Squish Pads And Rb26 Heads

[Piggaz]

Rightio guys.

I'm after some information about the pro's and con's of retaining/removing the squish pads in RB26 heads. I've had a bit of a sniff around both SAU and the UK forum and the opinions are very inconsistant. Some guys almost puke at the thought of removing them, others swear by it.

On my current engine, the head was ported by HKS Japan and combustion chamber CNC work was done by NAPREC Japan. I had the option of A) leaving both in, B) Removing the inlet, C) removing both. I chose B and I can't say it had a negative affect. The car definitely drove better from idle to redline than the previous head which had both pads in, throttle response was like a lightswitch.

It seem's that the pads are there for emissions and fuel economy, two things I couldn't give a toss about. What i'm after is the best performing combination. The extra space in the chamber is easily sorted by a piston to suit so the disadvantage of the compression ratio dropping becomes a mute point.

When I was going through the build of the last head, it was advised that above 800 HP to take both out. I have noticed that JUN also do this too. I also believe the Porka 996 911 turbo doesn't have squish pads.

The rough spec of the engine will be

- Engine capacity of 3.15 - 3.4 L

- EFR 9180 (more than likely. I believe the 8374 is going to be too small for such a large donk)

- Comp ratio of something between 9.0-9.5:1

- Cams undecided yet. Possibility of V cam.

- Max RPM of 8000.

[Roy]

Dont waste your time and money. A stroked RB26 will always be laggy and a waste of time. People use to stroke RB26s before alloy chevs were around or the XR6 motor came out so I .... would just put a Barra XR6 motor in it, so much more responsive. Or maybe just put an LS1 in it.

[MJTru]

Do you have any photos mate.

[Piggaz]

There is no farken way I'm putting a bent 8 or a Ford engine in a GTR. Apart from it being the "wrong thing to do" that just has a roll on effect of gearbox issues, wiring headaches and just general shitness.

[Roy]

LOL, just trying to turn this into an RB25 > RB20 thread due to displacement

Interesting discussion and the only person I know who had really spent time and folding stuff on a head was Doughboy with what was a very expensive head which sadly got sold as he went the route of the Ford V8 for his drag R33. But I am guessing you know Rams in Windsor and have spoken to them about the whole head/piston combination options?

[Mick_o]

Dont waste your time and money. A stroked RB26 will always be laggy and a waste of time. People use to stroke RB26s before alloy chevs were around or the XR6 motor came out so I .... would just put a Barra XR6 motor in it, so much more responsive. Or maybe just put an LS1 in it.

LOL! Thats cheap coming from the Minister of RB20's who finally woke up from his 2L dream and realized an extra 500cc made his dreams a reality

[Piggaz]

LOL, just trying to turn this into an RB25 > RB20 thread due to displacement

Interesting discussion and the only person I know who had really spent time and folding stuff on a head was Doughboy with what was a very expensive head which sadly got sold as he went the route of the Ford V8 for his drag R33. But I am guessing you know Rams in Windsor and have spoken to them about the whole head/piston combination options?

Haha!!!

No, I haven't spoken to RAMS at all yet. That may be an idea.

Unfortunately it is a subject that only a small % of the forum would have first hand experience in. Even sniffing around on google you can't get a solid answer.

[Roy]

The tough thing is you are really all out there on a ledge.

Can't look to late model production engines, race engines etc because your rev limit, power level etc are all very different. I was reading about the 1.6L turbo Toyota engines that are being developed for the WRC program as a platform are rated up to 600hp for various classes of racing. The problem is what impact do inlet restrictors etc have on head design. Anecdotally looking at pics of their head and also other turbo LMP engines they all seem to have squish pads. Ditto F1 V8 and V10 engines so it doesnt seem to be a high rpm NA thing either.

So, i think the main thing is to go with the one mob for concept ensuring piston shape, injector type location etc are all factored in...

[GTSBoy]

Squish is a good thing for mixture motion. Mixture motion is a good thing for all sorts of OEM preferred things, like complete burnout (ie fuel consumption), emissions, etc, etc. Also turns out to be really good for performance outcomes too. I suspect that when the power levels start to get really high, the need/want to reduce compression so as to enable more boost starts to win out over the real benefits supplied by decent squish design, and the pads just get thrown away. Engine still makes bulk power, courtesy of monster boost. No idea how much better it could have been if squish was retained and something else done to make it all work.

