Single carb heat-risers drilling...

[Nico86]

... do you drill them on a 4in1/sport exhaust system?

I noticed on most aftermarket "sporty" exhaust systems the heat-risers plates are not drilled and are just welded directly on the tube. I am running a 4in1 exhaust on one of my cars since more than 10 years and I've never drilled them, I've never noticed any real difference from the stock exhaust system whether the engine is cold or warm.

I just got another exhaust for my other car, and since it's not mounted yet, I was wondering : do you recommend drilling them or it doesn't really matter? (with a stock engine and stock single carb)

[Nico86]

I dd some reading online and on old magazines and I got my answer, I'll drill them. Even though it won't be as efficent as the stock pre-heat system, that takes exhaust gases from a high and a low pressure point to create a flow, but it will still be better than nothing.

I've found interesting infos on both of these links :
https://www.thesamba.com/vw/forum/viewtopic.php?t=333608&start=0&postdays=0&postorder=asc&highlight=
http://vwparts.aircooled.net/Pre-Heat-Modification-to-VW-Headers-Labor-p/exhaust-preheat-modification.htm

Now I am wondering : would using the normal exhaust gasket on one side, and those gaskets with a smaller hole on the other side, would create enough pressure difference and then creat a flow through the pre-heat tube to the carb ?



I guess this would have to be tried and checked, to see if it actually warms the carb manifold more.

[modnrod]

I have a cheap old Empi sidewinder-type of 4into1 on my 1600, CB centre manifold and Solex at first. I didn't drill them because they were bent and would leak badly I thought, and since my ambient temps here in winter are 20*C during the day I didn't see much point.
Until I pulled the manifolds off so I could change the intake rubbers, and even tho it had been sitting there for about a week something like 100mL of raw fuel that had been sitting in the centre poured out everywhere. 

I drilled the risers out, but with only a 10mm drillbit on each side, bent and hammered and swore a fair bit until the CB heat tubes lined up with the Empi risers, then away I went. Strangely the fuelly smell went away after that too.

No puddled fuel at all since (I've had the centre off twice more for other stuff), and no black soot or varnish deposits either.

[Nico86]

I have a cheap old Empi sidewinder-type of 4into1 on my 1600, CB centre manifold and Solex at first. I didn't drill them because they were bent and would leak badly I thought, and since my ambient temps here in winter are 20*C during the day I didn't see much point.
Until I pulled the manifolds off so I could change the intake rubbers, and even tho it had been sitting there for about a week something like 100mL of raw fuel that had been sitting in the centre poured out everywhere. 

I drilled the risers out, but with only a 10mm drillbit on each side, bent and hammered and swore a fair bit until the CB heat tubes lined up with the Empi risers, then away I went. Strangely the fuelly smell went away after that too.

No puddled fuel at all since (I've had the centre off twice more for other stuff), and no black soot or varnish deposits either.

I ended up drilling them too, only 10mm too as I was afraid to go through the welds of the risers that were not greatly aligned.