Say I stick a Weiand 177 on my engine and keep the NOS cheater plate system hooked up with the 250 shot. Anyone wanna guess what's going to happen? Or if you have done it, what was your experience with the nitrous and blower setup.

 

Learning from my experience with my little 142 blower I can tell you a roots-blown engine is a very different animal than running either N/A or NA+nitrous. You can do 10:1 compression on nitrous and still use pump gas if you're careful. 10:1 with a roots blower and it's going to go "bang" on pump gas. Detonation with a roots is merciless.

I've tried it at 9.2:1 with iron heads and blew it up.

I've tried it at 9.2:1 with aluminum heads and blew it up.

I've tried it at 8.7:1 with aluminum heads and kept it together for 2 years with the timing at only 26*. Then I stepped it up to 28* and scattered the motor on the next pass.

All were killed by detonation.

My next build: 8.0:1 with aluminum heads (as soon as I get them welded up and remachined from the piston chunks that tore the chambers up the last time it went bang). Don't mess with high compression and a roots blower on pump gas.

My suggestion: build it to run SAFELY on boost alone. TANK the compression ratio. Then when you lay the nitrous to it it'll probably run about as safely as your current N/A combo does on the bottle.

It's obviously been very difficult for me to wrap my brain around just how low you need your compression ratio to be with a roots blower on pump gas, but I'm a believer now.

 

Ya need to get friendly with your local Methanol dealer.

A max effort *reliable* "street" roots blown motor (10-12lbs boost) should have a cr of 7.5:1 with cast heads and about 8:1 with aluminum. maximizes reliability on "pump gas" with minimal ignition ratard.
If I was also going to hit it with that much N20 I'd be looking at race gas and/or water/methanol injection combined with the low compression ratio.

If you want to do it with 10:1 and have it live, think 110+ octane race gas and water injection or 100%methanol fuel.
Going to likely need O ringed block decks and head studs too.

It's a lot cheaper in the long run to work within the laws of physics then trying to work against them.

 

Well, this car is turning more and more into a toy car only I have no problem running 110 in it all the time since it's really not driven much. The engine does have head studs, main studs, good rods and good forged pistons already plus a nice thick deck on the heads. Compression is right close to 10:1 and I'd probably only run 6 lbs of boost at most. I'd also get a timing retard for when the nitrous is activated.

This engine seems to be pretty good at not pinging (or at least I've never heard it). It's been run on 89 with no problems for most of it's life. I do put in 108 - 110 when going to the track though. Friend of mine has messed around with blowers for years along with nitrous so he'll be able to help with things also. Thanks for the info so far, I'll have to read up on the injection stuff.

 

Methanol is your friend.