924Board.org

[ideola]

So after much time and consideration, I've actually made some progress on the intake modification concept. I considered PowerGTOGuy's ITB approach, as well as picking up Bass GT's old ITB setup, but both options were in the $1K + range, with the added disadvantage of having to move stuff around in the engine compartment, most notably the alternator, as well as the added expense of having to convert immediately to EFI.

To refresh everyone's memory, my goal was to create a manifold that would not require me to re-engineer the main plenum & runner designs, would require minimal (if any) relocation of other engine bay components, and would orient the throttle body for a direct, short run from a FMIC. Here are the preliminary results:




After reading Todd's post on the diffuser concept, I did some more research and validated the idea of using a secondary diffuser plenum to evenly distribute the airflow across the four runners (as the air approaches the rear of the diffuser, it is theoretically accelerated, thereby delivering relatively equal airflow across the interface port).

I strongly considered using the N/A manifold due to its shorter runners, which would give better clearance for routing the TB into the manifold from the driver side. However, this has the adverse affect of positioning the TB in direct interference with the alternator.

The current iteration uses a Series I intake manifold. We cut an interface port 170mm long by 18mm high, which keeps the diffuser opening larger than the TB opening (3060 sq. mm. for the former vs. 2826 sq. mm. for the latter) so as not to create a negative pressure differential. The top of the interface port was cut directly along the mold line on the intake.

The diffuser was made out of a piece of 2.5" diameter aluminum tubing. A cone was fashioned by cutting four longitudinal triangular shapes out of the tube, bending the resulting "wings" together and welding the seams, resulting in a small-end opening about the size of a quarter. The large end opening will receive a 1/8" mounting plate for the TB. In order to provide better clearance between the rear of intake manifold and the brake booster, the small end of the diffuser was cut off at a more acute angle and will be sealed.

A matching interface port was then cut into the diffuser, which was subsequently welded onto the intake manifold. As noted above, the top of the interface port is directly along the molding seam on the manifold. It could not be any higher, because it would place the TB too high at its more forward location, potentially causing the throttle linkage to bind on the hood (bonnet) when closed.

The resulting configuration places the TB directly between the alternator and the coolant tank in their stock locations, and in precisely the correct orientation to attach the charge tube from a FMIC. The original TB mounting location will be sealed with a bolt-on block-off plate, which will subsequently be engineered to receive one or more fuel enrichment injectors that will be driven by a rising rate fuel pressure regulator. The ONLY engine bay mod required will be to re-orient some of the plumbing and to remove the rear sensor on the brake master cylinder by converting it over to the earlier style sensor contained within the reservoir cap (I have a spare from one of my 931 donor cars).

I don't want to launch another EFI-CIS war / debate. However, it is worth noting that I have validated with multiple sources the rising-rate FPR fuel enrichment approach as a suitable way of adjuncting the stock CIS system. In fact, this is precisely how at least one 80s vintage 924 GTx variant was configured (don't remember now which one, but there is an extensive discussion of it over on Rennlist). It is also worth noting that positioning the injectors to spray TOWARD the airflow is a technique espoused by the esteemed Corky Bell in "Maximum Boost". I know this approach is not as fine-tunable or efficient as EFI. But I also believe it will work just fine in the short term. It will also cost about 1/4 of a complete EFI conversion.

To complete the intake manifold (now that I have verified test fitment), the remaining welds will be made, the TB adapter plate will be added, everything will be sandblasted and polished, and she'll be ready for paint / powder coat. Should be done within a couple of weeks.

Total cost: <$400 for materials and welding (not including the fuel enrichment setup, of course).
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erstwhile owner of just about every 924 variant ever made

[endwrench]

Nice excecution! I still like the whole concept. More than one way to skin a cat.

Todd
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'79 924NA. Rebuilt 9.5:1, MSDS header, Mega Squirt Injection, MJLJ-EDIS Ignition, 1.6L Whipple Charger and Intercooler, 10lbs Boost, 944 Trans, Custom HD Clutch.
"simsport" said....superchargers are better than turbos its official!....

[Rasta Monsta]

Me likie. I think it's important to preserve runner volume.
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Toofah King Bad

• WeiBe (1987 924S 2.5t) - 931 S3

[leadfoot]

Make sure you don't hit the bonnet with the throttle body. Consider also going with a thicker mounting plate for the throttle as you will get better clamping force and be less likely to blow out a gasket.
Looks good though...
leadfoot
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1981 ROW 924 Turbo -
carbon fiber GT mish mash
LS1 conversion in progress...

[Peter_in_AU]

Wow! That is very motivating.
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1979 924 (Gone to a better place)
1974 Lotus 7 S4 "Big Valve" Twin-cam (waiting)
1982 924 (As featured on Wikipedia)

Learn to love your multimeter and may the search be with you

[ideola]

[ideola]

BTW, here is the link to the aforementioned Rennlist thread.
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erstwhile owner of just about every 924 variant ever made

[john h]

[leadfoot]

I was just about to suggest rotation, for the linkage, attach a small angle piece about 10/15cm away from the throttl on the side of the plenum and drill a hole in it to accomodate the cable. The cable should have to nuts that sit on either side of the hole to fix the cable.
You can get end pieces for the cable that have a screw in them too so if you need to adjust the length of the cable you can.
I ended up using a 951 cable as it was about 30cm longer than the 924 cable.
I do believe a 944 which is somewhere inbetween these length would work for you application.
Consider a throttle that has the capabilities for air bypass solenoid too.
Leadfoot
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1981 ROW 924 Turbo -
carbon fiber GT mish mash
LS1 conversion in progress...

[ideola]

Leadfoot, thanks for the tips on the throttle linkage stuff. I'm also wondering if I could just rig up an angle bracket that mounts directly to the (to-be-added) throttle plate itself, rather than having to attach it to the plenum...

[leadfoot]

The stock engine uses the Aux Air Valve i.e bypasses the trottle and allows more air at start up when you have a cold engine. This is the item to replace if your ECU allows air bypass control.

There will be one of two systems generally used
1. stepper motor - and are generally bolted to the body
2. pwm solenoid - most are mounted remotely

Most stepper motors have two speeds, fast or slow.
PWM alows a much finer control and has the abilit to adjust speeds from really fast to really slow and anywhere inbetween.
Both will adjust air volume

Ford explorer I believe has a 63mm diameter. just saves on drilling holes and spending money on fittings. I think it might also have a built in TPS like mine.

As for the linkage, as long as the cam is round that shouldn't be an issue. Mine was more oval and pulled at an angle so I had it mounted further back to alleviate any rubbing of the cable.
Stuart
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1981 ROW 924 Turbo -
carbon fiber GT mish mash
LS1 conversion in progress...

[ideola]

All ready for powder-coating






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erstwhile owner of just about every 924 variant ever made

[tuurbo]

Pretty nice - was that walnut blasted or plastic bead blasted or what? How'd ya clean it up?

[ideola]

I think he used plastic media to clean things up...
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erstwhile owner of just about every 924 variant ever made

[bass gt]

Dan,

Great work!! What percentage reduction have you used over the length of the diffusser? Is there an ideal figure for this, as i am thinking down this route as well

Steve
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Front Wheel Drive is the Devil's work.