View Full Version : drill and tap edelbrock manifold

10-22-2012, 12:35 AM
I have a Edelbrock RPM Air Gap manifold on my 340. That manifold only has one heater hose port in the front. I have my mechanical temp gauge sender on that port. I am wanting to install a heater in the car. Can I tap the other side of the manifold in front with another heater hose pipe thread the same size without too much trouble? I would like to do it without removing the manifold if possible. The regular RPM manifold and not the Air Gap has heater hose ports the same size on both sides in the front but the Air Gap only has the one and I'm already using it for the temp gauge sender.
It is the same size thread for the hose port in the top of the cast iron water pump. (68, 69) One more question, anyone know what that size pipe thread is? (maybe 3/8 pipe thread? don't know.)
This is clear as mud isn't it? Anyone got a clue? Thanks

10-22-2012, 05:32 AM
If there's a "thick spot" no problem. Be careful. If you try and drill anywhere that the watter passage is just normal thickness, there very likely is not enough to seal. But the only photos I've found in a quick search of the www looks to be several ports on that manifold. Can you post a photo? What is the manifold part no?

10-22-2012, 09:02 AM
You could use a tee. But it seems to me there should be a smaller threaded hole for the temp sender.

John Kunkel
10-22-2012, 05:37 PM
The RPM Air Gap should have three threaded ports in the front, two large and one smaller 1/8"-NPT for the sender.

10-22-2012, 08:54 PM
The manifold is a 7576 Air gap for the small block chrysler but it might be one of the first air gaps. It still looks new but I got it with a 340 I bought off of ebay a few years ago. It does not have the two larger holes on each side like in the picture you sent. It just has the one larger hole on the drivers front and two smaller holes on the drivers side front. It does have the part number 7576 on the rear of the manifold I will try and post a picture of it shortly. My temp gauge is a Stuart Warner mechanical and has the larger size pipe thread that fits the only larger hole on the manifold in the front. The only other hole that size is the vacuum port on top of the manifold on the passenger side just behind the carburetor. Thought maybe I could just drill out and tap one of the smaller holes and enlarge it to the size I need. It should be thick enough there but I hate to screw it up.

10-22-2012, 09:12 PM
What about using an adapter on the gauge hardware to decrease the pipe size? Hardware store items.

10-22-2012, 09:25 PM
The size of the thermostat itself that goes inside the hole is too big (in diameter) to go into the smaller holes. I could go to an electric gauge but I hate to do that. The electric sender is made to fit the smaller diameter threads.

10-22-2012, 09:27 PM
Tried uploading picture but won't upload it for some reason. Gave up. Going to watch debate.

10-22-2012, 11:34 PM
I would bet you can drill and tap one of the smaller holes. Most mechanical gauges can be installed into a 3/8" pipe thread with the proper adaptor. These are a proprietary fitting, not a standard item. Normally comes with the gauge, or you can order it from whoever made the thing

10-23-2012, 12:21 AM
picture of manifold

Rich Kinsley
10-23-2012, 12:28 AM
I just swapped my brand new still in box Weiand 7503 manifold for another 7503 manifold that has been modified so that I can switch to FastEZ EFI. It has had several drilled and tapped holes for extra uses.

This is for my 318 poly but it's still the same principle.

10-23-2012, 09:08 AM
So you want to put that big brass sending unit that is to the right of the thermostat into one of the small plugged bosses to the left of the thermostat? Looks like there is plenty of meat there to drill & tap the boss closest to the thermostat to the next size or even 2 sizes.

.................................................. ..................................

How to Measure Threaded Pipe and Pipe Fittings:
Pipe size is an industry designation, not an actual size. Use a ruler to measure the outside diameter (OD) Then, round up the measurement to the closest OD listed in the chart and select the corresponding pipe size.

5/16" OD = 1/16 NPT
3/8" OD = 1/8 NPT
1/2" OD = 1/4 NPT
5/8" OD = 3/8 NPT
3/4" OD = 1/2 NPT
1" OD = 3/4 NPT
1 3/8" OD = 1 NPT

10-23-2012, 01:46 PM
Yes that is what I will need to do but I'm not sure of the size. It needs to be another one like the one my sending unit is using. I intend to use it for a heater hose. I wanted to email edelbrock and ask them what size it was but they no longer use email for tech questions. I guess I will call them instead.

10-23-2012, 02:14 PM
Talked to Edelbrock tech line. They said the large heater hose port on the front of the manifold is 1/2 " pipe thread. He also said the bosses on the other side can be drilled and tapped to 1/2" pipe. I will try it I guess. Thanks for all the help.

10-23-2012, 03:40 PM
I would AVOID 1/2" if at all possible. It's just that much larger, just that much more invite for trouble. Depending on who made your gauge, you should be able to get the piece which fits the intake down to at least 3/8. For the record, a 3/8 pipe nipple is JUST RIGHT for 5/8" ID heater hose!!

10-23-2012, 04:07 PM
You know after I talked to Edelbrock tech guy I looked at the one on the manifold that he said is 1/2" pipe thread and I believe it is actually 3/8"
1/2" is a lot bigger than the one on my manifold. I hate to say he is wrong but it can't be a 1/2"

10-23-2012, 07:18 PM
Measure it and use my table in my previous post to determine the NPT size. I'm almost positive that's a 3/8 NPT.

John Kunkel
10-24-2012, 05:09 PM
5/8" heater hoses need a 1/2"-NPT thread, 1/2" hoses can get by with 3/8"-NPT.

John Kunkel
10-25-2012, 07:09 PM
Here's an alternative to drilling/tapping the manifold, Vintage Air makes a spacer block to go under trhe thermostat housing that's drilled and tapped 1/2"-NPT.


10-26-2012, 02:18 AM
John, Thank you very much for the info. I did not know anything like that was available. That is probably the best rout to go. It should work well with routing of the hose down on front of the engine and along the frame to the firewall.

10-26-2012, 12:15 PM
Here's an alternative to drilling/tapping the manifold, Vintage Air makes a spacer block to go under trhe thermostat housing that's drilled and tapped 1/2"-NPT.


That IS an interesting piece

10-26-2012, 07:06 PM
I wonder if my chrysler hose inlet top will fit on that Vintage air water neck riser or if it is made for a chevy engine only. I know the chrysler thermostat that fits this manifold is quite larger than the chevy. I will have to contact Vintage Air tech.

10-29-2012, 11:26 PM
Vintage Air contacted me today and told me that the water neck riser they sell will not fit a small block chrysler intake or the Edelbrock intake for the chrysler. He said it is made to fit a chevy and probably could not be adapted to the chrysler. So I guess its back to trying to drill and tap the manifold.

John Kunkel
10-30-2012, 03:55 PM
Sorry, I musta had a senior moment. I knew it was for Chevy but I intend to make one like it for a Mopar and got confused. :zzz:

10-30-2012, 10:11 PM
My vote would have been for a T under the original sender at first, but looking at this part manufactured for GM's, I would be tempted to take that pic, a thermostat and the manifold to a machine shop and see what it would cost to make a Chrysler one... could be a market for a limited number of these through a major supplier.

10-31-2012, 01:58 PM
I am pretty sure you can take the one for Chevys and elongate the holes a little to fit the Mopar bolt spacing.

11-09-2012, 04:17 PM
I know i'm late to this post, but they do make that thermostat adapter for
chrysler small block. Had one on our circle track car. I think it came from either Speedway motors or possible Jegs.

02-17-2013, 12:35 AM
this may be a dumb suggestion, but could he maybe run it off where the bypass is??