I'm building a 383 right now, and the plan is to spray it with a good amount of nitrous. I'm just wondering what I should be going for as far as compression ratio is concerned.. In other words, I'm just wondering if there are any downsides/upsides to higher/lower compression ratios, when using nitrous. I know for boosted applications, you typically want lower compression, I'm not sure if this would be the same concept. I'm about to buy headgaskets, and may have my heads decked soon, which is why I'm asking this now.

By the way, the block is decked .010, the (stock) heads may be decked a little as well soon, pistons have 16cc dish.

A couple other questions:
Which spark plugs would be good for me to use, for the nitrous?
I'm assuming 92 octane fuel is what I'll need to run?

 

Higher compression is from what Ive been told is best for no2. If I ever finish my 383 it will be around 12:1, which might be a little higher than some would recommend, but alot of guys go a little higher with good results. Also without using nitrous compression should add power. Besides being able to run high compression is a plus of LT engines so I plan on taking advantage of it.

 

nitrous loves everything... only thing is when you are building a nitrous motor you tend to gap rings different/port heads a little different/ and some other things here and there.

the only way i would see a lower compression motor being good for n2o is if you are using a large shot of n2o...i am thinking like 300 plus shot. could be wrong though

 

Well, until I get a strong enough clutch/rear/tranny/etc to back up the shot, I probably won't go over 150, but I'd eventually like to see 250.

So something around 11:1ish would be fine then?

And on a side note, I'm just taking my heads/intake/throttle body off now, and I'm planning on doing a little DIY port&polish job (nothing major). Any good writeups or anything on what exactly I should concentrate on "cleaning up"?

 

n2o loves compression. i would go between 11.1 to 12.1 would a street/strip n2o 383. The gap on the rings and the actual rings need to be n2o rings for a 250 shot. Normal na gaps wont work, or wont work for long. Same for the pistons, they also need a specific n2o style. THe heads and cam- samething, you want heads with good exhaust ports. The cam will want a early exhaust opening and a tighter lsa.
Unless you ported many sets of lt1 heads i wouldnt do your own for a 383. THey need to be opened up a lot cc wise for the added cubes. AI's 200cc head would be a good fit. Those or le2/3's. You would really want the intake matched, but if funds are low leave it stock and do it later. As for the tb, dont touch it. Buy a 52 or 58mm, porting a tb correctly is a very hard task. Not something to be done with a dremel or anything. good luck

 

Well, for the time being, would it be ok if I just cleaned the heads and intake up a little (just smooth the ports a little better), and replaced the heads or have them professionally ported later on? My goal is to have it running for the summer, and I can't really afford to put new heads on it and all that other stuff, as well as clutch, building a rear, etc.
In other words, I probably wouldn't go over 150 shot until I had the heads done, and the rest of the drivetrain upgraded enough.

Thanks for the replies guys, I appreciate it!

 

Anyone else have some input?

 

11.1 should be fine for a streetcar on pumpgas, that really isnt anything crazy.

As for your heads, get them worked over now. Send them off, do whatever. But you dont make power from displacment, you make power from your topend.

Good Luck.

 

Anyone else have input?

 

Reply, Be careful doing your own porting, and be sure to use a low RPM pneumatic grinder or other porting tools. There are some electric tools that will work, but most electric tools have very HIGH RPMs. This makes muck ups much easier. Also if this is your first time porting, go buy some junk heads from a salvage yard and practice before you use your good heads. This way if you remove too much area and say uncover water passages you will know to take off less material on your real heads. When porting use the 85% Rule. Basically dont make your throat area more than 85% the diameter of the valve-seat. If you do it will disrupt are flow rather than help it. Rather than truely porting your heads try PORT MATCHING. This means you want to match your intake and heads. Use you intake gaskets as a guide and use a permanent marker to mark how much material you should remove from the intake. Be very conservative, less is more especially when you consider trashing parts for small HP gains. Do lots of research. Car Craft and HotRod have both done articles about porting. Check their archived articles on their webpages, and if you cant find them their check your local library. Good luck.

 

Nitrous is very fun and can be tricky to figure out, be careful with compression and nitrous, on a relatively small shot (100 to 200hp) a high compression motor will run exceptional with it. but when the nitrous shot get large you have to pretend like youre running a blower motor, and lower the compression a tad to keep the pressure somewhat manageable.

On a street motor with a 150 shot 11 to 11.5 will be fine, they don't call it blower in a bottle for nuthin!!!

 

Awesome, thanks for the good info guys, I appreciate it!