Datsun Roadster Forum-311s.org

If someone wanted to get the most bang for the buck, on stroking a 5 main R16, what would a reasonable HP/TQ expectation be? I want to eliminate the head work, so expect a perfect head/valves/guides/etc. U20 crank/rods/ overbore, how big? electronic dizzy/header/ bigger carbs? I heard a rumor that the R16 carbs were originally made for a 1500, and would choke a 2 litre stroker. Let's list choices, like bore, cam, carbs, header, and reasonable output. A friend wants to know, but doesn't want to re-design the head. Pat

My Canadian brother Daryl should be able to tell us some info as to what a stock head will do. However, it's always been my understanding that, since an engine is an air pump, the power is in the head. Asking an engine to create more power without some head work is like asking an athlete to improve their cardio system without allowing them to breath deeply. Daryl may be able to give some insight as to what head mods are most effective and cost/time efficient, and based on that maybe a cam profile for duration that creates max power at the heads flow rate. Explain to your owner that it's all a system, and the more things change to one area the more likely other limitations will present themselves. Once the engine is done there are few things you can easily change to overcome restrictions. Yes, you can upgrade carbs and exhaust, but if the head doesn't flow the air a different carb/size won't make that much difference.
However, it may be that a bump in displacement, an appropriate cam with a duration that hits the desired powerband, and carbs large enough to meet the flow needs without killing velocity will work acceptably well with a stock head. I think your biggest decision will be how the owner drives the car and where they want power/torque and selecting a cam/carb to reflect this.

Thanks Greg, I was getting worried that the stroker fan club had shut down. We can assume the owner won't be driving like you or I, and certainly not like Gordon, but more like Dan or Dave. It would save him a chunk of change, on what is already going to give him sticker shock, after all the new parts and machine work.
I'm guessing the motor won't see more than 5K rpm wise, wich would be perfect with the head being flow limited. Also, if they turn into speed racer, the head work can be done later. I hope Daryl chimes in, also the other motor owner dyno'd at the same time as Peter. Peter wasn't much help, info wise, unless you wanted to talk about fishing, hunting, or cooking.(insert smiley face here) Think about an athlete who has to perform while only being able to take rapid short breaths. Pat

One member of the STROKER Fan Club, is still alive and well.....me....You might find some useful info in the "Stroker Poll", that was started some years back. But it would be an even greater benefit if the stroker engines had more dyno info included. As for me, my build was pretty much, very conservative (dollars)...I'll keep it brief...yeah right.. LOL....
EVERYTHING on my R16 / 5 main stroker used STOCK components, all of the short block parts: cam, rod, and crank bearings, lifters, and timing components (gears, chain, and tensioner), and all gaskets and seals, were sourced thru my local Nissan Forklift parts supplier, the only parts not replaced were the pushrods....I added a 4:1 header (but using OEM Nissan exhaust, muffler, and resonator all the way back), new, longer stroked crankshaft from Rallye, used U20 con rods, and standard bore, NOS OEM U20 flat top pistons w/ new Perfect Circle rings, and Isky 266 cam,... . I'm still using the same original R16 / 3-main CARBS, but with Keith's ADQ needles....the crank, con rods w/ bearings, pistons w/ rings, and flywheel were all balanced together, at a local "speed shop"...Could I be any happier ?....Yes.... My first wish would be a lightened flywheel....starting to add dollars now...$500 to $900 (with clutch assembly),...larger bore & pistons, which would mean more swept volume, and therefore more compression, so... I would probably want more cam overlap and lift, with more flow through larger exhaust valves, so ....then it might make sense to include a larger exhaust system,...now with more displacement, and a way to exhaust it, one might consider more intake volume,...ie...larger carbs and enlarged intake manifold to match....In other words...what Greg said....But at the initial, least expensive stage of a stroker, what I gathered from Daryl's, and others' opinions, is that the exhaust valves enlargement, and large exhaust system is the next step to helping a stock R16 head to breathe better...
I did forget the to mention, that I LOOOVVVE my build, and that it was mated with the 5-speed trans, going back to the original 3:89 rear end...
Mike

Mike, If this father/son duo built a stout bottom end, U20 crank, rods and pistons, new everything, including lifters and camshaft, .040 over bore, re-sised rods, balancing where needed, they would be okay with a stock head? I know, not optimal, but a significant improvement over stock. I am also suggesting electronic ignition, header, etc. Later, the money can be spent on porting, larger valves, etc. Am I off base, or can a R16 owner gain substantial torque without head modification? Pat

