Datsun Roadster Forum-311s.org

I'm not sure what the overall goal or intent is to this discussion but I can tell you that adding material to the ports is and has always been illegal in SCCA production car racing. This is why you're not going to find much about it.
Mike, I thought that might be the case - so...want to experiment? Not sure it would be legal....but....I have read of 'tongues' of metal being welded onto the header flange that fit into the port at the bottom, improving the SSR and decreasing the port size...just saying....every bit helps on the track? (I have been unable to find any pictures of this)


If this is for a street car and not for racing and a rules set then I would just add displacement, a different engine or some other more cost affective method to gain power and especial torque. Regarding flow, that alone from a flow bench is not a good measure of power output for these engines. How that flow induces swirl to the mixture and helps scavenging is more important in my opinion and experience. A head with great flow numbers may not make the best power.
Street car. Displacement added (2065 cc). Cost effective....oooooh...that was thrown out when I bought the Datsun.
Flow bench....I agree, flow alone is a poor measure. Flow and velocity together, on a flowbench however can be a good measure. Smallest port that will support my targeted horsepower is the goal. High velocity should help with swirl and mixture motion and also support higher torque at lower rpms.


Looking at the deposits in a cylinder head after it's run can tell you a lot about how things are burning. IF I was going to add material to the port I would increase the bottom radius of the exhaust port and increase the radius above to make a larger overall bend in the exhaust port. I do this to some extent when I port Datsun heads but I make the port larger as I can't add material and my engines run at high rpms. More attention should be placed in the combustion chamber to unshroud the valves and then tuliping the port above the valve to help the venturi effect and the transition to the seat. Porting should be done with bias towards one side of the port to help induce swirl and contribute to scavenging especially as you increase overlap in the cam. All the this is lots of work and time for a street car when other options are available IMO.
Mike Unger
Thanks for the thoughtful advice. I am looking at most of this. All of the 1600 heads I've looked at have carbon buildup in both the intake and exhaust, not sure if this is just bad tune, or the fact that both ports are oversized for the output of the stock engine. Any advice on the shape of the backside of the valve? 'Penny on a stick' for the intake? Slight 'tulip' for the exhaust?

Cheers

I think everyone on the thread really is trying to help out Daryl in reality.

Eh, nothing ventured nothing gained! Carry On! Have Fun! Adventure Awaits! Onward Ho! Hey really, why not?

Daryl have you dyno'd the roadster before porting?

Alvin,
No...unfortunately. This is a new engine which will need to be dyno tuned with the EFI and ignition. I considered putting on a stock head to run until this head is done, but it would also need modifications to be able to run .500" valve lift. The expense of 2 separate dyno tunes and runs for a proper comparison is not in my budget, along with mods to the 2nd head.

Jim,
Yes, actually, the U20 head could use a little downsizing of the exhaust port....believe it or not. Not legal in most forms of racing you'll find these engines in.
Oversize ports were a common problem from the manufacturers of many makes. Ask around.....

I have also ruled out welding on this head.

No posts till I have more pictures or info.

IMHO For subtle port effects/port tuning, an engine dyno is certainly the way to go. If ALL the other variables are not tightly controlled, the data will be meaningless and misleading. Might be able to do it on a chassis dyno, but considering this would realistically involve a head swap, you'd have to be extra careful to preserve all the operating parameters. Since you can easily have chassis dyno error in the several percent range, these subtle port improvements may be in the error band.

Daryl, Most good engine builders will tell you that trying to cram the largest exhaust valve in the chamber possible is a mistake, and they are right. I think the U is quite good for a factory effort - most are worse.

Just to clarify, yes at 2065cc I think you will want a 34 or 35mm, but that will require good chamber work and pro seat work in the R head. If you aren't going to spend a lot of time & money on the seats, 33 is a better choice since 34,35mm valves will be "not so good" on a stock 1600 seat.

I'd say 33/34 would be very nice for an 1600+/1850-2000 stroker.

One problem with your logic on this topic Daryl is that you are attempting to use numerical approximations obtained from the internet or somewhere else as absolutes.

For example this 40% number you are relying on -that's a average, approximate estimation.

The actual optimal exhaust valve size is going to vary by engine desired power band and mechanical design parameters If you think a Ferrari 12, a Porsche 6, Granny's Volvo and an H20 are all optimized at 40%, that's fairly far off the mark. 37% is going to do the best for some, 43% will be best for other designs depending. 40 is just a average rule of thumb. So concluding that because a valve size isn't 40%, it is either too big or too small for your particular application is just psuedo science. Any professional engine designer would laugh at this premise. Ask around.

BTW we do agree on the U20, many of us have known that the u20 intake port is on the big side for decades. There is typically little reason to increase that. Clearly it isn't particularly harmful considering the output U's can make with stock valves.

Either way, there is a lot of very good advice on this thread about what will provide better yield. It has been fun.

"Daryl, Most good engine builders will tell you that trying to cram the largest exhaust valve in the chamber possible is a mistake, and they are right. I think the U is quite good for a factory effort - most are worse."

