What kind of RPM capabilites does a 250 series inline 6 have from the factory? I don't care about the cam or the flow of the head or the flow of the intake or carb. Assuming you've for the airflow, what gives first? I have a HEI ignition and I understand that with a few upgrades (coil, wires, plugs) they can be good to 7000 or so (have I heard right?). With a stock cylinder head at what point do the valves begin to float? I've always assumed it was around 5000 or so cause the inline 6 is a low RPM beast, but I don't actually know. If I wanted to run the engine occasionally to 6000 RPM with total reliability and good life what would I be looking at? I've heard of this with a stock bottom end.
That's the important part, now there's me thinking out loud (you can judge if it's as significant).
So I was thinking on the bus home tonight about turbocharging. And I was thinking about how turbocharging can be used to allow you to use RPM you otherwise can't. Basically the idea works like this. For every so many RPM (say 1000) you add another lb of boost or so. The intake ports and cam setup and whatnot begin to be restrictive at higher RPM but the increasing boost (which encourages flow) basically cancels them out. So what you have is a power out put that's dependent on RPM basically. I know it's more complicated than that but that's the most important part. So I decided to make a spreadsheet.
I assumed that torque is 200 lb*ft completely independent of RPM. I picked that cause my engine is rated at 200 lb*ft @ 1600. So we get power output that's dependent on RPM.
RPM Torque HorsePower
1600 200 61
2000 200 77
2250 200 86
2500 200 96
2750 200 105
3000 200 115
3250 200 124
3500 200 134
3750 200 143
4000 200 153
4250 200 162
4500 200 172
4750 200 181
5000 200 191
5250 200 200
5500 200 210
5750 200 219
6000 200 229
6250 200 239
6500 200 248
6750 200 258
7000 200 267
Now that in itself would be a feat for power. You'd be controlling a turbo pretty tight to keep at 200 lb*ft exactly. It'd be interesting. But say if I just wanted the top part of the graph - the part from 4K to 6K. That wouldn't be hard at all the do with a turbo, only a few lbs of boost. But of course this got me thinking. I have an engine with 8:1 compression. With premium fuel I could put a few lbs of boost on there to increase power output and still be able to compensate for the poor flow. So I made another graph. Same idea. The assumption though, is that torque is now 300 lb*ft. That represenst about 6 - 7 lbs of boost. That's totally reasonable. Now you assume another lb/1000 RPM to compensate for flow reduction at higher RPM. Even still. You're talking about 10 psi max at 6K RPM. Which is reasonable. But enough talk.
RPM Torque HorsePower
1600 300 92
2000 300 115
2250 300 129
2500 300 143
2750 300 158
3000 300 172
3250 300 186
3500 300 200
3750 300 215
4000 300 229
4250 300 243
4500 300 258
4750 300 272
5000 300 286
5250 300 300
5500 300 315
5750 300 329
6000 300 343
6250 300 358
6500 300 372
6750 300 386
7000 300 400
There's definetely a lot to consider with what I've said. It's not as simple as more boost to combat decreasing flow as there's more back pressure. But it's mostly true. God I love spreadsheets. I think I was meant to be an engineering (hey! that's what I'm going to school for.......). Anyways, I'd better go to bed
