Falcon, unfortunately you have a recipe for dog, whether you knew that was on the menu or not.

You have a small displacement engine. You have low compression pistons. You have large cams. You have a centrifugal blower. Any of these will yield somewhat lower torque numbers in the lower RPMs. All of these together will make it a real schnauzer down low. It's what you picked and you can moderate things a bit but it will be what it will be. But is should run like hell up high (300whp is strong for a 1.6!).

There are many valid points that others have voiced above and a few that may not help. Your cams and your Rotrex are designed to make power in a higher RPM range so you should keep your engine there. The tighter spacing of the gear changes on the 6 speed as Savington pointed out would certainly help you to keep your peaky engine in it's optimal operational range. Your lower compression pistons will let you use more boost and make more peak power without detonation, which is good, but they are another reason you need to keep the engine in its peak range.

As Miata2fast and Nitrodann have said, a larger exhaust may yield more high RPM power and be optimal for the range where your other components make peak power. As they pointed out, a larger header primary diameter and collector/exhaust diameter will negatively effect low and mid range torque due to poor primary velocity and scavenging. This is a very widely known and accepted fact with fifty plus years of testing to support it. Turbocharged vehicles are the only exception. With the change to a 6 speed helping your "being out of peak RPM range" issue, you may find that you will make more useful power up in the 5-8000 RPM operating range with the 3 inch exhaust. Experimentation will bear this out.

One of the classic mistakes in hot rodding was to pick components that did not work in the same RPM range with each other. Another classic mistake was to pick components that did not work in the range that the car would be operated in. Lots of muscle cars with ridiculous tunnel ram intakes sticking out of the hood have been beaten by far less flashy cars with better matched components. And likewise huge lumpy cams were often employed without enough compression, headwork, or bottom end strength to allow the cams to ever spin up into their effective peak range.

The point is that your car has several major features that are optimized for 5-8000 RPM so everything should be targeted to optimize power in that range if you want to make the most of what you have. Or you could tone it down and make less power by reverting to stock cams and increasing the ease of driveability (which is going backwards) and have a significantly slower car on the track.

Now, along with the 6speed you can make some more supporting mods to go faster and use the RPM range where you do make the powah. You have dialed in the cams on the dyno and that is good.
1. 3 inch exhaust, try it and see if it makes more power in the high RPMs. Your car will always be a low-RPM dog so go for it on top end.
2. Have you optimized your intake manifold with shorter, larger diameter runners yet? The factory runners are optimized for something like 3-4500k RPM.
3. How about a lighter flywheel with that 6 speed? It would likely help with snappier shifts and blips. This might be more important if you are shifting more often with an extra gear.
4. An extra pound or two of boost if your engine can take it. More power is more power. It should help a little bit everywhere.
5. Meth was suggested above but you have to beware of relying on it. An additional point of failure on a racecar is not usually advisable. Using it for cushion only can't hurt.
6. Reduce weight. A peaky engine with little low end torque is never a good match for a heavy car. Drag racers will run really low (high numerically) gears if they are stuck in this situation just to try to overcome the disadvantage. It takes torque to effectively move weight and you don't have much of it so you have to trim weight down if you are serious. Rotating mass and unsprung weight are of the first importance, then sprung weight. When you have very low torque it makes a much bigger difference. You will also have the benefit of being able to brake and corner better with less weight. It helps everywhere.

My advice is to make it better and try to keep it in the RPM range where it is already good and not to try to make it into something it isn't designed to be.

what rpms do you spin it to?
8k?
Whats stopping you from spinning to 9k? rotrex, valvetrain?
Doesn't look like your power or tq is dropping off at 8k yet so I would suggest you keep reving out unless something is in teh way of doing that.

I agree with the crowd: you built this engine to be this way, and just about every component is optimized for a torqueless/peaky curve. Don't try to make it something its not. You'll end up losing what you currently have, and I HIGHLY doubt you'll make any torque in the process. So FAIL and FAIL.

