chairchild

long = power in the lower rev-range

short = power in the higher rev-range

flubyux2

thats a broad generalization. he said something about the longer length utlizing the 3rd and 4th bounce where the short primary uses the 1st bounce

rotarygod

iTrader: (1)

So as not to get too technical, just use the long setup. Overall it will average about 5% more power then a properly designed short system. It still has excellent top end but the average power is so much nicer.

GUITARJUNKIE28

lemme post up a half-bridge stock manifold dyno sheet.

this is at the low boost settng with a bunk turbo...spooled 1200rpm faster once i rebuilt it, so move the beginning curve farter to the left to see what this thing actually did once it was running properly.

this is right on with what fred has been saying.

so my question is: how much would shortening up the manifold a bit affect the peak hp?

bolo_fd

iTrader: (2)

i haven't read the thread but i believe shorter runner will give u a higher peak hp

GUITARJUNKIE28

^ in a nutshell.

rotarygod

iTrader: (1)

Be careful. I've been told by many people here that I'm full of **** !!!

GUITARJUNKIE28

your being full of **** has nothing to do with the formula

rotarygod

iTrader: (1)

I don't know man. I'm apparently pretty damn stupid and overly negative. Maybe I can't do math after all and it's just a coincidence that it all works. (That's the negative side in me talking )

GUITARJUNKIE28

can you take my dyno graph and do the reverse math on it and figure out how much overlap i have?

GUITARJUNKIE28

^ i actually tried that last night, but i was a little tipsy and sleep deprived...didn't turn out how i expected

maybe i'll try again today for ***** and giggles.

JamesWade2002

This thread is absolutely fantastic. Its like literary crack, I just can't stop reading. One question though. If I get close to the correct length on a custom intake and exhaust runners, but not right smack on, will I have results close to maximum theoretical efficiency for a given combination? In other words, how sensative is this in a N/A 13B. Can I get within an inch on both and have 95% of the gain? The reason I ask is that packaging all of this in a 2nd gen RX-7 might be very hard or impossible. I don't really know, but after reading this, if I build a half bridge and shift at 9000rpm, the stock intake is not going to work at all. Plus, how can I fit more than one muffler in the exhaust if I make the primaries 94" long, or what ever they need to be (TBD)? What mufflers can I use. If I do all this work, they gotta be straight through, which is way too loud, or its gotta be collected too early and split into duals. Should I just stack 2" ultraflows on the primaries before they collect at the back of the car? What about after everything collects? 3" straight through ultraflow? All of this throws out racing beat's stuff so we all have to re-think our exhaust. I USED to think that I knew a thing or too about cars, now I am really thinking a turbo is the only way to make power on the street.
James
ps, or a SBC ;P

GUITARJUNKIE28

fred could answer this better than i could, but i'd maybe start witht he stock manifold and just start shortening it up an inch at a time... when you find the right length, then build a custom manifold.

rotarygod

iTrader: (1)

I've separated your post a little to answer it more clearly.

1: Only use the formula as a guideline. You should get in the vicinity. The reason it is only a guideline is because every port has a slightly different port opening and closing rate. A peripheral port engine opens the intake ports more suddenly over fewer rotating degrees than a side port engine does. Obviously if you didn't take this into account you'd get a slightly different result with each. I suggest that you do the math, build slightly longer, and then subtract length through actual testing. That's the only way you'll get it for sure. On a nonturbo engine, tuning is critical. With a turbo you can get away with alot of mistakes and still be fast. On a turbo car I like to use longer runers for good low end power and off idle drivability and then rely on the turbo and the boost pressure to give me the top end. It is a tradeoff since you need more boost up top to make the same power but the powerband is wider and spool is faster. For street use that's a trade that I'm willing to make. For race use I'd do it differently.

2: With a stock intake on a nonturbo engine, you are really wasting your time with any form of bridge. I'm sure someone will come in here and yell at me for this as they always seem to do since someone probably has this and doesn't realize how much performance potential they are wasting. As I said, if it's for turbo use, you can do alot of things differently and can get away with it. Your car will run with the stock intake and probably be faster than stock but you won't be getting nearly what you could out of this porting style with this intake. When you can't fully use the port you have to it's full potential, you'll made it too big and agressive. Smaller is better until you absolutely need larger.

3: It is not hard to use a long primary system on a 2nd gen. As you pointed out, you can only use 1 muffler. I personally don't like the look of only one but that's a personal preference. For max performance on a bridgeport, that's what it will take though.

4: The good thing about a turbo is that you don't have to make as many compromises to go fast as you do nonturbo. Porting is fun. Big porting is more fun. However it isn't always practical. Consider this, even if you built a full peripheral port race engine that had a proper intake and exhaust, it would be loud as hell, have a narrow powerband, would get terrible gas mileage, and have zero chance of passing emissions testing. (Personally for me the gas mileage things is the killer.) This engine might get up near 350 hp. Now consider that many people have taken a completely stock engine, intake, etc, and used a turbo to surpass this horsepower mark. On top of that the powerband is wider, the car is quieter (if you want it to be), it gets better gas mileage, can pass emissions if you need it to, and you didn't have to go to all the trouble to figure out perfect intake/exhaust length, or make compromises in any other area. For good power on the street, forced induction is the only way to go. Large porting styles were originally designed only for race use. The first peripheral ports were for street use but this way also back at the beginning of the rotary development. That's like making comparisons between the valve layout of an LS1 V8 vs a Model T Ford. It isn't valid. Larger porting style are needed for more power in classes that do not allow forced induction. Consider that even seriously high power turbo rotaries don't need bridge or peripheral ports to make that power. Sure some have done it but you don't need to go this route to get good or even fantastic power levels. I'm not saying it wouldn't be fun though!