[Blackkers]

this thread derailed before it started..

my only experience with adjusting squish is in a 2 stroke go kart. If we got the squish wrong the kart gave a noticeable power deficit on the dyno. The dyno was a homemade job out of a box trailer and never calibrated but it was a good tuning tool. anecdotal evidence is unlikely what you're after though

The other potential issue is getting the combustion chamber CCed for mild to high compression. Yes the right pistons should be chosen but there is a limit (ie valve clearance) and removing material won't help there

Edited March 30, 2015 by Blackkers

[GTRPSI]

This is going to be one of those threads again....(not in a bad way though)

There are pros and cons, 98, E85, low boost or high boost?.

To take both squish zones out you will need a custom piston, theres a mob in the US who CNC the heads and remove the pads and supply specially designed pistons that work to correctly return compression.

But lets throw a spanner in the works and say that a flat top piston would be better for the burn, but wouldnt be good with the squish removed if you want higher compression.

The biggest negative with squish areas remaining is detonation, everyones seen quish zones with tell tale marks and shits themselves, taking them out.

Most of ths is due to secondary combustion, that is enough room was left there for combustion to take effect.

Top engine builders work a little differently, and aim to reduce the piston to squish zone gap down to zero at full song, that is, to have the head and piston "just" kiss at full stretch of all components.

Generally speaking the aim is for "around" 40 thou (1mm) Quench to piston deck clearance, this at full song should close to virtually "Zero" clearance with forged rods with ARP fasteners at around the 9K+ RPM mark (also allowing for piston rock at ATDC).

No gap, no detonation, quench in, maximum sonic speed pulse of the mixture while maintaining maximum compression (without resorting to one of pistons)

If i was building 98 low boost, id leave them both there, 98 high power id take out one side, 98 full race id take them both out, by the nature of 98 octane its a bitch when boost starts getting cranked up.

E85 is a total different animal.

We are aiming for a "easy" limited to 650 Kw at all 4 on mildish boost levels with E85 on a RB26/30, both quenches will remain, but will not look like the standard quech zones as made by the factory, both will be modified in shape and remain in place.

Look at some Cosworth turbo era heads, champ car heads, look at the amount of quench left on them.

We will only be touching the Quench pads to deshroud the valves to assist maximum breathing.

Have a look around here...you should know what to research from there....

http://www.lolachampcar.com/Cosworth%20XB.htm

[bigmikespec]

Rightio guys.

I'm after some information about the pro's and con's of retaining/removing the squish pads in RB26 heads. I've had a bit of a sniff around both SAU and the UK forum and the opinions are very inconsistant. Some guys almost puke at the thought of removing them, others swear by it.

On my current engine, the head was ported by HKS Japan and combustion chamber CNC work was done by NAPREC Japan. I had the option of A) leaving both in, B) Removing the inlet, C) removing both. I chose B and I can't say it had a negative affect. The car definitely drove better from idle to redline than the previous head which had both pads in, throttle response was like a lightswitch.

It seem's that the pads are there for emissions and fuel economy, two things I couldn't give a toss about. What i'm after is the best performing combination. The extra space in the chamber is easily sorted by a piston to suit so the disadvantage of the compression ratio dropping becomes a mute point.

When I was going through the build of the last head, it was advised that above 800 HP to take both out. I have noticed that JUN also do this too. I also believe the Porka 996 911 turbo doesn't have squish pads.

The rough spec of the engine will be

- Engine capacity of 3.15 - 3.4 L

- EFR 9180 (more than likely. I believe the 8374 is going to be too small for such a large donk)

- Comp ratio of something between 9.0-9.5:1

- Cams undecided yet. Possibility of V cam.

- Max RPM of 8000.

Firstly, there is not a lot of 'squish' pad in a 4-valve chamber anyway.

The squish pads create an area of 'quench' which is a point where combustion will not occur. This is seen as a good thing, however, the problem occurs when the fuel/air mixture is accelerated past a sharp edge like the edge of a squish pad and this gets worse when there is high rpm, high cylinder pressures, etc... This creates a hot spot which can be the cause of detonation and other nasty things.

Personally I feel the best way to combat this is to do as was already suggested which is to un-shroud the valves which will probably eat into the material of the squish pad, remember, flow around the valve is more important. Secondly, spend some time removing the sharp edges of the remaining squish pad in the combustion chamber and 'lay it back'.

