Installing sidedrafts

[PROPEL]

After waffling for quite awhile over whether to install dual webers or go with a single sidedraft setup, I've reached my decision.

The Steinmetz ssd fits easily with better accessibility to components than even the stock downdraft setup, and it would provide greater torque with its longer ramtube possibilities.

However, I'm setting this GT up to be more of a long-distance, high-speed rallycar, so I've just begun installing twin 40 DCOM sidedrafts on the short Mattig manifolds (3/16" shorter than Irmschers). Even with these shorties, the area is very tight in front of the rearmost barrel. To get a decent airhorn or aircleaner on, I don't think I'll be able to avoid notching into the heater box area at this point.

My question is, what's behind there that I might run into? How close do the heater tubes run against the sheetmetal? I don't intend to remove or alter my heater at all. Notavette had posted some pictures of the inside of this area, but I can't find his gallery on this site anymore.

My alternative is to go with really short 13mm stacks with some kind of mesh screen over them. Does anybody know of a company that sells a short aircleaner/trumpet combo like this to fit over each horn? (The one pictured is for IDF/IDAs.)

I will document this installation as I progress and take pics.

-Walter

[nobody]

I used the short Weiand air cleaners and removed the horns. It would be nice to keep both, but I decided I'd rather have a good air cleaner than the horns. You could do an air box but that is pretty limited for space too. You can see the water lines that go to the heating coil from the engine compartment. they are straight from that point going back for another 3 inches or so. The biggest problem with cutting the heater box is getting the air flow right again for a heater.

[RallyBob]

Walter, definitely run the shorty air horns. I've flowed Weber sidedrafts with and without them, and the difference is substantial. And as stated by nobody, ya gotta run air filters! I cringe at the thought of the damage that occurs from not running them, might as well sandblast your rings!

Better yet, run the shallow air horns, a shallow fabricated air box, and a remote front-mounted inlet and filter. This way you get filtered air, improved airflow, and cold air from out in front of the car, not the hot underhood air.

[baz]

propel
this is the area just behind the heater matrix in the footwell
sorry i cant zoom out any more but the black dot witha screw in it is a carpet clip and the heater box is just back from the edge of the pic on top

[Killer Texas GT]

I'm in the process of putting dual 45s on mine with the cannon intakes. I cut 2 1/2" out of the heater box. Right at the level of the side drafts the 1/2" metal water supply and return tubes to the heater are about 1/2" to 3/4" beyound, they run in an upward direction just below the radius portion of the heater box. I think in my case I can salvage the heater but will have to re-route the supply and return tubes which won't be that difficult. Need pictures I can come up with some, let me know.

Rodney

[Killer Texas GT]

Go to general discussion and go to "Ga. parts trip", I have a picture there of the side drafts and cut out of heater box, not all that clear though.

[PROPEL]

Thanks for the heater box photos, guys! They are very helpful.

Still hoping that I won't need to cut anything, but it's good to know how much room I have to play with just in case.

I am working on the mockup of my airbox. There are lots of details to consider and a weird space to fit it all in. It still has to be accessible enough to install the airhorns and also the mounting screws to the carbs. I just purchased a set of 12mm shorty airhorns from TWM. According to TWM data, these really improve power at the top end (as Bob mentioned). They should also fit inside the airbox with no problem.

However, my immediate project is to grind away all the webbing between the runners of my sprint manifold (a la Otto). I can't access the lower bolts of the carb manifolds unless I do this. (And I can't run studs on the manifolds because then there's not enough room to slide the carbs on.)

-Walter

wishing for just another half inch

[RallyBob]

A guy I used to know years ago wanted to run long Cannon intakes and Weber 45's on his GT, but wanted to retain his heater box in it's entirety.

So he did two things...first he cut the flanges of the Cannons a bit thinner, as well as angling-milling the cut at the head so the intakes pointed upwards a bit more (he had to weld a bit of material to the flange so the shoulder bolts still contacted correctly).

He then shifted his entire engine/tranny over a fraction of an inch...I couldn't say how much, it was years ago, but he basically just drilled new holes on all his engine/tranny mounting brackets and shifted the sucker towards the driver's side!

Seems simple enough in concept, but I don't know if he ever ran into other clearance troubles.

HTH

[ConreroGT]

you check out the "naked" heaterbox at www.opelgtmotorsport.com

Look under the DCOE Engine section. I have even more detailed photos of the exposed heaterbox just before I demo'd it.

You can see what's behind the sheetmetal....

[nobody]

I think it is easier to just go for it. I even wound up with more air across the heater coil after doing it. I can use what I want for filter or whatever. Check the pic

http://www.opelgt.com/photos/showpho...cat/all/page/1

[PROPEL]

Btw, how's everyone plumbing their manifold crossover tubes?

[nobody]

The only things that cross from one side to the other are gas and vacuum depending on if you use DCOE or DCOM. OEs don't have metered vacuum ports for the distributor advance and OMs do. My manifold is one piece but if I wanted to I could have removed the center bar. I don't know of any other common connections.

Rallybob; if you angle your manifold wouldn't that put you in an uncharted area for floats? I always figured the angles were there for a reason.

[GTJIM]

DOCEs' and DOCMs' will work quite happily with 5 degrees downdraft - Weber recommend a maximum of 7 degrees.

