Stock manifold versus Greddy and others..

[Dramier]

This is purely theoretical, and kind of for my own curiousity...

I was pouring through my Maximum Boost book (Corky Bell version) and doing some fuel stuff, when I read some stuff about the intake manifold...

Seems the best design he recommends is exactly like the factory intake manifold, with the intake placed centrally over the intakes. However, I can't help but notice many of the aftermarket intakes are designed with the intake on the end rather than centrally. This is the design he specifies as being the poorest performer.

Now, understandably the Greddy/Top Hat/etc versions main benefit is relocation for intercooler piping and increased diameter, but the real question I'm wondering is if the design is so flawed (according to Bell), why are all of the aftermarket manifolds like that?

The first obvious problem with a larger diameter stock design style intake is the overhead clearance between the hood and intake, and the routing of the IC piping, but what other reasons are there for NOT designing their intakes like the factory? Or is Bell just flawed in his reasoning?

The main reason I'm wondering is I'm seriously considering designing a sheet metal manifold. Obviously it puts a burr in my saddle when the aftermarket big names are using one design, and a guy who is supposed to be an experienced veteran simultaneously debunks that style as the most poorly designed...

I know there are some folks on here with better understandings of the engineering side of the house, and I would really like to hear a clear explanation of which method is better and why.

[AmoebAssassin]

I'm certain that the reason he dislikes front intake plenums is because with a long engine and improper design, it's easy to starve the last couple cylinders of air and generate nonideal air/fuel conditions.

HOWEVER, if you notice the shape of GReddy and the GTR stock plenum, it tapers off and is angled towards the last cylinders. This prevents starvation of the last cylinders.

This is all speculation, of course. I haven't run or seen any CFD analysis on either plenums. However, when designing my college's FSAE car for last year, we were using a cylindrical plenum with a front intake design. If the plenum was just a cylinder, there was a flow differenential that decreased flow through the last runner. However, adding an angle plate to the end of the plenum effectively removed any flow differential through the runners.

That's just my .02. Feel free to critique.

[Dramier]

I may be misunderstanding things because of a lack of education on the subject, but I'll ask anyway..

On a manifold like the Greddy 'Large mouth' intake, I would think air intake would be highest in the 3rd, 4th, and 5th ports, with less intake in the 1st, 2nd and 6th ports. My reasoning being the air rushes in bypassing the 1st port and hitting between the 2nd and 3rd ports... Is that incorrect?

[SeVa-S13]

This is forced induction, not NA so the rear cylinders are never starved for air, quite the opposite really. The charge, traveling at quite the speed, smacks the rear wall and typically gives the rear couple cylinders a little more air than the rest but the whole manifold is pressurized so there really shouldn't be too great of a difference, but that's why you tune a little rich. (More air in the rear cylinders = leaner condition)

[Dramier]

I didn't even think about the FI pressurization... That makes alot more sense..

Thanks for the explanations, cleared up my questions completely.

[eh?]

I remember seeing some bench flow #'s from the stock IM on SAU. Turns out #3 and #4 runners flowed the most air. While on the Greddy IM #5 and #6 flowed more.

[silent dave]

i have a greddy intake manifold sitting around that i've been thinking about taking to my friends that work at a performance engine shop and getting the manifold flow tested and then having the runners flow matched if they are off. sound like a good idea? i'll be taking the manifold to them either tomorrow or early next week depending on ambition.

[eh?]

If it's free why not. But it's common practice to just put the higher flowing injectors in the rear cylinders.

[silent dave]

i've read about people doing that but it makes more sense to me to actually make the flow on each runner match than to guess on how much extra fuel to add to a those cylinders. that and i'm curious how the manifold will do on the flow bench. its not gonna be free but i got nothing better to do and want to get everything all ready to go on my car over the winter.

[SeVa-S13]

So you're going to magically even the flow on the GReddy runnees or what? Just plan on porting them out until they match? Good luck...

[silent dave]

that was the basic plan, only without the magic. i'm not a machinist or an engine builder, i have freinds that are and when it comes to things that i don't feel i know enough about i do what the guys with experience say. however they told me that they don't think they can flow my head and therefore can not check my runners because they don't have a plate to get the rb head on their flowbench. so as of right now it looks like i will magically have the injectors done so i can put the higher flowing ones at the rear like eh? said, rather than have fun with porting at the machine shop.

[RBTALLY]

no problems with mine so far.. I am building a few more for a few friends

[Aznboi64]

I was thinking to help eleviate the leaning in the cylinders by making an extra chamber/tunnel that goes to the cylinder that is being starved. Does this sound correct?

[JonPowell]

no problems with mine so far.. I am building a few more for a few friends

Nate, Call me!

