Haha...yeah, I will end up in all likelihood with another tach, but I want to see what 10k looks like on a stock tach, lol. I am thinking I might try to do something with the tach, just haven't come up with a solution that I like. If the stock tach went to the same spot every time, then I would just use it and mark where 8,9,10k rpm are on it, but I dunno that it will be consistent. Also dunno if 10k will actually wrap the tach around and hit the resting peg, lol
My Wild? KL Build
- Thread starter JKPgt96
- Start date
Sounds good.
Just to ask a question, why 10,000+ RPM? Is it just for the "cool factor" or is that where you plan on making peak power? I'm not trying to dissuade you or anything but making maximum power at 10,000 RPM is going to leave a lot to be desired at lower RPM. I own an RX-7 so I know a little about making power at rediculous engine speeds at the expense of low-RPM driveability
Peak power isn't where its all you should be concerned with... even if you lose a truck load of power say, past 8k rpm, with the right gearing you can still generate greater force at the wheels by turning the engine faster due to gearing....
thats why anyone who says "shift at peak power" is most of the time speaking out of their ass, unless of course peak power happens to also be redline
But yeah, 10krpm and the cams required to pull it off in a piston engine, she's going to be one angry, nigh on undrivable beast at 2k rpm
...but thats what piston NA is all about...he does have the advantage of significantly higher displacement than a rotary though - so its probably not going to be quite as gutless in the low range (but conversely wont have nearly the grunt in the top end as a rotary will....mainly because rotaries make stupid amounts of power up top with nowhere near the kind of considerations required to do this with a piston motor)
Last edited:
jonridinhi
Member
- :
- 2001 MP3/2010 MX5/1996 MILLINIA (donor)
What EMS will you be running?
Very true. My question was really more along the lines of "If you're only going to be making peak power at 8,000 RPM, why spin up to 10,000 RPM?"Peak power isn't where its all you should be concerned with... even if you lose a truck load of power say, past 8k rpm, with the right gearing you can still generate greater force at the wheels by turning the engine faster due to gearing....
thats why anyone who says "shift at peak power" is most of the time speaking out of their ass, unless of course peak power happens to also be redline
This reminds me, the one thing I have not seen the OP mention are the intake and exhaust designs. Cams and high engine speeds will only get you so far. You have to have an intake and exhaust to suppliment. Exhaust is going to be critical to make power (read: torque) where you want. Even ITBs require some form of fine tuning in the form of horn/runner lengths and taper/diameter.But yeah, 10krpm and the cams required to pull it off in a piston engine, she's going to be one angry, nigh on undrivable beast at 2k rpm
Also, I'll +1 the engine management question.
because of the gearing advantage... my car makes peak power at around 6000rpm...but i spin the motor to 7500rpm and the timeslips show the difference. by calculating the wheel torque and plotting it on a graph you will see why.. it only becomes stupid if the torque fall off at the road drops below the wheel torque you will pick up in the next gear.
indeed... in fact, the exhaust manifold and intake manifold designs are going to be absolutely key to making engine power. A very well respected header designer once told me the LAST place you have an opportunity to make power is at the collector(s) in your header(s)... beyond that no matter what you do you will not generate any more power. For an aspirated motor, the combined effect of a tuned intake manifold (of whatever design) coupled with a tuned exhaust manifold reduces pumping losses and improves overall effeciency. In fact, these 2 components are the very reason why you can exceed 100% VE on an NA motor... but screw them up and the RPM range that your engine scavenges in will be outside your ideal (and often even usable) rev range - and no amount of compression, RPM, head work or cams will help you if these are wrong.
Long runner exhaust manifold and longish runners feeding the ITBs are going to be key here...i've posted the formulas many times and generally assume that people who are going this far have done the research or have gotten themselves smart people around them to help them out.
I'd be hoping to see something like a haltech platinum sport powering this thing - its the only "affordable" computer i can think of with the fidelity required to deal with what is going to be a very lumpy idle....