The trans idea, to me, sounds like a fantastic one. You built the motor to spin to 8k, so gear the driveline to use more of that band.
GEARING is a TORQUE MULTIPLIER. Think about that;)

Keep the engine at its boiling point with highest fd rp you can find, a 6sp, and smallest diameter wheels you can get away with
OR
Just sell this setup to someone that actually wants this kinda power curve and start over with a 1.8+turbo like you should have from the start:giggle:

I think his 4.10 gear with a 6 speed will keep him pretty busy rowing gears and keeping it on boil up to, what, 140mph or so? I'm too lazy to chase the FM calculator down to see what 8k with a 4.10 yields.

my excel sheet says a 4.1 with a 6-speed [3.76, 2.27, 1.65, 1.00, 0.84]
@ 8000 rpm [34 mph, 57, 78, 103, 130, 154]

So even a 4.30 should work if he really wants to squeeze as much out of it as possible.

The motor he built can easily do double the power. Run more boost, then talk of changing things.

MOAR BOOST

Also gears.

Yeah, especially if he's only on tracks that he can only run 140 and below. But with a 3000+ RPM powerband I think he will be just fine with the 4.10s. First gear will be quicker than a hiccup as is, but he should find better useful overlap in 3,4,5 than he was used to.

Thanks for that long post sixshooter it kind of opened my eyes a bit with the way you explained it. You're right my motor has everything (except perhaps the exhaust) that tailors to the high RPM. I have a lot of what you listed already, a GotPSI IM, light FW/clutch (maybe I'll go with the 949 in the near future) and it's making just shy of 17PSI at 8kRPM. I could gear the blower a bit higher as it's still under the limit by 100RPM or so. IIRC you can overspin them %5 with a good oil cooler and not really worry about them grenading.

A 6sp is on the list now. Although it's going to be hard to find one here in BC. May have to ship or scavenge the parts yards.

And techsalvager, the bottom end would not likely last at 9kRPM. The head should be OK (although the springs may be on the edge) but the bottom end is only statically balanced and the flywheel was not balanced with the assy. 8k is enough anyways :D.

That MPH calculation you did with the 6spd and 4.1, is that with 15's? The 13's are gone, I needed more tire so I got rid of them. Also didn't feel like having $1500 tied up in a set of wheels.

Oh, and my local track I top out at 185kph. So I think a 140/150MPH limit is not the end of the world. I doubt I would be hitting much higher at Seattle but Portland and the new Ridge Motorsports Park are quite high speed. But 150mph high speed? Not sure... I think I will leave the 4.1 for now if I feel I want a higher final drive I can swap it out.

Its to bad, looks like your losing out on power up on top due the camshafts, tq hasn't even fallen off yet. Personally I wouldn't think of going with that cam if you aren't gonna spin it out. No idea how much R&D it took for those cams but I'd look into a cam that would bring the power band back eariler into the rpm range.

Tech, you clearly don't understand how centrifugal blowers work. Go away.

Lol, I just logged in to come mention that...

Cams have nothing to do with the torque not falling off. IIRC TrackDayHookey's car runs stock cams and his car is a beast and the power just keep climing.

Anyways....

6Sp
15's
3'' exhaust
add lightness

That's what I'm doing and leaving the rest of the car as is. I'm kinda getting tired of spending money....

List corrected.

stock 1.6L cams

https://www.miataturbo.net/attachmen...ine=1325008791

:eek:

After reading Techsalvager's post, I looked at your dyno graph and noticed something. You have not made a dyno pull at a high enough rpm to get the dip in torque and horsepower.

If you are not willing to spin the motor high enough to fully utilize the camshaft you are running, you have a serious combination problem. You need to either pull the motor and fix the bottom so it is capable of spinning to the rpm of the cylinder head/cam combo, or install a camshaft that will peak out in the rpm you are willing to run.

You need to dyno the car at a higher rpm to see when the motor runs out of steam. I would at least run it to 8500. If you have a good balancer and flywheel, you should be ok with a few dyno pulls.

