Mazmart

iTrader: (12)

How could I say no to you. Come try it out .

Paul.

RIWWP

iTrader: (2)

Awesome

I'd bet that Paul was probably the first, so neither of us could be

ukmiata

My car is as you described, there is not a lot of space for the exhaust manifold, mine will go back for a bit of big hammer work to make the space.

The tuner built my engine from scratch and did the same for the off-road racer, no difference in the engine. The difference is the exhaust manifold and rest of exhaust system. There are no cats on either car and neither engine is ported (yet).

The power jumped from 195rwhp (mine) to 220rwhp with just the exhaust changes. Note that neither exhaust is fitted in an RX8 engine bay so don't yet know if there will be space for it. The 220rwhp engine is still being run in and currently limited to 8000rpm so there is more to come, guess another +10/15bhp at 9krpm.

Initial mpg for mine during developement was 14mpg, now 17mpg on short commute (<3miles) and 21mpg on a run, now basically the same as my RX7. I've only just started tuning for low mpg, lambda currently 0.91 when rpms are static, don't know what the lambda is yet during throttle on/off. I'm hoping to get to 25mpg, the MX5 has the aerodynamics of a brick.

I'll post my dyno up next, torque is good at 170+lbft, but the power dies above 7krpm, now we know where it went


The off road racer gets single figure mpg, its mostly at full throttle. Thread is http://www.mx5nutz.com/forum/index.php?showtopic=84257

Engine before latest changes. Owner is PhillipM, posts on here sometimes I believe.





More pics of mine:

http://www.mx5nutz.com/forum/index.p...c=45731&st=120

ukmiata

That was a big factor for my intake, costing a few months on the project. It was discovered that anything other than a short and perfectly straight path from the stock intake to the air filter cost power, on the order of 5-10bhp.

This was the reason for the final intake design, the rad had to be tilted back 45' so the airbox could go over the top and provide the short/straight path to the stock intake manifold (see pics in build thread).

rotarygod

No intake manifold is perfect. This is by far the best one ever factory installed on a rotary engine. You can probably get a few horsepower more out of it but if you can't get at least 10% more, you won't feel it. You aren't getting 10% more out of any mod on a stock intake manifold.

VDI is most certainly not useless. It definitely helps. If it doesn't something is wrong with your engine.

A bigger throttle body may seem to help low and midrange but it isn't. It is only allowing more air to enter at a lower opening which fools you into thinking it is helping. It's a placebo effect. The only way to determine if a larger throttle body is an improvement is at full throttle at max rpm's. If power went up a little bit up top, it helped. If it didn't go up, the extra size did nothing. Once you exceed what the engine needs, more isn't helping. The stock tb far exceeds any demand at lower rpms and loads. With drive by wire you can reprogram the throttle opening rate to simulate the same thing anyways.

RIWWP

iTrader: (2)

Fantastic! Yup, PhillipM is known around here.

I don't think that the header in that pic would fit in an RX-8 bay without firewall modification, but my god it looks good.

bse50

You can always route it underneath and let it merge some centimetres after the oe cat is.
O2 sensor in the center tube or wire a short extension, job done.
A miata is way smaller though and you have tighter spaces.

Phillip is awesome!

RIWWP

iTrader: (2)

^ yeah. When I was planning my Renesis Miata () I was figuring on having the individual runners run next to each other rather than "bundled" like in that picture until I could get it back decently far to where the OE cat space is, then merge them. Keep the exhaust vertical profile of the runners as 'short' as possible and set be no taller than the diameter of a single runner.

olddragger

iTrader: (3)

totally agree RG that no intake is perfect and mazda for the most part did do a pretty good job within its design limitations.
With a bigger TB the power continues up top--it is just felt better in the low/mid range--exactly for the reason you mentioned. It is much more evident after you place even low boost FI on the car. The new Pettit kit with a 2.1 blower will have a dual TB ( modified to use the oem TB sensors) and a total of 125mm opening--it will suck up small rodents:0

The VDI has shown to lose power time after time on the dynos. Not much--but just a tad. In theory it shouldnt--IDK.
I still think that the oem intake runners are unequal in lenght. Many have disagreed. I measured them (inside)the best I could and one is a little longer than the other--maybe that is why the vdi doesnt work as well --again IDK.

Agree with the op--straight intake runners are the best. I even hate the way the ssv makes the front intake runner curve.