[RallyBob]

I don't know how much the guy angle-milled the intake in degrees, but it kinda makes sense that it would still work, as the GT engine is tilted 'downward' towards the intake side anyway. All he did was compensate for the tilt really.

[Gary]

Originally posted by RallyBob I don't know how much the guy angle-milled the intake in degrees, but it kinda makes sense that it would still work, as the GT engine is tilted 'downward' towards the intake side anyway. All he did was compensate for the tilt really.

Now this brings up an interesting question...

Would reversing the GT mounts so the engine is tilted the toward the drivers side and milling an angle on the intake to keep the overall "tilt" within the 7°max. give enough clearance for the DCOE's?

[oldopelguy]

Or, if swapping the GT mounts is too much, how about a mix and match with Kadett mounts? Gary might be on to something here.

[PROPEL]

Don't think I'll be able to avoid surgery... my airbox would be right up against the heater area sheetmetal and likely cause rattles and vibrations. So I'm resigned to cutting.

But I'm just curious if anyone thinks something like this would work for now (until my airbox is finished). I'm thinking of creating a screen filter "sandwich" under my velocity stacks. Is this a bad idea???

[nobody]

For a DCOE the air horn also locates your choke tube. That is the small band towards the carb end of the air horn. Also all of the horns I have seen actually fit around the choke tube. This would not give you a flat area to put a filter element in. When I did this the first time I used what looked like a foam sock that fit over the end of the air horns. They were cheap and simple, but they didn't last a long time. They might be just the ticket till you get everything you want.

[nobody]

like these
http://www.piercemanifolds.com/airfilters.htm

[Andreas]

Just run into the same -no space to mount the airfilter situation.
So my first attenmpt was changing the motor mounts. That gives a little more than half an inch. Now the carbs fit nicely, the large airbox made for the Asconas still does not.
Will try to shift the engine further and even consider milling the intake, but my main concern - since I would prefer an enclosed airbox for both carbs without cutting my sweet thing into pieces - would be if this is a good idea in the first place, because the rear carb is in squeeze that I do not know if you ever get enough "good quality air" in the furthers away carb. Any ideas? I can imagine issues of temperature imbalance as well as flow. Or is the air request from carbs strong enough to even those issues out if you are providing air in an enclosed box? Part two: I'd need some help getting a box together. Where would I find hints?
Thanks!

[PROPEL]

Started up my car today with its new dual 40's!

Sorry I haven't been able to post pics, but I need a new digital camera.

Anyway, here's a rundown of what I did:

- Minimal modification of heater area. I cut out a small section of the original sheetmetal and created a notch back there to accommodate my airhorns.

- Removed the webbing from my sprint manifold, painted it, installed new studs, and then had it machined true again so it'd bolt up.

- Bolted on the shorty manifolds and the shorty thermostat housing. Attached the carbs using softmounts and thackery system.

- Italian airhorns are 30mm stacks with an integrated mesh screen cover. I cut some foam air cleaner element into round pads (like sponges) that insert into these airhorns. They are kept from being sucked into the carbs by their press fit and a separate mesh backing screen. The only trouble came in fitting the rearmost airhorn...but a couple of hammer whacks against the steel meshing deformed it enough to fit nicely. You can barely notice. I still have a set of those ultrashort TWM airhorns and will save these for when I finally build a righteous airbox.

- I am using a Magard top linkage setup between the carbs, and it looks like it'll work out well. My throttle rod still needs some welding done to it tomorrow; but I'm all done for today.

-Tuning to come after my throttle system is finished. I was happy that when I turned the key, the car fired up! There was just a little bit of carb spitting at 2000rpm, but at least I'm in the ballpark right out of the box.

- 30mm chokes, 25 mains, 50f9 idle, f16 emulsion, 180 air

Once I get these dual carbs sorted... it's roller rocker time. YEAH!

Walter

[PROPEL]

This is what my airhorns/aircleaners look like... except mine are 30mm tall.

[PROPEL]

Went for a drive tonight, and everything seems to be working fine with the carbs and linkage. My only regret is that I did not plumb crossover tubes so that the brake booster could draw from all four manifold runners.

Factor in low vacuum from a lumpy cam, and now the the brake pedal feels really bad... like 2" of dead travel before anything starts to happen. Is there any way to adjust the stock brake pedal arrangement? I didn't expect it to feel this spongy afterwards... how do racers deal with this (since they're not allowed to run crossover tubes)?

Perhaps this is something I just need to live with and get used to pumping up the brakes? I have '75 big brakes, proportioning valve, and 3/4" rear cylinders on this car.

I'd hate to take it all apart now to plumb those tubes...and I sure don't want to risk drilling the manifolds while they're in place (metal shavings, etc.)

Walter

[GTJIM]

The Jap diesels have a similar problem and they solve it by using a vacuum pump off the back of the alternator - food for thought! Might be a good high output alternator/vacuum pump from one of them that can be used on your GT

[PROPEL]

Jim, you're like the automotive MacGiver! Scavenging alternative part sources must be part of the New Zealand spirit... similar to how folks in Cuba can keep those 1950's-era American cars running.

Thank you...that's a VERY interesting suggestion, and I'm going to check it out.

Walter