cabin heat question

[Belgian1979vette]

Have changed to a 195°F thermostat and I now have an issue with hot air entering the ventilation. I think it has to do with the L88 high rise hoods and cutouts I made in the hood reinforcement where it meets the firewall and the underhood heat getting into that area.

I would have expected the higher pressure in front of the windscreen to push cold air under the hood but apparently not.

didn't have the issue with a 180°F thermostat.

So what's the solution here ?

 

[7t9l82]

truthfully all this 195 degree thermostat stuff is nonsense. you shouldn't need anything over 180 , i run a 160.
i think people miss the mark on this low pressure at the base of the windshield. if you open it up hot air has to flow through. but if you seal the carburetor to that open plenum then the low pressure area will allow cool air to be vacuumed into the carburetor. an engine is an air pump ( vacum cleaner ) don't know if any of that makes sense to you but i hope it helps.

 

[JPhil]

i think people miss the mark on this low pressure at the base of the windshield. if you open it up hot air has to flow through. but if you seal the carburetor to that open plenum then the low pressure area will allow cool air to be vacuumed into the carburetor. an engine is an air pump ( vacum cleaner ) don't know if any of that makes sense to you but i hope it helps.

It's a higher pressure area at the base of the windshield, and lower pressure in the engine bay despite the turbulence.




Note that on the front of the grill there are two more threads sucked completely in so as to be almost invisible. One almost in the middle between the left & center threads, and one in a corresponding point between the right and center threads, hard to see because of the long hood thread dancing in the vortex.

 

[JPhil]

Here's another, you can see all the threads sucked in: there are 5 across the lip of the cowl (including 2 farther outboard not visible in the first picture), the two at the front of the cowl grill, plus the long one from the hood.

This is the stock hood with the OEM downshift-switch-operated hood cowl flapper removed and a typical store-bought 14" X 3" chrome drop base paper open element air filter on the Q-jet. Even up to 100 MPH it was drawing air like this, if I remember correctly. This was years ago.

Doesn't really help answer your question, Yves, but it shows what's going on there. I don't know the details of what you did, but perhaps your cutouts are now allowing engine compartment air to suck in to the cabin intakes on the far outboard of the cowl. Notice the thread at the lower corner of the windshield is blowing out around the cabin rather than being sucked in.

 

[mrvette]

I did something similar on my '72, with the wiper door....long time ago....

I noted that the BB add on air scoop with the back open had totally neutral airflow, the strings just hung there, as if nothing happening, same for any air around the hood edge.....

but I had electric fans mounted flat to the radiator, so aimed lo, not high up like a stock belt driven fan would do....

I also have my inside flapper in the right kick panel removed, and the one near the blower motor is sealed shut so my car is on constant recirculate.....I also have a C4 blower motor/cage with 3/4" spacer for more airflow....

:smash:

 

[Belgian1979vette]

This solved my issue today.



This is getting really close to my wipers, so after my run I cut out about 5cm from the edge. Have to see if it prevents warm air from entering the ventilation.

I have to add, this was during slow speeds of up to 50 km/h doing tuning to my fuel tables.

It kinda makes me wonder if the CAI would really work from this location. However with the ITB setups and the double 90mm ducts I need to supply air to them, this is probably my last option.