So, to my knowledge, 8000 rpm is ungodly high and pretty unheard of in our cars, mainly due to VVT and stroke (feel free to comment if any info is wrong, which it very well could be.). Hell, even 7500 is extreme. Maybe I'm just jealous of engines like a K24 that can go 10k+ or even a SRT4 A588 that drop some valves and porting to go from 6500 to ~8k.. Does anybody have a more "technical" explanation to this? I admit I'm no engine guru, but surely there's similarly sized engines employing a valve timing mechanism that can rev higher than 6500 rpm? Right? Please? Just let me dream.
I rev my engine to 7000 rpms for road racing, @phate; revs his to 7500 for autox, both engines have stock internals.
Personally, I'm not jealous of those engines. Those Hondas have no torque at all. You see stats like 250whp with 170wtq. It's a totally different type of powerband. I mean they're ridiculously low in comparison. For me, it's not about having to rev to the sky to finally reach a high hp peak; it's about having a broad, usable powerband with guts, not something that only has high hp numbers at some super-high rpm. I'm driving a car, not a motorcycle, LOL.
I agree, torque is very nice. But I guess I'm looking at it as more of.. why not have both? Displacement for torque and a slightly higher rev range to have an even longer power band. There may not be a perfect engine that can do both, but that combination sounds pretty damn awesome.
Because the engine designs aiming toward those various goals are quintessentially different. Higher tq motors have a longer stroke. This means rod angles and forces that are not ideal for high-rpm operation, and can cause major problems. High-rpm motors, conversely, have a proportionately much shorter stroke. This lends to revving high without issues, but limits torque in a major way compared to long-bore or stroker engines. Unfortunately, you can't really have your cake and eat it too. Turbo selection can help, but those tiny, short stroke Honda engines even with turbos don't have the guts we have with the MZR DISI, unless we put on a ridiculously big turbo, which limits our lower torque a lot. I honestly don't see why anyone would do that unless they're making a dyno queen. IMHO, the DD enjoyment of a Speed with a BNR S3, or even a GTX3071/76 or especially an EFR7163 is much more responsive than something with a 6466 or GT3582/6 on it.
Thanks for the tech knowledge, for real. I agree as far as the turbo choice, I would hate having something on there that would spool 2500 before I had to shift and drive that every day. I guess to shift the talk a little bit from 8k+ rpms to more of what most of us can/will use, is there one limiting factor to our engine design that sticks out more than another or a combination of factors influencing it's "rev-ability?" I've seen VVT, bore/stroke, Rod bolts, and at the same time that the valve train is pretty stout.
Definitely, the differences I touched on are precisely what he's trying to implement in his new engine.
Stock block, stock intake mani (with fully functional VCTS), FR exhaust mani and EFR 6758, spinning to 7500: Outside the car, 3rd gear pull from ~40 to ~85 MPH (7000 RPM, before I raised redline in the above vid): Having both low end torque in abounds AND high RPM power is a tough order to fill; this is usually where stuff like compound turbos, twin charging or nitrous+boost come into play, depending on the desired effect. My build aims for a bit of a middle ground; a reduction in overall displacement of the engine combined with a significantly raised redline, better compression, longer rods and cams / headwork to match. Check out the science as to why a gutless car with no torque can be fast in OP of this thread: http://mazdaspeeds.org/index.php?threads/disi-mzresponse.457/ Can you spin a built 2.3 out to the moon? Sure. Is it going to cost a lot to have the engine survive up there? You betcha.
^^^^^^^ This. Having both low-end, top-end, and everything in-between is the reason things like VTEC and cam phasing were invented, besides complex turbo setups, like the compound forced induction systems you've mentioned, and newer tech like variable-geometry turbos, such as on the Koenigsegg One:1. I think there was even a twin-charged Speed on MSF, wasn't there (supercharger + turbocharger)? Then we have the extremes on the opposite ends of the continuum: on one end, the diesel motor that only revs to 3k yet makes over 1,000tq, on the other end, F1 and motorcycle engines that rev to 15,000 and have ridiculous top-ends. Maybe one day we'll have engines that are optimal everywhere, but I think internal combustion engine theory/physics make this the Holy Grail of powerplant engineers.
You could probably toss upgraded valve springs on the stock head and spin to 8k RPM's no problem if you really wanted to. Won't be able to tune up there without Versatune, though.
Yeah tuning is the other issue outside of mechanical considerations. The AP wont get you there. Will versatune go that high?
Most of the VT tables (that you would need) go to 4.0 load and 8k RPM, and once my build is done I'll probably be getting a software build that will go higher. Edit: For every gen and MS6.
I made the decision to go Versatune right off the bat, but I'm not sure how much I trust 130k mile valvetrain components to spin above 7k. Maybe after I get my block built and need something else to blow money on, I'll see about delving into the head. By then I'm sure there will be more options for products, specifically cams, and probably even more experience with stuff like valve springs, oversized valves, porting, etc.
Yeah springs are probably a bit sloppy now; 7k *should* still be fine though. Edit: As for cam options, the grind I came up with looks promising but still needs to be tested. It also requires new buckets as the lift changes due to the regrind.
