Which one; pre or post turbo?

[sturgeon-phish]

Finally (really this time) going to get the gauges. Going with a triple pod pillar, Boost, tranny temp and EGT from Kennedy. My BIG question is EGT pre or post? I've read the threads over and over for each the pros and cons. I'm leaning to the pre turbo but the drilling and tapping for the probe has me concerned. How is the best way to get access, to drill and tap with grease loaded bits and tap?
Or should I just got post turbo? Thanks ahead of time
Jim

[cudaaa]

Pre turbo will give you the most accurate temps. I removed the tin cover on the turbo. There is a flat spot on the manifold. I drilled mine with air blowing accross the bit then tapped with grease loaded tap fitted to a socket with an extension. If you have a tool pickup magnet that fits threw the hole use that to help clear out the metel shavings. Install your probe with antisieze, when you start the truck bring it up to about 2000 rpm for a short time to blow out what ended up in the manifold. Hope this helps cudaaa

[DmaxMaverick]

Drill/tap with the engine running at idle. The air (exhaust) coming out won't be hot (believe me), and will blow out any chips. Don't use grease. If you think the air coming out is too little, block the exhaust pipe slightly (piece of wood works well...don't plug it completely) to increase the backpressure while drilling/tapping. It doesn't take much. Be sure to wear a face shield because the chips fly out. Get the engine up to operating temp (hot manifold) and drill/tap slowly, don't stress the cast iron (prevents cracks later). Drilling or tapping cold cast iron can lead to cracks after several heating cycles. I've done this several times with 100% success.

Using grease on the drill bit and tap is not a very good idea. It does cause chips to stick to the bit/tap, but grease will also stick to the inside of the manifold, and some chips will stick there, also. The best method is to use a completely dry bit and tap, and make sure they are sharp. Drilling a small pilot hole first will decrease the likelyhood of any chips falling inside. Just make sure the engine is running during any drilling, tapping, or reaming.

Use a nickel based anti-seize (messy silver stuff) when installing the bushing, and do not overtighten.

[Hubert]

Drilling / tapping cast iron hot instead of cold ????

Thats the first time I have ever heard that. Not that that means a whole lot but I do have a lot machining experience with padded reamers and fine hole making. Would you mind explaining that a little more and where that comes from.

My first thought is not tap it warm with a cold tap. Especially with a tappered tap (NPT). Because as a cold tap warms up to a hot manifold temp it would grow in size and have some extra force trying to split the hole open especially if you did not work tap back and forth enough. Maybe not a lot but I can see it stressing material and tap a little. I'd work the tap back and forth to break chip and keep tap as loose as possible. Cast Iron the chip is small usually anyway.

Chip evacuation is really important in any machining. Anytime you "smear" a chip into a workpiece or build a chip wad it really increases tooling load and material stresses. The size of the chip, sharpness of tooling, and lubrication also greatly affect workpiece stress.

I would highly recommend not using a dull tap or drill. Cutting oil or tapping fluid etc is much better than grease for machining but something is better than nothing. They do make tapping "greases".

on edit

For this application where you want chips to blow back out a light bodied tapping fluid is probably most desirable lubricant. Drilling dry with sharp bit is probably ok but I would not tap dry.

[DmaxMaverick]

I know it goes against what you know, but it is better in this case. The heat we are talking about is very mild, compared to heating/welding. The tap will not expand any appreciable amount, and because it is tappered, it does not matter. It's should be always moving. The bushing will have the same condition once it's installed, and if not tight enough, it WILL loosen up, and cause cracking. Heating up the cast allows the metals to normalize, and will hold in place much better, and both will contract at the same rate. I do agree that frequent back-turning is necessary to keep the cut clean. It's important to CUT the treads, not gal them. I will repeat that it is better to tap dry. Slow and easy, with much back-turning. A sharp tool will have no problem, unless the cast is cold. The best option is to remove the manifold and complete the job on the bench, but installation of the bushing should be while the manifold is at least at idle tempurature. Believe me, if you don't do it this way, you greatly increase the chances of cracking. I've done this many times and have seen the long term results, of both methods.

[sturgeon-phish]

I will go with the pre turbo, your replys have given me the confidence. With the turbo heat shield removed, will that give me access to do the drilling and tapping or as I've read on other threads, will it be necessary to remove the inner fender?
Thanks again for your replys!
Jim

[DmaxMaverick]

I will go with the pre turbo, your replys have given me the confidence. With the turbo heat shield removed, will that give me access to do the drilling and tapping or as I've read on other threads, will it be necessary to remove the inner fender?
Thanks again for your replys!
Jim

You could probably get away with it if you have an angled drill, but vision will be a problem. I suggest you remove the inner fender so you can get a straight look at it. It's important the hole is drilled and tapped straight.