Might Demon annualar Booster Conversion

[73c34me]

Looking to have my 825 might demon converted this winter. Anyone in Michigan perform this? Other referrals? Thanks

383 SBC, Victor jr. intake

[BradH]

The 825 has a 1.42" venturi, which I believe is far too small to use with annulars. What is your current tune, and what are you looking to improve? Also, do you have a wideband O2 sensor to monitor air-fuel ratios?

[73c34me]

Tune seems to be good. I.F.R. A bit smaller, low and high speed air bleeds tweaked and slight jetting improvements. No O2 sensors. Just wanting to improve the torque from 1800- 3500 rom. The victor jr has been cleaned up, dimpled surface in the plenum and runner entries. Also has an 1-1/2” spacer welded and blended on to the top. I just don’t get much opportunity to use the top end power anymore.

[WeingartnerRacing]

I have a race demon that you can change out boosters. I went from down leg to annular. It lost power on the dyno on two engines,355 and 406. At the track it was slower too. Something to think about before making the switch.

[Frankshaft]

Whats the car this engine is in? Drivetrain? If you want more power from 1800-3500, switch to a performer rpm air gap dual plane.

[jmarkaudio]

While I am a fan of annular boosters with that body you will have a lot of work to do it. The boosters that were used by Barry Grant had a larger hole thru the body, so you can't use a Holley annular banjo without sleeving the body. It's a lot of machine time, for the cost to do it unless you can do it yourself is not worth it. And then the gains with the body size you have will be minimal to a possible loss of peak power.

[FC-Pilot]

I built an annular booster holley with a 1.4" bore venturi body and spent a few days on the dyno getting it dialed in. After it was as good as it was going to get I threw the dyno 750 on and it was almost 30 HP more on its first pull. This was on a 330 SBC that revved to 6500. Power was down across the board.

If I were in your shoes I would look for a good stepped booster if I were to change boosters. If you are looking for better low RPM and drivability then I might find a Vacuum secondary carb.

Paul

[73c34me]

Thanks for sharing guys. The drivability is good and throttle response is good. It just seems rare that I actually get above 5000 rpm anymore. I am making a tapered 4 hole spacer out of a 2" 4 hole spacer that will fit down into the plenum a bit to increase velocity. I will see how this works.
2950 lb. car- 4:1 Ring and pinion with a 2.52 muncie. It is pretty good. It just doesn't have as much low end power since I added plenum volume. I have a bit of time on the victor jr. so I am reluctant to replace it with an RPM. Plus, I don't really want to begin the tuning process again...

[PRH]

If you want more power from 1800-3500, switch to a performer rpm air gap dual plane.

That's how I'd tackle it.

[treyrags]

I have a race demon that you can change out boosters. I went from down leg to annular. It lost power on the dyno on two engines,355 and 406. At the track it was slower too. Something to think about before making the switch.

If you only changed from downleg to annular in the same body you made it a significantly smaller carb

[PRH]

I have a race demon that you can change out boosters. I went from down leg to annular. It lost power on the dyno on two engines,355 and 406. At the track it was slower too. Something to think about before making the switch.

If you only changed from downleg to annular in the same body you made it a significantly smaller carb

That's true, but it's exactly what the OP is looking to do...... So it would also become a smaller carb.

I think as an alternative approach to having the boosters replaced in the MD825 body, maybe try buying an aftermarket body that has them installed already, and reuse all the other components.
Then, if it turned out it wasn't quite what you were hoping for, you can simply swap the original body right back in.

[BradH]

I.F.R. A bit smaller, low and high speed air bleeds tweaked and slight jetting improvements.

That tells me nothing. I have run a BG 1.42" downleg w/ good results and was interested in seeing where your tune is compared to both OOB and what I've used myself. But it you're looking for 1800-3500 RPM improvements, I don't know that I can help, considering my street car has 4500-stall converter and that's not a "high priority" RPM range for me.

I say go w/ the intake change that others suggested. Your Victor is probably holding you back more than your carb at that low an RPM.

[73c34me]

The carb ran horrible out of the box. I don’t have my notes here at home, but. I.D.F. Reduced a few steps, increased p.v. Rating of vacuum drop, leaned out(?) air bleeds hi and low speed, locked out timing w/ vacuum advance and jetted to just above a lean spot it runs well with no bogs or surges. 11-1/2:1 compression ratio.

[WeingartnerRacing]

I have a race demon that you can change out boosters. I went from down leg to annular. It lost power on the dyno on two engines,355 and 406. At the track it was slower too. Something to think about before making the switch.

If you only changed from downleg to annular in the same body you made it a significantly smaller carb

Yes but it was 1000cfm so it should be more than enough for a 355.

[jmarkaudio]

Should be... with my 461ci SB2 I've run my fastest time with a billet 2.800 throttle blade carb...

My 23˚ 427 likes a 1050 Dominator, bigger or smaller loses a little. That 750 likely flowed more air than the 1.4 venturi annular.