turbo intake manifold design

[IH8TEC]

hello,

i have searched this site in regards to intake manifold design, i found one kinda useful post that ended up with good information, but didn't quite give me all the answers. this will be my first intake manifold i've made, so figure it wont be perfect first time,

i have read and come to the conclusion (from what 90% of people say) that the plenum volumn needs to be around 1.5-2 times the size of the engine capacity, 1600cc, so around 3-3.2L.

i've also been researching runner lengths, and most aftermarket manifolds seem to be made with alot shorter runners than their standard NA equivalent. so i was thinking around 4-5inchs long. would this help move the torque up higher? i will be using 2inch 3mm wall tube, as i will form the end to match the port size.

now the thing i want some advice on is bellmouths, originally i was going to use a 10mm alloy plate and machine a bellmouth into it. would this be ok, or is it more beneficial to use proper bellmouths that extend above the base of the plenum like most NA guys do to increase torque higher up and hold longer?

here is a pic of my standard manifold. it also has tvis in there, i will be getting rid of this.



and a pic of the engine bay


i plan on getting a re-tune done just without tvis, then bolting this on and re-tune for a comparison.

any other thoughts are welcome.
thanks.

[toymaz]

I always thought for turbo about 1.5 times capicity, but i know some one who made their own with volumes from a program, mind you its nissan ca18, but it has 2.5lt plenum, about 120mm runners, proper bellmouths. doesn't sound massive and i guess it doesn't need to be, It uses an 80mm t body to get the required amount of air and makes
475hp@wheels.
So don't go over the top in size.
cheers

[IH8TEC]

cheers, yeah that will be another thing i will have to upgrade is the throttle body, cheers,

[toymaz]

upgrade throttle body to what? don't go anything like 80mm .He only uses that size to pass the cfm air his engine requires. 55-60mm is a good size for a 4a.
cheers

[IH8TEC]

55mm is standard, i'm thinking of 60-70mm.

anyone have an idea about the bellmouths? i've heard it's not a major disadvantage having them machined into the flange? just wanna see from people experience.

[_FNQ_rolla_]

Hi there mate, looks great ........ you have done a good job.

Sorry a little off topic here but do you have any pics of your turbo exhaust manifold as i have to build one for mine and from them pics that you have there it looks like something that i would want to make for mine.

Thanks
Gav

[IH8TEC]

cheers, i will put a post up with pics of the build once its legal in two weeks.

in mean time lol



had it heat wrapped when motor was in my old car, but caused it to crack around the trubo flange. so got it pro-coated this time after having the crack fixed







back on topic haha

bellmouths

[The Real Roadrunner]

bellmouths will improve flow but to what extent depends on the rest of the design dont just get them milled into a 10mm plate as you wont get a nice profile on it make sure they are rolled over and protrude at least 15mm above the baseplate from the back of the roll over.

id shoot for over 8" of runner length unless your just after top end.

TB of 60mm would be plenty. ive had good results using s14 N/A TBs and they have inbuilt wax pallets which makes cold starts a breeze (and tuning less hassle)

cheers
linden

[IH8TEC]

yeah not too worried about bottom end haha, so shorter is better for top end? would this also increase the torque up higher? i'm also reving it out to 8-8.5k thanks for advice on bellmouths, anyone else have any thoughts or opinions

[30psi 4agte]

it would pay to keep harmonic vibratios in the back of you mind when using long ( more than 100mm) on a 4a inlet manifold.

They seem to have a harmonic problem due to port design ?? To be honest i dont know what causes it ( i wish i did ) all i can say is if you have read my rides thread ...... i know you have you would remember all the hassels i had with harmonic vibratios and plenums cracking .... This is not to say yours will but is something to consider with runner length.

FWIW my runners bell out (rolled the runner) and sit flush with the base plate..... What linden said is the best way to do it but not always the easiest and some times just not practical unless you want the best of the best.


P.S motor looks the goods.

[The Real Roadrunner]

it would pay to keep harmonic vibratios in the back of you mind when using long ( more than 100mm) on a 4a inlet manifold.

They seem to have a harmonic problem due to port design ?? To be honest i dont know what causes it ( i wish i did ) all i can say is if you have read my rides thread ...... i know you have you would remember all the hassels i had with harmonic vibratios and plenums cracking .... This is not to say yours will but is something to consider with runner length.

harmonics causing poor flow or causing cracking? two completely seperate issues but both of equall importance.

ive only ever had one plenum crack and it was due the manifold face not being machined. the ones i build for starlets etc have about 11" from manifold face to tip of bell and i havn't had one crack yet but they are braced in 2 positions to the block.

i also use 6mm base plates and 4mm everything else so they get welded using about 140+amps which could be why they don't fail.

on the same engine (4efte) we had 116kw, 108kw and 126kw all averaged over 4 runs each and on the same night, first the stock mani then a 5" bellmouthed custom unit then changed to the 11" unit.

11" unit had more mid and top than the factory unit and shat all over the 5" version.

unless you want the best of the best.

would you expect any less

cheers
linden

ps just saw your PM about the watts link (dont know how i missed it) did you get it sorted?

[30psi 4agte]

there is a bit of both there ........ harmonics causing both cracking and poor flow but mainly talking about cracking...
my plenum is 4mm also but the runners are thiner mabe 2mm this is prob where the issue is caused...... but hey you live and learn... it is very light though

in saying that though, i have torn the mounting tab off of the 4mm plenum and also split it in a different spot.

If i was to ever make a new one id do things again different but since i cut the runners ive had no probs.

As for the watts link bit ... i couldnt find one off the shelf so just made one...
I have super slack with the car of late...just cant be bothered at the moment ( I know you know what im talking about here mate ! )
it has just been little by little.
i do miss the thing though.

[The Real Roadrunner]

I have super slack with the car of late...just cant be bothered at the moment ( I know you know what im talking about here mate ! )

i hear you loud and clear, all day/night on customers cars leaves me too tired and frustrated to work on my own stuff.

2mm runners will crack every time, seen it on atleast 7 different occasions by companies that should have known better.

the transition into the ports and having a nice taper on the bellmouths are the bit you have to get right if you want it to perform well.

cheers
linden

[IH8TEC]

cheers guys, looks like i'll make it out of 4mm for the durability. 30psi4agte, one idea i got from yours, is how you've done the silicone joiners on each runner, has anyone actually tried to use a longer joiner, adn thought about losening clamps, and moving it in and out to make different runner lengths while doing back to back runs? throught that might be a good way to see whats best, then once you find what best suits, either weld in a bit of pipe fo extra length, or just leave it if its short?

there are a couple of 300kw 16v 4agte's over here, one in a red dx wagon with 320kw atw, his runners are the shape of the port out to the plenum, but he has a 4x30mm alloy plate bit that goes across the top of all four runners right by the plenum, and welded to all, assuming to prevent cracking like you say.

some good advice, cheers guys

[Talasas]

Again off topic but I'm liking your setup a lot, I really like you cam breathers too - I really need to do that with mine as well. Tell me, how are they baffled inside?