A good day at the dyno...

[Top Toy]

Had a good day at the dyno with my '93. Questions frequently come up here about what various mods can do for our motors. Thought I'd post a comparison of my 2009 dyno results and today's. Mods as of '09 included siamesed plenum and injector housings, 63 mm throttle body, and B&B exhaust (stock manifolds and cats). Since then the heads have been ported, cams have been swapped, and SW headers (no cats) and mufflers have been added. Picked up 80 RWHP and 33 ft. lbs. torque. Using a 15% driveline loss, HP at the crank is now 558. Pretty amazing for a stock short block. HP/liter is almost as much as a supercharged LS9! Gotta love these motors!

[5ABI VT]

Awesome numbers ! . Very cool to see it picked up everywhere. How big are the cams vs stock?

[Top Toy]

Thanks! Intakes are 0.435"/238 deg. Exhausts are 0.432"/220 deg.

[XfireZ51]

Originally Posted by Top Toy

Had a good day at the dyno with my '93. Questions frequently come up here about what various mods can do for our motors. Thought I'd post a comparison of my 2009 dyno results and today's. Mods as of '09 included siamesed plenum and injector housings, 63 mm throttle body, and B&B exhaust (stock manifolds and cats). Since then the heads have been ported, cams have been swapped, and SW headers (no cats) and mufflers have been added. Picked up 80 RWHP and 33 ft. lbs. torque. Using a 15% driveline loss, HP at the crank is now 558. Pretty amazing for a stock short block. HP/liter is almost as much as a supercharged LS9! Gotta love these motors!

Which is why GMs use of the LT5 moniker for a pushrod motor is sooooo frustrating. Thx Dennis.

[Hib Halverson]

Actually, your engine is making more than 558. The parsitic loss number for C4 manual powertrains which GM gave me an number of years ago was 18%. If you use that, you're making 578, but, either way that's impressive from a 350 and that's the good news.

The bad news is that, in reading the small print at the bottom of that .pdf, I noted that the data is "[ CF: Uncorrected 1.00 ]"

That means the numbers are raw data uncorrected for any atmospheric conditions present at the time the tests were run.

Any comparison between "before" and "after" power and torque numbers is not credible.

Why not go back to the dyno operator and ask him/her to provide SAE corrected data for both tests?

Lastly, looking at the AFR data at the bottom of the sheet, Dennis you need to be careful as I think you've got that engine running lean at WOT. If it was me, I'd be looking for someone to put a little more fuel to that engine...get that AFR so it's averages 12.5:1, if you're using non-blended fuel, and 12.2:1 if you're using E10 gas.

[Top Toy]

Thanks Hib!

Appreciate your comments! Yes, the numbers as shown are uncorrected. There are several different correction factors that can be applied, SAE being the most conservative. And. But I don't trust any of them to accurately adjust for changes in ambient conditions, especially when you're testing in conditions that are significantly different from Standard. The only truly valid comparisons are between tests on the same Dyno on the same day and even the same time of day. I threw out the comparison just to give those interested in similar mods an idea of what to expect. Individual results will vary, as they say, and by a lot! Re the AFR, I was shooting for an average of 12.7 which is where power and torque peaked across the rpm range. I made a few more tweaks after this last run to bring the high spots down. I have an A pillar mounted AFR gauge and keep an eye on it all the time. Have never had an issue or seen any evidence of same (I inspect the plugs and piston tops and Marc was most recently in the motor and reported no problems) running around 12.7. If you're aware of anyone that's run into problems running there, please pass it on. Timing was also optimized across most of the range (I didn't spend any time messing with it below 3000 RPM). The knock sensor kicked in a few times as I was looking for the sweet spots and was backed off accordingly.

Bottom line is the car runs great and never ceases to thrill me, even after 25 years of ownership! There's good reason why we're all so passionate about these cars!

[tiegsd]

Cool post. I dig this kind of tech stuff. Thanks!

Sent from my SM-N920V using ZR-1 Net Registry mobile app

[tpepmeie]

Originally Posted by Hib Halverson

Actually, your engine is making more than 558. The parsitic loss number for C4 manual powertrains which GM gave me an number of years ago was 18%. If you use that, you're making 578, but, either way that's impressive from a 350 and that's the good news.

Hib,
My personal experience doesn't back up the fixed 18% driveline loss. I believe that may have been relevant for a 300hp LT-1, with a 55 hp loss through the driveline (18%).

In my experience, a 703 BHP (STP corrected), 669 bhp (SAE 1367) engine horsepower made 638 SAE 1367 rwhp on a dynojet.

The engine dyno numbers were "green", the engine was more broken in by the time of the chassis dyno.

The chassis dyno was confirmed and consistent over three sessions and two different dynojets.

I was also surprised by the losses, given the urban legends about 15 or 18% and so on.

YMMV,
Todd

[jss06c6]

My engine was running AFR's in the 12.2 range. My understanding from Marc's writeup and my own tuning experience is this was pretty fat. Marc recommends between 12.9 and 13.1 I believe. I changed my tune to lock in at 12.9 at WOT to 7000 rpm. Coupled with a colder plug and .050 plug gap, the engine runs like a scalded dog and purrs at idle. My experience says Marc is on point. 12.9 to 13.1 AFR is a sweet spot.

Sent from my XT1585 using ZR-1 Net Registry mobile app

[Top Toy]

So, Todd, your results suggest that driveline loss is closer to a fixed number (approximately 50 for our cars?) rather than a percentage of FWHP. Correct? Awesome numbers, btw!