If I didn't answer your question on why spin to 10k..I honestly will be spinning to whatever makes sense given my powerband. Judging from where the other two people (PRM Gerry and Leo) spin their cars to and comparing my setup with theirs and their power curves I should have no issue making power up high enough to justify and usefully spin to 10k rpm.
I realize the exhaust and intake are big tuning points, here are my plans in a nut shell..though I don't want to say too much yet
.Intake-Get the base ITB setup on the car with no horns to see the clearances and such. Then fine a happy medium between having a stupid huge cowl in the hood versus performance.
Exhaust-Having custom longtubes built for the car, along with a 3" Cat-back with a chambered resonator in it. This is to keep the car relatively quiet. But also have a 3" cut-out for when I am racing and such.
EMS-Starting on MS2, but setting the car up to ultimately run MS3 full sequential. I have MS1 in the car right now, with MS2 on the shelf waiting for some time to get the bugs worked out with my MS2 setup. Haltech has been contacted however, and I am tossing the idea of the platinum2000 (I believe it is called) running the car.
Last edited:
no way on earth would i consider anything from megasquirt up to the task... no "serious" tuners use the things....
the Platinum Sport 2000 is a beautiful (and affordable, considering everything else) piece of kit...
dude..i'm giving it more credit than it deserves by saying its a pile of junk....
seriously... i hang around top tuners all the time...i'm heavilly into the local sport compact drag racing scene...a scene where "drivability" isn't even a concern - and they wont even touch the things...
if you wern't going so wild, then i'd have no problem with it...but getting the idle to lock nicely...to get the coldstart to work reliably, to get the input throttle response nice and crisp - with a setup like you're describing here you want something better than a piece of kit cobbled together by squabbling community...and i'm not even starting to talk about injector driver accuracy at high fuel loads and short cycle times
MS is nice for learning what makes up an ECU - or for converting an old carby beater to efi.... but for a sophisticated near-race prepped engine....dude, it deserves something better
Just remember what Lordworm posted. After the collector, the exhaust really doesn't care what's going on assuming you aren't restricting flow (restrictive muffler, tiny pipes, etc.). Basically you want the pressure to drop to atmospheric after the merge. Most race exhausts I've seen either terminate at the merge collector or use a megaphone (when a muffler isn't required). Another way of doing this is to go with a very large pipe diamater or muffler box if you want to keep things quiet. The fine tuning comes from how long the primaries are - whether you want long or short (I prefer long), the pipe diameter, the merge collector and megaphone (if you have one). Just having "custom longtubes" built is likely not going to get you where you want - there's lots of math involved, but I'm sure you knew that
Now I'm not very familiar with N/A piston setups, but what constitutes a "long" versus a "short" primary? I know for my rotary build, my long primary plan (1.75" primaries to 3" merge) isn't going to merge until right before the rear differential!
Last edited:
I realize this, but thank you for the input. I just don't want it to be unbearably loud ALL the time, thus I want the chambered resonator and such in there. I had one on my old exhaust and loved how quiet it was.
I am having a very reputable shop build the manifolds for me, but I am working on some of the math to at least get them some numbers for lengths. FWIW Leo in his 323 did 270+ n/a with a set of stock shorty primaries with a custom Y-pipe, which was simply a enlarged version of the hotshot one..
I just don't want it to be unbearably loud ALL the time, thus I want the chambered resonator and such in there. I had one on my old exhaust and loved how quiet it was. I am having a very reputable shop build the manifolds for me, but I am working on some of the math to at least get them some numbers for lengths. FWIW Leo in his 323 did 270+ n/a with a set of stock shorty primaries with a custom Y-pipe, which was simply a enlarged version of the hotshot one..
"long" and "short" is really not the way to look at it.
