saturday i took 8 intake manifolds apart.....2 dual port intakes .....and 6 single port intakes ....all had plugged heat risers ....so here is the thing to remember ....if you drive a summer car you do not need these tubes ....they are used to heat up the larger tube to keep the throat from icing up ...i cut the aluminium coverings off all them to find that they had rusted so bad that they rusted the larger tube right through......so there is no way you can make the car idle or run good at all ....just a big vacuum leak period ...so i removed the bad ones ....welded the tubes back up ...so no holes in big tube ....so these can be put back on the engines i build for summer cars ....i also drilled out the smaller tunes with a elongated 3/8 drill bit then migged the ends shut ....to be used on a vintage intake that i make ...all this took two days ....but i fixed them all ....all set for the next few rebuilds i do ..gets harder and harder to find good intakes that are no plugged or rotted out ....40 or 50 years kills the metal ....hope this blog helps anyone building and engine .....cya
Joe you still can get icing in the summer especially on high humidity days so while yes you could probably go without the heat risers 80% of the time depending on the temp and humidity you could still ice up. The experience that I based it on was a 1700 cc 72 bus with a holley weber 5200 carb and headers
Hi @ghianowbug, I suppose on the Holley/Weber setup, you had no carburetor pre-heat system. (just a guess) That would probably exacerbate things, but I think your point is still fair and valid. I'm surprised we haven't seen an aftermarket retrofit kit for manifold heat risers.
probably because the market is predominantly in the southwest where icing is even less likely (dry and hotter). Then the trend was dual carbs where you need an isolating plate to keep the carb from getting too hot and cooking the gas giving you vapour lock. (the plate acts as a thermal break) and now fuel injection where there are no worries(as far as I know but my experience with aircooled FI was a 70 squareback) . By the way I still have the 39 year old holley weber sitting on the shelf. was going to fit it to a 1600 that I had but changed engine directions midway through the project . The manifold that I have for the type 1 was with heat risers as I did not want a repeat of the icing.