Dual manifold pre-heat with PICT34-3?

[ccowx]

There is lots of talk about manifold pre- heat with center mount carbs. I am doing some upgrades to my 1835 with a 34-3 and the usual headers, etc. probably pushing in the 80 hp range if I do it right.

I live in the Yukon and temperatures around -30 to -35 C (roughly the same in Farenheit at those temps) are not unusual in the winter. I will be using the stock air cleaner with inlet heat etc. I was thinking, since I am modifying my headers for proper cross flow manifold heat anyway, is there any value to adding a second preheat line into the manifold and running two of the pre-heats, both with cross flow to the collector? Or, more hassle than it is worth?

Thanks

Chris

[Pruneman99]

VW did it for 1974 California models. Maybe others. It was most likely done to help with emissions by keeping the fuel in suspense longer for a cleaner burn.

From a performance standpoint in cold weather I'm not sure how much difference it would make but it might help? Probably couldn't hurt.

If you use a center section with the dual risers all you would need to do is modify the exhaust so I guess it just depends on you fabrication skills. It would take me a lot longer to do than someone with a set up shop and loads of fabrication tools.

[Glenn]

[rodjr]

Alstrup gets about 80 hp out of 1600's with modified 34 pict-3 carbs, We are not all Alstrup but, follow his advise to the letter and a 80 hp 1835 should not be an issue. He has a 77 hp 1600 combo with details in the builds/combo's sticky, page 6 about half way down.

With those temperatures, i would give it a try, if it does not help, or if it makes for too much heat in the summer, add a heavy gasket with no center hole to one set of risers.

[ccowx]

Thanks for the thoughts on the manifold heat. I was thinking that I could use the two hook ups at the flange and head end of the headers for the high pressure end and then plumb the other ends both to the collector at the other end. I would probably have a channel machined into the thick collar on the intake center section to inset the second heat pipe into.

My real question is would I be into the law of diminishing returns for a second pipe, compared to simply making sure the factory one is working as designed? At the temperatures I will be dealing with, it does not hurt to ask!

As for can I get 80 hp out of it, I am pretty optomistic. The engine has a 34-3 with a 28mm venturi, SVDA distributor, modified air cleaner, 8.5:1 compression, Engle 100 cam and headers. Not sure about the heads, but I suspect some mild cleanup has been done. I am currently trying to optimize the combination with jetting, pre-heat, possibly a better muffler, etc. The limitations are the stock intake, air cleaner and quiet pack muffler. I am considering such things as ACN Super stock intake, better muffler and a bit of cleanup on the dp end castings. My parameters are that I want a practical engine in my 70 Westie with the cold weather start up aids and the stock filtration for dust. I also need to keep the original Eberspacher heater. All of this basically eliminates the dual carb option, which I am very well aware is better.

And yes, I have read Alstrup's posts, religiously! He is the man on the larger venturi 34-3's it seems.

Chris

[busdaddy]

Your time might be better spent lagging the intake manifold with header wrap or a similar insulation.
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[Pruneman99]

Here. You work is half done.

https://www.thesamba.com/vw/classifieds/detail.php?id=1854253

[ccowx]

Those 1974 manofolds are interesting. I assume they fit dp end pieces? Does it fit the 34-3? Is there matching sheet metal for the back of the engine to accomodate the extra tubing?

Thanks!

Chris

[Pruneman99]

[Pruneman99]

Here is the rear tin:

https://www.thesamba.com/vw/classifieds/detail.php?id=1556892

I also saw multiple ads for the little dual heat riser tins.

All in < 100 bucks.

If you keep your QP header, you will need to fab that side up.

[ccowx]

Good to know, but I am guessing that the stock exhaust that goes with it is not very good from a performance standpoint. I am not trying to create a drag racer out of a Bus, but I don't want to choke it down either, especially after modding the rest of the engine for performance.

Good to know that the manifold is there, now I need to think about whether it is what I need or if I should fab my own or not worry about it.

Thanks!

Chris

[Pruneman99]

For $35 plus shipping I wouldn't even think about buying that center section vs. fabbing my own. You can use stock end castings that have been ported.

For performance (with a centermount pict34 and that cold weather) I'd go ahead and use that 1974 center section and rear tin, ported VW endcastings, and fab the heat risers to a merged exhaust. Would cut down on a bunch of fab work, and look clean/stock from the top

[ach60]

I'd buy the rear tin & the manifold just to have them.
You can modify any good exhaust with a double tap for exhaust gasses to the intake, (That's the hard part)
and merge the outgoing double fitting tubes into one larger tube of the same area, and weld that tube into the center of your collector.
This whole thing only works if the out going tube has good draw like in a stock VW Muffler.
The common thing you see on a header with taps on #2 & #4 for the heat raiser don't work worth a damn.
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Good Luck
Al

[oprn]

You are definitely going in the right direction. I would avoid dual carbs unless you can find them with chokes for cold starting and can fabricate warm air feeds to the air cleaners.

I just came back now from an ice racing day at -18C with my Manx clone with Kadrons. I was the only one that could get it to run good enough to enter the race. My right foot aches now after only two runs from constantly pumping the gas pedal to keep it from falling flat on it's face below 2500 rpm. Winter running dual carbs requires a super rich mixture or pre heated air for the carbs.

Full stop!

[Slow 1200]

There is a NOS header for dual preheat in the classifieds, just saying