Joe, Duke Where did the HP go?

[Bob Mitchell]

Finally have some dyno runs on the 63, 327 340HP (advertized). The rebuild consisted of domed KB pistons +.040, a Melling "151" hyd. equivalent cam, stock 461x heads, stock "129" intake, and a Carter 3461S AFB carb.

Here is some stats.:
at 3800rpm, 342.8ft/lb torque (this was peak), 248HP, 12.0 a/f, 111.1 fuel mass.
at 5485rpm, 282.5ft/lb torque, 295HP (peak), 11.7 a/f, 146.9 fuel mass.

Now for the question. The torque appears close to the advertized torque of 344ft/lb @ 4000rpm, but what happened to the HP? Is the dyno program calculating different than what GM did?

One issue I had during initial start up was the AFB, floats, wrong primary and secondary jets and power piston pull down. These issues were corrected.

Any help to get engine to the advertized HP will be much appreciated.

Bob Mitchell #23202

[John C.]

Re: Joe, Duke Where did the HP go?

I know I'm not Joe or Duke but just out of curiousity, was this on an engine or chassis dyno (engine installed in car or not)?

[Joe L.]

Re: Joe, Duke Where did the HP go?

Johm and Bob------

Yes, that's precisely the first question that I would ask. The original 1963 hp rating was based on gross (or brake) horsepower. This was horsepower as measured at the flywheel on an engine dynomometer (engine out of chassis). The engine was not equipped with any accessories (fan, alternator, etc.).

So, you will need to find out if the rating that you received is REAR WHEEL horsepower, or if it's somehow "corrected" to SAE NET or SAE GROSS rating systems.

If it's rear wheel horsepower, then I would think that would equate to considerably more than 340 SAE gross horsepower at the engine.

[John H.]

Re: Joe, Duke Where did the HP go?

Bob -

It's unlikely that you'll see "advertised" 1962 horsepower on the dyno; in those days engines were rated as SAE "Gross" horsepower, which meant they were set up with optimized fuel and spark calibrations just for the WOT max power run, no accessories, low-restriction dyno exhaust, and no thought for driveability considerations. In the late 60's, they changed to SAE "Net" horsepower, which included accessories (like the alternator, connected and charging) and production fuel and spark calibrations as the engine would have when installed in the car, with production exhaust manifolds and exhaust restrictions. This brought some "reality" into the advertised horsepower game after years of exaggerated claims.

[Duke W.]

Re: Joe, Duke Where did the HP go?

Bob - I assume these numbers were taken on a test stand dyno. Are the numbers observed or corrected, and what conditions were they corrected to. Also, what was the configuration of the engine during the runs. Fan? Exhaust system? Air cleaner?

SAE gross was observed readings corrected to 29.92" and 59 F. The fuel-ar ratio and ignition advance were optimized, which did not necessarily represent the production configuration. There was no fan or alternator, and the manifolds were connected to generous sized pipes with an evacuation pump to insure that exhaust did not leak into the dyno cell. They may have either run with no air cleaner of a bigger one than production. Beyond this I think there might have been a little "rounding" off, if you know what I mean.

A couple of other questions.

What is the eighty percent torque bandwidth - the points where the engine makes 274 lb-ft at the low and high end.

What did they have to do to the 3461S - jets? rods? power piston springs?

What was the total ignition advance?

Was any work done to the heads other than a valve job?

It's rare to get real dyno numbers on a vintage SHP engine, so I'm interested in the details to validate my simulation work.

Duke

Duke

[Bob Mitchell]

Re: Joe, Duke Where did the HP go?

Duke,
Yes, it was on a test stand dyno (Mfg Dynomight, I believe). No fan or fan clutch, no alternator, no air cleaner(air volume monitor), 1 fan belt running the water pump, no flywheel, used a direct hook up to the dyno balancing system. The exhaust manifolds used were stock 2.5" dumped to 6" tubes.

We've done 3 runs so far and all readings have been adjusted to SAE weather conditions. The first run 2000 to 4000rpm we cut short due to a very high air to fuel ratio (+20:1), this was the effect of the wrong primary and secondary jets (undersize). At this point I must thank Bob Kunz for his expert advice while working through these issues. The second run was 2500 to 4500rpm and the third run was 3000 to 5500rpm, in all cases the torque was above 274ft/lb. The lowest was 276ft/lb @ 2000rpm on the first run and 280ft/lb @ 5500 on the third run.

The Heads are stock with 1.94/1.5 valves, the only thing done was clean up of seats, replace 2 valves and new springs and keepers (all checked to spec.).

I need to investigate what the program is calculating for HP (net or gross), the dyno does load the runs with pumped water weight. If you would like copies of these runs I would be happy to fax them to you monday. You can email your fax # to tqe@acd.net

Thanks to all,
Bob Mitchell #23202

[Bob Mitchell]

Re: Joe, Duke Where did the HP go?