518-330-3687

[240z4u]

Nate email me with a price for an rb25. I need an aftermarket intake BAD.

Evan

[Carl H]

Nate email me with a price for an rb25. I need an aftermarket intake BAD.

Evan

unless you are making over 450whp an aftermarket intake manifold is NOT required.

[240z4u]

Yeah, but my top feed rail does not fit comfortably under my intake manifold upper plenum. I would also like to get rid of quite a bit of my I/C plumbing. Honestly, I would prefer a well built plenum system that bolted to stock runners.

Evan

[mugengsr]

the stock manifold for the rb`s are fine the only advantage of having the front facing greddy ones or rips ones or any home made jobby is to have less ic pipeing = less lag/pressure drop .... and in the gtr the greddy manifold is of benefit clearly because of the problem of the stock manifolds causing a lean condition in the last cyl causing failure .. the greddy manifold eliminates this.. other than that its no better than the stock rb26 manifold

[RBTALLY]

just out of curiosity has any one ever burned up the number six cylinder from a lean condition ... I do not want to hear about a freind's car that did it... if it was your car speak up.

[Yellow4g63]

On Carls car it was #5 that got tosted.

[RBTALLY]

... I do not want to hear about a freind's car that did it... if it was your car speak up.

let Carl speak up

[Carl H]

yah, 5th cylinder took the most damage (melted piston and part of the ringlands), however 6th was nowhere near as bad.suprizingly even tho there was ringland "erosion" on 3 of the 6 pistons cyl 2 was next in line to 5th as being the worst, curious indeed.just run the system a hair rich and put the highest flowing injectors in 5 and 6, really the only thing that can be done.

[RBTALLY]

yah, 5th cylinder took the most damage (melted piston and part of the ringlands), however 6th was nowhere near as bad.suprizingly even tho there was ringland "erosion" on 3 of the 6 pistons cyl 2 was next in line to 5th as being the worst, curious indeed.just run the system a hair rich and put the highest flowing injectors in 5 and 6, really the only thing that can be done.

what intake do u have ?

[Carl H]

rips intake manifold.

[Wulfgang]

This is forced induction, not NA so the rear cylinders are never starved for air, quite the opposite really.

What makes you think that your intake manifold has a clue whether or not you run forced induction or NA? Your manifold does not care. Also, the air speed inside the manifold is relatively independent of boost pressure (or vacuum) since your engine is a constant volume pump at a given rpm.

Sorry fellas, but engineering a manifold without experimentation is still impossible. Put it on a flow bench and show me the results. Otherwise.... it's just a crapshoot. Rule of thumb: if it looks like a decent design, it's probably ok.

[ARGAMEMENON]

Built this for a drag GTR in Australia. I can't seen to get ahold of the bloke for results and such, otherwise I'd let you all know...

[IMG][/IMG] [IMG][/IMG]

[RBTALLY]

Carl do u think the failure was a manifold problem , or did u overrun the fuel system to cause the lean condition?

[Kansei240sx]

Well my greddy intake manifold came in yesterday, and by looking through the inside, i would say that its alot better looking that most manifolds which seem to just be large open plenums to a flatspace with holes in them ( holes being the indivdual runners. ) This looks somewhat staggered and its got more shape to it on the inside for each port to the cylinders. I like it.

[Carl H]

Carl do u think the failure was a manifold problem , or did u overrun the fuel system to cause the lean condition?

im not really sure, im sure the front facing plenum had something to do with it, but im not going to blame the manifold right off the bat.the real culprit was proly overadvanced ignition, as the timing map in the ecu had been mucked with in japan and i really didnt know about it till about late agust......afr's looked good on the wideband (11.5:1 iirc), so i dont think they were overly lean.last time i changed the plugs on the engine i did a quick boost run then changed the plugs and suprisingly the plugs were all about the same colour grey, indicating that they were all running about the same afr.there might have been damage done to the piston while it was running with the over advanced timing map and perhaps that damage turned into a hot spot of sorts.piston 6 showed no damage to the ringlands nor the severe melting that 5 endured, may have just been a fluke that it landed on cyl 5.as i said before 5 took the most damage but 6 took the least out of the 3 that were worn.i'll try to take some pics of the other 2 damaged pistons, but visualy they are almost mint.

[matt_calgary]

Well my greddy intake manifold came in yesterday, and by looking through the inside, i would say that its alot better looking that most manifolds which seem to just be large open plenums to a flatspace with holes in them ( holes being the indivdual runners. ) This looks somewhat staggered and its got more shape to it on the inside for each port to the cylinders. I like it.

Greddy has the budget, testing equipment and the engineering capabilities to know what flows best.

Although a waste of money, it would be interesting to see the design of the Greddy intake by using a horizontal cross-section of it.