That is one sweet looking buggy dude! Very envious

rotarygod

All of the RX-7's also had unequal length intake runners. It's definitely not optimal. VDI however works based on the total distance through the runners from one port to the other and where it is fed from is irrelevant for the effect. It's not to say that we shouldn't have it be equal though but Mazda is relying on the VDI effect being the dominant one over pure runner length tuning.

VDI may lose power in certain forced induction situations but it isn't doing so naturally aspirated. You can't just think in terms of full throttle dyno runs. Dyno's tell you so little about what is going on. It takes many dyno runs over many load ranges to tell you the whole story. A dyno is a 2D cutaway of a small section of a 3D picture. You'll find that VDI has a very important role even if it doesn't show up in one little cutaway.

Having a large throttle body with a blower is different than in a naturally aspirated situation. A blower is always pushing air towards the engine. A naturally aspirated engine is always trying to pull it and it requires some velocity to get max performance. With a blower, a larger throttle body is a good thing at it reduces pumping losses from the blower.

If I were building a race engine it would have straight runners (as straight as possible), non variable length with no VDI. It's throttle body would be sized so that there is no power loss anywhere within my chosen rpm range. It would be very different than my perfect street engine design.

The neat thing about airflow is that it doesn't always do what you think it will. Air is funny stuff. I haven't had a flow bench in probably 7 or 8 years now but I learned a lot when I did. When I was flowing an 88 n/a RX-7 manifold I found that a mod that I did hurt rather than helped. In that car the secondary injectors and their bosses protrude heavily into the airstream of the secondary intake runners in the outside of a corner. The runner loses lots of area here and logic said the added turbulence didn't help. I removed them, welded up the holes, and ground the runner smooth so there was no change in cross section or area. It should have been perfect. It actually lost airflow! Go figure.

I had also tested the flow through the auxiliary ports which on that engine share the secondary intake runners with the secondary intake ports. Their actuation was done pneumatically with a rod that went right through the airflow path to a bar that was connected across the rotating sleeve. The sleeve itself has a blunt end at the port and actually has a lip. Air can't flow through it smoothly.

With the manifold on the housing and flow measured through the port the first order of business was to add a radius to the back of the sleeve so air could more easily enter the engine at the port. This is a very common mod. It resulted in a whopping 1 cfm of improvement. That's it. There was so much turbulence from the actuator rods in the airflow that the air isn't smooth there anyways. Removing the rods from the airflow path however had a drastic improvement and this is when the radius really showed an improvement. Low end power is lost with the auxiliary ports open full time though so there was a tradeoff to high end/high load power.

Another interesting discovery was the flow differences between the S4 and S5 RX-7 intake manifolds. The S4 uses straighter shorter runners while the S5 uses longer runners that curve more but have VDI. The S4 flows more on a bench in a static situation but makes less power on an engine in a dynamic situation. Just looking at them your eyes tell you the S4 manifold should be better. It is definitely simpler I'll give it that.

The point is that you shouldn't judge the manifold based solely on what your eyes tell you. Those little things you see may be of no consequence to performance and something that you don't see might actually hurt it.

bse50

Mazda designed an intake that would make the car driveable and enjoyable at 3k rpms as much as it is at 8k. They resorted to 2 turbos on the fd for the same reason as peripheral exhausts aren't the best option when it comes to smooth\flat power deliveries (More or less).
There are dozens of things that can be done to make the stock intake manifold (upper\lower considered as an assembly) perform "better". The trade off is the power curve.
For a track car only driven between 6 and 9k rpms that's not an issue, for a street driven car it is.

Edit: As I posted RG had already replied with a smarter version of my post, lol.

olddragger

iTrader: (3)

Good info and points ---indeed--air is funny stuff. Lodgic at times also does not apply
Air velocity versus total flow can be a stay up all night discussion. But, the main point that we both 100% agree on is--measure your results and dynos only do give a snapshot.
I do stand corrected in that on a na engine--i dont have the data to support that more power will continue up top. Next time we have a track event i think i will swap my little 75 mm one with a na buddy, do some maf grams/sec collecting and see if where the engine is ingesting more and at what throttle/rpm position it does or doesnt. We also could measure the vacuum in the intake under what load/rpms.
dang it--ANOTHER thing that is interesting and for me to do

fyrious<>

ugh, i hate convertibles, soft or hard top. Main reason i went for the rx8, that and the rotary. Oh, and the miata /MX5 is just a tad too small, IMO. Unless they do something to make the MX5 look attractive/aggressive, i guess i won't be buying any sports cars through mazda in the near future if they keep the looks of the MX5. Mind you the rest of their line up is fine, my wife drives the 3 sport and we both love it.

