Stock exhaust on bigger type 1 engine?

[StefansBus]

Hi all,

I posted this already on the bay forum but had zero responses so I'm hoping I will have more luck here. It's not my intention to duplicate threads and I'm very happy for a mod to close the one over in the bay forum.

Anyway; here goes:

The bus (stock 1969 bay with 1600SP) could use more torque.

I'm not after high RPMs and lot's of horse power. I just want more pull.

At the same time I want things to look as stock as possible.

How big can I go with the stock exhaust system including heater boxes provided I keep the RPMs low (as low as stock or even lower) without running into heat problems due to too much restriction to exhaust gas flow?

I'm pretty sure 1776cc won't be a problem but what about 1956 or 2017cc?

As you can see I want to go 90.5 on the piston and cylinders.

I would keep head work to a minimum and valve size stock or close to stock. The cam would remain stock or close to stock, too.

I have an aluminum case which should not be needed but won't hurt.

I'm also planning on a quality, forged, counterweight crankshaft. I don't think this engine will need it but I wan't it to be as smooth and reliable as possible.

I think I will have to convert to dual port and while I am at it I would go for a single 37 PICT Solex carb (converted genuine 34 PICT 3). Not interested in dual carbs for this engine.

Will the stock exhaust system work with such a combo?

Looking forward to your thoughts on the exhaust question as well as the envisaged concept, keeping in mind I want stock looks, torque and reliability.

Stefan

[modok]

An exhaust system that is designed LIKE a stock muffler is not necessarily a bad idea.
If the flow passages are large enough there should be no problem just scaling it UP to a larger size, but I do not really know if such a thing exists.

[Alstrup]

If you want it to look absolutely stock, then cut the muffler open and gut it along with making 2 & 4 about the same legth as 1 & 3 (about 20" from cylinderhead) Make a noise reduction chamber in front of the outlet and a tube muffler in the exhaust tail pipe.
I have done this a couple of times and such a muffler can support approx 70 hp with good torque and very reasonable back pressure.

T

[mark tucker]

bigger engine should have a better flowing exhaust. I wish i was in a better place in my life as there sure seems to be a need for a better ex in the stock appearing / shape guys. I may make 1 some day for me. even though I dont need one.and dont think my 356 will have room for it. and my bug is halfass so not on it, I may get something else some day to put a big motor in.

[raygreenwood]

[mark tucker]

restrictive exhaust cracks heads. especialy if it's leen.
I never thought of a vw muffler as being all that small.

[AlteWagen]

[modok]

Very good!

[raygreenwood]

Yes!.....thats nice!
Ray

[AlteWagen]

Thanks!

Would you have any suggestions on improvement before I weld it all up?

End caps and internals all hand formed using aluminized 12ga and mesh scraps from another project. Do you think a large single or multi tips would work better?

_________________
Grapes of Wrath $200 Engine Rebuild
Official Dual Carb Thread
Cylinder Head Quick Reference Sheet

[modok]

I was wondering what would be inside.
Divided up by baffles as pictured you really can't go wrong.

I believe there could be some "boost" by tuning the end chambers as Helmholtz resonators, volume of each end chamber 2-3 liters, tube leading from end chamber to middle 6-8 inches length diameter 50-100% larger cross section than the primaries.
That was roughly the range that made sense in computer simulation.
I don't know how accurate it is, and adding in possibilities with perforated tubes and different entries and exist features of said tubes ends up with a very large number of possibilities, some which must work better than others but I have the feeling nobody will ever really try them all and actually know Take a look at the sebring design....what if we have two tubes leading from the end chamber IN LINE with the primaries? It'd be like a sebring all packed into one box..... or course the gap might need to be a certain range to make it work best, so teh primaries project into the ends a certain distance??? Good luck driving yourself mad.....but remember you asked

Certianly a KEy in either case is the primaries entering the end chambers of the muffler are not paired together into another tube for any length, rather they both exit into a sizable volume of the end chambers. Entering into some volume will prevent the shock wave of for instance #2 exhaust valve opening from traveling up #3 pipe and blowing clear into the carb at overlap, which otherwise would occur at certain RPM bands if both sequentially firing primaries are paired into a secondary or into a small glasspck or so forth.
This is where the hot-dog and other el-cheapo muffler designs really have no hope of ever being right with anything except the mildest of cams.

[StefansBus]

Gentlemen, greta input. Thanks very much.

Torben, your advise sounds very interesting. I intend to give it a try this winter.

AlteWagen, Nice work

Mark, Ray, modok, thank you all for your valuable input.

Stefan

[raygreenwood]

[raygreenwood]