I'm having fun spending money for my turbo 170 project. For a while I was on the fence thinking I might run stock pistons and cast rings, but decided against it. I bit the bullet and ordered ductile top rings from Total Seal and now custom pistons from Venolia. They aren't terribly trick as they are flat tops with the stock 5/64" ring package. I did spring for .875" tapered pins in 4340 steel and will have my rods bushed to match. I went with the smaller pin to keep more material in the small end of the rod. Since I plan on using a good windage tray and crank scraper I also opted for the pin oilers. It ended up a little over $75 a hole with pins and options.

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Joshua

By "custom" you mean what?

What specs did you give them?

How does a bushing leave any more metal in the rod? You're going to have to remove some metal to insert the bushing - a bushing to remove no metal would only be 13 thousandths wall (.9008â€￾ - .875" = .0258" = .0129"), definitely not safe. That makes me very nervous - one more thing that requires precision machining and heat-sensitive interference fit that has huge consequences if it fails. Going up to SBC size .927" only takes out .0262". My feeling would be to retain the stock size, float it, and use whatever pin wall shape they suggest for turbo. Bending stress is resisted by OD much more than by material thickness.

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By custom I mean not off the shelf. Different CD, different pin diameter, valve reliefs, etc. The ring package is stock, but that's about it.

For specs I filled out the order sheet on the Venolia web site and spoke with a tech about what I wanted. http://www.venolia.com/images/form.pdf

Fitting a smaller bushing leaves more of the original rod intact than a larger bushing. The rod will still have to be bored for the bushing, but a smaller hole for a smaller bushing. That's why the smaller pin. I know it's only ~.026" smaller, but I feel the extra material needs to be in the rod rather than the pin. It's a lot cheaper and easier to spec a good pin than use different rods. You could float the original size pin, but Venolia doesn't have stock size pins so it was easier to go this way. Does anyone actually make bushings for .9008" pins?

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Joshua

Yah, I was afraid of that - they can't work with the stock pin size, bummer.
Did you ask for the ring stack to be moved down, extra land thickness, heavier dome etc. - I think they prompt you for this if you say turbo?
The ductile rings are definitely what you want -they can live with some detonation that would kill anything else.
Do you have a cam spec'd out yet?
How about head work?

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We floated the pins in my first long rod motor steel on steel. It lasted a very long time, but they were pretty beat when we took the motor apart. It had been together 4 years, and had 1500 passes at the track and 50,000 street miles. I drove it most of the time with 3.91 gears in it too.

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Official Cookie and Mater Tormentor.

They can put whatever size hole you want in there for the pin, but it will be up to you to supply the pin and have it fitted to the piston.

I made sure the tech I worked with knew it was a turbo motor. They are the pros so they better get it right. I'll double check with them today just to be certain they do get it right. I do know I'm getting double spiro-locks and pin oilers.

The ductile rings are on order too. Just ductile top rings were $104.

I'm thinking of a cam with 270° advertised duration, 224° @ .050" lift on 114° centerline is what I'll use. Some people will think this is too much, and may even have experience that indicates it's too much overlap. My argument to them would be that they used too small a turbocharger with a much too small turbine and had a lot of exhaust pressure. Can you tell I'm not going to be using a tiny turbo?

I have some 1.70" and 1.44" valves that will probably go in the first head, but I'm not married to that idea either. I spoke to Mike Jeffrey about a head, but it would be about $1200 for what I want and I wouldn't have the completed head until December. The Ford 300 valve head I did for my last hot slant worked out pretty well so I'll do the first head for this engine with my regular Mopar machinist. I just ned to find some exhaust valves that will take the heat.

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Joshua

I would certainly not use the common valve oversizes, but begin with the largest exhaust valve that clears the wall, then notch the bore edge for clearance. Intake valve size = what's left.
Vizard makes a strong argument for cams like this:
IO: 35 ATDC
IC: 55 ABDC
Intake duration: 200
CL: 135 ATDC
Intake needs a big lobe, fast ramp and high rocker ratio
XO: 54 BBDC
XC: 0
Exhaust duration: 234
CL: 117 BTDC
Overlap: -35
LCA: 126
Engine is SBC, 28 psi, 1000 hp.

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David Vizard sure knows his stuff. I own three of his books. Do you have any more information on that turbo engine such as a full magazine article? Also what type of cam is that? Hyd flat tappet? Roller? It's hard to get a real big lobe or a high rocker ratio for our engines.

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Joshua

Panic, why would one want the Intake to open 35' AFTER the exhaust closes? (-35' overlap)

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Cheers!
Al T

Called Venolia again this morning. Since the pistons are for a turbo motor they automatically move the rings down and make nice heavy ring lands. The compression distance is 1.770" and the valve reliefs will be .100" deep. I specified 8.5:1 compression and a .039" gasket thickness and this is what they came up with. And I agree. I'm very glad I checked the deck height of the 170 since Venolia thought is was 9.68". That would have been a disaster.

I'll be able to adjust the compression ratio a little with chamber work or milling. I told Venolia a 55cc chamber which is probably a little small for my unmilled head so my actual compression ratio will likely be closer to 8:1 which will be just fine.

Gee custom pistons are nice. I get to keep nice thick decks on the block and head and still have the compression ratio I want.

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Joshua

Just wandering, what size turbo you going to use? You going to make a custom header?

The turbo will be either a T04E 60 trim or a 60-1. I haven't yet decided what I'll do for the manifold. I may cheap out and with fingers crossed buy a new cast iron manifold and modify it or I may buy header flanges and fab one. I keep focusing on the engine internals, but first I really need to mock up the alternator (as it's going on the power steering mount), manifold and turbo. I don't want to risk FOD (foreign object damage) to my new engine by playing mock up on a fresh assembly.

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Joshua