Ronny

If I port the intake port to get as early opening as possible (with out going to bp), beveling the rotor the get even earlier opening,

and keep the stock closing time. The ex. port will just be cleaned up.

How would this affect the power curve on a 13bt s5 engine?

Will it strenghten the low and midrange, or will the extra overlap do the opposit?



Ronny

Liborek

It should be more powerful everywhere, at load. But tell us more, turbocharger will have huge impact, it must flow very well on turbine

Ronny

This will be for my daily drive s5 convertible.

The turbo is a gt3540, with a A/R 0.84 T3 twin entry hotside, and a fully divided short runner manifold with a 45mm wg.

When you look at the rx8 port timing, the intake opens at Tdc, just after the ex.port has just closed, 0° overlap.

On the rx7 engine ex. closes at 48°atdc, and the intake opens at 32° ATDC, this gives 16° overlap and let the ex.port be the only open port for 32° into the intake stroke.

If I can get the Intake to open at 8°atdc and leave the ex.port stock, I get 40° overlap and let the ex.port be the only open port for only 8° into the intake stroke.



My thought is by reducing the time the ex.port is the only open port into the intake stroke, down to a minimum, and let the engine start sucking air from the intake port as close to tdc as possible, and not force it to try to suck the exhaust back from the open ex.port until the intake opens..

I would like to think this overlap is far better for low rpm/low load driving, and also increase the power in this rpm aera while stepping on it.



Compared to if you just ported the ex.closing time to 72° atdc (which also give 40° overlap, but let the ex.port be open 72° into the intake stroke), and leave the intake opening time stock,this will have a much bigger influence on the power curve of the engine, moving it up in the rpm range..



This is just my thoughts on this subject, and it might be totaly insane

So any input is appreciated

What I want to achieve is increased power in the 1500-4000rpm area and 350-400whp at no more than 7000 rpm.

I`m offcourse running standalone, and will soon be getting a Eomp controller



Cheers

Ronny

Liborek

No, Its not totally insane, actually it seems you have good understanding how port timing works. Opening intake ports earlier and keeping stock closing will increase VE% curve everywhere so this is good start. But for your power goals rotor beveling seems excessive and would call for larger hotside than you are suggesting. GT35R compressor is very capable, but again excessive for your goals. Garrett T04E 57/60 Trim would be better choose. But if you already have GT35R go with it. For even better response you could use high compression rotors.

Ronny

I will only bevel the opening edge on the rotors to gain a couple more degrees earlier opening.

This shouldnt affect the hotside as the ex.port timing wont change.

What conserns me is how the light load everyday driving,off throttle responce and 2500-4000rpm low load throttle respons will be affected, compared to a streetport that also moves the power curve upp in the rpm range..

Any

thoughts

Liborek

It will effect intake/exhaust relationship big time. Early opening intake gives high VE%, but of course, we are assuming low turbine inlet pressure, lower than intake pressure, which would work with GT35R to certain RPMs.... Then it would be rather detrimental.





Any porting that gives good VE% at high load, suffers at low load. Its not RPM based, just LOAD based. Street port moves powerband up because of LATER closing, its same with every porting. Most people have no idea why they are porting in the way they do and then wonder why their engine has peaky powerband and weak low-end. Most funny but at the same time sad is, that their reasoning behind late closing and almost stock opening is, that they didnīt want to lose low-end "because of overlap"





Hence for goals you want I suggesting early opening street port with modest closing and for better off-boost response high CR rotors.

Mazdanowski

Ronny you mentioned you would like to get the intake to open at 8 degrees ATDC. How will you be able to do that? I"m under the impression that we can't open before around 25 degrees ATDC.

I am guessing your are not using Renesis rotors.

j9fd3s

i agree that doing nothing but opening the intake earlier will take the existing power curve and just move it up, IE it'll make more power everywhere.



more power = more air flow = you need a bigger turbine.



i think id rather add overlap with bigger/better intake timing vs a bigger exhaust port, i'll take the bigger intake port.

Trots*88TII-AE*

I'm glad someone brought this discussion up, it's been on my mind a lot lately. Sorry to hijack the thread, but there's some things I wanted to talk about too, due to some testing done by Defined Autoworks' 20B semi-pp N/A engine. Basically, when he closed off the small peripheral ports for testing to compare streetport vs. semi-pp, which in turn severely retarded intake port opening, his low-end power was nearly identical. It wasn't until higher RPM's (I believe 7,000 RPM +) that the streetport-only configuration ran out of airflow, and the additional port volume/overlap of the additional peripheral ports allowed it to maintain the same torque to 10,000 RPM.



So, how is it possible that reducing overlap, reducing port volume, retarding port closing and seemingly increasing intake velocity due to some of these factors not increase output in lower RPM's? That's contrary to all of the porting theory that's been common to all (I thought...) Is it possible that after a certain amount of intake port open advancing and close delaying, further advancing or retarding nets nothing because VE has effectively topped out up to a certain RPM, and if so where would that point be? Or does going more aggressively on the intake port never lose you any bottom end?



This is the post about the 20B N/A: http://www.rx7club.com/showpost.php?...&postcount=187



I guess what I'm asking is if anyone else has done back-to-back testing, in different circumstances, between porting, all else remaining relatively equal (including boost if turbo'ed) to show the relationship between porting and output characteristics.

Liborek

Loganīs approach of semi-pp that are opened with more than 50% throttle is perfect. In regards of powerband, he should try close side ports and let engine in very low end and mid range - at load, run only with semi-pp, it should give more power, before exceeding semiīs flow capabilities.





Common to all on internet forums?



Mazda themselves and not only Mazda, many decades ago shown in tech. papers that VE% in whole rev range is increasing when intake ports are opened early, as much as 90° BTDC in case of PP and as much as 110° BTDC in case of BP, but, and it is very important, with free flowing exhaust and full load. These testīs were carried out with fixed intake closing, so in case of PP, port volume - area, increased substantially with earier and earlier opening, and still neted more VE, to the point, which I mentioned before.



With closing, its pretty straightforward. Later intake closing, loss of low end and mid range till enough RPMs where inertia of air/fuel mixture and pulse tuning will overcome delayed closing.



So simply said, intake opening - the earlier, the better , but its load dependent. Closing is purely RPM dependent, and sadly, there is no point of closing intake ports extremelly late, when owner is not going to rev engine enough, intake canīt support that, engine is not balanced, whole package is not build to take advantage of it