I have built a couple similar but different stroker engines, one was actually a rebuild of a Vern Colvin build from the 90's, the other one was from scratch. Both used U20 lower end parts and pistons, both have high lift stroker cams from our venders, both have had intake manifold porting to match Ztherapy U20 s/u carbs with RA needles and gasket matched ports on the head side on the intake. Both have lightened flywheels. The Colvin engine has oversized valves and has been bored .040 and runs .370 gears and can pull away from stock 1600 like a u20 will. The engine from scratch has stock size valves, .020 over bored if I remember right, runs .389 gears and will impress anyone who rides or drives it, ask Dave Neal who owns it. Both have custom made woodruff keys at the crank sprocket, ones that I made to help dial in the cam with a degree wheel to make it all work like I wanted the build to work. Also the Colvin engine has the snout cut off the crank with the sprocket and pulley sharing one elongated key. The engine from scratch has the elongated key, a full length crank with a spacer on the snout to make up the difference to use the stock crank bolt and washer. Both engines are in 68spl's with 5 speeds. My opinion is that with big valves or not, a stroker is a very fun engine to have in your car, sure they max out when a U20 can keep revving up the RPM but the seat of the pants torque is a very big difference from a stock 1600. Nothing on a stoker build has to be done a certain way, you build it your way...

If you build with stock components, most 5-main versions will fall in the 115-125hp range. Probably 25-35% torque increase over R16. Maybe 110 with a scrappy R16 head/no improvements. Here is why:

Even with a "perfectly optimized" 1600 head(which doesn't exist of course) , the stroker R-20 will never flow equivalent to the u20 head, that means the HP number will be less all other factors being equal. (bore, CR etc.)

The SU U20 was rated at 135bhp at the crank. That was probably also an optimistic number, but the additional stroke, much higher flowing head, bigger cam specs and larger SU carbs produced the 135 vs. 96 for the R16 with a proportional bump in torque.

It's a misnomer to think the 1600 SU's are a huge part of the problem-they actually will improve the torque spec for strokers through the typical street rpm range 2000-5k. They are good to at least 125hp and only become a limitation at higher rpm. Larger SU's will do nothing to improve low end.
We routinely test 1600 SU carbs on a U20, and they do great up till about 5k. Solexes or webers (or HSR's) are the best plan for higher rpm versions.
U20/240z carbs will work too-the outcome depends on the condition of them and your ability to tune them.


Most strokers, especially stock-type builds suffer from self imposed rev limitation- that is they run out of steam above 5k.

Since HP is Torque x Hp. If you want to brag about HP, the easiest way to make HP is get the revs up.

That is easier said than done. For the stroker, the CR needs to get a bit higher, lots of valve and port work$$$, and careful camshaft selection and timing is in order. Too much camshaft is always detrimental too. As Mike mentioned, the easiest way to help it rev is reduce the rotating and reciprocating mass. That means lighter pistons, lighter rods, and a lighter flywheel.

It's kinda obvious if you think about it...using a U20 crank, U20rods and heavy cast pistons increases the weight of ALL the main rotating assembly SUBSTANCIALLY. Add to that the smaller 1600 valves, smaller ports, smaller camshaft and smaller carbs and you get the typical R stroker engine. Noticeably more torque than an R16, but certainly not a U20.

If you are wanting to match the U20 power, a very different formula is required.

The 3main strokers are really a different topic since they have the distinct advantage of a much lighter rotating assembly.


Most of the things you mention Pat have little or no impact on power output: " .040 over bore-very slight, re-sized rods-none, balancing where needed-always a good idea, stock head-not even close to optimal, electronic ignition-none, header-none"

"Later, the money can be spent on porting, larger valves, etc." Yes, there will be a substantial increase in low-end torque without head modification , but it certainly won't want to rev very well. Will be very similar to a stock H20, maybe less powerful due to head improvements on the H. (and the H rotating assembly is lighter as well)

