Rb26 Low Mount Tubular Manifolds - Do They Make Any Difference?

[femno]

So, I was thinking how it would be cool to have a set of 6boost low mount tubular manifolds or similar to replace the factory items on my RB26.

Around 18months ago I had a small problem with my engine that meant it had to be pulled out so it was a good opportunity to investigate and experiment with the manifolds. The current setup was the usual -5s and 18psi making about 340kw with a tune suitable for track use, so pretty conservative and safe.

Looking at the factory cast unequal length units with no sort of proper merge collector I thought anything that could improve the features of the manifold could yield some better spool-up times and maybe shift the graph a little to the left, maybe even allow the setup to produce some more power overall. So features such as having a nice merge collector, equal length runners, constant radius runners, smooth ID runners.

Also having the extra length in the runners, like big single setups, would maybe change the exhaust note a bit and give a bit more of an angry bark to it, which would be a cool bonus.

So looking firstly at the 6boost steampipe manifolds, closely following Matt (BoostedR) in his thread (http://www.skylinesaustralia.com/forums/topic/355887-6boost-rb26dettt-manifold-install/) about getting them to fit his engine, I found that they werent a good option due to the issues with fowling the head, the 2 manifolds sitting the turbos in different positions to each other, and sagging after little use. After closer inspection I also saw that the 3rd runners used some short radius bends (as oppose to large radius bends) which wouldnt be ideal for good gas flow. The $1200 pricetag to buy all those problems didnt help either.

Next were Fullrace. Man they make some awesome manifolds. They didnt list any for factory low mount position on a 26 but im sure they could have done some quite easily. Im also assuming the price tag would of been of the order of $2000+. I wasnt about to spend that much on something that wasnt guaranteed to give incredible results.

The Tomei stainless manifolds arent equal length and are known to crack, so those were out.

So i decided the only way to get what I wanted was to go custom. I decided I would make my own. Id never done anything like this before so I thought id give it a go and learn some stuff in the meantime, inspired by the crazy Fullrace stuff.

The cost was nothing compared to buying a set and my time was free so even if the manifolds didnt work I wouldnt be losing alot, so I was prepared to have the results go either way.

I did some(alot) of research and decided how I was going to do it all.

I used the factory manifold to make a jig, as I wanted the turbos to sit in the factory positions.

I modelled the manifolds up on CAD. Equal length within about 1 or 2mm of each other. 1.25" Schedule 40 (aka Steampipe) 316 Stainless.

I made the runners as short as possible while still fitting them in. The ideal length of the runners I could not determine without knowing exhaust gas pressures and EGTs, but im sure the manifolds could be used to optimise an area of the graph based on that data.

I drew and had a mate of mine cut some flanges out for me from 12mm Mild Steel, nice and thick to seal well.

I had the computer spit out patterns for the merge collector parts and the angles required for the runner bends.

Spent ages grinding and tacking them together. Pain in the ass working with 3mm stainless, its so tough!

All welded up. Man stainless steel pulls so hard when you weld it! A quick bead blast as well to clean them up. A quick de-bur inside too. CNC Flange machine by my mate at Wheeler Engineering. Farking top machinist, 100% flat.

Fitted up to the engine. Looks mad.

They required new water lines to be made just to replace the factory one that usually runs over the top. Just a few fittings.

New intercooler and intake piping with factory BOVs plumbed back to suit. I got over bov/compressor noise long ago. Ally flanges by Wheeler Engineering.

Finished bay. Pretty happy with all my hard work.

So the complete project probably took 2-ish months (in between other stuff) to make the manifolds and do the piping to suit, including me overcoming the problems associated with welding ally (absolute pain in the ass, Brad (Risking) helped heaps). The ONLY other change I made to the setup was to replace the 100mm HKS drag cooler with a Greddy 76mm Twin entry tube and fin cooler, which was better suited to track and kinda worked out well with having to make new piping anyway. I also changed from HKS mushroom pods to 3A racing filters. Absolutely everything else remained the same. The engine had just a quick freshen up and some top end stuff done. Nothing upgraded. Oh, except for the Tomei oil pump and nice Racepace baffled sump for extra street cred.

I took the car back down to Racepace for its run-in and re tune with the new manifolds and cooler.

Results: The previous dyno graph was done in August 2007, (Blue graph), new graph in Feb 2012, (Red graph). The boost was the exact same, its just that the boost measuring module was playing up back in 2007. Same dyno, same wheels and tyres, same high level Racepace tuning method.

The difference in the dyno results I think is negligible, considering the 2 extremes in climate; summer, winter, among other uncontrollable things.

