E31 Compression Chamber Unshrouding

[a_z_story]

Hello,

I'm going to take a die grinder to my E31 combustion chambers and intake and exhaust ports to deshroud and port match the intake and exhaust manifolds.  Not looking to go too crazy, but I have a steady hand and feel pretty confident that I can make improvements.    I believe the green lines in the image below are the areas to focus on.  Is there any reason to cut into the quench pads? Maybe use that material to equalize combustion chamber volume?   The first photo shows some some rough surfaces that I would also assume should also be smoothed out. 

 

I'm having the larger valves from an N47 cylinder head installed, so does it even make sense to deshroud prior to the valve job?  I''ll be mating this head to a N42 L28 bottom end with flat tops.Thanks in advance for your input.

 

    

 

 

Edited April 8, 2020 by a_z_story

[DuffyMahoney]

I did the dsi valves. Nothing was done to the chamber. But I installed dsi valves. Lots of port work though. Flows awesome. 

[a_z_story]

Looks good @DuffyMahoney - what are your thoughts on keeping the intake ports rough to stir up the A/F Mix?  Those valves loook yuuuge. And what's going on with those valve guides?  Looks like they have a portion cut out?  Your combustion chambers look like they had the edges knocked down at least.  Did you volume test them? If so, I'm curious to know how they compared, and what the acceptable tolerance is between them.  I keep editing my post as I answer my own questions, and come up with new ones..ha!

Edited April 8, 2020 by a_z_story
busy mind

[DuffyMahoney]

Not keeping the intake ports rough. They are done already. Flow data is attached. 
 

Valve guides were left in during porting then replaced after by a machine shop. 
 

I don’t believe the chambers were touched. But I will ask Andrew (engine builder) I went through 4 E-31 heads before i found one that was cast nicely and no flaws. 

[a_z_story]

Those seem like some really impressive flow numbers compared to those other cylinder heads.  Makes me feel a little better about going down this E31 path, although I realize these results are likely unobtainable for noobs like myself.   

 

I found this thread saved in FAQs that touches on some of my questions from my OP (more N42 focused) , and have an active thread running on the Church of L series as well on the subject if anyone's curious.  The question that I have not seen an answer to is what material should be targeted to balance combustion chamber volumes?  Quench pads?  Material around the Spark Plug?  Or is this not even a valid concern?   Pure speculation at this point from me.

 

Thanks all!

   

[JMortensen]

I would do all your chamber work before you have the valves installed. If memory serves the exhaust is the same size and the intake is a bit larger. What you don't want to do is nick the seat, so you should leave the old exhaust valve in while you're working. I already had larger valves in my head, so I left both in. If you're replacing both seats then I think you're safe to leave them out. They do get in the way.

What I did was to take a head gasket, set it on the dowels in the head, then shifted it left and scratched the head on the right side of the chamber with a pick to show the fire ring line, then shifted right and marked the left. You don't want to remove metal under the fire ring on the gasket, so I probably stayed .010 or so away from the line. I did the same on the block. Notched the block to a little above the piston ring mark in the cylinder, then removed the metal in the head and block out to the line. This should improve airflow on the cylinder side of the valve. Also smoothed the rings around the valves, mine had some fairly rough areas in the triangle areas between the valves. 

It's been 20 years, but I don't recall having to pick an area of the chamber to remove metal from to even out the volumes. I think all of it came from the areas described above. If you took a measurement of the cc's before you unshrouded the valves, then you could figure out which cylinders to be more aggressive with.

Seems to me I had more quench than you appear to. Is than an L24 gasket? If the cylinder ring were bigger the quench pad would look bigger. I made an exaggerated drawing of what I tried to accomplish on mine. I did all the spots you marked in green, but most of the effort on mine was put in where I marked in red.

Edited April 8, 2020 by JMortensen

[JMortensen]

BTW I got nearly all of this from the book "How to Modify Your Nissan/Datsun OHC Engine":
https://www.amazon.com/Modify-Your-Nissan-Datsun-Engine-ebook/dp/B0092WMDCK/ref=sr_1_1?dchild=1&keywords=how+to+modify+your+nissan+datsun+ohc+engine&qid=1586372446&sr=8-1

[a_z_story]

1 hour ago, JMortensen said:

BTW I got nearly all of this from the book "How to Modify Your Nissan/Datsun OHC Engine":
https://www.amazon.com/Modify-Your-Nissan-Datsun-Engine-ebook/dp/B0092WMDCK/ref=sr_1_1?dchild=1&keywords=how+to+modify+your+nissan+datsun+ohc+engine&qid=1586372446&sr=8-1

 

I just bought this book last night off Amazon.  Looking forward to nerding out while in lock down at home!

