Manifold Tech Discussion
 

Here's the deal, i'm porting/polishing my manifolds on my stock port s4 engine, and i wanna change the stock design of the manifolds. I dont wanna go all out and build a manifold from scratch, but just modify the stock ones.

Plan:
1) Keep the LIM, polish the primary ports, sand the secondary ports to keep up fuel atomization, and fill in any holes and the 5th 6th actuator holes with JB weld.

2) Cut the end of the UIM where the fuel injectors go so i can use the stock fuel rail and injector positions, and mount this peice to the LIM.

3) Ok, this is where i need help i would like to start a discussion with u guys. I wanna shorten the whole manifold by about 200 mm, more or less, to gain high end HP. I take my car to a road course so I am not overly concerned about losing low end power. Also, i dont wanna use the stock plenum because i dont think it flows air very well.

My idea is to cut the UIM and merge the two primary runners into a single pipe, kinda like a header, then run it into the primary port on the stock TB. Then have each of the secondary runners go into their own secondary port on the TB (see pictures attatched). This would shorten the manifold by about 200mm since i would be getting rid of the plenum, and also it would help improve air flow since the stock plenum is bad for this, and since i am getting rid of a 180degree bend in the manifold. My concern is that this design would not have as good of a scavanging effect with the pressure pulses in the intake as the stock plenum does.

So, I need some input on what u guys think about how scavanging works and how neccessary it is to have a plenum. My opinion is that scavanging would be reduced in my design but, it would still occur where the 2 primary runners meet, and it would also occur inside the TB where the 2 secondary runners meet.

it woudl be hard to join 4 pipes that are on the same centerline into a triangular throttle body. the pulses from the runners will be lost, all you do in this case is tune the runner length to the powerband that you want to achieve. otherwise this doesnt sloudn too bad

Confused
 

Why do you say that the pulses will be lost? Also, I thought that tuning the runner length to a certain powerband relied on using this scavanging effect? Otherwise i dont see why the length of the runners would matter.

anyone have any ideas? links? opinions? i tried doing some research but i cant find anything about intake plenums other than how to build one:(

to use the pulses you need to constict it in a U shape so the bounces will "supercharge" the air into the runner that has the port open. if its just runners going straight to a TB well then you see the point.

a manifold that has a vacuum chamber will usually get higher peak # but a itb setup will get you more throttle responce and a bit more midrange power.
seeing as you are looking to road race the car an itb setup will most likely be more beneficial to you.

http://www.thecarricos.com/ACRE/ there were at least 2 pdfs here that had some info on intake manifolds i dont recall which ones ill try and look for you though

thanks nevarmore:D heres one about the s5 manifolds and how the pulses work http://www.thecarricos.com/ACRE/Docu...tech90-1-6.pdf

kahren, i see what ur saying... hmmm. well, im not ready to go individual TB yet. maybe later if i am still runnning an na motor. when u say "a manifold that has a vacuum chamber", are u talking about the large volume chamber where all the intake runners meet? any idea why this gives more power than just joining runners into one pipe like an exhaust header? aaaaand, do u think that the system mazda made yields more power from the rotary than one of these vacuum chambers? my guess is yes, otherwise why didnt they use a vacuum chamber right?

anyways, thanks guys. some new things for me to think about.

hey check my thread out this showes an after amarket upper intake manafold for your rx7

https://www.rx7club.com/3rd-generation-specific-1993-2002-16/there-any-intakes-like-these-us-405082/

the stock Tb is pretty much an itb setup, and the plates are pretty big, the throttle body is probably teh best part of the stock induction system.

yes, the reason for more power is because of the supercharging effect, you take advantage of the pressure waives, like the stock system. a header collector does the same thing basicly but at an exhaust side, if the collector is made properly it helps scavenge the exhaust gasses from the other runner, the angle and design of a collector is a bit diffrent then that of the one thats on the intake runner, since the air is traveling in the other direction in the exhaust. so you want more of a V for a exhaust collector and more of a U on the intake side.


the stock sytem was tuned for a lower rpm, for low end tq, and to still have a somewhat nice powerband, they had a turbo model they needed to have a significatn diffrence between teh two models or noone would buy the turbo one. they could have easily made same 200hp with the NA that they did with turbo why they didnt i dont know :)

part of the reason why you can make more power with a shorter runner system is because it is tuned for higer rpm, and another reason is because there are less turns and restrictions. if a you can design a well made short style intake manifold then you can gain more power in the midrange and top end while only loosing very little to the stock manifold in the low end rpm range.

