Jump to content

B210 A13 with 728 round port cylinder head...

74 B210

Recommended Posts

Hi guys, in my attempt for ever better fuel economy on my 74 B210 coupe, I replaced the stock head

with a 728 FU round port head and I have a 990 81 head to try as well on my A13, I know they were used on a 

A14, but the engine  runs and starts better then with the stock head all other parts are original.  the car has more

pep, the only thing is it pings pretty good under light to med load on the road. I have 5 degrees of timing and from what I am

reading online, I need to take some out maybe 3 to 2 degrees??   cause there is a smaller amount of cylinder head, and higher compression.  I will adjust tuesday hopefully will solve my prob. I want o run 87 gas in it.   any other thoughts for my tuning???

thanks Jim

Link to comment
  • Replies 71
  • Created
  • Last Reply

Top Posters In This Topic

Top Posters In This Topic

While higher compression increases efficiency it can ping which means the timing has to be retarded and you loose some of that efficiency. Reduce the timing and drive several tank fulls and record the mileage and distance to calculate the MPG. Now with a base line switch to a higher octane gas and increase the timing and do the same. The answer is... do you get enough of a mileage increase to off set the increased cost of the higher octane gas? You may be surprised.

Link to comment

There is probably a good explanation as to why the distributor curve in early Datsuns is the way it is, but you can definitely make adjustments to improve it.


First off, the base or idle timing is always a tad too low. Obviously this was done for emissions. Bumping it up to 8-12 degrees or sometimes even 15 degrees BTDC can help with low end throttle response. The problem is that you also have a centrifugal mechanical advance that provides too much total timing. More initial timing will give you more pep, but you also need to make sure the total timing is limited. 32 degrees is a good number for total timing, but some have good luck with up to 35 degrees. The mechanical/centrifugal advance can be limited by welding up the slots in the distributor cam, thus limiting the amount of travel available in the slots. Careful welding, ie-TIG, can be a one-and-done job. Either way, if you're MIG or TIG welding the slots, you should go through them with a fine file and make sure the cam rotates smoothly, without hanging up, before you reinstall the distributor.


Then there is the middle. Even if you set the mechanical advance to be limited to 32 degrees, the curve in the middle is too slow. What to do? loosen up the middle of the curve, or the rate at which the centrifugal timing is introduced. You can do this by selecting weaker springs, or by simply removing one of them.


Vacuum advance also comes into play. One way to maximize the timing curve without running the risk of adding too much timing at any given RPM is to disconnect the vacuum advance and use only the centrifugal advance.


Note that I am speaking in terms of horsepower and throttle response, not economy. I have never spent much time on tuning engines for economy. My point is that you can dig into the distributor's internals and make adjustments suitable to your needs.

Link to comment

I think your right datzenmike, I retarded the timing a few degrees and it stopped the pinging, engine still didnt sound happy,  prob. wants at least 5 degrees,  does anybody know if  can build a engine with A15 parts to A14 block like swapping out the pistons for more of a dish, to decrease compression  ratio?  or possible use A15 pistons in my A13 block? Because the the A15 pistons I have, have a dish in them?? 

Link to comment

Well I did say you can retard the ignition and loose some efficiency OR use a higher octane gas and keep the timing. I had a work van and always ran the cheap regular fuel and always kept a mileage log, but just for kicks I filled up with the expensive premium fuel. I did this for several tanks and the mileage increase more than made up for the increased price. I couldn't believe it or get my head around it but it did. Now this was EFI and the ignition timing is determined by the knock sensor so it's timed as close to knock as possible to maximize efficiency.


You would have to test this out by running several tanks and record the MPG to see if it's worth the extra cost.


The A13 has a 73mm bore so 76mm A14 or A15 pistons won't fit.

Link to comment
11 hours ago, 74 B210 said:

I think your right datzenmike, I retarded the timing a few degrees and it stopped the pinging, engine still didnt sound happy,  prob. wants at least 5 degrees,  does anybody know if  can build a engine with A15 parts to A14 block like swapping out the pistons for more of a dish, to decrease compression  ratio?  or possible use A15 pistons in my A13 block? Because the the A15 pistons I have, have a dish in them?? 

I think you're going the wrong way. Keep the compression and figure out the timing curve.


Case in point - I had a built 2200 L motor with 12:1 CR that I ran on pump gas with 32 degrees of total timing, and 12 degrees of initial timing. It can be done.

Link to comment

The A15 pistons have a different pin height so you cannot use those in an A13. The A12-A14 pistons have a 32.5mm pin height vs 30mm for the A15.


The A14 & A15 have a 76mm bore vs the 73mm of the A13. If you bore the block to 76mm you can use the A15 crank and pistons.

  • Thanks 1
Link to comment

Thanks Datzenmike, I will do that on Monday. also I have a scheme of throwing my 990 head on my A15 engine with dish pistons.  Does anyone have or can sell A14 dished pistons... thanks for the info Tom1200. which means I got to find A14 dish pistons or use my A15 like it is to match the MPG 1981 Motor. minus the A14 Engine... 

