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Old 12-14-2015, 02:37 AM   #41
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Originally Posted by Madjak View Post
Sure it does... I get 200whp N/A out of a 1.85L BP engine. That's not bad for an engine of a similar era and design (ie 16v, twin cam). You take any 1.8 / 2.0L Toyota, Ford, Honda engine from that same time and apply similar mods and you'll get a similar power range +/- 10% per L. Sure the Honda engine might rev a bit more, but you _can_ also make the BP rev to 9000 with a bit of work.
Ummm. No it doesn't flow as well, and never will. Check out these ports.

Mazda B series.



Honda B16




Wonder which will flow better.
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Old 12-14-2015, 03:03 AM   #42
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Originally Posted by Guy Farting View Post
So how does an engine like a rotrex 1.8 BP burn so much air and fuel at nearly 7000rpm to produce 230hp but only 170 lb-ft?

If the rotrex comes on late to boost and doesnt produce it until later in the RPM range why does the torque not follow the HP closer?

Maybe I just need to bone up on my maths and undestanding of engines and basic crap.
You need to read about what HP and torque are. And reread my post after you have a clear understanding of what each are, and how they are mathematically calculated or measured. Torque is measured, it's twisting force. HP is calculated by the equation HP = (torque x RPM) / 5252 if memory serves me correct.
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Old 12-14-2015, 03:52 AM   #43
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Originally Posted by aidandj View Post
Ummm. No it doesn't flow as well, and never will. Check out these ports.

Wonder which will flow better.
Sure stock, but a highly developed head looks nothing like those cross sections. A BP-05 fully developed can flow close to a BP-4W fully developed. The starting points are much further apart, but the BP-05 has a lot more meat in the head to be worked.

The ports aren't the only part of the equation. Because the piston sizes for all 1.8L engines are all around the 84-85mm diameter, you can only fit 4 valves of a certain size in there. Valve lift, duration and ramp angle are restricted by mechanical boundaries which are the same on all engines (ie piston positioning) so as long as the head flow isn't the bottleneck and can supply a clean laminar flow the engines will perform similarly.

I think the advantage a Honda has is less to do with the flow through the head and more to do with how well it can rev. That's harder to match with a BP engine.

Anyway, my point is... A Rotrex is a good match for a highly developed BP race engine, as it is an application where torque is not required as much as power.
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Old 12-14-2015, 05:50 AM   #44
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I always try to equate everything to water and how it flows. It makes sense to me as I can visualise it better! You can do this with electronics too.

So Torque is basically how big your bucket is. It's a measure of strength and how much someone can lift. Whilst power is how much water you can move in a minute. It is a combination of how fast someone can run multiplied by how much water they can carry.

A Rotrex BP hitting 300whp @ 8500 will only have a torque rating of 185ft lbs. So it can only carry a small bucket of water (18.5L) but can sprint the water forwards and backwards rapidly (ie 8500 rpm), so it can fill the tank to 300L within a set time period. (replace 'L' with your preferred unit of choice)

A turbo BP hitting 300whp @ 4500 will have 350ft lbs of torque. So the turbo car has a much bigger bucket (nearly double), but it can't move as fast. It takes longer between trips but can fill the tank to the same 300L mark as the sprinter.

A diesel truck can hit 300whp @ 2000 and has 780ft lbs of torque. It has a massive bucket but a low cyclic rate... but a couple of trips will fill the bucket to the the same level.

Each of those options, if they can operate at their peak power will be equally as fast as each other at filling the end tank. The end tank is a representation of total power, which is equal to acceleration.

Where it gets complicated in a car is that the torque curve isn't flat, ie the bucket size isn't constant. Also the gearbox isn't a CVT so the engine must cycle through the revs. The Rotrex BP will have close to a flat torque curve in the upper RPM range (ie it's bucket stays the same size) but it's peak power will be somewhere very high in the rev range. The engine needs to stay as close as possible to it's peak power to maintain it's work rate. The further away from that peak, the less water it can move per second (ie the person with the bucket has to sprint forwards and backwards to move the water because they have a small bucket. Any slow down in the speed also slows down the rate of water being moved).

The Turbo BP will also have a flat curve and peak torque in the midrange somewhere. This means there is a far larger rev range for the power to be generated over. ie, the person with the bucket can jog backwards and forwards and it matters less if they slow or speed up a bit, as the size of the bucket stays the same and can move lots of water in one go. It does take a while to get going though which is a downside of a turbo, ie turbo lag... the first trip the bucket is small, and gets bigger with the first few goes.

Not sure if that helps...
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Old 12-14-2015, 07:30 AM   #45
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I also use the bucket analogy to explain this.

I talk about how if you have a weak handle you need to lift half as many rocks, at double the speed to do the same amount of work to stop the handle from breaking. But if you have a set of forged handles you can fill the bucket to the brim with rocks and do it at half the speed for the same amount of work done, or the same speed for double the work.

I use the amount its filled to represent torque, the handle to represent internal strength, and the amount its filled multiplied with the rate at which you fill and empty it to explain the work being done over time, which is HP.

