Datsun Roadster Forum-311s.org

We had the pleasure of dyno tuning Kurt's 1967 SRL earlier this week.




You can see Kurt's restoration thread here:
viewtopic.php?f=2&t=29455&p=272436&hilit=kurt#p272436


The U20 with Solexes, Steve Pettersen did a nice job setting this engine up:



At Z Car Garage


Dyno video:

Dyno results:
Baseline was 99hp/107tq at the wheels
After Rob's tuning it picked up ~10% more power throughout the entire rev range, making 108p/114tq at the wheels:


An interesting tidbit, Sora Blue (Calspeed's now Rob Fuller's #0248) dyno'd at 108p/115tq in 2012!

Thanks for letting us tune your SRL Kurt! Let's do a run soon

Thanks for sharing,
Mind if I copy your post to the Dyno Sheet thread?

I saw this car at Steve’s shop last year - soooo nice! I hope it’s coming to Solvang this year.

Pjackb wrote: ↑Fri Mar 30, 2018 9:53 am Thanks for sharing,
Mind if I copy your post to the Dyno Sheet thread?

go for it!

Nice gain. Just jetting and ignition/timing?
Dan

Wow, thanks Alvin!

And thanks to all who helped along the way...! You know who you are...Steve Pettersen did such a phenomenal job! It was like it was his car. He was teasing me about the plates that were previously registered. He said he was hoping I'd get new plates that said something like BAD ASS. Ha! I think they do. You are a bad ass builder Steve!!! You're an artist!

The sound of the car that resonated throughout the building as it went up the RPMs, -my goodness! I won't forget it. Thanks for dialing it in Rob! I must say she is quite frisky and fun for my driving habits the way it's now set up. These were new in the box Solexes I hoarded along the way. Steve left them pretty much at factory setings. Z-car Garage's dyno technology brought it into a nice sweet spot for me.

See some of you soon at Solvang! I'm waiting for UPS to deliver my top as I write this. Signature required is like I'm under house arrest. Its 5 o'clock and 80 degrees outside and I should be tooling around in 520!

10% bump is pretty good! Dont dynojets typically read on the lower end? That being said, its just shy of what is advertised for a Solex U20, right? 15-20% loss means its just under 150bhp?

2mAn wrote: ↑Fri Mar 30, 2018 7:11 pm 10% bump is pretty good! Dont dynojets typically read on the lower end? That being said, its just shy of what is advertised for a Solex U20, right? 15-20% loss means its just under 150bhp?

Simon the Z Car Garage dyno is known as a "heartbreaker" dyno. I wouldn't take the 135/150hp figures from the ID tag seriously. Just use the baseline reading from your dyno result and make changes from there. Yes, the common conversion factor from chassis dyno to crank hp is ~15%. For bench racing I love to use this calculator!
https://www.mk5cortinaestate.co.uk/calculator4.php

108hp at the wheels = 134hp at the crank

Worth mentioning...alot of folks focus on the "peak" power gains/figures. While that is nice to see, it's the area under the curve that reflects significant gains from tuning...something that is tough to attain "by ear" or by "feeling" with your butt dyno. The gains seen on Kurts plot show increased power throughout the rev range, not just one part of the powerband.

This is why I highly recommend getting a dyno tune if you are curious about changes in power from modifications (carbs/exhaust/ignition) or want to know engine health, etc.
If you are happy with your car's performance...a dyno is not needed!

2mAn wrote: ↑Fri Mar 30, 2018 7:11 pm 10% bump is pretty good! Dont dynojets typically read on the lower end? That being said, its just shy of what is advertised for a Solex U20, right? 15-20% loss means its just under 150bhp?

Simon,
15-20 % would mean 127-135 bhp
Now that being said There are a lot of things to take into consideration when looking at drivetrain loss to calculate BHP from WHP and no 2 cars are exactly the same. A car with things like lightweight flywheel, lightweight wheels and tires or electric fan will put more power to the ground. It doesn’t mean that the engine is making more power but these things reduces parasitic loss and therefore increase BHP.

I was reading an arcticle recently where they made 6.5% more WHP (134 vs 126) after installing a lightweight flywheel , i’ve also seen gain of almost 2% from lightweight wheels and tires , what was interesting about the article is that the power gain was across the rpm range.

Alvin wrote: ↑Fri Mar 30, 2018 11:56 pm Worth mentioning...alot of folks focus on the "peak" power gains/figures. While that is nice to see, it's the area under the curve that reflects significant gains from tuning...something that is tough to attain "by ear" or by "feeling" with your butt dyno. The gains seen on Kurts plot show increased power throughout the rev range, not just one part of the powerband.

This is why I highly recommend getting a dyno tune if you are curious about changes in power from modifications (carbs/exhaust/ignition) or want to know engine health, etc.
If you are happy with your car's performance...a dyno is not needed!

This is so true, the way the power is delivered especially the torque curve is so much more important than the peak HP ,

Max torque at same rpm, but previous max torque now being made 1k revs lower, so you bet it woke her up in terms of feeling the pull.
Great info, thanks Alvin.

I wonder what retarding the cam a degree or two would do to the power curve and peak hp. Looks like the ignition timing and Jetting made good improvement, but on the pull prior to that the power is dropping off at 5500 rpms on a B cam. Retarding the cam should move the power band up a tad and may be more to the liking of a B grind. Just a thought!

Gregs672000 wrote: ↑Sat Mar 31, 2018 10:29 pm I wonder what retarding the cam a degree or two would do to the power curve and peak hp. Looks like the ignition timing and Jetting made good improvement, but on the pull prior to that the power is dropping off at 5500 rpms on a B cam. Retarding the cam should move the power band up a tad and may be more to the liking of a B grind. Just a thought!

It is a B cam. Rob did not change the jetting. These were new out of box Solexes for U20 at factory settings. I haven't looked at the factory jetting to report what is installed. Neither Rob nor Steve bothered to confirm either. The timing was changed and the air/fuel ratio optimized. I don't dare oversimplify those changes, but I'd characterize them as screwdriver refinements. A skilled tuner with the best tool, -a dyno. The power and torque gains at the lower revs has been immediately noticed as the curve shows.

I might be inclined seek peak horsepower at a slightly elevated level, -maybe 4500 RPM would be absolutely perfect for me. But it's great as is.

Thanks again Alvin and Rob!

You might try a set of 40mm venturis in it (with the correct rejet of course). I'm currently running a stock head with a B cam, 40mm venturis, 2.25" exhaust, wild guess jetting, and I have to say it pulls really well. (Even with a very suspect valve seat)

Will