Starting to research and read about turbos for the future turbo build. I'm reading about mass flow rate and seeing how it all interacts. What I want to know is what does an iron early type slant six head with larger valves and a good porting job flow? What about a late style iron head? They don't have to be exact numbers, just ballpark figures.


From what I can tell, the head on the slant six is more or less the main restriction on flow capability; is this correct?

Thanks,
Stephan

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Stephan Nelle

I can tell you that an average ported intake will flow 180ish.

Many will claim numbers much higher than that.

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Official Cookie and Mater Tormentor.

yes a little less than 200cfm is a well ported head. I personally am shooting to get somewhere between 180-190, but this is for the 170 engine. Engines that can flow a cfm per a cube is really where you want to be. Some have got 220cfm out of the slant, however, to get there you really need a flow bench.
Out of curoisity which turbo books are you reading. I think I've read all the big ones so I was curious.

I'm reading Maximum Boost by Corky Bell and Turbochargers by Hugh Macinnes. I'm reading through turbocharger sizing at the moment. I'm getting an idea of what I want to do and maybe a little bit of how I want to do it, but for sure nothing in stone or even any definite numbers yet. Still playing with all the calculations to see where I'd land with what.

This may sound like an elementary question, but how are head flow and carburetor flow related? Assuming you have a head that will flow 200 CFM, and a carb that flows 500 CFM, then what gives, or where does it go? What justifies using a higher CFM carb than with head will flow?

Thanks,
Stephan

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Stephan Nelle

I do have the following figures




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Regards,
Fanie Gerber
It's never junk, it's just a part you're not currently using

http://www.valiant50.co.za
Just say I own a few Mopars

Sweet! Thanks a ton!

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Stephan Nelle

Well, CFM is simply a measurement of flow, um... like MPH is a unit for velocity, Celcius for temperature, or feet for distance. The second point, and correct me if I'm wrong anyone, that the carb feeds 6 or 8 cylinders and the head flow is per a runner. So where it really starts to add up is point of restriction and overall flow, so keep in mind water if it helps. You have an unlimited supply of air that flows into a 600cfm carb, that than branches into 6 intake runners that flow 100cfm a piece. Now that is an ideal simplified version, but should give you some idea. Of course 100cfm doesn't make it to each cylinder and ect.
Second, after reading those flow numbers I want to cry. I thought a home porter could do a little bit better than that. I kinda plan on making a makeshift flow table at home. There is some plans/ideas out there that can tell you if your improving or hurting your flow. You don't get any numbers, but will help over not having it.
Onto those books.... Corky Bell is a great author and that is a reknown book. However, I picked up Superchargers by Bell so I didn't read your copy. I had someone earlier ask why you couldn't run 13:1 compression with a turbo after reading that book. So take what you get with a grain of salt.
Next, Hugh's book is awesome. It helps you select a turbo and gets you on the path of making your system. You'll notice though that the first couple chapters are great for sizing and calculations and the rest of the book starts to peter off. This is the book I would use for calculations and helping you take this project seriously.
So, after doing a ton of research for a turbo build I bought a supercharger. Kinda funny huh? So here are some suggestions, and I won't be hurt if you blow me off. First off your in the right mind for big power or reliabilty for medium power. Get that head built right like you weren't going to blow it.
1) A turbo isn't a crutch it's a tool, so do some home porting and bigger valves. If your going to spin the motor (k1 rods, light internals, 170 short stroke) I would suggest roller rockers. Otherwise, if your going to stop at 6000rpm which is fine, stick with good stock rockers.
2) Pistons are a must, for less than 6lbs you can live with stock cast. More than that I would/am spend the money for good forged. Get the assembly balanced.
3) The t60 or GT35r will serve the slant for 300-400hp and less than 300hp I would go with the Grand National turbo, mostly for price.
4) This is do-able for not a ton, just be determined and do your homework. One thing is to make a list of everything you want and you'll probably cross somethings off for costs as you go.

Haha, boy do I feel dumb. I must have had a major brain fart-I guess I didn't realize flow bench numbers were per port. I was thinking those numbers looked very low for an entire head...

Thanks for all the good info. I won't be skimping on tthis build, so I'm not too worried about getting nice parts (forged pistons, K1 rods, etc.) One question for you: when use said use the 170 short storke, are you just saying putting a 170 crank in a 225 block to lower compression? What are your thoughts/ideas in these regards?

Thanks,
Stephan

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Stephan Nelle

Nope, I meant using the 170. I figure that a boosted 170 can comfortably spin 7000rpm if not more, and needs to so it can make up for the size difference. A 225 will probably be comfortable with a 6000rpm redline and plan for accordingly. This means that the stock rockers will be fine, especially since they have the cool curve already built in. That was a wierd thing I first noticed about the slant. The compression should be dealt with by the pistons and it is ok to go with 9:1 compression, just not anymore. The thing to remember is that these are peak numbers, not a true area to focus on. I've seen 350's do 500hp at the peak, but the torque curve wasn't near flat.
It's good you have a decent budget to work with. However, I still stick with my original statement that you don't need a ton of money for this project if your a little bit smart about it. For example, a custom cam can be ordered through a cam grinder, K1 has all the fun stuff, and Jagger's might be able to build you a set of headers for the turbo. I would contemplate building my own header if your able! I plan on building the intake (obviously) and possibly the headers. Good luck all in all.