Dann
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Old 12-14-2015, 11:30 AM   #46
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Originally Posted by Madjak View Post
If ever I get around to it, that's exactly what I want to build. A 400hp+ Rotrex, 6 speed, 4.3 diff, powerband between 6250 - 8500rpm. To get that sort of power you need a very efficient intake/head/exhaust, a whack of compression, E85 and the C30-94 Rotex... nothing too difficult and I'm surprised there aren't more cars like this out there.
or install a $20 boost control solenoid on your turbo setup...
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Old 12-14-2015, 12:04 PM   #47
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Originally Posted by nitrodann View Post
I also use the bucket analogy to explain this.

I talk about how if you have a weak handle you need to lift half as many rocks, at double the speed to do the same amount of work to stop the handle from breaking. But if you have a set of forged handles you can fill the bucket to the brim with rocks and do it at half the speed for the same amount of work done, or the same speed for double the work.

I use the amount its filled to represent torque, the handle to represent internal strength, and the amount its filled multiplied with the rate at which you fill and empty it to explain the work being done over time, which is HP.

Dann
Actually, the rods are subject to more force from RPM than they are from torque (as long as you arn't deting or pinging). Doubling the torque only increases stress on the rods somewhere between 20-50% (forget the exact number and don't feel like mathing) but the relation on rod stress to rpm is a 3rd or 4th power relation.

So a better metafore would be that you can load the bucket with a weak handle with a lot of rocks, if you move it very slowly. But a stronger handle will let you move the same rocks faster.
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Old 12-14-2015, 12:08 PM   #48
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Originally Posted by Braineack View Post
or install a $20 boost control solenoid on your turbo setup...
What up the boost from 0PSI? Would need a turbo for that to help!

I know this is a turbo forum but for a track car a Rotrex is ideal. They are an easy install, will run all day, get the power where you want it, ie up high to protect the gearbox, are safer on the engine and have no lag.

They don't really work well on a stock motor that is driven on the street and the dyno results show that.
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Old 12-14-2015, 12:11 PM   #49
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Look at the angle of the Honda ports. The head is much taller which allows for totally different entrance angles. You say look at a ported BP head, but what about comparing that to a ported B16 head.
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Old 12-14-2015, 12:48 PM   #50
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Originally Posted by Madjak View Post
What up the boost from 0PSI? Would need a turbo for that to help!

I know this is a turbo forum but for a track car a Rotrex is ideal. They are an easy install, will run all day, get the power where you want it, ie up high to protect the gearbox, are safer on the engine and have no lag.

They don't really work well on a stock motor that is driven on the street and the dyno results show that.
all im suggesting is that you can more or less replicate the power output of a rotrex on a turbo setup. That's all.

still an easy install, run all day, and get the lack of power you want. just as easy on the gearbox and engine, but you'll still have the "lag".
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Old 12-14-2015, 01:36 PM   #51
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The BP was designed to power the gasoline versions of these, not sportscars:

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Why do Rotrex suck at torque?-mazda-truck-4.jpg  
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Old 12-14-2015, 01:40 PM   #52
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you want a 1.6 B6 in your sportscare, amirite
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Old 12-14-2015, 02:08 PM   #53
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Originally Posted by Madjak View Post
If ever I get around to it, that's exactly what I want to build. A 400hp+ Rotrex, 6 speed, 4.3 diff, powerband between 6250 - 8500rpm. To get that sort of power you need a very efficient intake/head/exhaust, a whack of compression, E85 and the C30-94 Rotex... nothing too difficult and I'm surprised there aren't more cars like this out there.
I've seen the car you speak of built. 430whp from a big unrestricted Rotrex. Redline was 7400rpm. My 350whp turbocharged car made more horsepower from idle to 6700rpm.
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Old 12-14-2015, 02:15 PM   #54
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I've seen the car you speak of built. 430whp from a big unrestricted Rotrex. Redline was 7400rpm. My 350whp turbocharged car made more horsepower from idle to 6700rpm.
clearly, you've never been on track
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Originally Posted by emilio700 View Post
What facts are those? Are we referring to the difference in torque and throttle response? Beat to death. Low RPM torque wins torque braked roll ons in street cars and of course that is the only thing that should matter to anybody!!

100% of the forum members that troll every mention of a Rotrex:

A) Do not have DPE (direct personal experience) with making a 250whp+ F/I Miata last on track for a 3hr weekend of track time without opening the hood

B) Have never driven a Rotrex on track

C) Work at McDonald's at the mall

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Originally Posted by emilio700 View Post
Um you're the one whining about your broken trubo in a Rotrex thread. Why?

Entertainment? No.

None of the Rotrex owners are insecure enough to spend hours in turbo thread saying stuff like "manifold studs much?" "Boost lags!" "melted everythings!"

If you guys weren't so damned insecure and threatened by the idea of the Rotrex, we wouldn't be having this troll fest.

The vulgar language really helps to make your point though. Clearly you are righteous.

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Old 12-14-2015, 02:19 PM   #55
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Response to Madjak:
The Honda doesn't rev better because it has a miracle bottom end design. It revs better because the heads breathe well and ours do not. We have engines with limited engineering $ invested in them. They are designed to be reliable, inexpensive, rudimentary, and make moderate mid range power. They are not designed to be performance engines.

