RB26 Poly Quad valve setup + porting

[JET240]

Building a forged RB26/30 at the moment with a brand new RB26 head and I am aiming a reliable 700hp in a Datsun 240z.

I am booked in for TAW Performance to get porting done plus machine work for what I planned to be 1mm oversize Tomei Valves + supporting parts.

They suggested running "Poly Quad" arrangement for better low down power and torque (intake standard size and exhaust 1mm oversize for example) which creates a swirl effect.

Has anyone had any experience with different sized valves and can share their experiences?

Supporting mods:

RB30 Block, CP 9:1 forged pistons, Spool i-beam rods, RB26 GTR bearings, ARP mains, Nitto pump and collar, ARP 12mm GTR head studs, RIPS RB26 intake, 6Boost manifold + GT35r.

Thanks!

[KiwiRS4T]

You'll be doing well to get 700hp from that turbo. Have you already bought it or can you get something better?

[JET240]

7 minutes ago, KiwiRS4T said:

You'll be doing well to get 700hp from that turbo. Have you already bought it or can you get something better?

Haven’t bought it yet was aiming to peak it with a large rear housing. Got everything else pretty much.

[Ben C34]

How do bigger exhaust valves make a swirl? That makes no sense.

[Old man 32 GTR]

Hi Jet240, going to be an awesome ride, love the 240. Anyway in regards to your question, my GTR with a built 26/30 was running oversized valves on one side and standard on the other, however I think mine was oversized on the inlet side, this setup was being run with Kelford 270 cams with 9.8mm lift. Was very responsive on both my twin set up (which was a pair or -5’s and my 68/70 single set up. 
Recently I had the head serviced and we replaced the valve train, went 1mm oversized on both sides and camtech 278 cams with 10.8mm lift, response stayed basically the same however the top end improved dramatically, engine Revs really freely now. 
I think the higher lift really helped and there wasn’t a lot of difference between staggered oversized valves and all oversized, from what I could feel, also it wasn’t just the valves that were changed so there could be other contributing factors. But that’s my experience with it. 
Also turbo choice, with the 3.0 bottom end opens up your options, even with the 68/70 it’s quite responsive, but you could hit your target hp with a 64/66 and be really snappy 

[GTSBoy]

The definition of polyquad is to have one large and one small valve on each of the inlet and exhaust, with the large ones diagonally opposite each other. The intention is to have more flow in through the larger intake which will create a swirl and then the outflow through the exhaust will be higher through the large exhaust valve also, continuing the swirl and at the very least leaving the remaining gas in the cylinder swirling as the inlet opens and starts flowing again.

You have to have quite extreme differences in valve sizes for it to really work. It's not something that you will see much out of with 1mm size differences (IIRC the original work, which by Vizard, I think. if not him, then someone equivalent).

[JET240]

Thanks for the reply lads! Yeah it will be awesome - It's getting restoration work + strengthening done atm.

Yep that's the one GTS boy.. I wrote my first post incorrectly.

There doesn't seem to be a huge amount of info around but I felt it must be more common than I thought for the machine shop to flat out recommend it straight up.

I can see how it would help if it creates a vacuum but it looks like the port jobs need to also be done around it to make it work?

032 JET - Thanks for the info! For the power I am looking to dial - do you think the 278 would be better for my scenario?

I will definitely re-think my turbo choice! I want to dial high power but really try and keep my low down power and minimal lag.

[Old man 32 GTR]

this is my cam specs and my car feels strong down low, and really strong up top, nice idle and comes on nice, the 68/70 isn’t a small turbo, but isn’t big either. From about 2500rpm, if you roll on the throttle it will build boost fairly quick. 

[JET240]

7 hours ago, Old man 32 GTR said:

this is my cam specs and my car feels strong down low, and really strong up top, nice idle and comes on nice, the 68/70 isn’t a small turbo, but isn’t big either. From about 2500rpm, if you roll on the throttle it will build boost fairly quick. 

Thanks very much for the cam specs. If you don't mind me asking - what power are you putting out with these?

 

[Old man 32 GTR]

2 hours ago, JET240 said:

Thanks very much for the cam specs. If you don't mind me asking - what power are you putting out with these?

 

With the 68/70 turbo, 770hp @ 32psi boost 

[Komdotkom]

Kelford also do a split duration camshaft which although not a traditional PolyQuad (yes this is one of Vizard's projects) it does provide a similar effect, I'm running them in mine with reasonable success. I was supposed to be on the dyno today but with Stage 4 lock down in Melbourne I can only sit in the car in my garage and make wooshing noises.

[33GTRV]

Polyquad is not something done lightly. On an engine that sees 7500+rpm forced, it is not necessary nor is it of any real gain given the compression rates we see as street cars. It can be beneficial, but very seldomly in a street car case. The best returns are from Port matching, a larger valve and improvements in the short turn. Pick your camshafts and powerband you want to achieve. You may need to juggle valvetrain to suit