Joe,
Good point, I will investigate the programs calculations for net vs. gross HP.

I've also posted more detail under Dukes post.

Thanks Again,
Bob Mitchell #23202

[Duke W.]

Re: Joe, Duke Where did the HP go?

I'm not sure what "SAE weather conditions" are. (There are several SAE standards that one can use.) Can you quote the pressure, temp. and humidity. Sounds like your test set up is close to SAE gross.

On all my dyno simulations I've never seen 340 SAE gross with the production heads. It takes some head work, but pocket porting, port matching and a three angle valve job appears to be good for about and extra 10 percent power at the high end, which gets you pretty close to the gross rating. For a stock 340 my simulation programs show about 300 HP. There's not a lot of difference between the Duntov and 151 cams. The 151 is marginally better at the bottom end and might be marginally better at the top, but the LT-1 beats both of them from off idle to the redline. That's why I like the LT-1 cam.

From the chart or curve can you see if the power has actually peaked at 5500. Could be there's a little more at 5800 to 6000. The bottom end of the 80 percent torque bandwith is about 2000, which is what I figured for the 151 cam and it looks like the top of the 80 percent bandwidth is a bit over 5500. That's why the 151 cam is a winner if you want to run a high perf. hydraulic cam in a 327, or, in your case, a 333!

Duke

[Bob Mitchell]

Re: Joe, Duke Where did the HP go?

Duke,
Weather Conditions:
Air Temp. 68 deg. F - correction factor 1.009
Baro. 28.94 in. Hg. - correction factor 1.034
Rel. Humidity 36% - correction factor 1.009
Vapor Pressure 0.259 in. Hg.
Rel. Air Desity 94.24
Final Correction Factor 1.052, Standard Correction Method

your simulation may be right on, I do need to verify the HP calculation as either net or gross.

I had to pull it off the dyno today to make room for a big block but will be able to put it back on. Just to let you know I was using 110 octane racing fuel during the runs. I may change the fuel for other runs.
Bob #23202

[Duke W.]

Correction factors

Okay, you listed the actual measured conditions and listed the correction factors, so you were correcting to 29.92" 59F, and zero humidity, right? These conditions and the configuration of the engine, exhaust,etc. would be essentially SAE gross conditions. SAE net conditions include all engine accessories, inlet system, vehicle exhaust system and correct to 29.38" and 85 F.

I ran some quicky simulations last night on both Desktop Dyno 2000 and Engine analyser. EA gave about 300 peak power at 5000, 350 lb-ft peak at 4000 and about 270 lb-ft at 2000. Pretty close to your numbers. DeskTop Dyno 2000 gave about the same peak torque and power, but a bit less torque at 2000. Used the data I have for both the Duntov and 151s cams and they are very close.

When you run again, I hope you take it to at least 6000 or preferably 6500 to see where it actually peaks and what the power rolloff looks like.

Duke

[Jack H.]

Disagree....

Built a '60 dual 4-Bbl engine for a customer in Europe. Could NOT take the chance of trans-ocean ship and discover problems! So, we rented space/time on an engine dyno and ran 'er in....

Dyno shop operator was really 'tickled' when we showed up with dual 4-Bbl setup! It'd been better than 10-years since he'd had a need for his 2x4 carb air horn....

With real-time correction for altitude/measured O2 density, the engine BEAT factory torque/HP specs (about 6 HP above GM rating). I suspect the original poster has NOT forked out the $500-1000 to hire a real dyno and run/test his completed engine; my hunch is he's using a computer desk top simulator and there's a 'cockpit' problem with understanding definition(s) in loading/using the computer simulation code....

[Bob Mitchell]

Re: Why these results?

Duke,
I also did some simulation runs with my stats. Approx. 300HP ? Was GM runs so finely tuned, with dyno headers and no external power eaters like water pumps etc. to grossly overrate a 300HP engine to 340 "Gross" HP?

Another simulation run I did was with 2.02/1.60 valves. Much improved. Give it a try (the same config. as a 67 327/350HP?).

Some things were going to try are better timing, street fuel with additive, carb jetting (a/f was about 11.5:1) and possible new rockers to ensure a 1.5 ratio when it goes back on the dyno.

Bob

[Duke W.]

Re: Why these results?

I don't think it's any secret that gross power ratings were grossly overrated, but when they went over 400 in the BB they actually may have underrated them slightly.

I don't think the bigger valves make that much real world difference, but pocket porting to get ride of that crummy ridge will definately help. One issue to consider is that the later 461s with the larger valve were prone to developing a crack between the inlet and exhaust seats. The smaller valve versions are bulletproof.

What simulation programs are you using? I have DeskTop Dyno 2000 and Engine Analyser.

Duke