Basically (really dumbing it down here!) the shorter the primaries are, the HIGHER the rpm where scavenging will occur is. This should work in much the same way on a rotary..you go "long" to improve midrange RPM efficiency and improve drivability...but if you want outright power you tune it to occur at or just before peak power. When people refer to "long" runner manifolds they are usually saying "tuned length" manifolds...when they talk about "short" runner manifolds they are talking about off the shelf parts that work as stock replacements and are about as useful as a waterproof teabag.
Same is true of intake manifolds - the longer the runners the lower order of resonance you get and the larger positive pressure wave you achieve...
For outright power, ITB's are not the way to go....they kill for midrange and flow (and on rotaries they are great because of the enormous swept volumes involved) - but the "ultimate" intake manifold for a piston engine is a good old fashioned tuned length single throttle tunnel ram design.
Ehh...not like in a n/a small displacement motor that turns 10k rpm is really going to have amazing midrange anyway without a LOT more time and money designing a manifold..the ITBs (I know this sounds dumb) get that 'wow' response more so than a sheetmetal design. This initial build is not the final configuration, there are other things that I would like to do with it to find some more power down the road..
FWIW, longtubes vary in length from company to company for the same application, I suppose they just have different ideas of what 'tuned' is..
FWIW, longtubes vary in length from company to company for the same application, I suppose they just have different ideas of what 'tuned' is..
2.5L plus whatever your overbore is isn't exactly "tiny"...but you're right...
long tubes *shouldn't* vary..the physics is always the same. The only reason they will vary is if the maths is wrong or inaccurate, or they are too lazy to work out how to get perfect equal length runners within whatever space you have free.
Exactly what I was thinking.
Like what was mentioned before the primary length can be adjusted to achieve the desired powerband. If you want absolute power shorter primaries work better (thanks Lordworm) whereas longer primaries will give you more even power/torque curves. Being a rotary guy now, I'd kill for more torque...
Last edited:
Yeah..I agree its not a tiny motor, but as you know it is a very different animal than a v8 spinning to a high rpm in terms of midrange and driveability.
I will have plenty of room underneath the car for the primaries to be as long as they need to be, the rear bank will have to run back a ways to even be close to equal, but I figure if they are close they should scavenge some and be alright..
Change your gearing
you'll have enough power to do it... the torque at the engine means next to nothing..its the torque at the wheels that matters and you can adjust that by changing your gearing and *nothing else*.I should clarify....the physics is the same for ANY engine..but lengths will vary from engine to engine, and build to build.... but the calculations are always the same... that is to say, for any given individual engine build, every exhaust shop SHOULD come up with near on the same mathematically correct lengths... unfortunately anyone who can weld thinks of themselves as an exhaust system fabricator - so plenty of them are douchebags who dont really know what they hell they are doing...
Shop around and find an expert ... you'll pay for it but it'll be more than worth it.
you have some effeciency benefits over bad old V8's... such as not using antique push rod/rocker arm crap... but yes displacement will mean you will have a hard time in the low/mid range... but that doesn't mean you have to make it worse for yourself...
scarifice a *touch* of top end speed and make the car a little more civilised... trust me when i say you will appreciate it more that way
I'm not suggesting you water the build down - just get your manifold biased ever so slightly towards midrange.Close ratio Miata gears and a 4.30:1 rear end (up from 4.10:1) is plannedChange your gearing
Also, to go back to the ITB discussion have you looked at the Jenvey ITBs at all? They're a company out of Great Britain and they have a large assortment of single and triple ITBs worth looking at.
I have...they have nothing for me..and they want a fortune to build a setup for me that is real low profile.
The Final drive in my car is going from a 4.39 to somewhere in the 4.60 range, I had a trans with a 4.66 final and it was great for acceleration, but not for cruising..with this much rpm to work with and such I think something similar would be nice. PAR sells a 4.43 final..
The Final drive in my car is going from a 4.39 to somewhere in the 4.60 range, I had a trans with a 4.66 final and it was great for acceleration, but not for cruising..with this much rpm to work with and such I think something similar would be nice. PAR sells a 4.43 final..