If you are going all out, next step is to get some custom pistons made with a mold of the combustion chamber when it is finished.

[Piggaz]

http://www.learntotune.com/discussions/topic/twin-cam-high-comp-rbs-squish-pads-and-pre-ignition-on-e85/

Have read this before but I thought I'd throw this up.

[brad 110]

Champ cars run meth, most hi comp hi boost classes run race fuel. e85,s low resistance to pre ignition is where squish pads create another entire sandpit.

[ido09s]

My reply wont be very technical but both sides are gone on my engine. Peter from Advan ported the head and the 2 squish zones were the first thing that went. We use standard GReddy/OS pistons and thinner head gasket just to bring up the compression a touch

The engine seems to make decent power (485rwkw with a 6766, 1.0 rear, Caltex E-Flex at 23/24psi on the Unigroup dyno) It drives well off boost and is happy to cruise around. Car is a full weight S14a luxury spec with sunroof and runs a consistent 138mph down the strip. Yes it is RB26

[GTRPSI]

Deshouding the valves eats into the squish zone reducing the area to some degree and helping.

While on the subject of combustion chamber designs.....Google "Singh Grooves", interesting reading towards reducting issues on vehicles runing a lot of squish to piston clearance should you do that.

While your at it, if your in the mood to do your head in a little, read up on dimpled combustion chambers and intakes.

Principal works like the dimples on a golf ball, less air drag when in flight.

[GTSBoy]

Principal works like the dimples on a golf ball, less air drag when in flight.

That's actually a load of poop. The golf ball analogy. The dimples on a golf ball do not reduce drag. They grab a thicker boundary layer, which when the ball is spinning, creates additional lift. It is the lift generated that keeps the ball in the air for longer, and hence allows it to travel further. If you can launch a dimpled golf ball with spinning it, you will see that it does not travel further than a smooth ball. In fact, the thicker boundary layer should slightly increase drag and make it drop a tiny bit earlier.

Dimpling in ports is also about controlling the boundary layer, which is far more important than most people realise. So whilst dimpling ports has a benefit, it is not for the same reason that dimpled golf balls fly further - even though it IS all about the boundary layer!

[GTRPSI]

Here.....does NOT creat additional lift, does create a boundry layer with benifits, less wake from a thinner wake resulting in less drag from the pull of turbulance from behind.......

Tested on a car with results...

http://www.discovery.com/tv-shows/mythbusters/videos/dimpled-car-minimyth/

Better explenation of the golf ball theory...

http://www.aerospaceweb.org/question/aerodynamics/q0215.shtml

[GTSBoy]

I disagree with that explanation. It runs counter to the findings of a 3rd year aero prac I did.

[discopotato03]

My take on "squish" and detonation is different . I believe short flame paths mean most/all of the charge is burnt quickly before it gets the chance to heat and auto ignite . If the gap between the piston and the "quench pads" could be zero then the volume and last gasses to be burnt would be zip too . Naturally you can't do this because pistons and rods effectively stretch (higher revs more inertia) and eventually the pistons hit the head .

Something else to remember is that no RB head was designed specifically to be a competition solution so factors such as packaging compromise the design and effective performance .

A purpose built comp twin cam head often has narrow included valve angles so the chambers can be quite shallow and ditto piston crown valve reliefs . I believe Cosworth BDA heads are like this are they are hardly current cutting designs .

From a production engine perspective narrow valve angles (inlet to exhaust) make the head casting tall and that doesn't fit well in sporty cars with low noses .

One thing that wider valve angles does suit is heads with ports relatively low down on the sides , reduces the flow angle on the backs of the inlet valves .

The reason low ports are good for crowded low engine bays is that the inlet manifold can be more compact and lower in height .

Personally I would want a very good demonstrable reason to remove the quench pads from an RB26 head particularly one on a higher capacity block . My reason being the greater the engines capacity becomes the less the issue with chamber volume becomes . It gives you freedoms with piston crown designs because you don't need substantial raised sections on the piston crown to get the static CR up to a reasonable figure . Great lumps of aluminium have often been put on pistons because the CR took priority over extreme power potential . In an ideal world I'd like RB25 Neo sized chambers on a 26 head and more ideal piston crown design than R33 RB25s and all 26s have .

Sad fact of life is that the RB26 design is an escapee of the late 1980s and its showing its age .

My 2c spent cheers A .