Hey guys since my motor toasted some bearings im building a forged 383 and am wondering what kind of compression ratio i should shoot for to use nitrous the best on pump gas.

And also what would be the optimal rod length for this motor?

Thanks a lot

 

My approach was to build a mild street motor that would pass NJ rolling emissions at 500HP, and then spray the crap out of it for the track. I'm running 10.8:1 and spraying 300HP. I have friends who have taken the other approach, making mega-NA HP with 12+:1, and then spraying the crap out of it. But they weren't concerned with emissions. Both approaches will work... just depends what you want out of the motor, and how you plan to use it.

My preference for the rods was 5.85"..... even with that length, the wrist pin ends up in the bottom ring groove, because of the need to drop the ring pack down a bit to get it out of the heat, and to strengthen the top of the piston.

 

Fred said it well. Of course, to him 500hp is a "mild street motor" . Basically, you want to build a good NA motor and add spray to that. Obviously, you need a good piston and want to avoid very long rods to avoid crowding the ring package. So a 5.85" rod is a good compromise.

If you want to really optimize the gains from N2O you need to concentrate your head mods to the exhaust side and also go with a fairly large "split" between exhaust and intake duration on the cam, also to optimize exhaust flow. A good exhaust system also helps a lot. If you go thise moderate-high compression route you will need to run race gas when spraying.

One other thing, you will note in Fred's sig that he has a "381". You should also consider just a 0.010" or a 0.020" overbore. The thicker cylinders are stronger and you will still have room to go up another 0.010" a couple of times. I am now 0.040" over and have my fingers crossed. Another block is sitting in the shop if needed, however!

Rich Krause

 

i use 6" rods.

 

So will i be able to spray safely 200 shot or less with a CR in the high 10s low 11s with pump gas? are 5.85" rods readily available at the same price as 6" and 5.7"? I dont see 5.85 too often in the magazines.

The heads flow 190ish at teh peak cam lift, and im gonna see if i can squeeze a little more out of them during the rebuild

thansk for the help!

 

Exactly why I went that route also. Im running 16cc dish pistons and my compression ratio is 10.7:1 with the .029 head gaskets.

 

I don't like to spray more than 150 shot on 93 octane. Not saying you can't do it but you should beware of the consequences. Also some sort of timing retard function will be necessary especially with 200 shot and pump gas.

 

Ya, i was planning on pulling a few degrees of timing out anyways with a 150, better safe than sorry IMO. and a bigger Fuel pump.

i probably wont even run the bigger shots until i can afford a 12bolt/streettwin, etc since all it will do is spin.

what kind of cam would you guys recommend for this 383 motor that will be juiced?

currently the heads flow:

0.100 64.2 47.8
0.200 132.8 92.3
0.300 188.6 134.5
0.400 237.7 160.0
0.500 267.1 179.1
0.550 277.8 186.9
0.600 279.0 191.7

im gonna see if i can get them worked a little more while they are off so i can get the exhaust flow numbers up some since the juice needs good exhaust. any input on the cam?