412 Sedan Decklid Standoffs?

[gearheadgreg]

So, I am contemplating making standoffs for the rear decklid of a 412 sedan - to get more air into the engine compartment for the carbs/efi, but I don't want to do that at the expense of the cooling air for the engine itself, of course. If I tilt the front of the decklid up, just like Bug guys do, I'll likely get a lot more air into the compartment but then have to reseal the engine cooling intake, and will the different angle and airflow reduce the airflow/pressure pushing air in there? I could always put a little lip spoiler after the air slots on the decklid to create a little more positive pressure over the slots...

Just wondering if anyone has played with this or tried it?

[Ol'fogasaurus]

Do the tuft thing.

Make a cardboard design then tape it onto where you are talking about. Then take some cotton tufts and tape then around the area from the window down and around the area. Then video what happens to the tufts when you drive the car at different speeds. It may take several designs to get it right or maybe not at all but it is a cheap way to do the right thing to your car w/o cutting it up.

Lee

[gearheadgreg]

Thinking about it some more, I think I'll get a super cheap temp probe, and pressure probe, and put them in the fan intake and engine compartment stock, and then with the decklid spaced out and see what that tells me.

[raygreenwood]

If you have a sedan...there is no shortage at all of both cooling and intake air....unless you are missing the scoop and bellows. Ray

[Jadewombat]

Those decklid standoffs were all the rage in the '90s for a while, then people took them off because the engine compartment got so dirty it wasn't worth it.

[gearheadgreg]

If you have a sedan...there is no shortage at all of both cooling and intake air....unless you are missing the scoop and bellows. Ray

For a stock engine and intake - I suspect yes. For a modified engine, making much more power, and a modified intake using ITBs (and likely ducted airboxes) - you can't say, and neither can I. Have you measured oil & cyl head temps with stock and modified or different cooling air intakes? Or air intake temps?

When I get a chance, that's what I will do. If I have time and am lucky, I could measure pressures at different speeds as well. I would think more knowledge would be the goal, not squashing ideas.

[raygreenwood]

Squashing what ideas?.....and yes....I have measured it. Unless you are pushing 3.0 liters.....the stock inlet pipe from the nylon inlet funnel will flow more than you can ever use. Thats a 75mm pipe....with no load on the intake side of the funnel....and a pretty damn good airflow design on the inlet louvers. It has no issues upwards to 2.2 liters.
A 2.1 liter draws about 180 cfm at 5000 rpm. The fan already guarantees high velocity air in the duct with no restrictive load on that pipe.

I think it would be great to test it just to see something new...more power to you!....but I have already seen a 2.2 liter running twin carbs in a 411 four door sedan.....and it had "0" issues. Just my two cents...and having been through more type 4 cars than most crowds of 1000+ vw freaks....I dont think I am squashing your ideas. Ray

[raygreenwood]

Just so you know where I am coming from....lets say you have a 2.2 liter engine. That is 136 cubic inches. That is 0.078037 cubic feet of air pumping capacity. Divide that by two because in a four stroke....each cylinder only pulls in a cylinder full of air once in four revolutions of the crank but there is some overlap....so lets keep it at two so... 0.0390185 cubic feet for rev. Lets say you are going to be hitting 6000 rpm...so the engine needs an average of 234 cubic feet per minute.
And the cooling fan stalls at around 1700-cfm around 4400 rpm....so lets call that 1700. So 1700 cfm+234 cfm= 1,934 cfm of inletair at low or no load/static pressure is required at nearly max rpm. So at highway speed of 3400k-ish....you will be at about 1300 cfm+ 120-ish = 1420 cfm

The 411 and 412 sedans have 46 slots in the deck lid ...and I am going off a picture because I am not close to my car...but they are about 4" long with a 0.4" width minimum to a 0.5" width maximum. That equals out to about 92 square inches of inlet.

That is EQUAL to the cross section of an 11" air duct at 0" of mercury static pressure...a pipe of that diameter flows about 400 cfm. At the high suction rates and static pressure rise of teh fan system pulling through these louvers.... flow rate quickly out flows anything both the fan and engine pumping requires.

My point...not to squash your ideas...because I would really like to see what you get when you hook a manometer up to a sealed type 4 engine compartment...is that an 11" duct cross section will easily flow more than you need without issues.
The type 4 airflow inlet did not have the issues of the beetle. Ray