Link to comment
On 10/7/2022 at 10:21 AM, 74 B210 said:

I have run the motor with 0 timing and it really didn't like it. So I have to go to 5 degrees at least and try it out. It seam not to shake as much and more in time with 5 degrees put it pinged at light throttle.


On 10/7/2022 at 12:40 PM, datzenmike said:

Go to higher octane gas!!!!!!! Turn the timing up till it pings and back off slightly till it stops.

This is an issue with a vacuum advance. Yours is pulling in more timing at partial throttle. Advance it to 5 degrees and disconnect the vacuum advance and run it that way to see if it pings.

Link to comment

I got some higher octane gas to run and I do have another dizzy to try out.  this one changes degress at idle 5 to 3 it dances around a little, it is a rebuilt rock auto unit, try and get a new one!!! right!!  I just spent last week, changing my rear end over to a 76 with a H150 unit for hopefully lower rpms on the freeway and put poly bushs on the rear from the rotten rubber ones. so a lot of work!

  • Like 1
Link to comment

Thanks datzen mike.  for info. the H150 I put in was out of a 76 AC coupe B210 with a manual in it. it did have a swapped trans in it a  60 series 5 speed.  but the trans tunnel is smaller.  I cant read the vin plate under the hood so hopefully the door will give me the info. that it is a 3.700 as I have tired to find a 3.54 but it seems like they are rare as hens teeth....so monday is the big day to test and tune again my hybrid engine. 

Link to comment
  • 2 weeks later...

Well all the driving tests my new rear end has a higher gear 3.88, so I will swap out to a 3.7 next monday. 

the MPG with a leaner jet change to a 112 to a 110 is on A/F of 14 to 15. maybe a 107 I have handy will bump it a bit richer.  

she still pings on light throttle going to supreme gas, I put in 89 not much diff in driving. and the timing is set to 5 degrees. took off the dizzy vaccum advance and didnt help... mpg is 38  at 62mph... flat ground disappointing...I tested with and without cold air intake. it did better with cold air.  only thing left is to jet leaner and lower rear gear..  I wish I can get a 3.54 gear...I have all the upgrades 5 speed 60 series, rear gear, round port head... any thoughts?? 


Link to comment

Going down to 107 in jet size makes the mixture leaner.


Keep the vacuum advance. It adds or subtracts advance in proportion to engine load . Light throttle more advance heavy throttle less advance.


How are you keeping track of mileage???

A differential change will make the odometer read lower than actual traveled distance.

Find out the stock tire size. By now they will have been replaced. If larger diameter they will read lower mileage than traveled.



My 710 was from Nevada. I'm at sea level and I noticed on trips in the interior and in the mountains my mileage was better. My primary jet was a 99 or 102 either way close to 100. I found Nevada averages 5,000 feet above sea level. My at home air is denser so a 99 was too lean. I put a 112 in and mileage went up. Hard to believe that adding more gas got better mileage. As a side note, the performance was better also.

Link to comment

oh for sure they are not the stock tires. my spare reads 155-13/6.15-13, my tire size is 155/80/R13. I am keeping track of the miles with the trip odometer.  using gps, the sepdo is off by 8 to ten miles. so if your  going 60 its accurate at 68 to 70 mph.  I hoping with a lower gear maybe the spedo will get better or off more. I thought soo too,... with more fuel, no knocking and better mpg, but when I lean it out it seems the numbers say better mpg. I tested the intake and I thought warmer air is better mileage but, the numbers show colder air is favored. I got better mpg..

Link to comment

I think 155R13 is the same as 155/80R13


GPS doesn't give distance traveled just the speed. The speedometer needle could be messed up. Odometer is better but tire diameter could throw it off so it must be confirmed.


 Go out on the highway and start at a mileage marker. Mark the mileage to the 10ths. Drive at least 10 miles and stop at the marker and mark down the mileage. Do the same on the way back. You went 20 measured miles... what does the odometer read? A 2% error is a reasonable amount. Somewhere between 19.6 and 20.4 miles should be good enough to say accurate enough.


You would be 2 miles out every 100 miles driven. If you got 33.3 MPG the distance error would only be 0.666 miles. Pretty much nothing. If you got 50 MPG the distance error would be only 1.0 mile.



If intending any mileage improvements you need to be able to trust the actual distance traveled.

Link to comment

Leaning out the mixture can be disastrous if you already have a ping.


Are you sure the timing pointer is reading TDC? Easy to verify TDC by pulling a spark plug.


Is there an EGR system on the engine? A clogged EGR can cause a ping.


How about spark plugs? Are you using a hotter plug than came stock? Also, a projected tip spark plug can exacerbate detonation.

Link to comment

By '74 all Datsuns had EGR I believe. It may have been blocked off by previous owner, or hose off to disable it in an attempt to gain back some power. (which it never lost in the first place) It's located on a bolt on EGR manifold on the left side of the intake below the carburetor, just like the L series intake. There is also a solenoid that activates the EGR under certain conditions and it may be stuck off.

  • Like 1
Link to comment

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.
Note: Your post will require moderator approval before it will be visible.

Reply to this topic...

×   Pasted as rich text.   Paste as plain text instead

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.

  • Create New...

Important Information

By using this site, you agree to our Terms of Use.