Engine Crankcase vent tube “relocation”?

Mcmahst · Nov 20, 2025

I’ve got a question regarding relocating the vent tube that goes from the throttle body to the valve cover. The engine is a 5.0 from an 87 TBird (throttle body on passenger side) and it’s installed in a 73 Mustang. The metal 90ish degree tube that exits the throttle body is in conflict with the hood. Has anyone either relocated the tube to a different location or is there a throttle body that will work with my linkage that has that vent tube lower? I do not have photos of the hood to tube conflict, yet. I will next month when I get back to my car. Was just hoping this is a know problem with good solutions. Thanks for the help.

AeroCoupe · Nov 20, 2025

Have you thought about posting over on VMF? They would probably have some good input as there are quite a few swapped cars on there.

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KRUISR · Nov 20, 2025

Stock intake? Stock throttle body? How much clearance is needed?

Noobz347 · Nov 20, 2025

Mcmahst · Nov 20, 2025

I know, I’m just fishing for an easy answer from the person who had this problem before me. I like VMF, but when I’ve had issues like this, I usually get nothing useful. Same with 7173mustangs. Both sites are great, but the VMF guys are not 71-73 guys and the 71-73 guys are not much into anything but stockish situations. Not painting with a broad brush, just my personal experience.

I’ve find on this site, you guys are up for anything; it’s why I asked the question here. First week of Dec I’ll be back in Az (where the car is) and I’ll post photos of the issue. To answer, all stock setup. And, I’m not sure how much clearance is needed because the hood is sitting on paint stands to be sanded. But, I’ll get my neighbor to help set it on the car, with the correct rubber parts needed, to get the photos needed. Thanks for responding: See, I knew this was the place to ask.

AeroCoupe · Nov 20, 2025

More like we can Google-fu some .

https://www.corral.net/threads/throttle-body-vacuum-tube-relocation.885237/

Mcmahst · Nov 20, 2025

Excellent find @AeroCoupe. My google skills are below average.

AeroCoupe · Nov 21, 2025

Hopefully that helps with the project.

Mcmahst · Nov 21, 2025

@AeroCoupe , you have no idea. I could write a dissertation on this issue; engine location verses radiator/fan shroud fit/driveline angle. After an entire year finally getting that right, the hood now “looks” like it’s gonna hit that tube. I definitely was overthinking the solution. I could just put a filtered breather cap on the valve cover and remove tube and plug the hole. I was so deep in the weeds, it never would have come to me. Thank you and @Noobz347 for the help, post past and future. Steve

AeroCoupe · Nov 21, 2025

You absolutely do not want to put a breather cap on the oil filler neck. Read that thread I send you as that is covered in there and it has been covered here multiple times. It is called "unmetered air" and can/will cause issues with the ECU.

Mcmahst · Nov 21, 2025

I have a SD system. Does it matter? I would agree if it was a MA. I was thinking about attaching a high bypass filter to the current nipple on the valve cover oil fill. I couldn’t find anything to fill that need, but I have time. Thanks again for the help.

Noobz347 · Nov 21, 2025

Mcmahst said:
I have a SD system. Does it matter?

Yes. If you're not metering air, you should be able to get away with a breather that does not have a check valve.

The down side to this is that your PCV scavenging will include any air pulled through the breather. Not a [huge] deal but it can affect how quickly your oil gets dirty.

Also, you can plumb that vent tube into the inlet right before the throttle body, if that helps ( since we still don't have any pics ). Just drill a hole and install a fitting or barb.

FastDriver · Nov 21, 2025

It's essentially a vacuum leak if you still have a PCV system, but not a problem for SD. Depending on how freer flowing it is, you might have to adjust the throttle stop to maintain your original idle RPM. Just run it both baffled and filtered. The only negative trade off I can think of is that you're going to have oil vapor in the engine bay, whereas any of that would normally be drawn through the intake & through combustion. Plug the port on the TB.

Mcmahst · Nov 21, 2025

Ok, this photo is not my current 73 Vert, but when this engine was in my 73 Coup, but the principle/issue is the same. I could run a tube to the straight section of the air cleaner housing hose (just after the air cleaner housing) to that nipple on the oil fill tube on the passenger valve cover. I noticed when I reviewed my photos that the actual hole in the throttle body, where the current fresh air enters the tube, is slightly smaller than the ID of the tube. So, I could put a small restriction in the line to reduce air flow.

