Forced Induction Intake Manifolds
07-02-03, 04:59 PM
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Forced Induction Intake Manifolds
I have heard about several aftermarket intake manifolds that can be used in forced induction applications (jaytech?) but I have seen no real information on any of them. Can anybody list the different designs and where to get them and possibly any information on the design.
I am also looking into fabricating my own. I have access to a full machine shop, so it is the design that has me befuddled. I have read corky bell's section on intake manifolds in his forced induction book, but it doesn't apply to rotary's specifically which is what i am looking for. Here are my design concerns, please add to them with any further knowledge that you have.
-Short small primary runners for high intake velocity at low engine speeds, with design attention payed to engine operating in vacuum.
-Long large secondary runners for good powerband (forced so design has less impact?).
-Individual throttle bodies or dual XXmm or single XXmm, which is best?
-Plenum 50-70% engine displacement (according to corky bell) how important is this in forced induction application.
What exactly are the specs to build to? This manifold will be on a stock port s5 13BT, to4s, e6k. Just how important is intake manifold design on a forced induction rotary? How many whp are we talking? Is it worth making your own manifold? I am shooting for over 400whp on 16lbs stock port and later down the road 500whp on 20+lbs with porting.
I am also looking into fabricating my own. I have access to a full machine shop, so it is the design that has me befuddled. I have read corky bell's section on intake manifolds in his forced induction book, but it doesn't apply to rotary's specifically which is what i am looking for. Here are my design concerns, please add to them with any further knowledge that you have.
-Short small primary runners for high intake velocity at low engine speeds, with design attention payed to engine operating in vacuum.
-Long large secondary runners for good powerband (forced so design has less impact?).
-Individual throttle bodies or dual XXmm or single XXmm, which is best?
-Plenum 50-70% engine displacement (according to corky bell) how important is this in forced induction application.
What exactly are the specs to build to? This manifold will be on a stock port s5 13BT, to4s, e6k. Just how important is intake manifold design on a forced induction rotary? How many whp are we talking? Is it worth making your own manifold? I am shooting for over 400whp on 16lbs stock port and later down the road 500whp on 20+lbs with porting.
07-02-03, 05:57 PM
#3
Read my thread on how to calculate intake runner length.
Yes, absolutely runner length is just as important on a turbo car as a nonturbo. Many highly modded turbo cars will still show good top end power with more radical porting even though the stock manifold is used. This is solely based on the efficiency range of the turbo. The turbo doesn't know that the manifold is or is not tuned to the same efficiency range. The turbo can keep on forcing more air in to the engine regardless of if the manifold is past its efficiency zone or not. This is why we can tune a manifold to make great low end power but still have nice top end. This doesn't mean that the engine couldn't be making more power here with the proper manifold though. If you want to use stock ports but want a higher rpm range then it is really quite simple. Shorter runners or a larger turbo or both. Since you want to use a T-04S, you do have the flow necessary to give you the power you want. Probably not from the stock length manifold though. To tune for the power band you want you will need a total runner length of about 14.5"-15". Stock it is more or less 17.1" or so. They aren't quite equal. Plenum volume isn't nearly as critical on a turbo car as it is an n/a. At least not for the rpm range that you want. As long as it can flow the desired air, it should do fine. The custom manifold that I built for my T-II is just an upper manifold that mates to the stock lower. It has a total runner length of 15" and a plenum size of 100 cubic inches. It is designed to be used with a Mustang throttlebody. It flows tons more than the stock upper manifold and tunes the powerband a little higher on a stock port or about the same powerband on a streetport.
You can not tune one set of runners around low rpm power and then tune other runners to high rpm power unless they completely switch from one set to another. They can not both be working at the same time. Each port has to be tuned for peak power at the same rpm. You can close 2 runners at lower rpms like the RX-8 to get more low end power but you can't tune these runners to a different rpm.
What do you mean by wanting your powerband fattened? Do you want power over a wider range or are you just looking for a flatter powerband between 4000-6000 rpm? A usable powerband that is 6000 rpm wide is an unreasonable request for the 400 hp goal and quite unnecessary. Your transmission is only geared around a certain smaller powerband anyways so why go outside of this area? You won't be any faster. If you want to design a manifold that tunes your power peak up a little higher, your powerband will get narrower. For a really wide powerband tune to a low rpm and then let the turbo make up for manifold inefficiencies. You will not hit 400 hp this way though. I think what you really need is a constantly changing length manifold with a large enough variable area turbine nozzle (VATN) turbo. This isn't going to happen though.
Yes, absolutely runner length is just as important on a turbo car as a nonturbo. Many highly modded turbo cars will still show good top end power with more radical porting even though the stock manifold is used. This is solely based on the efficiency range of the turbo. The turbo doesn't know that the manifold is or is not tuned to the same efficiency range. The turbo can keep on forcing more air in to the engine regardless of if the manifold is past its efficiency zone or not. This is why we can tune a manifold to make great low end power but still have nice top end. This doesn't mean that the engine couldn't be making more power here with the proper manifold though. If you want to use stock ports but want a higher rpm range then it is really quite simple. Shorter runners or a larger turbo or both. Since you want to use a T-04S, you do have the flow necessary to give you the power you want. Probably not from the stock length manifold though. To tune for the power band you want you will need a total runner length of about 14.5"-15". Stock it is more or less 17.1" or so. They aren't quite equal. Plenum volume isn't nearly as critical on a turbo car as it is an n/a. At least not for the rpm range that you want. As long as it can flow the desired air, it should do fine. The custom manifold that I built for my T-II is just an upper manifold that mates to the stock lower. It has a total runner length of 15" and a plenum size of 100 cubic inches. It is designed to be used with a Mustang throttlebody. It flows tons more than the stock upper manifold and tunes the powerband a little higher on a stock port or about the same powerband on a streetport.
You can not tune one set of runners around low rpm power and then tune other runners to high rpm power unless they completely switch from one set to another. They can not both be working at the same time. Each port has to be tuned for peak power at the same rpm. You can close 2 runners at lower rpms like the RX-8 to get more low end power but you can't tune these runners to a different rpm.
What do you mean by wanting your powerband fattened? Do you want power over a wider range or are you just looking for a flatter powerband between 4000-6000 rpm? A usable powerband that is 6000 rpm wide is an unreasonable request for the 400 hp goal and quite unnecessary. Your transmission is only geared around a certain smaller powerband anyways so why go outside of this area? You won't be any faster. If you want to design a manifold that tunes your power peak up a little higher, your powerband will get narrower. For a really wide powerband tune to a low rpm and then let the turbo make up for manifold inefficiencies. You will not hit 400 hp this way though. I think what you really need is a constantly changing length manifold with a large enough variable area turbine nozzle (VATN) turbo. This isn't going to happen though.
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