Rethinking stroker design

[Habitat.pat]

I'm preparing to build a stroker for my 67.5. I've read through the stroker posts in the tech wiki & have some concerns as to what I am doing.

I have:
5 bearing block w/new standard sleeves
Shortened 2L crank
2L flat top standard pistons
2L rods
Dean's Performance 3 stroker cam (1497ACS)
New 5-angle valve job
5 speed transmission

I am in line with Ztherapy for a carb rebuild. My throttle shafts are quite loose.

I didn't do enough research before buying parts so I'm backtracking now before it's too late to correct things.

I plan on replacing the distributor with an EI unit, it needs to be replaced or totally gone through. Would a "Gary Boone" equivalent distributor be enough, or should I consider something else?

I am looking to build a peppy road car. No track, just fun seat of the pants acceleration so I have no need or desire to eek every last bit of power out of the engine. This car will also be used for road trips.

One thing I know I didn't consider before purchasing this cam is that I am looking for a cam that kicks in at lower RPM. I haven't been able to find out anything about how this cam runs. If it is a high reving cam it will be of no use to me. Also, since it is a higher lift than the standard cam, I assume that head work will be needed to change out the valve springs. Will the pistons need to be relieved for the valves? With Dean closed until next month I have not been able to get any information from him so I'm hoping there is someone on this list that is familiar with this cam. Hopefully there are folks on this site with some first hand experience of this cam.

As an option I could go with a different cam & sell this one.

I am not against sending my head to someone who knows our engines who can do the head work & if necessary, supply me with a cam. I haven't tried to contact American Cam Grinding, but not being an engine builder I wouldn't be able to select a cam profile so I want to leave that up to the builder.

I don't have unlimited $$ to put into this, but I will consider spending what I need to to get this job done well.

I'm hoping this thread gets some good additional information to add to the stroker tech wiki.

That's about it. Have I forgotten anything? Let the discussion begin.

Peace,
Pat

[23yrRebuild]

Check out the Stroker Poll Sticky for lots of info regarding stroker builds. I went with an Isky 266 cam for my 9.5:1 CR engine with 5-main R16 block, std. U20 pistons and rods, and Nissan Stroker Crank. Coupled with the 5-speed trans, stock head and R16 carbs (SU) w/ ADQ needles, and a Gary Boone EI...it is a PEPPY and FUN, FUN car to drive ! ...Looking back, I don't think I would have done anything different for the performance I was looking for....much like what you want.. without having to spend significantly more money....possibly a lightened flywheel, lighter H20 rods. Maybe larger headers, but I'm not sure if another $300-$400 for one, would give much noticeable difference. Don't "over-cam" your build unless you have enough CR to go with it. Opinions are welcome....

[Curtis]

"5 bearing block w/new standard sleeves"

Sleeves?

[JT68]

If the block has 4 sleeves in it, suggest you throw it away and find a good/free block to start over with..

[baxtersit]

I built a stroker 2 years ago and have an American Cams M13. Runs great and the only change I wish I had made was to lighten the flywheel.

[JT68]

There is zero reason to increase the exhaust size or header size with that formula (the head and valvetrain is the limiting factor, not the exhaust).

You are basically building a forklift engine with~9:1 compression. You have the heaviest rotating assembly possible.

It will have more torque than a 1600, but won't want to rev as happily.

Add this:

https://www.datsunrestorationproducts.c ... l-flywheel

It is the best improvement you can make for the money- You would have to spend WAY, way more in engine modifications to effect the same improvement. Money back if you don't agree. (but you will)

[notoptoy]

I have an H20 (Forklift motor) bored .030 over with a 9:1 CR and it is a torque monster. JT's billet flywheel wasn't available when I built it, but I did have a speed shop lighten the stock steel one to 13 pounds. It is a very "rev-responsive" happy little torque monster. It would be nice to be able to comfortably rev up into higher RPM's but it isn't really necessary as the power and torque are all in the low end. I have it coupled with the 5 speed and standard 1600 Pumpkin for an all around nice experience. My only regret is that I need a better, beefier clutch.

[Gregs672000]

As JT68 said, lighten as much as you can within budget. Custom flywheel or gets yours lightened. Regarding your cam, first let me say I'm not an expert, but I have spent a lot of time on this and this is my best understanding. It is hard to "know" what a cam will do where, but you can get a pretty good idea by looking at the duration of the cam. Duration determines where in the rpm range it makes maximum torque. Typically, the lower the duration the earlier in the range it makes power, and the earlier it begins to drop off. To do accurate comparisons you really need to know what the cam duration specs are at "50 thousands" which is more or less an accepted industry standard to compare cams, as their "advertised" duration is not very helpful. Most folks are familiar with U20 A, B, and C cams and that they change where the engine makes power. I used that to judge what duration I was looking for. For example, my Isky 197 cam has an advertised duration of 278, but it's spec at 50thou is 246, virtually the same as a B cam (advertised at 280). It makes max torque at 4800rpm. An A cam has less duration and makes max torque at 4400rpm. A C cam has an advertised duration of 300 as I recall, moving the power band up even further. Per my manual the stock cam listed for an R engine makes max torque at 4000rpm. I would compare the duration of a stock cam to what ever cam you have or are considering, and if the duration is higher know it will make max torque at a different/higher rpm. The other spec we're considering is lift, or how far the valve is opened, and this is where you can help fill your cylinders up a bit more... to a point. In general, more lift is better but it has diminishing returns and is limited mainly by coil binding the valve springs. Also, the higher the lift the more aggressive the ramp on the cam when the duration is smaller, as the cam lobe is actually more "pointy", which can increase wear... but I don't think we need to worry about that here. Coil bind would be the main issue, as a coil spring becomes solid when fully compressed and then things get broken. I doubt that the lifts being offered by Dean and others are in this category, but it always pays to check for clearance between coils with the cam at max lift and with the valves adjusted to spec. Unfortunately for you, this has to be done with the engine fully assembled, and the cam is not as easy to change out. You can check it on the engine stand before installing the engine. Still, assuming everything is not out of whack, you'll much more than likely be fine, but do check it for peace of mind.
So, long story short, decide on where you want to make peak torque by comparing duration at 50thou, and increase your lift some to help fill the increase in displacement. Changing the lift does influence peak torque rpm some (move it up, but shouldn't decrease power at lower rpms like a high duration can) , but not a lot as I understand it. Hope this helps!

