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Old 11-10-2010, 10:22 PM
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Nitrous Questions on a Gen 1 355 sbc.

Alright to start off, I've got a 355 sbc in a nissan 240sx.

I'd like to run a wet plate system on my carb'd 355.

Specs are as follows:
010 block .30 over
Compression should be about 10.0 or 10.5-1
keith black flattop pistons with 5cc valve relief (hyper)
cast rotating assembly with shot peened rods
arp rod bolts.
summit 1106 cam
cloyes double roller timing gears and chain
air gap dual plane intake
461 heads ported and shaved with 1.6 roller tip rockers and 2.02/1.60 valves and dual springs of course.
long tube headers
edelbrock 750 carb
my ignition is a simple summit HEI unit with msd wires
I'm running an electric fuel pump and fuel cell, so my fuel system performs quite well.

I have a few questions,

1: How much nitrous could I VERY safely run. I want this motor to make it 50,000-100,000 miles if possible without too many problems.

2: How much should i change the timing? right now the cam is installed straight up, and timing is set to stock.

3: What about plugs? i currently have AC delco r45's (i think its r45.. i know it ends in 45) which i believe are fairly hot plugs.

4: one other thing I just thought of, part of my fuel line is 5/16" instead of 3/8" should I change that to keep up with the nitrous? I could very well be pushing 450-475hp with the nitrous and I'm afraid the 5/16" just won't keep up.

5: when installing the fuel solenoid, should I run it on a dedicated fuel line, or off the other port in my regulator?

I'd like to run a 100hp shot, but I would be content with a 75. Looking back I wish I would have built the motor for more nitrous, but of course that's hindsight.

I'm not new to engines, I'm new to nitrous

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Old 11-11-2010, 01:33 AM
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Honestly I stopped reading your parts list when I saw the KB hypereutectic pistons. First hand experience and it was all my fault...I built a 383, had the wrong cam and timing set up, rattled it once and BAM!! lifted the tops off 2 pistons. That was with no nitrous, just pulling a boat up a hill. Since then I have heard the same thing happening to a number of guys.

I don't know if they have changed them but then the KB top ring land was way too close to the piston top, thats why you had to have a very wide top ring gap. That being said, I wouldn't use any nitrous with a KB hyper piston....unless they have re-engineered them.
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Old 11-11-2010, 01:33 AM
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150 hp is safe on hyper pistons as long as the timing and fuel systems are right.

Retard timing 2 spark timing for every 50 hp nitrous added. Cam timing remains the same.

Switch to R43 plugs for use with the nitrous, colder than 45's and you don't want the "S"(as in R43S) designation which means extended tip(it can act like a glow plug).

A seperate fuel system on another 5/16" line would be fine, but don't run both off a single 5/16" line, it is asking for problems. If you want to run both off the same line you have to go bigger, and no sense doing 3/8", it is smarter to go right to 1/2" line so you only do it once, and know you won't have to change anything in the future. A single 3/8" fed by a rear electric pump(110gph minimum) will do the engine and nitrous at 100hp but will be starting to get too small at anything higher unless on 1/2" line.

Motor will handle a 100 hp shot forever if you control timing and fuel.

If going over 100hp you should raise the fuel octane above 93. Easy to do with a seperate pump and line for the nitrous from a small 2-3 gallon cell of race fuel. If running all off one line you'll have to mix race with pump or go all race fuel.

You may find you need a hotter coil and possibly a better module to fire the increased density mixture you get with nitrous.
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Old 11-11-2010, 11:06 AM
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thanks very much for the help, also, on the keith black, i believe i lied, i was going to go with keith black and ended up with mahle pistons. still hyper pistons though.

I'll probably just up my fuel lines to 3/8" all the rubber lines already are, the hardline is just 5/16" so i'll re run that.

I planned on upping the octane anyway, I wouldnt spray often, so i have no problem with running part race fuel when i decide to use it.

I won't be spraying over 100hp, i'd rather be safe than sorry. I will switch to the 43 plugs when I spray and make sure to pull timing as well.

My pump is a 110gph pump so it should suffice, it's drawing from a sumped fuel cell so it should pick up well. I do have another pump laying in the garage though, and another port on my cell, as well as an extra 5/16" line left on the car from the old return style regulator. If i end up needing the extra fuel, i'll probably go that route

I've been looking into adding an msd module to my hei dist. what else would you reccommend if I do need more ignition?
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Old 11-11-2010, 03:27 PM
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I ran up to 250hp shot on my 350 in a 240z.

similar build as yours (kb's, 10.5 cr, 750 holley, rpm intake, hei, 292H compcam...)

I used a 1 gallon fuel cell for the n02 with a mallory comp70 pump for the no2. And used racing fuel in the 1 gallon cell. 1 gallon of fuel lasted for 1 10lb bottle of n02. 5 or 6 passes.

ran 35 degrees of timing.

a 200 shot would get me around 15mph more trap speed (120 vs. 135) and 1 second drop in et (11.7 vs 10.7).

You can easily run a 150 or 175 shot.

set the no2 at full throttle.

A friend of mine sprayed a 300 shot on a autozone short block for a few years without any issues. used at least a bottle a week (street and strip racer). set the timing low enough and get the right amount of fuel and the engine will live a long life on n02. He ran a 4.56 gear, 9.5:1 cr, 292H compcam, sportsman heads, 3500 stall, th350 in a late 70's camaro and drove it daily to work. crazy.
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