front mounted throttle body on stock manifold?

[gibbon]

hey, i'm getting around to setting up the intercooler piping for my rb20 280zx. obviously the original crossover pipe design could be improved on, and i was thinking about getting the thottlebody welded onto the front of the manifold to shorten the intercooler pipe length. my question is how will this affect flow within the standard manifold, ie with cylinders leaning out and so forth. im not planning to run masssive power through this engine so im not really requiring something thats 100% efficient, hence why im going for the cheaper option of modifying the orginial manifold over buying a custom built ($$$$$$$) one. surely people have done this before, was just hoping to get the general opinion on whether or not its a good idea. cheers

[240Z_Master]

I'm sorry I can't help you out on this, but this has been brought up to me a couple times about doing that same thing.

 

I opted out and spent a lot of money on the GReddy manifold just for the fact that I love having the TB about 6-9 inches away from the intercooler.

[drunkenmaster]

Why could the OEM design obviously be improved upon?

OEM engineers rarely get it wrong and I would say it would be near impssible for a private "backyard" modification as crude as cutting and shutting the manifold with the TB in a different place could ever improve on an OEM design with their large R&D budget, knowledge and equipment.

 

The modification you suggest has been done many times in australia. The result? uneven airflow and leaning out on cylinders.

 

There have been flow bench shoot outs with mass produced aftermarket manifolds like that from GREDDY and even with properly flowbench designed manifolds like this, differences are really negligable.

[Zhadman]

You would probably be better off just using the Greddy manifold. Sometimes buying a part is more beneficial (and cost effective) than making a part. Assuming you had the ability to weld cast aluminum you could surely modify the manifold, attain your desired end result, and still retain some modicum of functionality. But... like drunkenmaster stated... what happens when you lean out a few cylinders and increase the potential of damaging the motor?

The cost of the Greddy (ROUGHLY ~$600) is worth, atleast in my opinion, the ability to bolt on an engineered piece that will achieve your goal. And the time fabricating can probably be better served on another area of the car. Never under-value the cost of YOUR time! Cheers

[S15 200sx owner]

Like Zhadman said

[gibbon]

as far as i'd been told, the stock setup isnt the greatest either, tho... (i admit that ive only been told this, dont have the numbers to back it up or anything). as far as i can see, the center t/b is biased towards the center two cylinders, and (again apparently) cylinder #1 will lean out under heavy boost. the 'obvious' improvements i was referring to are eliminating the crossover pipe over the hot engine, and the big bend and double back the piping would have to do on the inlet side of the intercooler in order to bring the pipe back around to that side of the engine. i understand the advantages of such a setup though, especially if its an existing setup. if i was going from an l28et equipped car with a front mount already in place, to an rb, i'd be tempted to keep the crossover as the pipes are already both on that side of the car. however, im going from an n/a, and so im looking at making up a whole new set of pipes, and i cant say that the idea of making up pipes turning 180 degrees, travelling back past the intercooler, squeezing through the front wall where theres already the one intercooler pipe as well as the inlet pipe (which i might have to change anyway) and back up over the engine.. well it seems a bit wasteful *IF* there is a viable alternative. to me, paying $600ish (dont know what that converts into NZ dollars) for an inlet manifold isnt really what i'd call a viable alternative. getting something like an l28 inlet manifold with the throttle body already on the front, and mating that up to the bottom half of the rb manifold however....

 

come on guys this is hybridz! dont go telling me to buy prefabricated stuff

[S15 200sx owner]

come on guys this is hybridz! dont go telling me to buy prefabricated stuff

 

 

Hmmmmm... Good call

 

I am sure that the top part of the manifold will un-bolt from the lower on the RB25, I know there are some companies that make a new top part to convert to front TB, you could make something like that which bolts on to the lower (runner section) of the manifold, this would allow you to re-design the plenum to suit etc, ie tapper off towards the back of the plenum to even up the flow distubution between cyl's (like the plenum on my manifold, see my album)

 

There is that better

[240Z_Master]

Incase you didn't see the photos in the other thread, I decied to repost them here so you can take a gander at this marvel of a product.