I don’t agree that it would create a vacuum leak; no more than the current design. They’re just using the stock air cleaner to ensure the air entering the crankcase is filtered. You could put a filter on that hose as a stand-alone and it would function in the same way. But, I like the idea of making it look like it could have been stock, so taping into the duct sounds like it would work.

General karthief · Nov 21, 2025

Mcmahst said:
so taping into the duct sounds like it would work.

All it needs is filtered air so yes anywhere between the filter and the TB will work.
If it was MAF it goes between the meter and the TB,
Just think'n, now I have a headache....

FastDriver · Nov 22, 2025

Mcmahst said:
Ok, this photo is not my current 73 Vert, but when this engine was in my 73 Coup, but the principle/issue is the same. I could run a tube to the straight section of the air cleaner housing hose (just after the air cleaner housing) to that nipple on the oil fill tube on the passenger valve cover. I noticed when I reviewed my photos that the actual hole in the throttle body, where the current fresh air enters the tube, is slightly smaller than the ID of the tube. So, I could put a small restriction in the line to reduce air flow.

I don’t agree that it would create a vacuum leak; no more than the current design. They’re just using the stock air cleaner to ensure the air entering the crankcase is filtered. You could put a filter on that hose as a stand-alone and it would function in the same way. But, I like the idea of making it look like it could have been stock, so taping into the duct sounds like it would work.

No, it literally is a vacuum leak in the sense that its air that enters the intake's vacuum port, bypassing the throttle body. But you're right that it may not be any more airflow than stock. My point is that IF it is, it will idle differently, and then you can adjust the stop screw as needed to reestablish idle.

Mcmahst · Dec 5, 2025

Well, I finally got back to Az to install the hood to verify my clearance issue. I didn’t do the greatest job installing the hood. No hinges, bumpers, etc. Just laid it on top, when it would sat, x and y. I wasn’t able to get any pics since it was a tight clearance. I did mock-up the front latch to get the front height close to correct, and then did the same on the rear quarters.

After all of that, it appears I have about 1/4” to 1/2” of clearance at the top of the highest point on the throttle body. I think I’m gonna be ok. I won’t know till next year as I’m at the start of my one yearish body/paint process. I still have the idea to relocate the crankcase fresh air tube if it turns out I’m wrong. Thanks again.

manicmechanic007 · Dec 20, 2025

Unmetered air is no good
but
Early carbureted 1.6l Escorts had adjustable altitude compensators that were essentially controlled vacuum leaks
That would be considered metered air
We had to play with them to get them to pass I/M when it started for us in 84
You can put them in the PCV hose of an old hotrod to lean them out some

Engine Crankcase vent tube “relocation”?

Mcmahst

AeroCoupe

lube between the nut and the face. I know my lubes

Vintage Mustang Forums

KRUISR

Noobz347

Stangnet Facilities Maint Tech... Er... Janitor

Mcmahst

AeroCoupe

lube between the nut and the face. I know my lubes

Mcmahst

AeroCoupe

lube between the nut and the face. I know my lubes

Mcmahst

AeroCoupe

lube between the nut and the face. I know my lubes

Mcmahst

Noobz347

Stangnet Facilities Maint Tech... Er... Janitor

FastDriver

I was uncomfortably high & wearing a helmet

Mcmahst

General karthief

wonder how much it would cost to ship you a pair

FastDriver

I was uncomfortably high & wearing a helmet

Mcmahst

manicmechanic007

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Engine Crankcase vent tube “relocation”?

lube between the nut and the face. I know my lubes

Stangnet Facilities Maint Tech... Er... Janitor

lube between the nut and the face. I know my lubes

lube between the nut and the face. I know my lubes

lube between the nut and the face. I know my lubes

Stangnet Facilities Maint Tech... Er... Janitor

I was uncomfortably high & wearing a helmet

wonder how much it would cost to ship you a pair

I was uncomfortably high & wearing a helmet

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