When did I say anything about cramming the largest possible exhaust valve in??

"Just to clarify, yes at 2065cc I think you will want a 34 or 35mm, but that will require good chamber work and pro seat work in the R head. If you aren't going to spend a lot of time & money on the seats, 33 is a better choice since 34,35mm valves will be "not so good" on a stock 1600 seat.
I'd say 33/34 would be very nice for an 1600+/1850-2000 stroker."
Glad to see you are coming around to the idea of a larger valve. As you know, I was originally only going to install a 34 mm valve, but, upon reveiw of some information, decided 35 mm would be better for my target power output, still not 40%, but closer. I may go larger.

"One problem with your logic on this topic Daryl is that you are attempting to use numerical approximations obtained from the internet or somewhere else as absolutes.
For example this 40% number you are relying on -that's a average, approximate estimation."
Actually, I tend to think of it as a very worthwhile TARGET. There are reasons to go with smaller or larger, but, for a 'performance', high output, 2 valve piston engine in the compression range I'm looking at, there is no reason not to shoot for that target.
Also, it is actually an "approximation", based on much reading and research, a basic dyno program, a header design program, calculations based on bore, stroke, compression, and rpm targets - much the same as goes into choosing a cam, although cams have much more clout in the equation for power.

Now, as far as your casting aspersions upon my information and research ability, I have to admit to getting somewhat annoyed, but, I understand, somewhat. I am throwing out ideas that just don't jive with your experience or thought processes. I like to think that I am quite thorough when trying to find the information I am looking for, and quite often come across interesting tidbits that bear further investigation, hence the diesel transmission and 4-2-1 header thread (which got a lot of negative posts at first - still waiting for someone to try a 4-2-1 on a U20).
Instead of attacking my abilities you should have just asked where I got my information....and here it is (for the head), in no particular order:
David Vizard (books/internet)
Philip Smith/John Morrison (book)
Harold Bettes (book)
Peter Burgess/David Gollan (book - on order)
Farrell Vaughn (head porter)
Larry Meaux (Head Porter/PipeMax creator)
Various internet sites (at this point, for me, it's pretty easy to tell who doesn't know what they are talking about, and who does.)
- Speed Talk (engine tech/car website) There is no better resource if you want to learn about engines and have a background that will allow you to understand what's being said when things get technical (over my head more than I like to admit). Frequented by a number of high end engine experts of all specialties. And it is all up to date information!!

Unfortunately, there aren't too many people in the know on this site that care to share relevant info, so I have to go and stick my neck out and talk about the things that nobody seems to want to talk about....and poke the damn bear....
The few with real experience with this don't post much if at all, like Mike Unger.....

"The actual optimal exhaust valve size is going to vary by engine desired power band and mechanical design parameters If you think a Ferrari 12, a Porsche 6, Granny's Volvo and an H20 are all optimized at 40%, that's fairly far off the mark. 37% is going to do the best for some, 43% will be best for other designs depending. 40 is just a average rule of thumb. So concluding that because a valve size isn't 40%, it is either too big or too small for your particular application is just psuedo science. Any professional engine designer would laugh at this premise. Ask around."
As above on the 40%. Nobody is talking about Ferraris, Porsche, Granny's Volvo, or the tractor you drove on the farm. (Although, I would be very surprised if the Ferrari and Porsche didn't meet the 40% threshold (for a 2 valve head) and only moderately surprised if the Volvo didn't.)
I am talking about getting near double the power from a 2 valve pushrod engine head designed for an engine with near 30% LESS displacement, approximately 6500 rpm peak HP, in the 9.5 to 10:1 compression range (in case all that wasn't clear earlier).

"BTW we do agree on the U20, many of us have known that the u20 intake valve is on the big side for decades. There is typically little reason to increase that. Clearly it isn't particularly harmful considering the output U's can make with stock valves."
I thought we were talking exhaust port/valve....which, someone has mentioned Rebello has been installing smaller exhaust valves, likely helps with reversion...
Intake valve....That really comes from the racing aspirations, exhaust too, likely. The '67s make me think 'Homologation' run specifically for racing....

Here is a site listing flow #s for a road race R16 head:
http://users.erols.com/srweiss/tablehdc.htm#NISSAN

Interesting that they only increased the Intake valve by less than a millimeter (42.93 mm), but, exhaust valve increased by more than 3 mm (35.05 mm)
I beleive these are SCCA mandated max valve sizes?

*Looking at the site above, it does not specify R16 or L16....(edit April 20/19)

So... the opposition to the 40% of bore target for the exhaust valve got me thinking, and doubting....What were the OEMs doing as far as valve sizes in contemporary 2 valve motors?
Below is a list of some run of the mill 2 valve, 4 cylinder engines, and a modern V8 for comparison.