 

[ZXRockie]

240Z_master how much did you get it for? and how far are you to be done?

[240Z_Master]

Got it for 578, but I usually buy them at 595 a piece my cost.

 

When am I close to being done? Well, gotta do the oil pump and water pump, put the new pan on, ATI Damper, then manifold. Otherwise it's one of those "if I don't stop I can finish within 6 weeks" kinda thing.

 

I'm having trouble getting some help to have someone come weld a tranny bracket, but in due time we'll figure that one out.

[Jsquared]

OEM engineers rarely get it wrong

AHAHAHAHA! You must be joking... yes, the OEM get it right most of the time, but on ANY car with ANY manufacturer there are going to be glaring inefficiencies.

[drunkenmaster]

cost compromises yes, inefficiencies very rarely...although GM and it's subs globally hold a special place in every OEM suppliers heart in regard to glaring inefficiencies and are probably one of the exceptions to my statement

[240Z_Master]

I know Nismo doesn't count as OEM, but it's got a special place in my heart too!

[Jsquared]

I'm not talking about "inefficiencies"... I'm talking about plain old bad designs and/or bad ideas. Nissan's choice of valvetrain with the SR is one example. Porsche running the fuel lines on the exhaust side of the engine bay on the 924/944 is another. Mid/late-90s Toyota Camry 4-bangers eating rod bearings (or was it mains?) like a fat kid at Krispy Kreme. I could go on for minutes, but the fact is that NO manufacturer is perfect and there are frequently design elements in every car that are either badly executed, or just plain bad ideas in the first place. Assuming that one design is better over another simply because it is OEM or name-brand is a bad assumption. That was the only point I was trying to make I wouldn't trust a sheetmetal intake manifold any less than an OEM or Greddy assuming the design and fabricator were good and assuming it was tested.

[mjfawke]

There was a big discussion on SkylinesAustralia about uneven flow in the RB20/RB25 manifolds and moving the throttle body - message from someone with dyno and race experience to back it up was that uneven flow wan't an issue until you headed towards 2-bar boost. Moving the throttle body to the front allows shorter piping length, which is a good thing.

[gibbon]

well thats the answer i was hoping for... that no problems come up until the system has to do that much work. by the time i make a setup pushing 2 bar, i'll probably fork out for the proper manifold (read: never)

[mjfawke]

FWIW, there is an RB20DET running 1.3bar on a HKS turbo, making 230Kw at the wheels, which has had the throttle body relocated to the front of the manifold.

[gibbon]

argh. just welded the throttlebody on the front, didnt check for clearances.... now the little bit of set piping under the throttlebody is interfering with some valve looking thing on the fuel rail. i suppose i could space the top half of the manifold up another 5mm or the throttlebody out 5mm.. but my first option cuts down clearance space under the bonnet, and the second option will tighten the angle of my intercooler piping... what does that little pipe under the throttlebody do anyway? one pipe comes off it to the square unit that *was* on the front of the manifold, and the other seems to head off round behind the engine. if its all disposable i can cut the whole lot off (no emissions laws here ). any ideas?

[240Z_Master]

It's not that water passage is it?

[gibbon]

im not too sure.. i bought my engine in bits so am still in the process of playing around with the hoses. yes it would be nice to differentiate between the water and air hoses early on in the project, as opposed to by trial and error!

 

i cant get a picture up right now as its pitch black outside, and i dont have power in the garage, but i can tell you a little bit more about it if you think you can identify it, its got a solid pipe that runs crosswise under the t/b. theres another little vacuum hose coming off it too. if its water related and running under the t/b, i wonder if it's cold start related? its still looking like the easiest way to get everything to fit. does anyone know if the solid pipe actually has anything to do with the t/b, or if its just that-a pipe that runs past the throttle that nissan decided to cast into the unit for who knows what reason? because if its just that, i'll cut the whole lot off and reroute the rubber hoses together....