Why do rotrex make more horsepower than torque? They increase speed linearly in relation to the crank speed and crank speed is integral to the calculation of HP.
Again, math.
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Old 12-14-2015, 02:23 PM   #56
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It's exceedingly rare that I look at a thread on this forum and think to myself "you know, this thread really deserved to be locked, m.net style..."
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Old 12-14-2015, 02:31 PM   #57
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The 430whp track Rotrex was built by, and resides in the garage of a good friend of ours. A few interesting notes:

It was by far, the most reliable 300+whp F/I Miata I have ever seen or heard of. Nothing else even comes close. He ran that car for over a year (50+hrs of flogging in California heat) at 400whp (detuned) on what was basically a stock NB1 engine. Forged 9.0:1 pistons, forged rods and that's about it. Stock head and everything else. He did at least one 2hr enduro with it. Ran on 100 race gas.

Because of the very conservative tune and stock long block, it did not make any torque anywhere. The one I built with a blower two sizes smaller but with a built Whammy engine made a lot more torque through the midrange. Enough to rocket off slow turns below 4500rpm on the edge of wheelspin. So a Rotrex build that's easily capable of shredding teeth of every gear in an AZ-6 is easily done. Just no one has built one yet.

The question anyone who cares has to ask themselves, is how much torque is needed and how do you want it delivered. The latest EFR based turbo kits like TSE's, with a big exhaust and good engine management deliver pretty close to the perfect powerband and boost vs TPS response. IMO, anything with an older non EFR turbo, or tiny GT2554R or crappy engine management, gives up total performance to a well tuned Rotrex setup.

It boils down to having more torque but having to wait for the torque to build after asking for it, then having to modulate if its too much for available traction, or with the Rotrex having less peak torque but all of it directly connected to TPS like a big N/A engine.

The guys who have most fun drag racing, playing on the dyno or hooning on public roads, tend to like turbos because of the big torque numbers, even if peak power is the same as an equivalent Rotrex. The Rotrex enthusiasts tend to be those who prefer canyon roads or race tracks and don't feel like working on the car to get it to stay together. Two different users.

I'm looking forward to driving a car with TSE's 6258 kit. FWIW, we have a street car here with a C30-94 and mildly built engine. We're aiming for 260tq/330whp on 91 at about 7000rpm.

Last edited by emilio700; 12-14-2015 at 03:12 PM. Reason: speling
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Old 12-14-2015, 02:42 PM   #58
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clearly, you've never been on track
Car was still very fast on track, but had to be driven to match its powerband.

The point is that they have pros and cons. They are not "ideal" for any application, same as a turbo is not "ideal" for any application. It's a personal choice to sacrifice powerband for response. This forum is full of turbo enthusiasts (myself included) who value midrange torque over N/A-esque response, so we all like turbos. Rotrex owners value the response over all else, and that's fine. They are polar opposite kits and I've never talked to someone who's been trying to decide between them for longer than about 30 seconds. You're either a turbo guy, or a Rotrex guy. Hence the endless on the topic.

As Emilio alluded to, my goal with the TSE EFR kit is to blend the two. Turbos have always had the edge on powerband, so all of my effort has gone into maximizing response.
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Old 12-14-2015, 03:09 PM   #59
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It's exceedingly rare that I look at a thread on this forum and think to myself "you know, this thread really deserved to be locked, m.net style..."
May as well just shut down the supercharger subforum if threads can't go half a page without trolling.
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Old 12-14-2015, 09:12 PM   #60
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Originally Posted by sixshooter View Post
Response to Madjak:
The Honda doesn't rev better because it has a miracle bottom end design. It revs better because the heads breathe well and ours do not. We have engines with limited engineering $ invested in them. They are designed to be reliable, inexpensive, rudimentary, and make moderate mid range power. They are not designed to be performance engine.
There are some design limitations that can't be overcome with a BP most of which limit the max revs. Head flow is not the issue and can be made to work with good porting... it's in the vibration frequencies and valve train. A Honda motor revs well because the engineers designed the engine with revs in mind. And yes they do have a better bottom end.

The power curve on my engine is still heading upwards at 8300... it needs to rev to 9000 to hit peak power. It could probably get there a few times on a dyno but not constantly and risks floating a valve. I will be upgrading the valve springs to help stop the valve float and when I do I think 220whp is achievable with a BP-05... You don't get power that high with a head that can't flow. Its the valves, intake and exhaust that limit a ported head.

In terms of turbo vs rotrex, I know where I sit. There is something about driving a fast N/A car that fits with my driving style. Every turbo car I've driven on the track has left me wanting better response. They are just so hard to push at the limit through sweepers and on corner exits. Rather than balancing the car through corners you're left fighting the car itself.

A good example is the current F1 season. The turbo cars have lost the magic of the old high reving V8s. The low down torque, strangled exhaust, difficult setup and engine faults all highlight why I prefer F1 from the past. Sure the cars are still fast but at the cost of all the great things in the sport.
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