JamesWade2002

yeah I think what I will do for now is just cutt like 2" out of the stock upper manifold. It will really depend on how far I can stretch the throttle cable. This and a dual exhaust back to some number of inches in the 90's (like 96"), a merged collector and a 3" ultraflow muffler should get my power peak at 7,000rpms which will work great with my ports, even though now with the stock s4 manifold, the car pulls hard up too 7700 fuel cutt. some how the other day I pulled past a 4.6L mustang GT at the top of first and then kept walking in second. If he wasn't racing then man he sucks, cause he sure did rev hard and jump out in front fast. can't believe it if I did beat him.

ronbros3

SORRY to intrude here what happened to variable length intake system, adjustble by boost or vacuum , and forget about all that MATH, remember that real hotrodding WAS DONE WITHOUT COMPLICATING IT. P.R. has 10 cars with 13BS in the 7 sec. range. and I dont think they are all mathematicins. they do things that go against laws of physics and make it work. they do it because they dont know it cant be done.

ronbros3

HOW many of you have ever questioned reality?

JamesWade2002

dude we aren't talking about turbos here. if you had read the previous posts you would understand this. Anybody can put one of those overgrown hair dryers on their car and out run people without one. The point is that you can cutt your R&D time down to nothing if you do the math right. plus you can cutt other's B.S. out too. People like you. You've been reading Super Street again, haven't you? I got one thing for ya, go get a civic, pay someone $3K to put a B18C in it and have your fun. you won't have to think that way, and when I blow past you in my RX-7, you can just think, well my car makes more power for its engine size, or my car is cleaner, or my girlfriend likes my car better. RICER.

rotarygod

iTrader: (1)

Nice avatar James!

No need to start a fight here. "Real hotrodding" was also done back in the days when no one put much research into anything except the size engine of the muscle cars which btw were fast for their day but can be walked all over today by the average family car. Did you know the original Jaguar E Type was completely designed on paper in the form of math equations? There were no pictures or drawings of any kind. The designer gave the formulas to the engineers and told them to build a car based on the equations he had written. (There were lots of them!) The result was the E Jag. That's actually pretty cool.

A turbo is very easy to make fast. You can do alot wrong and go very fast when you have a turbo. You can't mess up very much naturally aspirated and expect to make good power. You should never completely rely on formulas but they can be very effectively used as guidelines to get you close. I suppose a "real hotrodder" would just throw something on the car and see how and if it works. Trial and error will certainly get you there. It will just take alot longer.

I think everyone has questioned reality as some point or another. Does the problem actually lie with reality itself or is it our perception of it? Go watch the Matrix. What is real?

JamesWade2002

woo haa! I like the avitar because of the flames! Now, I tried the hotrodder approach to my first engine build. The engine in question is the one in the car right now. I just cutt the wall out between the secondaries and the auxilary ports, added TII rotor housings, a TII intermidiate plate, cleaned up the flash, butchered the lower intake, and added a pacesetter header (came with the car), and 2.5" single to 2.25" dual out exhaust with cheap mufflers. Guess what.........the car is fast. Guess what else, my hotrod approach made an explosion of power above 6,000rpm, just in time to shift at 7,700rpm. My hotrodder approach worked for a little while, but I got walked by a mustang GT the other day on the interstate cause I couldn't get above 6,000rpms in time. now I have alot of thinking to do. At a certain point, you can't avoid the math, If I had known what I know now, I would have done stuff differently from the beginning. As is, you don't really notice the loss of power in the lower gears cause the car revs out so fast, you are just there, in the power quick, but wait till third and fourth...then you think "come on, come on...damn he is walking....ahhh...there...we are stabilizing...now I'm catching him.....oh **** he just let out, he thinks he's won!" and for all intents and perposes, your competition has. When I autocross, I could really use some more power from 4,000 to 6,000. While I have my doubts that the factory fuel injection is anywhere near the money, I also think my exhaust could be changed and the intake for that matter too. I never knew this until I read this thread.

TT_Rex_7

I'm sorry to bring this thread back up, but does anyone know where I can get a book that shows you all the calculations to design your own intake manifold?! I've been searching on google and can't seem to come up with anything solid.

-Alex

GUITARJUNKIE28

http://www.amazon.com/exec/obidos/tg...glance&s=books

that the one you talking about?

rotarygod

iTrader: (1)

That's a good book. I do have that one.

GUITARJUNKIE28

i picked it up last week

TT_Rex_7

I'm just speaking of any in general. Anybody have anymore?!

-Alex

Edit: BTW, thanks!!