The dynamic chamber isn't the restriction that you think it is. On a flowbench you'd find that the dynamic chamber is actually the best flowing part of the intake system. The worst part is the lower manifold. Getting the auxillary port sleeves and rods out of the airstream helps airflow through here somewhat and it seems you are already planning to go this route. Do not use JB Weld. After about 150 degrees, it gets a little softer than some other epoxies and can potentially come loose. Use Devcon platic steel epoxy instead. It looks the same but is far and away better.

I've taken both turbo and nonturbo dynamic chambers, cut them in half, hogged them out into one large chamber, and then welded them back together. Since have 3 throttle plates was no longer necessary I modded mine to use a single plate Mustang throttlebody. When you do this the throttle gets alot more sensitive and low end power goes down. Since this is going to be a track car you probably won't care. I would never do it on a car that has any intention of being driven on the street other than as a play car.

Uncommon to poplual belief, porting and polishing your intake manifold won't be noticable in the power department. Too many people waste their time here and many end up hurting power. If you were to leave the dynamic chamber in place as is and just do everything to the manifold that you can, you can get a few more cfm in airflow. Somewhere around 7-8% or so. This doesn't mean that you'll get 7-8% more power though. Not even close. You'd be hard pressed to feel it or even notice a difference in track times.

If you already have a standalone ecu, ignore the next 2 paragraphs. The single biggest mistake people make is to do all of these mods to the intake system but still retain the stock ecu. This is a terrible waste of time. You obviously are looking for more top end power and are willing to sacrifice low end power to get it. That's how race cars are designed. With a stock air flow meter, you have 5 square inches or airflow area and even that is restricted further by a spring loaded trap door in the air stream. This is the single biggest restriction in the entire system and people still ignore it. There isn't much point in making other areas of the intake system flow better if they already flow better than the worst part. This is where the key to power is and this is what should be focused on. Would you use an air intake tube going to the throttlebody that was only a 2 3/8" pipe? Probably not. This is the size of you afm with the flapper door removed except that a 2 3/8" pipe flows much better than the afm. In truth your engine might as well be breathing through a 2" pipe! That's how restricted the intake side is. If this flow is limited here, there isn't much point in going for more power anywhere else until this has been addressed.

Kahren's car with stock ports and his custom manifold made great power. He made as much if not more power with a better power curve than most people's streetported engines. This is because he got rid of the pos factory ecu and used a standalone ecu. I believe his is a Haltech. Your engine has alot of potential and none of it is being realized with the stock ecu. When I installed my standalone, power went way up. They are easy to tune. They aren't near as hard as everyone says they are. With a standalone, you can tune based on whatever mods you want to do. They also don't have to be expensive. When you add up the cost of porting an engine, intake, exhaust, etc on a stock engine and then compare it to Kahren's, the expense is well worth it. Mine is a Megasquirt with less than $200 in the project. Others are more pricey. It is the first thing to be done in any serious effort for power.

If you are going to be road racing you DO NOT want to give up ANY low end torque... You will spend the entire straight just getting close again, and then get trounced coming out of the corners. Have you road raced before??? Carl

Rotarygod,
Do you have any pictures of the modification you do to the dynamic chambers?

Are you talking to me? I've road raced. Since it's not my car, I have no idea what type of racing he is designing it for. Just responding to what he said.

