Stone stock (Except for Exhaust Manifolds) L72 on a Dyno by Jerry MacNeish

[Larry E.]

https://www.facebook.com/jerry.macneish/posts/10215491124333826?comment_id=10215513889822949&notif_id=1521385793898433&notif_t=feed_comment_reply&ref=notif

Though this to be interesting for our L72 owners. (Myself Included)

Another day on the dyno at Burtonsville Performance Machine, COPO 427 with very good hp numbers, 466 hp on the first few pulls. Enjoy and turn up the volum

I ask Jerry if this was "stone stock"> His reply>

Yes, this is a stone stock L72, no head work, bigger cam, etc. We only pull the retoration engines to about 6300 rpm. They make closer to 485-500 if you pull them to 7000 rpm. No need to do that for a resto engine in an original car.

One great engine--Thanks-Larry P.S. Below is Non-Radio L-72

[Tim G.]

Re: Stone stock(Except for the Exhaust Maniforlds) L72 on a Dyno by Jerry MacNeish

Wow, that's great. I was in an L72 on Saturday and they're wicked motors.

[Duke W.]

Re: Stone stock(Except for the Exhaust Maniforlds) L72 on a Dyno by Jerry MacNeish

In the car with the OE exhaust system it will be lucky to make 350 SAE corrected RWHP on a chassis dyno. That's the trouble with lab dyno tests with headers and open exhaust with STP correction. The numbers are no where near what the engine will make installed in the car.

One of the big losers is the OE exhaust system. With a SHP small block back pressure is about 3 psi max, which is about the most I like to see on a high performance engine, but due to higher exhaust flow, a big block generates about 6 psi, and sidepipes are even worse.

Duke

[Larry E.]

Re: Stone stock(Except for the Exhaust Maniforlds) L72 on a Dyno by Jerry MacNeish

In the car with the OE exhaust system it will be lucky to make 350 SAE corrected RWHP on a chassis dyno. That's the trouble with lab dyno tests with headers and open exhaust with STP correction. The numbers are no where near what the engine will make installed in the car.

One of the big losers is the OE exhaust system. With a SHP small block back pressure is about 3 psi max, which is about the most I like to see, but due to higher exhaust flow, a big block generates about 6 psi, and sidepipes are even worse.

Duke

Thanks; Duke for your input. Always like to hear what you say. Larry

[Mark E.]

Re: Stone stock(Except for the Exhaust Maniforlds) L72 on a Dyno by Jerry MacNeish

In the car with the OE exhaust system it will be lucky to make 350 SAE corrected RWHP on a chassis dyno. That's the trouble with lab dyno tests with headers and open exhaust with STP correction. The numbers are no where near what the engine will make installed in the car.

One of the big losers is the OE exhaust system. With a SHP small block back pressure is about 3 psi max, which is about the most I like to see on a high performance engine, but due to higher exhaust flow, a big block generates about 6 psi, and sidepipes are even worse.

Duke

Yes, but 350HP at the rear wheels is a lot. This video shows something akin to SAE Gross HP. Then there's SAE Net HP which is also at the flywheel but with parasitic losses like full exhaust system, air cleaner, fan, etc. Rear wheel HP is considerably less than this.

Years ago I had my stock '90 ZR-1 on a dyno. Factory rated at 375HP SAE Net, it pulled little over 290HP at the rear wheels.

[Dick W.]

Re: Stone stock(Except for the Exhaust Maniforlds) L72 on a Dyno by Jerry MacNeish

Wow, that's great. I was in an L72 on Saturday and they're wicked motors.

A good L-72 will have a '67 L-71 for lunch

[Roy S.]

Re: Stone stock(Except for the Exhaust Maniforlds) L72 on a Dyno by Jerry MacNeish

A good L-72 will have a '67 L-71 for lunch

[Duke W.]

Re: Stone stock(Except for the Exhaust Maniforlds) L72 on a Dyno by Jerry MacNeish

Yes, but 350HP at the rear wheels is a lot. This video shows something akin to SAE Gross HP. Then there's SAE Net HP which is also at the flywheel but with parasitic losses like full exhaust system, air cleaner, fan, etc. Rear wheel HP is considerably less than this.

Years ago I had my stock '90 ZR-1 on a dyno. Factory rated at 375HP SAE Net, it pulled little over 290HP at the rear wheels.

