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View Full Version : Head Work - removal of quench pads



juggernaut
06-23-2008, 12:27 AM
Preparing to have some headwork done to my S15 sr20. Just curious as to whether most people are having the quench pads removed like on the GTiR heads or leave them in.

In summary there seems to be two schools of thought as to whether their removal actually prevents detonation or promotes detonation (through having increased timing).

Other comments I note is that the quench pad actually aids turbulence, and therefore flame propagation for a complete burn. On the other hand their removal de-shrouds the valves.

Interestingly the GTiR head had a 8.3:1 comp whereas as 'normal heads have a 8.5:1 comp. Was the GTiR head more prone to detonation hence the lower comp? Or was this simply by design due to the larger combustion chamber. Did the "normal" heads have them in to only to reduce emissions created by the turbulence to promote a cleaner burning engine.

I noticed Mazworx does this mod as does JUN and most Japanese tuners. However, are these heads more suited to purpose built drag cars.

Curious as to your thoughts for a street/track car.

srs14
06-23-2008, 12:22 PM
X2

i have been wondering this myself.

mack
06-28-2008, 02:22 PM
Mark at MAZWORX's can do it for you. They do a killer job of reshaping and porting if you need.....

nissanfanatic
06-28-2008, 02:42 PM
It seems like removal of the quench pads would be counter-productive in that the charge would not be focused towards the middle of the combustion chamber towards the spark plug. This would leave a lot more area for astray flame fronts to begin, and possibly uncontrolled propagation. I think focusing the charge near the spark plug is vital to having a well controlled burn.

I would bet that most drag cars do this simply for the reduction in compression ratio and very minute increase in displacement. They usually run fuels with slow burn rates and high octane, so errors aren't so detrimental to engine life. However, stuffing as much air and fuel in the cylinders as possible is detrimental to winning.

Epstein
06-28-2008, 10:11 PM
You also have to consider how violently everything is moving when you're shoving 10-20-30psi into a cylinder. The piston is rapidly approaching the head, and as things move fluidly, having a pad versus a ramp (which is what you wind up with) isn't going to make a whole hell of a lot of difference as to what direction the charge is moving. You should also understand that the pad also doen't correllate with the piston top that much.

I've had Mazworx do this to my head and I've not seen any ill effects. That said, I also didn't find 1 million magic hp either. My results aren't pure, and I'm not exactly pushing the limits though with 93 octane and 420whp.

Same dyno, same setup, switched from HKS step3 264/272 to JWT C1's, switched from Haltech E8 to ROM tune (Enthalpy tuned both in person), added Mazworx stock-sized valves and CNC chamber. Lost 4-10whp from 7k to 8k and gained 3-400rpms of spool. I attribute almost all of these differences to the smaller cams, although it's feasible the CNC job brought back some of the top end the the cams gave up. Standard logic would say that the bigger cams should have generated more than a 7whp peak difference, which is a vote for the CNC chamber. It's really hard to say.

A few points about this...
- compression was the same before and after. CNC makes the chamber bigger, but a light decking makes it smaller. I'm getting 165psi cold, which should be around 9.0 or just under. Pistons are Wiseco "8.8cr". Gasket is 1.1mm.
- no low-speed or driveability issues. This car only sees the street, and I'm very picky.
- Although I'm unsure about before, I'm doing 21psi pulls on the dyno and prolonged high speed street pulls without audible detonation. I also had the motor apart this weekend and didn't see any visible signs of detonation either. This is on 93octane with 11.5AFR's, higher compression, and sticking with the 0.75*/psi timing formula. Maybe people are doing this already on stock heads and it's been verified... you tell me. Increased detonation threshold was one of the suspected benefits, and I'd have to say that's what I'm seeing. This is probably what the drag cars are doing it for.
- The reshaped chambers did not want more ignition timing as previously guessed. We started with a normal timing map for this setup, ignoring the CNC job. When we started changing timing under boost we found that we were already at MBT.

I'm going to try and get my dyno files on Monday so I can report back on this and other tidbits (the cam difference).

juggernaut
06-28-2008, 11:24 PM
Great info Chris. Look forward to seeing your dyno files.

My tuner is also an advocate of this mod because it is also his view that the detonation threshold is also increased. I've just pulled the head off my 40,000 klm's virtually stock sr20 and it is clearly apparent from the colouring in the chambers that the edge of the quench pads on the exhaust side run hotter than any other part of the chamber.

If I was to do this mod I was going to run 1.1 Apexi head gasket, CC the chambers and then deck the head to restore any minor loss in comp ratio.

I also would have thought any flame propagation issues would have been from poor ignition setups and/or incorrect advance/timing.

Brian_W
06-29-2008, 02:39 PM
We do this to most of our race motors and have not had any ill effects ... thats for sure.