Jim, I appreciate your input, but this not a duplication of a U20. These people have a 1600 roadster, want to rebuild the motor and transmission, and the son will be a new driver. I've said before, sub 5K is the norm, and torque is preferred over hp, as torque generally occurs lower in the rpm range, much safer for a young driver. The question I posed, is what would you build, not modifying the head. you stated yourself that the head limitation is 5k, so what would you do? stock, stroker, what size, what cam, etc. We are not chasing hp, or rpm's, just a nice motor that doesn't cost an arm and a leg. Future upgrades might be an option, but not likely. Be honest,what would you do? Pat

unklpat wrote: Mon Sep 06, 2021 10:15 pm Jim, I appreciate your input, but this not a duplication of a U20. These people have a 1600 roadster, want to rebuild the motor and transmission, and the son will be a new driver. I've said before, sub 5K is the norm, and torque is preferred over hp, as torque generally occurs lower in the rpm range, much safer for a young driver. The question I posed, is what would you build, not modifying the head. you stated yourself that the head limitation is 5k, so what would you do? stock, stroker, what size, what cam, etc. We are not chasing hp, or rpm's, just a nice motor that doesn't cost an arm and a leg. Future upgrades might be an option, but not likely. Be honest,what would you do? Pat

Yes, a stock head will certainly work on a R-20 stroker, but with that approach, it will make less power across the power band than an H20. Just buy an H20 much less hassle?

- Or- maybe one of Brian Zana's inexpensive H20 cranks. (Not much sense in modifying a perfectly good U20 crank on an engine that will make LESS power than a decent H20). Stock R16 cam is fine or just a "stage 1" mild improved cam, 1600 carbs are fine. The header/exhaust manifold won't matter. Stock exhaust is fine.

Really, for what you are describing, a stroker is a big waste of time and money. A just slightly warmed r16 with a billet lightFW is a blast and way less expensive. The light FW with Z clutch is the best mod for a fraction of the money hands down. (Easy to drive and the Z clutch is a big+ for a novice driver unless dad likes pulling engines)

A stock r-16 with light FW will get the novice driver all the tickets he can pay. I know, my first car was a 68 1600! (The kid doesn't need a stroker)

unklpat wrote: Mon Sep 06, 2021 11:21 am I hope Daryl chimes in, also the other motor owner dyno'd at the same time as Peter.

I am that other motor owner. My build had extensive port work done, plus larger valves installed. So, I'm not much help in the "how will a stroker do without head work" category.

Seems like you've got some good advice here from people who know their stuff. Sounds like a stroked R20 with a stock top end should get you in the 110-115 hp range.

Does the H20 head flow better than the R16?

spl310 wrote: Tue Sep 07, 2021 8:39 am Does the H20 head flow better than the R16?

Yes. Significantly better for the 2-bolt thermostat style Y44 H20 head. (of course they weigh a ton...)

Okay, not everyone wants to turn their R16 into a U20. The crank will not be modified, and the rods are stronger than H20 rods, the displacement increase also helps. Rotating mass is not always a bad thing. I am looking for torque, not horsepower, at a power range used by most drivers. That is why a stroker. Buying a different engine adds more complexity, cost, adaptation, etc. Also storing your removed engine might be a factor. If ever needed, this motor can be put back to stock. I am grateful for the opinions, but lets get off the peak horsepower/high revving bandwagon. Thx Pat

Sorry Pat, you are misunderstanding.

The u20 crank HAS to be modified for a stroker. Typically a couple hundred bucks to do that at least depending (precision is necessary) that’s why I suggested using an h20 crank sInce those don’t require modification.

Rotating mass is a load on the engine, it doesn’t create hp or torque. A heavier FW or crank only feels good as you are letting out
the clutch, after that, it is dead weight that very literally resists acceleration or deceleration. It certainly doesn’t help you go faster or make more power.

Yes, the 2L rods are stronger, but that’s a complete non-issue in the rpm range of the engine you are proposing. H,R or U rods will be fine.

I also suggested just buying an H20. Cheaper and much easier if you are looking for a budget stroker. An H20-1 is pretty much a bolt-in.
Way easier than building a stroker from ground up.

I guess you don’t like the projected numbers, we could promise you big gains, but there is Zero chance the engine you are describing will make as much power as an SU u20. (135 factory fresh)

Call it an very optimistic 120hp at the crank.

Word to the wise, strokers ALWAYS cost more than planned.

Jim, you are misanderstanding, we are looking at a bit more torque, not re-creating a U20. The crank will not be modified, nor will the rods.Purchasing another motor is out of the question. I think a 20-25% increase in power is fine. and not something you could get from a R16 without modifying the head. If someone wants to go back to stock, they can. I'm not looking to have the direction changed, just advice. Help me here, what would you do, with the combo I mentioned? Thx Pat