My '75 2002 Sleeper

[tinkwithanr]

I've been second guessing myself for a couple of months as to whether or not the S54 ITB's are really a good fit for the engine, or more directly the 885 head. While they do give an easy solution for certain aspects of an itb setup (common vacuum rail, fuel injectors and fuel rail, proper spacing) I still couldn't ignore their overall size, and how that would effect the power curve of the engine. So long story short, I bit the bullet and ordered some new parts. Then I started machining the old 'i' manifold from my donor engine. When I got done it looked something like this:






The throttle bodies I will be using are from a late model BMW (keeping it in family of course) 1200RS. They are 38mm in diameter, and while some may argue they are to small for the engine, they will have no trouble out flowing the intake ports of the 885 head. This will help to keep charge velocities up, something that would have been lost with the monsterous S54 bits. Another plus of these throttle bodies is that they are mounted with 2 bolts on the top and bottom, so re-spacing them to fit the 91mm center distance for the M20 was as easy as drilling some holes in a piece of aluminum. Finally, because I'm using the stock M20 intake to interface with the head, I'm able to keep the stock fuel injector/rail location as well as the oil vent tube that runs down into the block.

Since they come in sets of four, I had to purchase two sets. Seeing as how I had two left over, I gutted one so that I could see how it would line up with everything without the throttle plate in the way.





Here I'm holding the TB in place roughly where it will be. It looks fairly far away from the head in the picture, but it's actually only ~0.5" from the edge of the manifold. That will leave me enough room to weld the aluminum tubes in place that I will be mating to the throttle bodies. As you can see from the picture the port leading to the head will need to be opened up slightly and rounded out. However it should be a very direct and smooth path into the head.







Then I took some aluminum angle and drilled the new mounting holes to properly space the rest of the throttle bodies. Then I bolted them onto the angle and held it in place.









I still need to weld on the new tubes onto the manifold, as well as extend the throttle tabs that translate the rotation from the center of the assembly to the outer throttle bodies. Overall I'm very happy with how they will look. The assembly will take up much less space than the S54 castings and throttle bodies, mostly because it doesn't have to open up the port from stock to 50mm diameter. This will leave me a lot more room for a proper plenum, which will either be aluminum or composite. It also puts the throttle bodies themselves much closer to the head, which will lead to better throttle response.


Thanks for looking.

[Dozyproductions]

Im glad im missing halloween for this

[knuklehead92]

over rated....




jk Looks awesome!! keep it up!

[downforce22]

I would love to build my own parts like you have on this build. Awesome!!

[future rs]

As usual great work!

[deutschman]

Great work on those ITBs!

[TrentW]

Great work on those ITBs!

Agreed. I've been contemplating ITB's for awhile and now you've got me started again dammit.

How bout possibly offering these as a kit or at least build plans?

This thread delivers!

[tinkwithanr]

Sorry, not really looking to make any kits or anything like that. Don't have the time or energy to put towards it.

As far as build plans:

1. Buy two sets of throttle bodies
2. Cut stock manifold
3. ???
4. Profit

[knuklehead92]

if you get the itbs working properly please do a diy lol

thanks for the fuel pump!

[tinkwithanr]

There's really nothing to complex about making them. The hardest part is having the tools to properly machine the manifold and then weld the tubes back together. Once that's done it pretty much just connecting them to an intake and making the throttle linkage.

[CubbyChowder]

With all this insane metal fab work going on, it bums me out that you're not welding in fender flares. I understand if you're going for a certain look with those flares, there's just something about fiberglass/plastic that doesn't settle well with me.

Regardless, I love the progress on this. You are really going hard at it as frequently as you can, and I really respect that. I've been having some lack of motivation to work on my '02 lately as every day solely consists of tedious filling/sanding/grinding/etc. and results come VERY slowly. Keep it up dude, you're a boss.

[tinkwithanr]

To each his own. I do like the look of the rabbit flares, but they just don't really give enough extra room for wide rubber. I wanna run at least 245's, and maybe even wider in a racing slick for track days, so that was a big concern for me. I definitely want some meat on the tires.

The fact that they are fiberglass doesn't really both me. I mean the entire body of corvettes are made from the stuff. Plus it's the OEM way BMW did it, I like to think they knew what they were doing back then lol.

[tinkwithanr]

Picked up some more parts for her over the past week.

Euro Turn signals. These sit flush with the fender as opposed to the stock US-spec bits, which stick out pretty far to the side. They aren't brand new, but they will fit the patina of the rest of the trim nicely.






5-Lug Rear hubs and new rear brake rotors. These will round out the rest of the 5-lug swap (pared with the e12 front struts) and the rotors match the vented front ones that came on my struts.






Then I got a box of goodies from IE, including: Front and rear sway bars (2002 front, e30 rear), Posi-lock Camber and toe adjusters, New poly bushings for the front and rear suspension/subframes, and a lower oil pan baffle. These (plus the coilovers) will let me mock up all the suspension parts and make sure everything fits and works together.







I also got some work done on the itb manifold. In this first picture you can see the adapters I turned on the lathe to mate the stock 'i' manifold runners to the throttle bodies. They started as aluminum tubing 1.5" i.d. (~38mm) and 2.0" o.d. This will leave me plenty of material to help merge the ovalish shape of the runners to the circular shape of the throttle bodies. With all 6 made I tacked them in place on the manifold, 91mm apart.









If you look at the above picture, you can see how the 2" o.d. of the adapter is wider than the sides of the runners. In the picture below, you'll see that the inside of the runners are narrower than the i.d. of the adapter. In order to help these transition from one shape to the next I'll weld extra material to the outside of the runners. Then the inside can be ported out to the adapter diameter without worrying about making the walls to thin.






Here you can see the opposite runner with the adapter fully welded on. You can see all of the extra material welded on the sides to help build up the wall thickness. Also don't mind how ugly the welds look. The intake casting is full of contaminants, so no matter how clean the surface is as soon as I start my arc it just bring more crap to the surface. Aggravating to say the least.





Here is a close up of the adapters and the throttle bodies. You can see how the lip on the adapter mirrors the lip on the throttle body. This will let me use the stock rubber boots that BMW used on the bike to seal the intake tubes.





And here is the boot. I ordered 2 new boots (only 1 set of throttle bodies included them) and 6 more hose clamps that fit on each side of the rubber for a complete set. The rubbers have a step on the i.d. that grabs the lip on the throttle bodies and adapters that will help to seal and hold them in place.






Lastly, here you can see how the linkage works. The middle throttle bodies have the standard cable operated rotary linkage, but only one of them will need to be operated in that manner. To 'link' the rest of the throttle bodies to the cable operated one, the 'tabs' on the left sit in between the two adjusters on the right. Because the throttle bodies are 18mm further apart now, I just need to weld gusseted extensions onto the tabs (304 stainless) so that they will function as they used to. This will let me adjust the plate position of each throttle individually with respect to the others, and dial them in properly.






Thanks for looking.

[Zreberlcoe]

This is sooo freaking cool. I'm 16 and I really want to just dive into a project like this.

[maniacmatt]

I find when you weld cast aluminum like that manifold, a good preheat works wonders.

I used to have a hell of a time with cast aluminum and then I was talking to a friend who does powdercoating who was telling me about how he has to pre-bake all his cast aluminum parts to keep them from "out gassing" while the powder is curing.

Basically the principle behind it is that cast aluminum is very porous. So air, containing oxygen, is trapped in those pores and then when you heat it during welding the air escapes or "out gases" right through your weld puddle. If you preheat it most of the air will escape during the preheating not while you are welding.

PS: I love your project and am super jealous of your work space.