Curtas

Hey guys,
I just got a copy of Onpol's turbo manifold. It is built for the T03 (Garrett, Turbonetics, etc). My turbo is a T25. It's only slightly too small for the holes. So I have two options:

Widen the holes just a bit on the manifold flange

or

Build an adapter plate.

Widening the holes would not be hard, and there's plenty of metal. The smaller hole would only overlap the larger by about 1/3rd. I'll try to post a diagram tomorrow. I think with a big enough washer and a through-bolt, I could get adequate sealing of the turbo.

Building an adapter plate would also not be too bad, but it costs money, which could go to other parts of the project. a 5/8" thick, 3"x4" steel plate costs ~$20, plus eight studs, washers, and nuts (not to mention about three hours of me machining the hole, tapping for the studs, etc). Overall, it will cost about $40, which isn't a lot, but I don't want to overkill it . . .

plus an adapter is another point for failure or exhaust leak.

Any thoughts from you turbo or machinist guys out there?

ac

Viper966

spend the 40 bux and do it rite

Veniston

You're talking about the bolt holes?

If there is enough metal I'd try widening, as a general guess smile.gif I can't tell you it's the right way to go though without seeing it.

Bascially if there seems to be enough support, go for it. If you're getting close to a weld it becomes a bit more iffy; and if you're shaving into a weld--well you never know when you'll hit an inclusion, it's pretty much begging for a hole or crack.

And anything will seal if you torque it down hard enough. What you want is to maintain a good amount of flat surface contact area, the more you get the easier it seals. Are you comfortable with the contact area after the mod?

I'm not machinist but have designed some custom metal stuff & had it built in the past--I'd probably do the widening for myself, but I wouldn't necessarily sell it to a client

Random

Go with the adapter plate. If you machine too much material away from the turbo, you can cause the turbo to break under load/thermal load. Ditto for the turbomanifold. Keep in mind the heat extremes those two pieces go through.

Curtas

Well, I did better measurements and held it up to the actual manifold, and while widening the holes won't interfere with the welds or pipes, there won't be enough room for a washer. 1/8" in any direction and I'd be fine, but oh well.

So I made a bunch of CAD drawings and will take them to a steel shop on Saturday to see what they have. The guy said there's a lot of scrap that they'll sell for cheap, so maybe I'll find something good.

Question about studs. I've seen some really expensive ones that are tap/fine on one end (the manifold have a smooth center section, and then are coarse threaded on the other end for a nut. I've also seen studs which are just threaded rod, the whole length. Any advantage to either?

thanks for the inputs,
ac

Veniston

Get the threads that work best for your application--if there is a big difference in price I'd suspect it was due to the material. I've seen threaded rods made out of cast iron, not the greatest for tensile strength.

A more 'coarse' thread has less contact area (metal-to-metal surfaces) than a fine thread, therefore less static friction holding it in place. Untreated, it will be more likely to vibrate loose. Fine threads have more contact area, but are also more prone to stripping(as I'm sure you've experienced). They can't take the same torque.

Random

"coarse" thread is better for materials with high thermal variances. "fine" threads are better for thermally stable materials.

The "coarse" thread allows for more room for uneven thermal expansion of the 2 metals.

In other words, on hot turbo parts that go from ambient to 1500 degrees, use coarse thread. On parts that stay near ambient temp, use fine thread.

You should also choose your bolts to match the metals you are using. Aluminum and Iron have vastly different thermal expansion rates, and vastly differ thermal load rates (heat up faster or slower). If you mis match the metals and bolts, you can break a bolt or seize a bolt.

Also, some materals should never be mixed. Aluminum should NEVER be mated to cast iron unless seperated by a gasket material. This includes Iron bolts in aluminum heads. There is an exchange of ions between cast iron and aluminum that causes both parts to corrode and seize. This is accelerated by heat.

I found most of this out the hard way with my apline turbo. They used aluminum bolts to hold the heatshield in place. 3 of the 4 bolts "snapped" off because the aluminum bolts had "coroded" themselves solid with the cast iron turbo manifold. I've tried 4-5 different "extractors" to attempt to remove the bolts. No luck. I am now forced to send the turbo manifold out to a machine shop and have the bolt holes reamed and re-threaded.

Curtas

cool. thanks for the advice. The manifold is steel (not stainless, though), and the turbo is steel, so I'm looking at a steel adapter plate.

So I'll probably look into 300 series stainless for the bolts, or 316 steel. I'm looking at around 18 to 24 threads per inch on the rods. that's what our manifold bolts are, that's what the stock turbo bolts are (that hold the exhaust elbow on).

I've been worried about the heat expansion all along. I'm going to use metric studs (I have a metric tap set) with about 0.75 mm clearance on each side. This should allow thermal expansion and shifting to occur without breaking the manifold, turbo housing, or studs (I'd hope the studs would break first smile.gif )

Now to find some scrap steel . . .

ac

DESIGN

I would recomend that you have the "adapter plate" welded to the manifold. The main disadvatage to this idea is it limits your chances of upgrading your tubine in the future. It will however limit your concerns about a leak.
I am somewhat confused about how the turbo mounts to the manifold. Is the manifold "tapped" or threaded to accept the bolt or does the bolt pass through it to be fastened by a nut on the back side? I thought that most turbo manifolds had studs affixed to them. Then the turbine housing would slide over them and be affixed with nuts. Do you have holes in both the turbine housing and the manifold? Are all these holes threaded?
Also when or if you build the adapter plate make sure that you ask many questions about the thermal properties of the steel that you will be using. Scrap steel is cheap and in many cases very reliable. The problem is that it usually comes from a pile of leftovers and no one can tell you anything about it. It may be worth your time to buy some new plate and be able to pick the quality. Also consider fabricating some copper gaskets to fit between the plate and manifold as well as the plate and turbine housing.
For the best studs, bolts, and other related fasterns contact ARP. They build the best fastners for automotive use. According to RED he is using them throughout his "MADD BOOST" engine. This is exactly where trying to save money is not wise.

[ March 07, 2002, 05:41 AM: Message edited by: DESIGN ]