[a_z_story]

6 hours ago, JMortensen said:

I would do all your chamber work before you have the valves installed. If memory serves the exhaust is the same size and the intake is a bit larger. What you don't want to do is nick the seat, so you should leave the old exhaust valve in while you're working. I already had larger valves in my head, so I left both in. If you're replacing both seats then I think you're safe to leave them out. They do get in the way.    This was my initial thought. Both intake and exhaust valves are larger, so I'll just keep the current valves out, deshroud around the openings, and trust that when the new valve seats and guides are installed they will machine those flush to the bowl surface when doing the valve job.

What I did was to take a head gasket, set it on the dowels in the head, then shifted it left and scratched the head on the right side of the chamber with a pick to show the fire ring line, then shifted right and marked the left. You don't want to remove metal under the fire ring on the gasket, so I probably stayed .010 or so away from the line. I did the same on the block. Notched the block to a little above the piston ring mark in the cylinder, then removed the metal in the head and block out to the line. This should improve airflow on the cylinder side of the valve. Also smoothed the rings around the valves, mine had some fairly rough areas in the triangle areas between the valves. 

It's been 20 years, but I don't recall having to pick an area of the chamber to remove metal from to even out the volumes. I think all of it came from the areas described above. If you took a measurement of the cc's before you unshrouded the valves, then you could figure out which cylinders to be more aggressive with. Good idea measuring before.  I'll do this first while my current valve seats are in tact and can make a good seal.  Going to try to rig up some home made system to measure volume with an syringe, a piece of clear hard plastic and a hose.  Getting a high degree of accuracy with the DIY system might be challenging.

Seems to me I had more quench than you appear to. Is than an L24 gasket?  If the cylinder ring were bigger the quench pad would look bigger. I made an exaggerated drawing of what I tried to accomplish on mine. I did all the spots you marked in green, but most of the effort on mine was put in where I marked in red. That is an L28 gasket.  ~87-88mm gasket bore measured with a metric tape.  I read elsewhere about removing material where you marked.  I don't have much to give, but I do have some casting blemishes in those areas, so I'll be sure to make them smooth.  

 

 

 

Edited April 9, 2020 by a_z_story

[JMortensen]

Just don't get super anal about your compression ratio with the old valves. My valves had been cut and the seats had sank into the head a bit. I gained a lot of compression by installing the new intake seats and those valves without the dish that I mentioned. I can't recall the numbers anymore, but the volume shrank quite a bit.
 

[a_z_story]

I measured the volume my combustion chambers tonight with the stock E31 valves in place to get a baseline volume comparison.  I used what I had layin' around - quarantine MacGyver style.  A skii wax scraper, and an equine syringe and some died water with a oil (thinking that might reduce the surface tension).  Measured from front to back, 43.5, 43.5, 43.5,43.5, 43, 44 cc.  I'd guess my instrumentation was accurate to the nearest .5 cc -  I think the diameter of my syringe made for some slop unfortunately.  I did each 3x and took the median.  The sneaky bit of volume that I didnt immediately realize I wasn't resetting each time was the space around the ceramic in the spark plug - I think this may account for .5 cc or so.  Anyhow, I figured I share to get thoughts from others, and maybe inspire others to do this.  I'd recommend the narrowest, tallest pipette/graduated cylinder/syringe that can do 50-60cc depending on the head you're measuring. 

 

 

Edited because I misread my syringe and noted all volumes off by +5.  

Edited April 9, 2020 by a_z_story
wrong numbers

[madkaw]

Those numbers seem high . Stock chamber should be around 42cc . Unshrouding the chamber is important and should be done . It’s easy and fast . I used a drum sander with a valve installed on the seat to protect things . I like the drum sander because it cuts at a low speed and has a radius to it - the bigger the better . A cordless drill will cut it fine . 
That extra area around the valve pocket helps flow as the valve first comes off the seat . 

[a_z_story]

3 hours ago, madkaw said:

Those numbers seem high . Stock chamber should be around 42cc . Unshrouding the chamber is important and should be done . It’s easy and fast . I used a drum sander with a valve installed on the seat to protect things . I like the drum sander because it cuts at a low speed and has a radius to it - the bigger the better . A cordless drill will cut it fine . 
That extra area around the valve pocket helps flow as the valve first comes off the seat . 

 

Yes, I misread the syringe and all of the numbers were off by +5.  I edited my post above to correct.  Even so, they all did measure over the reported 42.4cc CC volume for the E31..not sure what to think about that.  

[madkaw]

6 hours ago, a_z_story said:

 

Yes, I misread the syringe and all of the numbers were off by +5.  I edited my post above to correct.  Even so, they all did measure over the reported 42.4cc CC volume for the E31..not sure what to think about that.  

I wouldn’t fret over a CC - my MN47 head measures big also compared to spec