Then determine what final drive gear ratio by doing the calculations.

dude. because of the way the boost is built, there will unlikely ever be a drop in torque. Look at the above TURBO setup on stock 1.6L cams. We all know those cams drop torque at 5K.

tech & miata2:
Do you guys not know how a rotrex works? :facepalm:

Also LOL@revving to 9k. Didn't know we had honda motors, WHODATHUNKKKKK

Don't get too crazy if you are that close to Rotrex's terminal velocity, haha. It is important to keep things together.

Concentrate on weight, weight, weight.

And if you really want to get particular about maximizing what you've got for high RPMs, you might want to get a little ----. Along with the parts you put on your list I would look closely at streamlining the efficiency of every part you are running. For instance, have you checked the pressure gradient between the inlet and outlet of your intercooler at your peak power? It may provide ample cooling capacity but might still be a flow restriction at the full CFMs the Rotrex is providing. Any tight bends in the inlet tract you could straighten out? A rule of thumb in fluid dynamics is that every 90* bend in a pipe creates as much added drag on what flows through it as a 20 foot long section of the same diameter pipe. So we should look to minimize bends and when necessary we should make them wide and smooth radii. Obviously this would apply to exhaust design as well as pre-supercharger. And use a larger air filter element than you think you need, lol.


BTW, do you have the ATI damper and Boundary OPGs? I hope so at those RPMs.

185km is only about 114mph or so, right? If that's all you are seeing at your power level then that's a very tight track. I'm going to say the 6speed with the 4.10s will be quite a bit more advantageous than the 5 speed in that environment.

Well obviously, he owns a miata.
:giggle:

Let me help them. A belt driven centrifugal supercharger spins faster as the engine spins faster and continues to push more air into the engine as it increases in RPMs. It does not fall in efficiency and flow like a positive displacement supercharger does and therefore makes dyno graphs that look like laser beam trajectories instead of bottle rocket trajectories, if you get what I mean. The centrifugal looks like a turbo's compressor wheel. It actually does drop off eventually but you will actually have it typically disintegrate from overspeeding first.

I though you'd like that when I wrote it.

Couldn't have said it better myself.
The kicker is that it won't start blowing hot air like a turbo once its past its rpm limit. You get no warnings.

Yeah I was thinking about my IC. It's quite small. And the piping is definatley not ideal with all the couplers and bends. I have a Maruha oil pump but stock pulley. ATI is on the list too, just didn't mention it. The oil pump is debatable, I have a feeling it's a modified VVT pump but Ocean my motor builder builds high comp N/A 1.8's that spin to 9k and make 200whp with this pump and has never had a failure.

Yeah 114ish MPH. It's a small track with a short straight away. I mainly built the car for hill climbs though, and the 6spd should help with the light bog out of uphill hairpins I'm having right now.

Watch this vid and you can get what I mean. The red light on the dash is 7800RPM for reference. I am running a 5spd, 13's and a 4.1 in this vid. You can see where the car bogs.

Yeah, :53 and 1:22 and 1:51 it was pretty noticeable.

Big Chinese intercoolers are cheap. I doubt you are running A/C where you are so you should have plenty of room for one.

Yeah I have a "little" chinese IC right now. I have no PS or AC so yeah I have space. I'll look into it. If I'm going back to the dyno for a 3'' exhaust I'll do the IC too.

You don't understand how a centrifugal blower works either. Centrifugal blowers build boost with RPM. It has nothing to do with the camshafts.

falcon you really need to show us the boost plot, and better yet, calculate and plot torque divided by MAP every 500 RPM. With this plot you can tell what your VE is and where it peaks. You will know if the engine isn't breathing well.

Read this book excerpt of why BMEP is so important, from the book "4 stroke performance tuning" - he talks about n/a motors, and for a boosted motor the equivalent BMEP is BMEP divided by MAP:
http://books.google.com/books?id=OTO...ortant&f=false

Read this too:

https://www.miataturbo.net/engine-performance-56/bmep-divided-map-why-its-important-60527/

I know exactly how a centrifugal blower works. I have one, and have driven many.

