Thinking of Turbo...

So we're in the process of getting the 300 in the bus rebuilt. I've talked to a couple guys locally who have experience with big sixes in big old vehicles and they all tell me that the best way to maximize the potential of one of these things is with a turbocharger. So I figured 'why not?' Not now of course- we have a long way to go before we can really start having fun. But what I do want to do now is build an engine that will be capable of handling a boost of around 7-8 psi max, nothing fancy just want to increase potential output when needed: acceleration and hills. So far I am planning on going with hypereutectic pistons and aluminum timing gear set.

My first question involving component selection is (of course) in regards to camshaft selection. I had been thinking about the Isky TurboCycleA # 331-TA , it seems to me like it's pretty similar to a ''rv type'' cam with adv duration 265/260 and lift of .445 .415 but shorter on the exhaust to favor the conditions of a turbo setup. Now I was under the impression as was the builder that we could build up an engine with the intent of going to a turbo later on, and in the meantime it would operate fine with the stock intake/exhaust setup, when I called Isky to ask about cams I was told that the engine will not function at all with a turbo cam and no turbo. The tech guy told me to go with the 256 super cam instead and that if I wanted to add a turbo later I would have to switch out the cam to the turbocycle. Now what I was trying to avoid is having to break into the engine again when it comes time to turbocharge it (hopefully no later than 6-9 months from now). Is it possible to build an engine for the purpose of turbocharging but running it with stock intake and exhaust for a while before completing the upgrade to turbo? Or is it a matter of building it for specific application (non-turboed setup) now and then having to rebuild it again when the application changes (going to a turbo setup)? Any and all help is greatly appreciated!

Way cool project!

The engine will run just fine with a turbo cam, but it will be down on power when campared with a "normal" cam.

A better option might be to get a cam that'll be a good comprimise for both turbo and N/A.
Try and get one with 110-112 lobe seperation, as much lift as you can, and limit the amount of valve overlap and you'll be good!

Later,
Will

I have to admit a cam sap on a big six is much easyier than on almost any other engine.
Its just a timing cover, lifter cover, and valve cover away. All mainfolds stay put during a cam swap.

Now as far as if it will run ok without a turbo installed I am not 100% sure. But i think it would run just not up to its potential like it could with it.
It will be down on power anyway becasue the compression that would work well without a turbo is NOT what you run with a turbo.

Does10s":ywe0geay said:

Way cool project!

The engine will run just fine with a turbo cam, but it will be down on power when campared with a "normal" cam.

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Yep, especially with regards to overlap, specs that make NA motors happy will make turbo motors less happy. In general running a turbo on an NA cam will net you better results than NA on a turbo cam. The overlap (or lack thereof) will kill you.

80broncoman":ywe0geay said:

I have to admit a cam sap on a big six is much easyier than on almost any other engine.
Its just a timing cover, lifter cover, and valve cover away. All mainfolds stay put during a cam swap.

Click to expand...

Yeah, I would swap cams, personally, especially if there is going to be any length of time you're trying to run a turbo cam without a turbo. It'll make you sad.

It will be down on power anyway becasue the compression that would work well without a turbo is NOT what you run with a turbo.

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It's not really that simple, since 7-8psi is *very* modest. At those boost levels, you don't need an intercooler and should be able to run totally reasonable compression provided you can supply the fuel. Unless you just want big numbers, I am always a fan of relatively high compression and lower boost - let the compression get you moving, and the boost make up for breathing inadequacies at higher engine speed. Since you are not trying to cram a big engine in a small space you should have plenty of room for an intercooler or water/meth injection (or both), and I'd be inclined to built a stout, high-ish compression engine and then breathe on it a little. That will result in a nice, streetable engine. The key is keeping intake temps down (right-sized turbo and/or a charge cooler) and getting enough fuel in there.

The cam I am running on my turbo 300 has more overlap than I would like, but when the power band for the cam does kick in, the boost comes right up to the wastegate with out hesitation. If I keep it in that RPM band, it performs well. Around 2500 RPM or so. It runs well in the lower RPM ranges, but not as well as it could. The turbo in the exhaust stream really cuts down on performance naturally aspirated, or any MAP atmospheric and lower.

Thanks, you guys a great asset!

Looks like we'll be going with a more 'RV' type cam for now and when the Turbo comes along we'll think about swapping them out. Now, is there there any specific parts upgrades you guys would recommend with the idea that the engine will be turbocharged later one? Like I said before I'll be going with hypereutectic pistons at the least and metal timing gears. The Builder tells me he can get stainless steel valves for only a couple bucks extra per, so we'll probably do that as well. All your help is greatly appreciated.

For 7-8psi I am not sure I'd make any real investment in the engine. Good quality as-stock components are probably going to be fine for such modest boost. If this was 1960 again I would probably advise otherwise, but modern casting techniques are pretty good, and low boost like that shouldn't generate a lot of heat. Just make sure you choose rings that are designed for boost, and that your valve seals and guides are good quality, especially on the exhaust side. Boost and related temperatures are hard on that stuff!

If you have money burning a hole in your pocket, I would positively spring for forged internals. Not necessary, but IME boost is addictive and there is always the temptation to see what just 3psi more feels like. That's how my Saab went from 13psi to 22psi. Heh. Forged internals will result in a lower weight while adding substantial strength over even hypereutectic cast pistons. Up top, "stainless steel" is a vague descriptor of a valve, since that term describes a wide variety of alloys. The exact composition will lead to difference performance, so it's important to know what that composition is. Be sure whoever is building your head knows you plan on running boost, since that will influence material choices. Intake valves run cooler, but constant fuel tends to wash away oil - as such, a high-wear alloy is preferable. Exhaust valves don't have to deal with fuel but get baked by heat, especially on a boosted motor - on that side, heat tolerance is going to be more critical than wear resistance. Point being, you will probably want different intake than exhaust valves, each optimized for the intended duty. Assuming, of course, you have money burning a hole in your pocket.

Not sure what head you are going to be running, but if you've got a discrete exhaust manifold I would encourage you to look into ceramic coating it inside and out. Ceramics not only help reduce underhood temperatures, but also help keep heat in the exhaust stream where it can help the turbo work. Related, don't buy into the old hotrodder's myth about "back pressure." That was a term to describe a phenomenon (resonance) nobody understood. On a boosted motor, the goal is to move exhaust from manifold to downpipe as efficiently as possible. For all intents and purposes, your downpipe cannot be too big! An interesting concept which is gaining traction now is actually an exhaust that narrows in size as it goes along. Exhaust is hottest - and thus has the largest volume - immediately after the turbo, but as it cools it contracts. A big 3" or 4" chamber directly after the turbo that narrows to something manageable is not flawed, and gives you good performance without a goofy sized pipe hanging out the back. Of course, on a bus, a 3" exhaust from tip to tail probably wouldn't look misplaced.

There are a lot of neat things that you can do with boost, and in 2011 the cost of doing them isn't high. Intercoolers, water/meth/alcohol injection, compound turbos (the bee's knees!), huge mandrel bent exhausts. You can go nuts with this stuff.

But 7-8psi is nothing. I wouldn't worry too much about it. Just be sure your fuel system is built to handle it... the metal parts will do just fine.