von

I thought of something for 2nd gen. I have 89GXL. I have been lookin at the intake trac were the VDI is connected to. It has a bunch of turns were the vdi swiches from low(lone runners) to high(short runners) well for those of us like me and mzdsp7, bambam exc who wired them 0pen because of geting rid of pump and stock sleevs have no need for the long runners to function. So i was wondering if i can get 4 mandrel bent tubes and weld them to the upper intake and lower intake. It would smooth out flow with a streight shot of air. Probly gain a little low because of the velocity too. And most importantly you would be able to get a small hone and bore the entire intake tract unlike mazdspeed7s wich is only port matched. Pluss enlarging the intake by the ports only is decreasing velocity the same way a streight pipe on the exaust is better than having a gutted cat... His is better than stock obviously if hes runnin low 14s but wouldnt this work if i can get someone to mandrell the tubes?

mazdaspeed7

The VDI intake manifold is brilliant. Look at all the cars that have dual-stage intake manifolds now. They are just starting to use this stuff on piston engined cars, but Mazda had this on a production car 13 years ago. The only thing that leaves room for improvement is the runner taper and the upper manifold piece right after the TB. The runners in the middle of the VDI part(the big middle section) are about 50% larger than the runners in the upper and lower manifold pieces. You cant really do much on the upper part bue to the thin walls. This would be a good piece to replace, and not use a plenum for the primary runners. I might try this soon. The lower manifold, or the piece that bolts to the engine, is a problem area that can be fixed by porting. Right below the secondary injectors on the middle piece, the runners narrow down nearly 50%. But you can get to this part easily with a grinder, and make the port on the flange match the runner size. And then you can port the lower intake manifold to match.

von

Oh.. i see the light. I will do this your way.. seems a lot easier and cleaner. One more question. thiers four runners. I would only port the outer two right? the inner two are oval arent they? Anyways thnx for replying to this post.

mazdaspeed7

You can port all 4 runners. I did.

XimbueX

Mazdaspeed, out of curiosity, what does cutting the crush washers off do in terms of performance?

von

Cutting the crush washers off the plug would bring it closer to the engine thus raising the compression a tad.... a fraction of a tad.. but everybit helps. U probly wouldnt notice a difference. I will do this when i get more mods done.