4-spd with Nitrous - Best Way to Run?

[PurpleBeeper]

I've got a 70 Road Runner 4-speed car (a quick street car). I used to run a 4bbl. with a 125hp single stage nitrous system a long time ago and I remember only using the nitrous in 3rd & 4th gear or I'd smoke the tires bad. Now I've got a 250hp setup, so it should only get worse. I want to spray the motor as much as possible and I've got a few questions. I plan on putting in hardened axles and 10" slicks (maybe a Strange Dana).

440 4-speed
Centerforce Dual Friction clutch
Single stage NOS Cheater system (no window switch), WOT switch & trigger on shifter
MSD Multi-Stage retard box (not hooked up yet)
MSD 2-stage rev limiter
3.91 gears

My idea is to wire up a button connected to a line lock & the 1st level of the rev limiter (set at 3000-3200 rpm or so). The 2nd level of the rev limiter set at 6500 rpm or so.

Once I stage I will push a line lock/1st stage rev limiter button and put the gas pedal to the floor (3000-3200 rpm rev limited). At the third yellow light I let my finger off that button & let the clutch out (rev limiter now goes to 2nd level of 6500 rpm). Once the car hooks up I hit the nitrous button which is also connected to the MSD timing retard to pull maybe 5-7 degrees of timing out (retard) when the nitrous is activated. I "might" add a rpm window switch wired through the retard box to pull out another 2 degrees of timing over 5500 rpm or so.

1. Does this sound right or am I missing something?
2. Can I hold the nitrous on while I shift gears?
3. Will the clutch survive shifting gears with the nitrous on?
4. If I can get traction, could I leave on the nitrous? If so, should I spray while stagged?

I'd like to get this car into the 11's. Any ideas or comments are appreciated. Thanks Everyone!

 

[mark wickens]

four speed car = be careful. I would use a microswitch on the carb only and wire it to pull timing out (retard) when microswitch is active. Super easy timing retard with MSD. Just my opinion not gospel.

 

[99ss]

If you run it through a window switch it will take the guess work out of it. You set the perameters. No button needed

 

[Jeremiah]

You should avoid having the juice turned on in between shifts. If you put a micro switch where the clutch pedal rubber bump stop is you should be good. Say you miss a shift and decide (in a tenth of a second) to whack the clutch again to get it into gear do you want the N20 on or off at this point? I also like the WOT micro switch in case you decide to be a big shot and peddle the car back onto the road...er I mean track groove when it decides to attempt an agricultural detour.

 

[womanator]

Think about how you are going to wire you top end rev limiter.
You should have it wired to shut down the n2o and your engine at the same time.
It's best to be towed back to your pit and clear the cylinders out before restarting.

Many years ago I wrote a lengthy post about what can go wrong and one item was what happens when you hit limiters and excess n2o in the cylinders.
None of it's good.

 

[Budnicks]

a cut out switch on the clutch peddle would be a good idea for sure... always use a manual arming/override switch & always use/run Relays on all the electronics too... unless you use a clutch-less type tranny like a Jeffco Lenco Jericho etc., where you only use the clutch for starting, launching, stopping, shut down or downshifts... I have had cars with no protection & N20 with a manual trans, just speed shifting, even with a 23 spline 4 speed in a mid 11's et 69 RR, I never let off the N20 button {way back in the 70's} & I never blew one up, because of a missed shift or any other reason because of N20 for that matter, but I wouldn't ever recommend doing it either, ran the stuff off & on for 35+ years...

 

[FatJack]

I use a window switch on my 6 spd. SRT-10 truck. I have it set to start spraying at 3500 and stop at 5500. I always powershift and never have to worry about it. A window switch is the only way to go.

 

[benno440]

that hit and run movie with the lincoln continental, a guy goes upto the car and says to the driver does that thing have NOS. driver says NOS is for fags this has cubic inches lol

 

[womanator]

Forget my post on here and just use the window switch's.

 

[PurpleBeeper]

I need to put a window switch on my injected Mustang.... but I'm leary about using it on my Road Runner because it's a vacuum secondary six pack setup & the nitrous plates are on the outboard carburetors. I've heard from a variety of sources to only use the nitrous at wide-open-throttle and over 3000 rpm. I'm pretty sure I hit 3000 rpm before my front/back carbs are fully open. I do have a microswitch on the front carburetor (not the middle one) to make sure they're open before the spray kicks in.

If I understand you correctly Womanator, I should NOT try to set at the line with nitrous on while I'm bouncing off the rev limiter. The clutch pedal microswitch sounds like a good idea.

Nitrous vs. cubic inches? Well, I've got 445 cubes AND nitrous....hell I'd put an 8-71 blower on there too and run methanol if I had enough cash to do it.

When I started running nitrous on this car (1985) it was simple... just an arming switch and a button and no problems. One blown motor and one really bad nitrous backfire in my Mustang + the fact I've never run more than a 150-shot (this is 250) has me wanting to be very careful with this setup/motor.

 

[day1glo]

that hit and run movie with the lincoln continental, a guy goes upto the car and says to the driver does that thing have NOS. driver says NOS is for fags this has cubic inches lol

Yeah, that made me smile too. Although I am not against NOS, I just don't know enough about it. Love threads like this!

 

[99ss]

I use a window switch on my 6 spd. SRT-10 truck. I have it set to start spraying at 3500 and stop at 5500. I always powershift and never have to worry about it. A window switch is the only way to go.

Yep that with a WOT switch on the carb and a person would be safe

 

[Budnicks]

Yep that with a WOT switch on the carb and a person would be safe

I would say, "safer", it's never completely 100% safe, but better as long as either a fuel &/or N20 solenoid doesn't fail, clog, ice up, stick/jam open or some other unforseen issue...