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D52E

U67 Cylinder Head Valves

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I originally posted this on the 510 realm.  I was hoping to get more opinions.

 

I need some advice for a U67/L20B (0.5 mm to 1mm over-bore). The intent of this request is to decide on the best valve size option for the head.

The head will be used with a small Garrett GT2256 turbo. The head appears to have the original brass intake valve seats so I was thinking of getting new seats added. Since I was going to get this done I decided to get new valves. SI has intake valves in 43 mm, 44 mm and 46 mm. They also have exhaust valves in 35 mm and 38 mm. 


What valve sizes would be best for this combination? Keeping in mind that I plan to bore the L20B to 0.5 mm or 1.0 mm at this time and I'm not sure what the requirements would be for un-shrouding the valves in the combustion chambers. I'm also not sure if going for the largest valves is the best move.

 

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A one mm over bore adds only 2% extra volume per cylinder. At one bar of boost 4% more air. Nothing really. As to valve size if this were normally aspirated engine I would say go as large as you can but as larger valves only increase breathing above the point where smaller valves start to fall off, and you would be well up into the boost range by then anyway you could simply let the turbo do all the work. L heads breath rather well anyway so I don't think the bother is worth it. Up you you, and no matter what you decide, it won't be wrong.

 

Definitely get the newer hardened valve seats.

 

 

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Definitely un-shroud the valves and you can even slightly notch the tops of the bore near the intakes. Above, I tailored the tight fitting combustion chamber so that air coming out the intake valve follows out and across as large a radius as possible. In a way it's like the reverse of a velocity stack on a side draft.  I continued the radius about 60% of the way around the intake and almost half way round the exhaust.

 

 

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I would drill holes in the U67 head for a water cooled intake. If running a custom intake for this ...... still drill holes and connect (T) into the thermostat by pass line. This will bleed over heated water from around the intake ports and they will run cooler. Removing heat on a turbo engine is critical.

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get the 35mm valves, you may need to bore notch the block with the 38mm valves and you have to cut a bunch out of the side of the chamber to use them effectively. they are better for big bore builds with a 90mm gasket.

 

unshroud the chambers to the head gasket the best you can,  port work on the exhaust side will help too as they are pooey ports.

 

as for intakes, 44 seems popular. you will encounter shrouding issues with the 46mm valve as well.  

 

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Use the L20B head gasket and scribe a line around the combustion chamber in the soft aluminum. You'll notice that even the open chamber is not totally round as the gasket will show. You can remove anything inside that line near the valves. 

 

 

Scooter.... indeed the un-shrouding in my picture was for use on an 89mm bore. A stock L20B bore is smaller but there are gains to be made even on it. I even smoothed any tiny lip where the seat and the aluminum meet in the combustion chamber and also in the ports. Often when the valve seat is cut and leaves a burr. Z series heads are terrible for this and a rough valve pocket just below the seats, L not nearly as bad, good actually. If not sure, make anything smoother.  I port matched the head and the manifolds to the manifold gasket. I only smoothed this transition in for just over an inch rather than trying to open up the ports all the way through in both directions.  I didn't want a larger port slowing the air speed down in the mid range. As it is, the middle of the ports are the original diameter and will act like a venturi speeding up the the air just before the intake valve. This should all allow easier access for air to flow in with less turbulence. It's free extra few HP and never goes out of tune.

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A stock L20B head gasket will work fine, stock meaning OEM or equivalent. For added insurance against turbo boost, you should probably o-ring the block too.

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On 2/10/2019 at 10:06 AM, datzenmike said:

Use the L20B head gasket and scribe a line around the combustion chamber in the soft aluminum. You'll notice that even the open chamber is not totally round as the gasket will show. You can remove anything inside that line near the valves. 

 

 

Scooter.... indeed the un-shrouding in my picture was for use on an 89mm bore. A stock L20B bore is smaller but there are gains to be made even on it. I even smoothed any tiny lip where the seat and the aluminum meet in the combustion chamber and also in the ports. Often when the valve seat is cut and leaves a burr. Z series heads are terrible for this and a rough valve pocket just below the seats, L not nearly as bad, good actually. If not sure, make anything smoother.  I port matched the head and the manifolds to the manifold gasket. I only smoothed this transition in for just over an inch rather than trying to open up the ports all the way through in both directions.  I didn't want a larger port slowing the air speed down in the mid range. As it is, the middle of the ports are the original diameter and will act like a venturi speeding up the the air just before the intake valve. This should all allow easier access for air to flow in with less turbulence. It's free extra few HP and never goes out of tune.

you are correct sir.

 

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i may have gone hog wild..

 

For the sake of the original poster, this has had the seats knocked out and replaced with ones for 45 and 36mm valves. 

 

because its such a cute little turbskie you dont need to go nuts.. but smoothing things out is a good idea and i agree with mike.

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I would love to tig in some quench area on a U67. Even a raised flat spot that fits the piston dish for true squish. It would be a lot of work but I'd love to try.

 

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The heads take a lot of heat when welding up the chambers. Sometimes they twist during the cool down cycle. It is common practice on race engines.

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I would probably have it face up and filled with water.

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You just have to be sure to let it cool properly. Wrapped in leather blankets, in a box of kitty litter, whatever. Post-heating and peening might help too. Then once you're done, get it surfaced, maybe even on both sides, depending.