I used to. I'll have to go dig some up. I think I may even still have a T-II dynamic chamber in storage that was never welded back together. I'll look.

im trying to gain power above 5500 rpm since i will never drop below this rpm. some loss in power below 6000rpm for a large gain above 6000rpm is a worthwhile sacrifice and is pretty much what i am aiming for.

hmmm... k. heres the problem. the s4 na engine i am using righ tnow is already burning coolant so its life will not be long. most likely it is going to blow this summer depending how many times i hit the the track, and depending how lucky i am:P so when it does blow, i will have 2 choices. do and s5 turbo engine swap, or stay na. im still not sure what my decision is going to be so i dont wanna dump any money into this na engine right now. thats why im trying to do some mods to the stock manifold rather than make my own custom manifold from scratch. A programmable ecu does sound like a definate option since i could and would use it even if i decided to go turbo afterwards, but even this wouldnt happen till i saved up some money half way through summer. so for now i wanna try and gain as much power for as little money as possible. im doing all the work myself. so far i ported/polished the LIM but unfortunately used jbweld to fill all the holes:(:( hope it holds. right now im working on the TB. after the TB is done i will basically have 2 options of how to make an UIM.

1) the first option would be to make an intake manifold similar to how the stock s5 manifold looks under high rpm operation. this would have runners that face eachother to use the dynamic effect (all info here: http://www.thecarricos.com/ACRE/Doc...-tech90-1-6.pdf) like the stock s4 manifold, but with 200mm shorter runners to gain hp above 6000rpm.

2) my second option would be build an UIM with a vacuum chamber like this: http://www.sdsefi.com/techinta.htm.

now i have to decide which design would yeild the most power with my stock ports, ecu, and MAF. so far i KNOW that option 1 would yield about 5hp above 6000rpm just like it duz in the s5 engines. i may even get slightly more since it wont have the rotating valve or any other obstructions that the stock manifold may have. but i have still have no idea if using a vacuum chamber design would give decent power gains with my stock ports, ecu, and MAF.

thanks for all the help guys.

any pics kahren? did u use a vacumm chaber design?

click on my name and view my garage you will find a pic there.

niiiice. so did u make your own mounting positions for the fuel injectors? do the intake runners just go straight into the TB? i like how u moved the alternator, good idea.

Trying to bring this back to life....

So what happens if you tune your primaries for 5k max torque and your secondaries for 7k. Are you negating the benefits or would you get a flat TQ curve?

CW

yes new secondary rail mounting position, stock secondary rail. intake runners go straight to the tb, its one manifold instead of the 3 stock ones. i have finalized teh design on the new resvision of the intake manfiold and shortly after should be avalable for sale incase you are still interested.




you would get a flatter tq curve but not as much power. i would think that utilizing the length for the same rpm will make more power under the curve. there is always gearing u
can take advantage of.

I didn't get this whole thing with interfering waves. Lets think about this for a minute. Good example would be a 4 port. Primaries come in on the right, secondaries on the left, the pressure wave goes back through the runners where they expand (T2 little plenum, 3rd gen where the runers all merge) and reverse back down where they came from. Where is the interference???

Actually thinking about this a little more, whould a "2 pound pressure wave" be enough to push the charge back out the secondary port if it came down the primary right across from it? If so, then we would need to tune the runners perfectly even, so that the waves from both runners hit the combustion chamber at the same time.

SO now I am really confused....

you are not making much sense, atlest to me :)
please rephrase

That SDSEFI design will cause uneven distribution of airflow between the runners.
The middle two will get the majority of airflow while the outside two will get less than the two center runners.


-Ted

the first thing i would do is dump the airflow meter and upgrade to a stand alone. because if you still insist on using the airflow meter the amount of air entering your intake will still pass the flow meter. a stock motor can only pull in so much air through a airflow meter. I'm working on a NA soloII track car with a stock 6port. i eliminated the airflow meter by using a megasquirt. it looks so much bettter. i was considering of replacing the stock manifold with a ida downdraft manifold and IDA throttle bodies to increase port velocity on mid to high rpm but its a matter of cost. If you plan on using the sds manifold design with the single throttlebody, you are going to run into problems using the stock computer and flow meter. the problem is that stock ecu stage the primary and secondary injectors. im not sure until i actually try it but i think there will be issues with idle and low rpm drivebility. i think there will be a definite problem when the secondaries open. then again it might work well enough. just try it.

on Kahren design, during port everlap, exhaust gases go out the header creating a low pressure area in the intake port pulling intake air at a higher velocity because the manifold design has no bends to slow down air flow. Not only intake manifold design has to considered but also header design. they both have to work together. i think a flow bench would be needed to design the best flowing manifold.