HOWEVER, a result which cannot be seen and only felt is the difference in transient boost response at revs. It is INSANE. There is next to no delay in boost building going from light throttle to full throttle at 5k+ rpm. So that was something.

The car also absolutely roars when under boost, sounds very angry, and the volume has increased a bit too. Manifolds have also gone a nice goldy/purple colour!

Any questions, constructive criticisms please add.

Thanks for reading,

Mat.

[N1GTR]

Awesome stuff mate. Next Deca I bags a ride

Would be interesting to get the "seat of your pants" feeling of this and compare to a similar setup but larger engine (2.8, 3.0 etc)

[zebra]

Very good read

So the turbos bolt back up in the same spot with dumps etc?

[Piggaz]

Well done mate. Nice little project there!

A little surprised to see not difference in curve shape thats for sure!

What did the boys at RP say about it?

[BOOZTJUNKEY]

Awesome work mate .

It is quite surprising how much stainless pulls when welding .

U get use to it but there are ways to counter act it :-)

you a boiler by trade ?

Top work .

[R31Nismoid]

Good ole dyno not telling you the difference (same as -9s and -5s on the dyno coming on the same, but being very different when driven)

Nice work dude!

Will have to jump in passenger when I next see you around. Was hoping to see results as I saw your car/manifolds last week

[Deano 1]

wow man, nice craftsmanship, they are nice...... good work!!!

[r33_racer]

Nice work mate! Always great to see people having a go.

Love it! They look the shiz.

[rob82]

Good work dude - pity no power gains to be had. Shows how good the factory manifolds are at this power level. I think the transient response is most likely due to the smaller core though.

[KiwiRS4T]

Top marks for the job. Enviable skills and work ethic!!

[DVS JEZ]

Well done.

1 question though. Why do u have the breather from the bottom of the catch can into ur intake pipe?

[bigmikespec]

Look great.

Seeing as you have gone to the trouble I would get some external wastegate housings with a V-band exhaust outlet to put on the turbochargers then mod your manifolds for a wastegate... means you could make some simple dump pipes and free up some back pressure.

[gotRICE?]

Looks awesome! Im really keen on learning how to do shit like this.

Post up a video! Everyone loves a video!!

[zebra]

You have inspired me to do this to the 2j I'm building. I have a pair of -5s in my spare room too.

Out of intrest. Rough cost to do?

[bluejeans]

that is awesome mate!

the purple/gold colour they have gone looks great.

[femno]

Thanks alot guys appreciate the comments.

Turbos are exact factory position with dumps and fronts, oil and water lines going straight in.

RP said theyve toyed with something like this before, without any great results; but I was still happy to give it a go and glad I did.

Not a boiler maker but I did just finish my engineering degree.

I dont think I would consider pulling everything off to replace housings with external gate ones, if you can get them? Let alone the packaging issues, it was a squeeze to get the intake and cooler piping in there! Would also be very costly. Cant imaging having 2 gates with piping in there as well. Maybe another project for another rainy day!

Cost was awesome! Believe it or not the stainless 316 bends were like $5 each!! I think I spent $200 on the bends and pipe, $200 on the machining, the flanges and jig pieces were free and plus gas and other welding supplies which I dont know how much they added to, maybe $100. Overall the cost was nothing which made this option so attractive. So say $5-550. But having said that I now know why aftermarket manifolds cost $1200 and more, because theyre so damn labour intensive; but, the second manifold was made in half the time of the first..

What I dont understand is why Fullrace ones are double when the costs are not. But they look really good so I guess thats ok. Mine probably could have looked like theirs if I cleaned them with the special acid they clean them with to bring out the colours in the welds, but when to stop?

[N1GTR]

Go on Matty, start doing it on the side for mates etc and see if it picks up!

I've always thought full race could almost half their price and sell more than twice as much as they'd be in the realm of the tomei ones - clearly they're not interested and thats fine it's their business.

If you had the same finish (eg pretty colours) as full race, i think you'd be surprised by the people wanting them, just dont try make a massive margin on each set and see how they go

[GTRsean]

Labour is a big one.....$$

Very nice though!

[GTR_JOEY]

awesome work man, good to see actual results instead of just speculation every once in a while..

Rockin engine bay as well

[Risking]

Good to see the alloy came out well

Neat job of the manifolds

Would you agree with approximately 25hours start to finish in manifold time?

I did a set similar a month ago for an RB26 in a Gemini sports sedan.

When you factor in the $550-700 cost price on materials. Plus 20hrs @ say$90/hr minimum

You've got a set of $2,500 manifolds without even putting

a mark up on the raw materials, charging $$ for any design time, or charging any excessive labour rate.

It's easy to see why manifolds can run into the 1000's once you've actually designed and built a good set.