I’m looking to build a roots blown sbc. Never had anything like it before. From the calculations I used that are on the blower shops website I’ll need roughly 1650 cfm at 7500 rpm. So I’m thinking 2 holly 850s. Pretty sure after measuring the venturi they should be about 830 cfm each. Is anyone the king of roots blower carbs.

The engine was originally an outlaw Procharger motor. It’s a 388 with dart block. Afr 220 heads. Jessel shaft rockers. Not sure what cam is in it right now. Motor is only 8.5-1 compression Don’t wanna change pistons yet since they’re brand new. Planning on going with an 8-71 high helix blower with dual carbs.

Probably will run 10 psi to start then check the motor over winter. Then following year if all goes well run 12-14 psi.

The plan is to have a 440-450 bracket dragster in the end

This message has been edited. Last edited by: Holytown,

Would most likely run better and easier to tune if you put a Rons Terminator injection on it. Go to http://www.killerrons.com/?utm...y&utm_campaign=Link, lots of info available about running injection and bracket blower. Give James Monroe a call and at least talk to him about it before pulling the trigger on some carbs

I’ve been thinking hard about Ron’s. Just know nothing about injection

quote:

Originally posted by Holytown:
I’ve been thinking hard about Ron’s. Just know nothing about injection

It's super simple. Just made the switch from carbs/gas to Ron's injection/alky...James will set up your system and give you some pills to tune with. Nozzle jets will be sized accordingly, you'll just have to change the main pill to fine tune...that's it, one "jet" or pill....maybe a barrel valve adjustment at first, but that's it...no float bowls, air bleeds, etc.....

I definitely like the idea of having a single terminator vs 2 carbs for the same money.

Injection! Pretty sure god meant for blower to have injection or else it would not look and work so good together. Nothing against Ron's but always been Enderle guy myself and they all work off same principal and mechanics.

I'm thinking you will have to slow a high helix 8-71 way down to get 10 lbs. of boost on 388".

I Run a Rons system on my current 14/71 HH, ran it on my 10/71 from 9lbs up to 19 lbs Of boost. With the 8/71 can get away with the single toilet/terminator and no port injectors saving some money. Get Scott from Killerrons to get you a quote, he did a great job on my setup and had me laying down great passes from the first weekend down the track.

With an injection you can tune each cylinder for best mixture. I like the Enderle hat injection.

This year KillerRONS campaigned a 385 sbc with a 6-71 in the mid teens boost area. It was a 4.5x machine. It was a single Terminator with plate nozzles only. If you want to inquire more about it send me a private message.

Scott

I run twin 1800 CFM toilets on a tunnel ram. Always wondered how well they would work on a blower however my current compression ratio is close to 15:1 which isn't very good for a blower even with alcohol.

8.5:1 means this is a gas engine.
While injected alcohol is simple and fun, injected gasoline is only recommended for those that have to meet some rule. It's a bit fussy and probably should not be attempted by the inexperienced.

My recommendation would be raise the compression to 11:1 and run methanol or run carbs for the gas.
A couple of dominators should do it

I've always thought the blower would be much more efficient and you make more power by putting the majority of the fuel in below the blower. The "wet" cfm might not be ideal....... JB

quote:

Originally posted by pivotdoc:
I've always thought the blower would be much more efficient and you make more power by putting the majority of the fuel in below the blower. The "wet" cfm might not be ideal....... JB

I agree with that for fuel distribution but I would still want some fuel up on top of blower to cool the charge. Then use port nozzles to get right cylinder ratio. I do not have much experience with blown motor but I think it should be fine with 8.5 compression may not be ideal but should work.

quote:

Originally posted by pivotdoc:
I've always thought the blower would be much more efficient and you make more power by putting the majority of the fuel in below the blower. The "wet" cfm might not be ideal....... JB

Without fuel up top the roots blower overheats the air and worst case could have clearance problems between the rotors and the case.

quote:

Originally posted by AlkyIROC:
I run twin 1800 CFM toilets on a tunnel ram. Always wondered how well they would work on a blower however my current compression ratio is close to 15:1 which isn't very good for a blower even with alcohol.

We feel for most blown application that the Terminators are better. This is because the suction of the blower on the large surface area of the single blade throttle body blades at idle or when coming down from wot cause erractic behaviors due to flexing. The 4 blade Terminators do not have that issue. That said though if being used on a milder set such as the baby blowers or a mild 6-71 it isn't usually an issue

Scott

I was scared of injection. I took the plunge based mostly on JMOs word that it was easy. I landed a deal on used enderle stuff so never hooked up with JMO again, but he was totally right. I gave away all of my carb stuff within a year and have never regretted it.

I have to so say though, I was surprised to see a lot of alcohol carbs in the late rounds at a recent medium bucks bracket race. I haven’t done much brackets lately, seems like there was more injected stuff five years ago?? Maybe this race was unusual, but it did make me curious about the “state of the art” with regards to fuel systems these days

quote:

Originally posted by 358T:
We feel for most blown application that the Terminators are better. This is because the suction of the blower on the large surface area of the single blade throttle body blades at idle or when coming down from wot cause erractic behaviors due to flexing. The 4 blade Terminators do not have that issue.
Scott

The theory sounds good but how does that explain an enderle system? Three large butterflies on the hat must do the same thing as the large butterflies on a toilet and people still use Engerle systems??

quote:

Originally posted by AlkyIROC:

quote:

Originally posted by 358T:
We feel for most blown application that the Terminators are better. This is because the suction of the blower on the large surface area of the single blade throttle body blades at idle or when coming down from wot cause erractic behaviors due to flexing. The 4 blade Terminators do not have that issue.
Scott

The theory sounds good but how does that explain an enderle system? Three large butterflies on the hat must do the same thing as the large butterflies on a toilet and people still use Engerle systems??

I can not comment with certainty on the enderle. But it is done successfully all of the time with Enderle hats. Maybe it's because the blades are further away. Maybe it's because the blades are smaller than the toilets? Maybe the shaft and blades are stiffer in the enderle?

All I know is that what I mentioned is what has been experienced with the big flying toilets. The bigger the blade the worse the problem. A 5" toilets were the main issue. You will be fine with the 2 4.1's as long as you keep it on the milder side but after that my best advice is to use a 4 blade Terminator throttle body.

Scott

This message has been edited. Last edited by: 358T,

As nice as a blower is, I'll stick to NA with a tunnel ram. My crank also doesn't have a dual keyway for the blower pulley and I don't want to change my pistons to bring the compression ratio down for a blower.

Nothing screams HP better than a blower poking through the hood.