Basically correct. The SAE gross-net conversion takes into account both the exhaust system/accessories and a lower air density correction, which alone reduces output about 4.5 percent. Empirical evidence I have from a number of dyno tests indicates that a SHP 327 with massaged heads, the conversion factor is 0.89, but it's less for a big block due to the higher exhaust back pressure. Then the drivetrain efficiency must be taken into account, and that conversion factor is approximately 0.85 in direct drive with a manual transmission.

A "327 LT-1" with massaged heads will approach 290 SAE corrected RWHP, so it's about as strong as a stock '90 ZR-1, and the best SHP big blocks I've seen with massaged heads are good for about 350.

A current LT-1 at 460 SAE net at the flywheel should make about 390 SAE corrected RWHP based on the 0.85 driveline efficiency factor.

One other thing I've noted on chassis dyno tests is that it's very important to have enough external cooling to keep the fan clutch from tightening. If it fully tightens due to high radiator exit temperature it can reduce peak torque by about 10 lb-ft and cost about 15 HP at the top end. If it doesn't tighten, horsepower absorded is only about 1-2 HP. Big difference.

Duke

[Darryl D.]

Re: Stone stock(Except for the Exhaust Maniforlds) L72 on a Dyno by Jerry MacNeish

Horsepower rating from the factory back in the day were from an engine dyno (out of the car) with no accessories and with exhaust manifolds and pipes that went out the ceiling not a true exhaust system. The factory "played" with the rating with rpms to get the number they wanted. They did this for a variety of reasons such as rating for insurance companies, competing manufactures and race classifications. I do think that GM was more consistent with their rates with the rpms unlike Chrysler that was all over the board. EG, the Hemi being rated at 425 h.p. but at 5000 rpms when everybody knows those engines don't really begin to breathe until OVER 6000.

[Jack M.]

Re: Stone stock(Except for the Exhaust Maniforlds) L72 on a Dyno by Jerry MacNeish

Here are some L72 Gross & Net engine performance graphs from GM in 1965 (sorry for the poor quality):
L72-Gross & Net Power.pdf
L72-Net Power.pdf

[Duke W.]

Re: Stone stock(Except for the Exhaust Maniforlds) L72 on a Dyno by Jerry MacNeish

Great data, especially the second pdf. It took me awhile and some manipulation of the size to figure it all out, but in addition to the net HP and torque the graphs include BMEP, BSFC, manifold vacuum, exhaust backpressure, and fan power absorption, all of which pretty much jibe with my SAE net simulations.

I think the current definition of "SAE net" is different than back then, especially air density correction. The note at the top of the graph indicates correction to 100F - probably to account for underhood air temp - and probably uses 29.92" Hg standard sea level pressure and zero humidity.

I find the big hole in the torque curve between 2000 and 3000 quite interesting. My experience with manifolds has always been that the torque curve is quite flat, but assuming a medium to high overlap cam headers will usually increase peak torque, but cause a similar "hole" down low. I'm sure this test was done with manifolds as I don't believe GM ever used headers except when developing specific race engines like the 5L Trans-Am engines and L-88/ZL-1.

The two different length intake stacks used on Can-Am big blocks somewhat smoothed out the lumpy torque curves caused by the very long duration/very high overlap cams used on those engines to get maximum high rev power.

Can you state how you came across these graphs?

Duke

[Gene M.]

Re: Stone stock(Except for the Exhaust Maniforlds) L72 on a Dyno by Jerry MacNeish

That my friend is why I kept the early 66 L72 and moved the two L71’s on.

Your just saying what the racers always knew. The 4 barrel is much better than the triple duces for power. Tri power is just for looks under the hood.

[Mark L.]

Re: Stone stock(Except for the Exhaust Maniforlds) L72 on a Dyno by Jerry MacNeish

A while ago I had my 66 built and dyno'd. It is 30 over and has a comp cam 11-106-3 which I believe is the stock profile. Almost 450 hp at 5700 rpm. Not sure what we'd get at a higher rpm. Ditto Roy's comment.

[Jack M.]

Re: Stone stock(Except for the Exhaust Maniforlds) L72 on a Dyno by Jerry MacNeish

Can you state how you came across these graphs?

It was included with some other docs I've purchased in the past... sometimes, you get lucky.