I however do not know how a centrifugal is controlled, and have not studied the dyno plots of them and compared them with other induction methods. I assumed that there was a valve that kept it from continuing to build boost.

Also, Falcon said his advertised duration was somewhere close to 300. That is a fucking monster cam. My advertised duration is 237, and I turn my N/A motor 8000 rpm. After looking back did I realize that his @.050 was what he thinks maybe was at no more than 214. So what is it? A giant cam or a pussy cam. I am doing the best I can with the information brought before me.

Lol, A valve? You say you know how it works, but clearly you don't.

And the overall duration of the cams is 300, .050 is 207* and 213*. .050 and overall duration are not the same thing. you can have a cam with big overall duration and smaller .050. Dosen't make it a "monster cam or a pussy cam". Quite a bit of thought was put into the cam profiles by my motor builder and tuner, and it seems to be doing the job quite well. I doubt I would be making 300whp on stock cams. Sure more torque but not 300whp at 16-17PSI on a 1.6L.




Again... you really have no clue how centerfugal chargers work. Just to be clear.




I'll have to dig around for the boost curve. I'm in Europe right now and don't have access to a lot of car stuff. If I have it on my photobucket I can post it up, I'll go check.

First of all, I was not throwing you under the bus with my statement about the camshaft. Lets be clear on that.

I made some assumptions that you may have a really big cam. You said you were unsure of what you had. I am well aware that advertised duration is measured differently from manufacturer to manufacturer, but you stated that yours was a full 63* bigger than my cam at advertised duration. That is quite a difference.

For the record, I clearly said that I was unfamiliar with the control of centrifugal blowers. I do however have some experience with matching combos together like cylinder head and camshaft selection with proper final drive gear ratios. Let's not make this a pissing contest, thank you. Just trying to help.

You really don't get it, dude. His torque curve has nothing to do with the camshafts. The nature of the blower produces that torque curve regardless of the cam - I've seen motors with that blower and stock cams make the same curve.

It's clear that you and techsalvager have the same misconception about falcon's cams being so large that the motor never reaches its torque peak within the allowable RPM range, but that's just how a Rotrex works. Smaller cams may help, but we already talked about that a page or two ago, and they won't change the shape of the torque curve - if it has an effect, it will bump the midrange and decrease the top end (probably disproportionately).

I hope you've been here long enough to know that dickwaving your "experience" will not even slightly change our opinion of you.

Advertised duration is measured at .003 lift.

Ah, yes.. my mistake ^. I was going of memory.



At the end of the day, the cams are staying in. I don't feel like pulling them, re doing shims/swapping lifters etc. for other cams. Before I do any big changes, well... not that there is really anything much left to do other than the exhaust and maybe an IC I am going to get a 6pd and see how that changes the car.

You'll try it, it will be insufficient to mask the feminist characteristics of your setup, you'll start another thread like this in a year, and eventually you will man up and buy a built VVT/turbo package from TSE. :giggle:

Lol... yea prob. Seeing as how much you guys charge for motors it's a really really good deal. I wouldn't mind though, building a VVT Rotrex'd motor.

Until I get some competition that is faster than me, my current set up is enough for now. It's been enough to set a few records so it's no slouch. I really need to learn how to drive the car faster though.

Lol... yea prob. Seeing as how much you guys charge for motors it's a really really good deal. I wouldn't mind though, building a VVT Rotrex'd motor.

Until I get some competition that is faster than me, my current set up is enough for now. It's been enough to set a few records so it's no slouch. I really need to learn how to drive the car faster though.

falcon,

You are not going to gain 10% torque from diddling the exhaust or i/c. Forget it.
Next to the boost curve generated by the centri, the cams have the biggest effect on the shape of the torque curve.

Yes, in this thread we discussed him giving up on finding large quantities of low-end torque and instead trying to make the car better where it already makes power on top end. Top end is where the exhaust and intercooler being too small creates a problem. Don't you agree that at 300whp his exhaust being too small and his intercooler being, as he described it, "tiny" would possibly impede his production of even more top-end power?

