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Some oval-port SLS spacers / isolators (for the 32-valve engines) and round-port spacers (for the 16-valve engines) - all of them essentially flat or "square" with these shaftless ITBs, would be amazing!
Could you print a manifold (or 2, one for each bank, a la Ferrari)? There are folks doing some impressive CF manifolds for BMW M cars, but I haven't reached out to them about interest in a 928 application.
Nah - plenty of room! They are custom-made to fit the Busso V6 with an original bore of 88mm, a drop-down to 80mm (for the Italian and Portuguese market turbos), and then an OEM increase to 93mm. We build these to 100mm pretty regularly, with increases to as much as 101, 102, 103 and 104mm bores for individual cylinder displacements of 625+ CCs on 78mm strokes. The bore-spacing is also fairly tight, so it can be made to work.
These shaftless ITBs are from AT Power in England - and yes, you can scan the heads and send files - but for a custom design development on the Alfa project, I sent them a block and heads (bought and sent a set from within the UK.) They scanned it and completed the development there for us. Hans should chime in (and sorry if I jumped the gun here...)
That assembled rack is for an early air-cooled 911 with 104+mm bores! No issue to fit these on the 928 when spaced for it specifically. And yes - it is more the bore-SPACING that counts, but without the bore-centers numbers at my fingertips for comparison, the over-square design of all three engines is a good reference point.
I should have posted a picture of the bottom of the rack - those are round ITBs (for a 2-valve head like the older 911.) Those "oval" (football field-shaped) ITB units were custom-made for us - they can be as round or as oval as they need to be. They are not an off the shelf unit like buying a generic Jenvey and "just" making an adapter for example.
That said, on the 4-valve Alfa head that those were made for, the port-inlet shape to those two valves are much more elongated, whereas on the 928, they are far more round - even on the 32v. On the 16v head, the inlet port is quite round and ITBs with the shape of the 911 units on this black rack will work just fine! They can also be spaced closer.
Last edited by Rasant Products; 11-18-2023 at 08:42 AM.
I remember my Dad talking about putting velocity stacks on his '58 Corvette. After an all-nighter with a buddy, the car was running great. He shut the car off, closed the hood and they went inside to get their jackets and to go to breakfast. They came back out and the car wouldn't start. They lifted the hood, checked everything and it looked good. Started the car and it ran fine, close the hood and it died. Yup: Not enough space for the stacks to get enough air into the engine. My Dad, being practical, grabbed some sort of cutting tool and cut holes in the hood over the stacks and drove it that way until he sold it.
the problems don't stop and just the ITB's. you have clearance issues with the water bridge, you also need to clear the strut tower brace with the air horns, airbox and fuel lines. The you have to figure out how to get the air into the ITB's and clear the hood. Tons of fabrication and time to get it all right. Horns, length of horns and the list keeps on going.
As our Sasquatch friend suggests, trying to get anything fitted at cylinder 1 is extremely challenging. It is not possible without severe modifications to the water bridge, or designing a replacement.
Even with modifications, the stock water bridge limits the angle and injector placement at cylinder 1. Using the standard ATP units places the injector in a far from ideal location. The stock 928 injector location is actually quite good, and if used with a modern split-beam injector (like an EV14) the spray pattern is almost exactly hitting the back of the valve stems. With the port entry and normal ITB injector angle, you will likely have a lot of wall wetting, which is difficult to correct for with Sharktuner.
I have specifically modeled the 48, 50, and 52mm bodies from ATP. The 48 is the best overall fit, but it still will not clear the bridge. We did some preliminary investigation on making a lower profile dual unit (similar to the DCOE units, but with the correct bore spacing). Even going to a custom housing still had fit issues at cylinder 1.
I would suggest starting with a redesign of the coolant bridge before tackling the rest. It will save you a lot of time.
All very good perspective guys. I don't have a dog in this hunt (yet), as the team has their hands full with the re-launch of the legacy Rasant 911 ITB and custom GT3 intake plenum products, as well as the re-launch of the Rotrex 928 kits. (Doing two Rotex-blown 07K swaps to 944 chassis right now as well, so there's only SO much bandwith to go around.)
I was just here in the shop the other night, day-dreaming (or sleep-walking, depending on how you look at it.)
One thought though; on the 911 ITBs (specifically for ATP shaftless units for a 964 / 993 with an articulating wing), we have to install SLS printed trumpets which angle the bells forward towards the firewall - like this. Perhaps little angled spacers (adapters that you need to fit the ITBs anyway) and then runners that step towards the rear of the 928 like this...?
Or step-back spacers that angle the ITB above it rearwards and away from the problem areas already (at the base below the ITBs...?)
?
Last edited by Rasant Products; 11-18-2023 at 08:49 PM.
This works well enough, I'll post Louee Ott solution next... It is quite elegant...
Additionally. I appreciate you enthusiasm for the 928 and investing in R & D to improve the options available for owners. Lots of details to work out as others suggest!
The Louie Ott solution is elegant and functional. The attention to detail is exceptional with hand formed carbon fiber air horns and gorgeous carbon fiber housing for getting cold air to the airbox/plenum from in front of the radiator which also achieves a ram-air effect at speed. (The tubing over the air horns is the ethanol injection at WOT).
With 603.1 HP at the rear wheels this reliable and drivable monster is quite the fun beast to drive.
Last edited by 928 GT R; 11-20-2023 at 10:17 PM.
Reason: Spell check got me twice!
11-17-2023, 04:24 PM
928 ITBs - Just Some Ideas;