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I also have a closed chamber A87 head.  Maybe I can play with the combustion chamber quench shape and unshroud the valves to lower the static compression.

 

is it worth running higher static compression, low boost and less timing?  Perhaps it would have better drivability and wider power band at the expense of peak power.

Edited by D52E

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Sort of. You can only bring the timing down so far before that becomes your problem. 25 degrees total timing is about the lowest number these big motors like to run at. My 2200 which was almost 12:1 ran well at 25 degrees on pump gas.

 

I don't think anyone has asked, but what are you going to do with this motor? Track day car? Street car? If street car, take the extra steps to lower the CR down to about 10:1. It will be less of a headache in the long run.

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The plan is for a street car with ocasional auto cross or track day.  Drivability is desired if possible with some compromise.

 

I do want to run the GT2256 turbo (I think it’s a 22 mm turbine and 56 mm compressor) and a small water to air charge cooler.   I also have a megasquirt ecu (still need to build the intake) and Ford EDIS setup.  

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Run some compression but don't lower it to 7 and expect the boost to take up the slack. It would if boosting all the time but 99.9% of the time on the street you aren't and it will drive like a 7 to 1 compression engine. 

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On 2/13/2019 at 7:24 AM, Stoffregen Motorsports said:

Sort of. You can only bring the timing down so far before that becomes your problem. 25 degrees total timing is about the lowest number these big motors like to run at. My 2200 which was almost 12:1 ran well at 25 degrees on pump gas.

 

I don't think anyone has asked, but what are you going to do with this motor? Track day car? Street car? If street car, take the extra steps to lower the CR down to about 10:1. It will be less of a headache in the long run.

did you run that thing with the dizzy locked? i modified mine so i have 15 at idle and 32 all in.  it liked lots of advance at idle, if i tried to dial it back the header would start to glow.

 

On 2/12/2019 at 10:27 AM, datzenmike said:

I would love to tig in some quench area on a U67. Even a raised flat spot that fits the piston dish for true squish. It would be a lot of work but I'd love to try.

 

yuuuuup

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I removed the vacuum advance and installed a solid breaker plate from Nissan Motorsports. Then adjusted mechanical advance to limit it. Final adjustments were made to the springs to allow it to advance quicker. I remove one spring and leave one installed.

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Turbos like 16-20 degrees at idle, then a short advance curve totalling 30-32 degres for a street engine.  Our race motor is 13.7:1 (if I recall) and we run 29-32 total, depending on temp and altitude, 110 gas.  Our base timing is 24.  Ceramic chamber and piston coatings.  

 

Your turbo will be less temperamental to tune if you stay at 9:1 or less and have some quench with a closed chamber head.  Hog out the plug-side of the chamber and unshroud the valves as much as possible on the quench side.  Ceramic coating the pistons will give you significant detonation resistance.  

 

A stock A87 head only allows about 62% exhaust to intake flow ratio.  Go up a size on exhaust valves and leave the intake stock.  Focus on allowing the exhaust to breathe.  Scooter's photo will allow for about 85-90% exhaust to intake flow and will go up to about 200 cfm on the intake side.  WIth a turbo I'd shoot for about 85-86% exhaust flow since you;re suckingon the pipe.  With a supercharger closer to 93%.  

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So why doesn't the factory set the mechanical advance to optimum? 

 

Why does mechanical advance stop at 3,000 when the engine continues to rev to over 2 X that amount?

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Optimum for what? Optimum mileage and emissions or optimum performance. Two different aspects of engine tuning.

 

The factory settings were to increase mileage and decrease emissions. That's the main reason for the vacuum advance - to pull in timing at light throttle. This can be dangerous for a "maxed out" engine with higher compression. Too many variables. Setting the timing curve so you know exactly what it will do at a given RPM is optimal for piston ring health, connecting rod bearing life, as well as performance.

 

 

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Mechanical advance stops at around 3000 rpm because the dynamic compression of an engine only increase until about 4000 rpm (varies a lot with engine design) and it needs no further advance after 3000 -3500 psi or so.  

 

The factory rarely ever set the mechanical and vacuum advance to optimal for any vehicle.  If they did, it was for their best performance vehicle (most expensive anyway.)  Look at the small block Chevy as a good example.  The lighter Camaro which was the first to receive the 350 could have been faster than the Corvette in '68, but they chose to dumb down the timing to make sure it wasn't or Corvette sales would have suffered when the first Vette owner got his doors blown off by a car $$$thousands$$$ cheaper.  Trucks and station wagons were further de-tuned.  

 

The 620 got an advance curve that made torque, but went "over the top" with advance so horsepower would fall off and the usable rpm stayed a bit lower than was capable.  This added durability and longevity to the engine by limiting the rpm range over years worth of use.  The light pickup should never be as quick as a 240Z either, not that it could have been, but better timing may have made it faster off the line with its low gears.  

 

In later years, advance curves were used to pass emissions - starting in about 1970 changes started.  By '74, most import cars had vacuum retard instead of advance to further clean tailpipe emissions and de-tune the engines.  Then along came electronic ignitions and all those rules changed.  Cars ran better, but not because of the electronics.  It was because the timing curve rules changed. 

 

 

Edited by distributorguy
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