how much nos i can use on a high comp, tight engine?
 

I have a smallblock 472 ci sb2.2 domanater carb flows at 1279 from dan davinci, running 18:1 compression.6500 -7500 rpms at the most down the track. i use torco 118 nos fuel. We mud drag race 200 ft at a time.
I have to move up 2 classes to mods, this is a buggie nos class so i need to be competative. my engine is completely setup to be n/a so what nos package can i use without tearing down the engine. I dont have tappered wrist pins but everything else is pretty much best of the best. I guess i would like a nos system that doesnt come on when i w-o-t it but maybe toggle switch it like at half track or when i fill the need because i have more than enough hp at the starting line. I have a msd retarder box on it now retarding the timing 4* at 5000 rs to keep detonation down and a little extra top end power. Thanks guys.

Anthony

Excuse me for not agreeing, but I don't think so.

Possibly you or someone is not measuring or figuring it correct?

Ed

18 to 1????, its almost a desiel engine.

why is that hard to believe? my sb2.2 heads have 33cc or 38 cc chambers cant remember exactly off hand without getting the paper work out my engine builder and i talked this over and i recall him saying 18:1 would be the most i could run on pump gas before some kind problems would come into play with my setup. so we got je involved in on this also. This is why i use torco 118 nos fuel its 120 motor octane. So Ed why dont you explain to me why I couldnt possibly have 18: 1 comp. with no power add ons?

je pistons and brook from callies specs
 

je pistons and brook from callies

piston part# 246642 Acc#3671 Inverted Dome Job # 521517 Po.29313
head desc. sb2.2
bore 108.00mm
Invdome depth .087 (2.21mm)
top ring 1.2 mm
2nd ring1/16
oil ring3/16 + spacer
comp. dist1.170 (29.72mm)
Int .300 (7.62) 11 deg
Exh .075 (1.91) 8 deg

Grove Land
top .0475 (1.21mm) .300 (7.62mm)
2nd .064 (1.63mm) .160 (4.06mm)
oil .218 (5.54mm) .085 (2.1mm)

in Dia .927 (23.55mm)
Pin Length 2.750 (69.85mm)



Actual weight 498 grams

Set to Clearance to .0050 (.13mm)

Block Height 9300
-1/2 of stroke 2.125
Rod length 6.125
Deck Clearance - 005
Compression Height 1.045
0.40 head gasket thickness

Weather you have 18 to 1 or not, it's very uncommon to run that high of compression and no I wouldn't advise running nitrous. but then again I'm not real familar with the sb2's and what they can handle, maybe a standard 150 plate system wouldn't be to much? or a small fogger but either way your gonna want to get a programable nitrous controller to control detonation in a motor that's already prone to detonation refering back to what you stated, so I'd say you would be flirting with disaster by adding NOS to begin with.
I do know sb2's are nascar based engines and that they do run some pretty high compression ratio's to get the hp numbers they do, but then again they run their rpm's much higher than what you stated you were running yours at, perhaps all you need is more gearing to tap into the upper rpm power that's already there?
goodluck, Charles

instead of NOS
I would switch to alcohol at 18:1 compression
NOS will ruin a motor over time.

Thats why we stopped at 18 with my setup, thats when my engine builder said you would start having pump gas issues and would have to switch to alcohol and the class i was in didnt allow it.
Isnt that pretty much a small gain switching to alcohol? I know it runs cooler. Would like to possibly use 100 - 125 - maybe 150 shot of nos (would like to have more, but will refresh next year and do it right for nos) we only run 200 ft. so nos would only be on for 2 - 2.5 seconds.

If your going to run nitrous, use it at the lowest level and start working your way up, dont just slap a 200 shot on and hope for the best.
NOS systems makes an entry level kit called "the sniper" and its adjustable from 50hp all the way up to 150hp. You can activate it via a w.o.t. switch or you can activate it with a toggle swicth or some other type of pusbutton switch like a trans brake button whenever you want alittle extra.\
I used this same kit to much sucess in a footbrake bracket car and would only use it when I was either a tad late on the light or I just felt like I wasn't catching the car liek I thought I should be. Also fun to make a full nitrous pass after the races slowed soem at the end of the night. Warning though nitrous is very fun, addictive, so use with caution.
Alcohol would give your motor much more torque and a few more horses especially with the comp your running but I see your class has resistrictions so that's out of the question.
Nitrous would really wake up your motor and it doesnt take much to make big changes going down the track. Things will happen in a hurry so be careful.
Here'a link to the kit I was refering to.
Goodluck, Charles

http://www.jegs.com/webapp/wcs/store...45476_-1_12043

As someone who builds a ton of SB2.2 engines both for circle track and drag race I agree with edvancedengine something doesn't sound logical, first off 108 mm is 4.251 what block other than the new billet 4.5 bore spacing will handle that bore size. second 18.0-1 is diesel range. once you get above 15.5-1 we have found almost no gains in torque. we have several engines out there at 15.0-1 with a 400 shot and no problems. with a 1.045 c.d. and a .300 deep int pocket there is no room to run N20,the piston will fail at the int pocket.Bill