BOW DOWN to the might of big bore MFI!!!

[kenikh]

I have received my completely rebuilt and bored, big bore MFI stacks and TBs. While I do get some joy in soliciting jealous responses , I think everyone here would really like to get a close look at some fantastic work.

These TBs are the work of Aaron B, better known as "Burn-Bros" on this forum and of the twin plug dizzy fame. For context, this was an R&D project so don’t ask me if he'll do this kind of work for you, how much it cost or anything of the like. I want to give him credit, but at this point he wanted me to let everyone know up front that he isn't interested in soliciting work at this juncture.

Basic details. This MFI is for a 2.3L, modern take on a first generation 911ST motor. You've all seen my specs. You've also seen the heads, which were a major driver for the unusual bore spec for a motor this small. By unusual, I mean that these stacks taper from 52mm at the top, down to ~39mm at the throttle plates, through the irregular ports. The bottom line is that the entire intake tract acts like a tapered venturi from the top of the MFI, all the way to the valve surface. Air velocity of this set up is entirely against the laws of intuition - and equally eye popping.

Take special care to notice the irregular contours of the bottom of the TBs into the intake head bores. My heads have an irregular, custom shape and Aaron took the time to match taper these by hand for a perfect transition.

That said, time for the show!










The TB surface.


The port.

[kenikh]

The custom spun aluminum trumpets:

[boba]

OH DAMN, there goes the bar up another notch.

Very nice, I look forward to seeing more of this one.

Bob

[kenikh]

Thanks, Bob! I am hoping you'll get to see it in Cambria.

[Jeff Higgins]

Very, very cool there, Kenik. Can't wait to hear those things gulping vast quantities air, feeding that screaming little 2.3. That is going to be so freakin' cool...

[kenikh]

Don't get too close, I might suck all of the air out of your wussy little 36mm stacks.

[boba]

BTW, you will need one stout bottom end. That thing will not run out of air till 9500.

[kenikh]

Originally Posted by boba

BTW, you will need one stout bottom end. That thing will not run out of air till 9500.

Define stout and I will confirm or deny...

[Steve@Rennsport]

My compliments to Aaron for some really nice work!

Those will match the heads very nicely,...

Well done.

[boba]

Not to mention valve train.

[kenikh]

Originally Posted by boba

Not to mention valve train.

Forged rockers, Supertec springs, titanium retainers. BTW, I am only looking for 8200RPM on run out with this motor.

[Jeff Higgins]

Originally Posted by kenikh

Don't get too close, I might suck all of the air out of your wussy little 36mm stacks.

That's o.k., I'll just choke it with that massive "clearing its throat" cloud. I already turned your Light Ivory car brown, now I'll make those shiny aluminum stacks look like weathered brass...

[304065]

Coolness. Questions:

The matching of the bottom of the TB is to eliminate flow restrictions? Is there an anti-reversion step there or is it fair?

The big intake trumpets, is that because the stacks were tapered and the regular stuff is too small?

I see leftover bluing on the flange, how did he clearance these, do you know the technique? Milling machine or CNC, you say "by hand" I assume that means with his hands on a milling machine, not a die grinder.

Great stuff!

[kenikh]

John, there is a reversion ledge. I'd like to hear the rationale/theory behind it. I assume it breaks up the eeversion wave to keep the intake charge from fartin (too much) back up the stacks on high overlap cams. Steve, they're your heads...what are your thoughts? You are 100% correct on the trumpets.

[BURN-BROS]

Originally Posted by john_cramer

Coolness. Questions:

The matching of the bottom of the TB is to eliminate flow restrictions?

Yes.

Originally Posted by john_cramer

Is there an anti-reversion step there or is it fair?

The throttle body profile should be slightly smaller than the intake port. This step between the throttle and head should provide some reversion protection.

Originally Posted by john_cramer

The big intake trumpets, is that because the stacks were tapered and the regular stuff is too small?

Kenik's stacks are 52mm on top and taper to 41 at the bottom. One added benefit is with all that material gone the stacks come is around 16 oz per side. These are done on a CNC.

Also, the throttle bodies are 41mm/39mm. Throttle plates are 41mm.

Originally Posted by john_cramer

I see leftover bluing on the flange, how did he clearance these, do you know the technique? Milling machine or CNC, you say "by hand" I assume that means with his hands on a milling machine, not a die grinder.

Great stuff!

Man you're nosy.

Top part of the throttle body is done on a manual mill to establish the port size and location. The rest has to be done with a die grinder since a mill can only bore linearly.

[BURN-BROS]

Originally Posted by Steve@Rennsport

My compliments to Aaron for some really nice work!

Those will match the heads very nicely,...

Well done.

Thanks Steve, hope all is well.

[davidppp]

O man...

I am absolutely so impatient to see how this runs..its beautiful work for sure..

Tapered inlet tracts on various other engines of my long -in-the -tooth acquaintance sometimes work spectacularly well: sometimes not.

But I have no tips to offer as to why this might be..

Or, more pertinently, why the factory reduced the taper from the first 2.0L MFI S to the 2.2S..

Steve, any update on those tiny valve 2.0L FIA heads please?

The pistons are designed: I'm expecting to see some CAD files soon to send you..

Real Metal will take about 8 weeks unfortunately..

Kind regards
david

[Steve@Rennsport]

Hi David,

As soon as I get a moment, I'll flow one here and see what may be possible,..

[Henry Schmidt]

Wow those look amazingly similar to a set done at Supertec.
I wonder why?
Cheers

[Henry Schmidt]

Originally Posted by kenikh

The custom spun aluminum trumpets:

These beautiful velocity stacks a available from PMO. They were designed to fit the PMO 50 mm carburetors.
The bolt pattern is wider than the ones Porsche used on the their stacks so slotting and custom hardware is required.
The Porsche stacks use the same bolt pattern as the Weber velocity stacks.
Note the slotting on the stack where the trumpet mounts.
The other slotting (4 cut outs) on the stack where the air filter mounts is consistant with mounting of PMO air filters.