olddragger

iTrader: (3)

flame suit on---but i have to say that Mazda is going to have to change the MX5 if they want to continue to have a good competitive sports car. It has gotten too soft, handling ( from the factory) has been compromized, power to weight is not that great and its a tad too small interior wise for the american market.
Toyota and Subaru is now in the market with their new cars, and others have models that offer rear wheel drive too.
I would love to see a fastback hardtop ( 3 door type) mx5 with the rotary and keeping the weight down to 2600-2700.
Presently -I really dont see a future for the MX5 as it is today. I wouldnt buy one.
Flame suit --ON!

pdxhak

iTrader: (2)

Pretty sure you are basically describing a RX7

bse50

the mx5 got too fat and big.

Spin9k

imo even worse is too come...
as they downsize it to save weight, making it EVEN SMALLER inside
and then DOWNSIZE POWER to up the mileage rating
leaving it in the dust vs others performance
while keeping its current wallowmobile handling
maintaining or UPPING its ALREADY TOO HIGH price tag

FAIL

ASH8

As an owner I will come in here, Denny IMO you are basically correct.

The NC1 and NC2 (my car) factory handling package is appalling (even with 'sports suspension'), there is that much body roll it is a joke....what fixes it...Series 2 or RX-8 Sway Bars (front and rear), It TOTALLY transforms this car, why wouldn't it the front Suspension is RX-8 basically....it is now like my 8.

Power to weight (2.0l), for an engine close to 10 years of age, it is fine.

Size, well again, Mazda are saying they are going smaller/lighter, a larger MX-5 is not an MX-5, if you don't fit, then perhaps lose some weight or eat less

For summer I park the 8, the MX-5 IS WAY MORE FUN...NO Contest...top down naturally..that is what the 5 is about.

ASH8

Sway Bar fix ..about $200

neit_jnf

It's all a matter of opinion, the original was much smaller than a new one so they're basically going back to original size/weight. To some, myself included, this is a GOOD thing.

They did a good job on the CX-5, smaller and lighter than the CX-7 but MORE space inside.

they can just drop the 2.0 155hp Skyactiv in it and being much lighter than a Mazda3 it will surpass 40mpg hwy easily. Even if they go with the rumored smaller+turbo 170hp can have great mileage and better power to weight ratio.

ASH8

Yep, the ND MX-5 will be 7 mm shorter (WOW) and 4 mm narrower (WOW), that is much smaller.

The CX-5 has more rear cargo space, but has smaller cabin space than the CX-7.

Anyway, will be interesting to see how the SA Engine will fit with 4:2:1 Header in a 'narrower' ND, as it can not fit today in NC, just like it can't fit in a Mazda 3 with SA.

fyrious<>

its not a matter of "losing weight" nice shot though. Its about it being too small period. An average sized man IMO even has difficulty fitting in, i had the "luck" of test driving one a short time ago and i'm only 5'10 ~ 5'11 and about 180lbs by no means a big guy and i felt uncomfortable.

*flame suit on* - its a girls car really. its small and its a convertible. nuff said.

New Yorker

Or, the American market is too, ahem... large... for the Miata. Nah, that couldn't be possible.

FYI, the Miata is, by far, the most popular track car in the world, and deservedly so. That won't be changing anytime soon.

fyrious<>

i'll take a rx8 over a miata/mx5 any day. And in the near future it'll be a STi over mx5 if mazda ends up going with the dinky car convertible style. fingers crossed they make it decent and that doesn't happen.

Mazmart

iTrader: (12)

Yes. It will be a very special package arrangement I suspect. The current LF MZR in the MX-5 is angled to the right (US Passenger side), accommodating greater intake runner length which is on the left. I have observed firsthand, the difference in size and shape of the LF vs PE engines in the new 3 and the new engine may be a little wider and/or is tilted backward (Engine's right side) again perhaps to provide for the longest intake runners (Front or radiator side). With this design, there is no room for the elaborate header. In the case of the ND MX-5, I suspect they will have to widen the subframe opening (Much more similar to the RX-8) thereby allowing it's tilted engine more space. I'm sure there is much more to it than that. I hope I did nor confuse anyone. The 3 has a transverse engine (FWD) and the MX-5 longitudinal like the RX-8 (RWD).

Regarding those who would never buy a convertible: This sentiment reminds me of those who cannot appreciate the rotary . You don't know what you're missing. Will Mazda make it one car or two cars on the same platform? Who knows. I remain excited about the future.

Paul.