Dual progressive throtle bodies

[bettonracing]

Hey guys. I'm building a Mitsu Starion engine (2.7Lturbo) w/ about 550hp (maybe more in the future) in mind. I don't wanna go with too large of a throttle body b/c this is for street driving and at the same time I don't wanna choke off my top end (prolly a T-72 turbo w/ 18psi; 7500rpm redline; max piston speed = 4800fpm).

A setup I'm looking into is to use two progressive throttle bodies from a vw/audi turbo. Post-intercooler ducting would split right before the TB's and reunite just before the intake manifold (right after the TB's).

The intake manifold, turbo (etc) will be built for 4Krpm+ power so I'm trying to scavenge every bit of 'off-idle' power I can.

Plenum volume = about 80% of displacement (abot 2.15L)
still working on runner length/diam/v stack but will be midway between [short-fat hi-rpm] and [long-thin lo end-torque] size.

Whaddyu guys think about the dual progressive setup?
If not then what size do u recommend? (please give logic/ proof).

Thanks.


And keep up the good work with the info. Some good reading here. *thumbs up*



P.S.
(for anybody who's familiar with these engines: No. I am not gonna use the stock intake manifold/TBI. Custom MPFI manifold so spare me the fuel discussions. Happens everytime I bring up anything to do w/ my car)

 

[Ryan1982]

Hey man. Sounds like your gonna have a sweet motor when your all done. Im not familiar with Mitsu but can you tell me what the bore/stroke of your motor? What size connecting rods are u using?

Also I could be wrong but your piston speed is looking alittle on the high side, im guessing your gonna be using some good parts but piston speed kills motors.

Later,

Ryan

 

[bettonracing]

Thanks.

The motor has a undersquare bore stroke ratio (like .9:1 bore/stroke).

bore: 3.587" (91.1mm) (gonna bore .040&quot
stroke: 3.858" (98mm)
(prev mistake: 2.7L was supp to be 2.6L)

Conrods I'm not exactly sure of cause I can't find the factory specs but I used the shortest one I could find aftermarket: 6.527" b/c I don't think any manufacturer in their right mind would make a shorter than stock conrod, esp in this car. It could be longer than stock tho but I figure for safety margin tho I'll calculate with the shortest rod length I see (prolly gonna use some longer aftmrkt rods anyway).

I know those pistons speeds are high but I've spoken w/ a few people who are running those rpms in their motor. I'm hoping to coat the skirts of the pistons and I'll prolly set my rev limiter @ 7000rpm instead of 7.5krpm. Maybe at the drag strip I might put it back to 7.5krpm. I'm also looking into a tranny with longer gears from 3rd up (more top speed, better use of torque, better mpg & less time spent @ 6.5krpms+).

Right now the block is off to a friend of mine for blueprinting/ chamfering/ annealing/ etc and I'm still finalizing my research on rods & pistons but once I finish if u want I can send u the exact specs (with the results of the calculations I used).

Take care

 

[Ryan1982]

Ya man that would be great. I’ve never really heard of this motor before so in definitely interested.

Also what’s up with annealing the block? I know annealing is a process of softening a metal, seems something more like a stress relief process would be better? cant say ive heard about that before. Is the block cast iron or Aluminum?

Let me know,

Ryan