I read something in a post recently that made me think turbos like strokers. Something about reduced chance of detonation. Does stroking the engine help in a turbocharged setup? I'm thinking of a very long stroke and a mild cam (for the off idle torque and nice driveability) with the sts turbo kit for the serious power if you need it. What do you all think?

 

Since turbo's add the same amount of boost regardless of engine speed, they register huge low-end torque numbers. For instance, the 3.8 Buick turbos made 345 ft-lb at 2000 rpm. So, you can imagine what you get when you turbo a 5.7 liter motor.

In my opinion, by stroking and using a small cam in a turbo motor, you are possibly compromising top-end by adding to the already-abundant low-end torque inherent to a turbo motor.

Centrifugal supercharged motors, however, need a reasonably small cam and stroker crank to get the low-end they never had from boost.

However, if you want tremendous low-end torque, by all means, stroke it and use a small cam. Be prepared for 700+ ft-lb of torque at 3000 rpm and hope you have a good enough transmission, rear end, and tire.

Mike

 

What I'd really like is the torque curve of a big block. It starts off idle and acts like a hairy beast on a mixture of crack and pcp. In other words. I love the idea of 700 tq. I would like to avoid the sudden hit and the normal tq that you get before the boost hits, though. Well, I take that back. The sudden hit would be great, assuming I didn't break traction and it didn't happen unexpectedly. Gotta hate it when that happens in the middle of an on ramp.

 

What you're going to get is 400 ft-lb when you stomp it and another 300 ft-lb a second later when the turbo spools up.

The turbo set-up will not give you instant huge torque and lightning-quick throttle response. For that, a stroker or roots blower would be required.

Mike

 

That's why I'm thinking of stroking it. I havent seen any roots s/c that fit under the cowl of an f-body. It's driving me nuts. That's the perfect solution to my problem, but it can't happen. That is unless I get the cowl remodeled and cut back, then resealed.($$$$$$$$$$$) I would also have to have the windshield remade. (More $$$$$$$$$$$) Then I'd have to get an aftermarket injection setup. (Cubic $$$$$$$$$$) By the time I was done, I could have bought a top fueler.

 

guy named alvin on here done it pretty cheap. think his screen name is rooster or something like that.

check him out...

 

What I meant by stroker was a high compression, naturally aspirated 396. It would have very quick throttle response (unlike common turbo-lag) and huge torque output - probably around 425 ft-lb off idle and 500 ft-lb peak.

A turbo will not give you the tip-in off-idle torque I think you're looking for. Even with a turbo'd stroker, the off-idle low end wouldn't be that great because of the low compression.

Mike

 

Thanks for the tip. I searched and found him, then read his posts. He's rooster93v8. That setup is exactly what I'm looking for, only on a 383. (Gotta have that stroke, dontcha know) He's running about 9#, but since he's using the same size blower that the Lightnings use, he figures it should be able to run a lot more. Time to break out the water/methanol injector. He has to deal with speed density, but he burns chips for a living, so thats not too bad. I need to find out if he's going to make kits or at least sell detailed plans. I also need to know how it would be different on a newer car (not speed density).
He kept his price down because of several things. The blower was real cheap. He had some of the parts already. He may have traded some work, but I'm not sure about that. Even so, it would still be fairly inexpensive for the rest of us. Like I said, that suits me to a T.
After reading up, I've found one drawback. Apparently these type of blowers like to lift the head and blow the gasket. Why it would be more of a problem with this than comparable boost at a different rpm, I don't know. I've just read that it's more of a problem with a roots. Head studs, anyone? When the rings go or a piston dies, then O-ring the block. If you want that type of low end torque, that's a small price to pay in my opinion. It should probably be done in any high boost situation, anyhow.

 

Roots blowers (especially small ones) tend to blow head gaskets because they are very inefficient. The adiabatic efficiency is around 40% compared to 70% for centrifugal superchargers. This low efficiency causes the boosted air temperature to increase to abnormally high levels. High temperature boost causes detonation, which leads to blown head gaskets. O-ringing the block fixes the symptom, not the problem. It would be better to find a way to avoid detonation.

The Lightnings don't have this problem because of their large water-to-air intercoolers.

Mike

 

I don't know how I could fit an intercooler in the f-bod. Water/methanol might work if I could figure out how to inject it. I really know almost nothing about forced induction, but I've sure found a good place to learn. There is an incredible amount of info available here. Would the mixture have to be injected between the blower and the engine or could it be injected between the throttle body and the blower?
I've been following the sts turbo threads and that mixture seems to really cool down the intake charge. Could that work for this application? What about a small nitrous shot? Would I have to worry about thermal shock with the rotors? That would be a very expensive way to cool the intake charge, but it should give an extra kick in the pants. Can a wet system be injected between the t/b and the blower? How about dry, if the extra fuel could be added through the injectors?
Could you explain adiabatic efficiency to me? I keep reading aobut it, but don't really understand what it is or what it measures.

 

Adiabatic efficiency is a measure of how much additional heat a supercharger adds to the boost.

Water/Methanol injection is added after the blower/turbo.

Adding the Nitrous after the blower would be better. Either a wet or dry kit will work.

Mike

 

Ok, now I know what adiabatic efficiency is. How do they measure it? I know higher numbers are better, but how do they figure the percentages? I assume they compare the ambient temps to the inlet temps, but how do they actually compare them? Inlet divided by ambient?
Adding the water/methanol after a roots sounds kind of dicey.Would it be done with a spray bar (like an under the carb nitrous system) or would it need to be separate nozzles like a direct port system. The spray bar type would be a lot simpler and less likely to fail. Cheaper, too. I like cheaper. How do you figure out the amount needed? Once you know, I guess there is a formula to tell what orifice sizes would be needed at a given pressure.

 

It takes a thermodynamics book to calculate adiabatic efficiency. You measure the ambient air temp, the boosted air temp, and the boost pressure, then calculate efficiency. Many manufacturer's advertise these numbers. Very few centrifugal superchargers or turbochargers surpass 75%. I calculated 38% for my old car, which had a B&M 144 at 7 psi boost.

Water injection kits are pre-calibrated and can be bought for <$500. A spray bar probably wouldn't work because the orifice size and shape is very specific.

Mike

 

So, in order to use this with a roots and inject it after the compressor, would I need to have something almost like a direct port setup with 8 separate nozzles? Is that the type of thing that would be available for <$500? Not including the mods on the intake, of course. Or would it work some other way? I hope so, a DP setup seems to be overly complex. One bad nozzle could kill an entire engine.
Does cooling the intake charge in this way "raise" the adiabatic efficiency? If I cool it enough, do I get increased efficiency? I know I get more air/fuel in the combustion chamber b/c cooler air is denser. I know I reduce the chance of detonation, as well. I'm just not educated on the effects of adiabatic efficiency. I assume that less efficient systems heat the air more and get less mass into the cylinder per pound of boost than a more efficient design. So would a roots with water injection actually be a more adiabatically efficient system than it would be without injection, or is it still inefficient but band-aided. And if the band-aid works, does it really matter?

 

My friend Bob Kennedy makes a nice water injection kit with very high quality components. Depending on configuration it usually runs $550. Cheaper kits often have inferior parts, especially the pump, so be careful of anything much cheaper. My 4,100lb car runs over 140mph in the 1/4mi with water/alcohol injection and NO intercooler. It really works.

You can see Kennedy's kit at www.kennedysdynotune.com if you call and mention my name, it won't do any harm.

Rich Krause