[Gregs672000]

BTW, I don't think any piston to valve contact is likely with more lift. Most likely stock Springs will be fine and the head will not need specific work on that, again with the caveat of checking for coil bind. If you want to move the torque band down you will need a cam with less duration than stock, but be aware that it will begin to limit top end power. In the past, Isky has been very willing to talk with me on the phone, so you might try finding the best data you can on the specs for a stock cam and discuss it with them.

[JT68]

Greg, he’s dealing with r16 components. Changing the cam profile significantly definitely changes the valve spring requirements and the lobe ramps will be much more aggressive (much higher valve acceleration) than stock. The valve springs are not the same as U20. Also, one should not make an “across the board” supposition that there won’t be valve/piston issues without knowing anything about the head, valve heights, cam timing and and net lift. The flattops help, but you won’t know for sure without measuring.

I would say lighten a much as possible and back up one step with the cam for better midrange performance, you’ll have less issues over all and the engine will be much happier across the useful power band.

[Gregs672000]

I hear you JT. While stroking the engine is not "stock", it didn't sound as though the other changes were radical, but a fully admit I know nothing about R engine heads! I agree, check everything! It would be interesting to hear and know what cam specs with such an engine design would start to have potential contact/interference/coil binding/spring float problems and what to watch for. I was also considering that R pistons are domed and U20s flat.
Cheers!

[JT68]

I hear you JT.... It would be interesting to hear and know what cam specs with such an engine design would start to have potential contact/interference/coil binding/spring float problems and what to watch for. I was also considering that R pistons are domed and U20s flat.
Cheers!

The issue is you don't know valve height, head thickness, piston height, gasket thickness, cam timing, deck height and other variables each which vary by engine core and camshaft, so you can't make a blanket statement one way or the other. I can assure you the cam ramps are nothing close to stock, so assuming the stock springs are ok setup per factory is a very bad assumption.

[Curtis]

I was lucky enough to get two new sets of factory springs. If I recall correctly the one head was missing inner springs. I bought some calibration springs and measured my old ones. They were all different. Can't mess with old springs that's for sure.

[keith0alan]

For piston to valve clearance get some modeling clay and measure it on one of the trial assemblies of the motor.

[Daryl Smith]

As others have said, losing weight on engine components is always good, but, gets $$$ quickly.... Without costing you a bundle....my $0.02

Cam: "Performance #3 - R16 motor & 2000 Push rod Stroker - 430 Lift at the valve / 276 Duration. Order by PART#1497ACS"
Your compression might be slightly low for this cam but not too bad. I would recommend decking the block to bring the piston to zero deck or even .005" above deck to increase compression a bit and improve 'squish/quench' for improved combustion. You also want to check your head thickness/combustion chamber volume to figure your actual compression ratio. The head can also be cut to bring up compression, if wanted. Again, check valve clearance.
Edit: With a stock size chamber (head not cut ~49cc) your compression ratio should be around 9.3 to 9.5:1, going to 0 deck with the piston should bring it up to about 9.7:1. That range should be just about right for that cam. imo

Springs: I have not been able to ascertain max lift for the stock springs, but, I believe they should be good for .430" valve lift. Not sure how well they will control the valvetrain past 6,000 rpm...but, I ran my stock springs at .385" lift on my 1800cc stroker to almost 7,000 rpm a couple times without noticing a problem. I would not try that at .430" lift.
*If anyone is aware of the max lift for stock springs, a post of it would be appreciated.

Flywheel: Lightened, Aluminum, or aftermarket steel. Always a good bet for improved acceleration and a sportier feel, if that is your intention.

New 5-angle valve job: Good start, although I would recommend a larger exhaust valve for the stroker. For best performance with your stock valves, check to see that the valve 'throat' is 89 - 90% of the valve diameter.

Header/Exhaust: As JT stated you will NOT need a bigger header, Dean posted a little while back a 1 1/2" header was good for 180 hp on a stroker built/tested at Robello. As long as you have 1 3/4" exhaust and a free flowing muffler you will be fine. With your build the choke points will be your exhaust valve and the stock 38 mm 1600 carbs.....Good for low end grunt and cruising, mid level performance.

Again, just my $0.02, fwiw.