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What to consider in a nitrous engine

 
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Old 08-22-2018, 10:47 PM
Ikestang
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What to consider in a nitrous engine

So Iím building a 390 and will be putting a nitrous express main line system on it. It will go up to a 250 shot. What things should I focus while building the engine hardware wise. Itís not a race car just for a weekend fun machine. Forged pistons? H beams?
 
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Old 08-24-2018, 06:29 PM
Ikestang
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Also why are people so afraid of nitrous? I just talked to a guy who has been building FEs for 50 years and wouldn't even consider building an engine for me! Talked to my local machine shop and as soon as i mentioned it he dang near went full race engine on me. "you need steel crank, forged, pistons, H beams, steel caps, $$$$, $$$$, $$$$$$" I realize squeeze is not GOOD for your engine... I plan on running 150 shot tops. Forged pistons and H beams is what I plan to run and I think its a must. I would not trust stock rods. Its all in the tune right? Hell I ran a 100 shot on my stock Honda for the longest time. its not like I was juicing everywhere i went.
 
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Old 10-14-2018, 12:11 AM
pmuller
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One of the reasons people have engine failure with nitrous is because they don't have the proper safeguards in place in the nitrous control system.
Yes. Forged pistons with a wide upper ring land.
The Molnar "H" beam connecting rod is great rod for the money. FH6488ANPB8-A
Will you be using an automatic or standard transmission?
 
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Old 10-16-2018, 03:54 PM
Ikestang
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So I just got the short block components back from the machine shop. Iím going to assemble them with the ring gaps to my build. Iím going to be running a 150 shot with the nitrous express main line kit. Will be running forged pistons and eagle h beams. I also have a step timer that will be ran with it so it pulls timing when activated. I have a top loader 4 speed that will be behind it. Hope it holds up!
 
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Old 10-17-2018, 12:32 AM
pmuller
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One of the things that can hurt the engine is to bring the nitrous in below a certain rpm. The bigger the shot, the higher the rpm low limit point.
A 150 shot adds 150 ft/lbs of torque at 5200 rpm and 300 ft/lbs at 2600 and so on.
If nitrous is brought on below the power band it can ignite all the charge in the intake manifold.
If you are using a rev limiter ignition the nitrous needs to be turned off a few hundred rpm before the rev limit.

To safeguard against both ends of the rpm limits it is recommended to use an RPM Window Switch. MSD has several types.

Another safeguard is to use a fuel pressure switch to deactivate the nitrous if the fuel pressure drops below a certain point.

Here is a diagram with the above mentioned features for street use. Track application requires an additional launch deactivation relay triggered from a clutch pedal switch.





What Ignition system are you using?
What camshaft will be used?
 
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Old 10-17-2018, 12:57 AM
Ikestang
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I got a MSD 6AL and a step timer. New distributor with a mag pickup. I was looking at their window timer too but may end up getting one anyway. Even though is a street rig I want to be safe about the juice.
 
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Old 10-17-2018, 12:58 AM
Ikestang
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Here are my cam specs on the kit I got too.


 
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Old 10-17-2018, 11:08 AM
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That is the Comp Thumpr cam which is designed for rough idle and low rpm so it sounds like a big cam engine.
It has plenty of exhaust duration to help evacuate the extra exhaust volume from nitrous.

It also has 19.5 degrees of .050" duration overlap which means you definitely don't want the nitrous on before 2500 rpm. There would be a good chance of igniting the charge in the intake manifold.
An RPM window switch would help keep you and the engine safe.
 
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Old 10-17-2018, 12:53 PM
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Using a very low amount, such as a 150 shot on a fairly large engine, like the 390 is should yield you a very reliable engine. It isn't like you are asking much from it really, like a small engine being asked to stay reliable when used with a large shot. As long as the air to fuel ratio is not too far out of whack on the lean side your good.
 
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Old 10-17-2018, 11:30 PM
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What cylinder heads will you be using and what will the compression ratio be?
 

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