Yeah I'm past the point of finding more torque because it's going to be a neverending search.

Instead I figured I may as well maximize what I have with a better IC, and a 3'' exhaust.

Didn't notice if I asked this but whats your valve angles in your head?

It would be stock. Where are you going with this?

Really! Camshaft and cylinder head will not have anything to do with torque curve?

Well hell! Never a need to do any camshaft change WHAT SO EVER. The WHOLE WORLD needs to run the SAME CAM IN EVERY CENTRIFUGAL SUPERCHARGED CAR EVER PRODUCED AND RACED IN EVERY MOTORSPORT

I admit that I say a few misguided comments on some things that I may need to learn a little more about. But that my friend is a very misguided comment on your part. And I hear you say shit like that all the time about head and cam development, but I never call you out on it.

And yes, after some have explained what a torque curve from a supercharged car looks like and why, I got it. But we still have not determined if the camshaft is in fact the cam that he thinks it is, and if the car is geared appropriately.

One thing that will help for sure is finding an intercooler that has the lowest possible pressure drop. Trackdayhookey ditched his TDR intercooler for a cheap eBay unit because it had lower pressure drop (who knew) and picked up a bit of power everywhere on it. It's easy to measure.

You're being sarcastic, but I'm not. It won't. You might see the curve itself go up and down, but with a centrifugal blower, you will not make significant alterations to the shape of the torque curve by changing the head or cams (within reason). Your misguided argument is that he isn't revving the car hard enough to see the torque drop, when in reality there is nothing that will produce that torque drop on a Rotrex blower (aside from an inlet restrictor or a wastegate on the charge piping).

So call me out - you might be surprised at my opinions on head/cam development. If I have a strong opinion on this site, I haven't just pulled it from my ass - I will always have a direct experience or some hard, relevant evidence to back it up.

How would i go about doing this? Just run a vaccum/boost gauge on the IC inlet and outlet and measure the difference?

Yep. It's that easy.

Just two little gauges, before and after.

if you wanna get really technical just reroute your ms line to the two locations and log each.

You mean my Haltech line ;). That's a good idea... easier too. I'll do that.

If the pressure difference isn't too large a really simple device can work
http://www.engineeringtoolbox.com/u-...ter-d_611.html
It could work on Dyno and on straight road, but easiest with a leaf-blower or similar.

Mathematics? It is good that falcon is Canadian or he might be insulted that you expected him to perform math, lol.

BTW falcon, the mountain climb clip was far more treacherous than track driving. I could understand if it was being done illegally but that it could be sanctioned by anyone is ridiculous. There are big trees and drop-offs with no run off room. Nuts.

you can buy a electronic pressure diffierntial sensor for around 14 dollars off digikey

Looks fun as hell, I'd do it if they had a local event here.

Yeah it's crazy they let cars without roll bars do it too! There was a Miata that ran with an FM built motor/turbo kit that ran without roll protection. Stupid IMO.

There are other NHA (Northwest Hillclimb Ass.) events that have bigger drop offs. If you go back to the video and go under my name there is a video of Knox Mtn. Hillclimb. That's one in BC but with much stricter safety rules and fully sanctioned by the CACC. I hit way higher top speeds at Knox that Bible Creek, and I had 50whp less at Knox... :D

How many times do I have to say, "I got it"?



So tell me about all your highly developed camshaft and cylinder head experience.

You know what, lets forget about this stupid pissing match. You do what you do, and I do what I do. Lets leave it at that.

A hose with some water in it folded into a "U", run some air through the IC, use a tape measure and note down the pressure difference (the difference between the water levels in the "U"). Do the same with another IC.
The IC with the lower difference wins (assuming you can create the same airflow through the two while measuring them).

If one distance is larger than another is not that complicated math (unless you're a politician) :D

I can tell you if he plots Torque divided by MAP.