

What does all the elctronic stuff do to your nitrous and ign systems during a gearshift?

ie, how does it know to shut down and restart etc??

Pel

It is a manual tranny, the NOS will shut down during a gear change because of the micro switch in the throttle pedal.

For the NOS system to actually fire the revs have to be within the 'RPM Window' the system has to have been armed by the master switch and the throttle has to be on the floor. (Oh and the fuel pressure has to be above whatever the pressure switch is set to)

[mgbv8]

I guess you are running a manual tranny ??

What does all the elctronic stuff do to your nitrous and ign systems during a gearshift?

ie, how does it know to shut down and restart etc??

Pel

It is a manual tranny, the NOS will shut down during a gear change because of the micro switch in the throttle pedal.

For the NOS system to actually fire the revs have to be within the 'RPM Window' the system has to have been armed by the master switch and the throttle has to be on the floor. (Oh and the fuel pressure has to be above whatever the pressure switch is set to)

Thats all good mate...
Hopefully you will make to one of our meet ups so we can tinker??

Pel