Some interesting points of note:
None of the 2L engines has an exhaust valve less than 35mm.
The Porsche 914, even with a huge 94mm bore has a higher percentage exhaust valve/bore size than the R16.
No engines aside from the Porsche and R16 go below 39% of bore size for the exhaust valve. The Porsche also has a bore which is almost 7mm larger than the R/U engines, and the R16 has a comparatively small displacement for the bore size.
The L16, same displacement, has a larger exhaust valve (33mm) with a smaller bore.
The 2 newest engines (GM) on this list (year 2000+) both have 41%+ exhaust valve to bore size.

The last column, I decided to compare exhaust valve area to cylinder volume to see how that would play out...Not sure this really correlates to anything, but interesting info....
Surprisingly the R16 compared quite well with 2.01 sq mm/cc, the R20 with a stock 32 mm valve does not (1.61 sq mm/cc), it's at the very bottom. Considering the port behind the exhaust valve is bad also, I personally, think it's a very poor recipe for a 'performance' motor.
The LS 5.3 is on the lower side of the scale in this column as well @ 1.84, but, it is also likely to be the most highly developed/best flowing port on the list.

The strokers I've listed at the bottom. The 1st R20 is my current build, the R18 is the 1800cc stroker I built a while back. The green highlighted stroker is the common "U20/H20 crank rods and pistons" and stock head engine - this is not to say that this particular stroker is a dud. For a lot of people it works just fine, with the right cam, and has great torque increase over the 1600, it'll just peak much earlier in the rpm range.

My first attempt with some cutters and sanding rolls...very rough, but the general shape is where I'm headed. I have a couple of dud heads to practice on before I get to the good one. Will try to straighten out the one side so it doesn't curve so much...The standard 1/2" and 3/8" burrs are to big for me, so I've ordered and am waiting for a couple of 1/4" head burrs. Hard to keep from hitting 2 sides and having the burr jump around...on this one I've totally mangled the valve guide because of it. There really isn't much metal removed here....

Keep playing Daryl, I can relate. BTW, you mentioned EFI, are you running megasquirt now and if so what EFI system did you set up? I love my carbs but with the A/F meter and my ear I can always tell when it gets rich, especially in the mountains... if I could afford the cost and justify the added hassles of high fuel pressure and return lines etc I would love EFI. As it is, I thank you for the encouragement to convert to megajolt, couldn't run my car like it does without it!

Reality check:
The stock R16 exhaust valve is 32 mm diameter. You need room for the seat, which brings the 'throat' (the actual opening for the exhaust to flow out) at ~28 mm (measured stock) or 1.102".....
What makes you think that a 1 5/8" or even a 1 1/2" header is going to improve performance when the biggest restriction is right at the valve??

Even if you open it up with a 36mm valve (U20) the 'throat' at 90% (not stock) would still be only 32.4mm (1.276") in diameter.....still well short of the 1.5" & 1.625" headers, but, no one would recommend a header smaller than 1.5" for the U20.....

Lots going on with the exhaust that is not understood well....and not by me for sure, but, I am working towards a small understanding of what may work for this engine.

Greg,
Actually not running anything atm, but, yes, the Megasquirt II is what I run. Does the job without being too complicated, and still much better than a
carburettor, imo. Considering going to Microsquirt, which is basically the same, but, in a smaller, easier to hide package.

[quote="Daryl Smith" post_id=313124 time=1600972914

Greg,
Actually not running anything atm, but, yes, the Megasquirt II is what I run. Does the job without being too complicated, and still much better than a
carburettor, imo. Considering going to Microsquirt, which is basically the same, but, in a smaller, easier to hide package.
[/quote]

I'm in the process of converting, going Microsquirt. Just downloaded Tunerstudio to begin understanding that system. Gathering a few more pieces before the change over.

Found a paper with the #s for a stock head I had flowed years ago.....in case anyone is interested...
With the 1 cfm = 1 HP formula commonly found, this would have the intake flow enough for about 163 HP @ .400" lift. With some very mild port cleanup and a good valve job it would likely be closer to 170 cfm or higher. For most people, I don't think a larger intake valve is at all needed!!
Just a mild cleanup of the ports, a larger exhaust valve, and a good performance valve grind will get you what you need from the head. After that it is supporting parts - cam, carbs/efi, intake, exhaust, ignition....maybe some light exhaust port work(?).

Always good info and discussion my friend. Glad to see you're finding some time to play. For me, what's interesting is how much difference valve lift makes in flow, until it doesn't. Diminishing returns as you go past .400 lift, with more valve train stress and maybe a need for stiffer springs. On my U20 engine, I have noted a significant change (loss of power starting at about 3200rpm) going from my Isky (.531 total lift) to the Racer Brown (.478 total lift), enough that I plan to have the Isky cut down just a little (aiming for around .500-.510) because I'm petty sure I'm still tapping a valve and want that to stop (no known damage, running larger intake and exhaust valves, and probably unnecessary as we see, but what's done is done!). The car accident stopped me from playing much this winter and I'm still gimpy (getting up off the ground is slowwwwww) but I expect to be working on it again in the next couple of months.