MN80Vette

The GM 350 HO crate engine has come up in quite a few threads over the past few years. GM rates the HO at 330 hp and 380 of torque. “But,” you ask, “what does it really produce?” Well, here some real world numbers for you.

I dyno’ed my ’80 2 years ago (2008) with an unmodified 350 HO (inhaling through a 600 cfm Holley vacuum secondary carb and exhaling through Dynomax full length headers and true dual exhaust with a balance tube) connected to the stock Borg-Warner Super T-10 by a Centerforce 388144 clutch. The best it did was 258 hp (I don’t remember the measured torque). The hp, torque, and A/F ratio lines bouncing all over the place.

Since then last year, I shimmed the distributor gear (it had 3/16” of vertical play), rebuilt the carb, increased the squirters 2 sizes, replaced the accelerator pump and arm, installed a more aggressive accelerator pump cam, changed the distributor springs to the lightest in the MSD kit, set the timing to 12 deg initial and 34 total advance. I also made a custom cold air intake…more about that later.

It drove MUCH better, but I still wasn’t pleased with the overall performance. Our car club reserved the HiTech chassis dyno for a day, and I signed up for the dyno-tune. BTW, the guys at HiTech are awesome, especially Bart, one of the owners. If you ever go there (Elk River, MN), tell Bart that Dave with the dark blue ’80 Corvette says “hi” and sends his regards. Check them out at HiTech Motorsport, Inc..

The first pull was better than 2 years ago as I expected with the tuning changes I made: 269 hp (11 hp gain) and 302 torque. Not bad, but still not up to its potential. Bart showed me the bump in the A/F ratio that meant the secondaries weren’t opening soon enough. He replaced the purple (medium light) with the second lightest in the kit. He showed me that the compression on the spring I had in there was 450 grams and the spring he put in was 264 grams. That improved both hp and torque (284/329).

He also tried changing the timing to 36 deg all in from 34. HP and torque dropped to 282/321.

Then he showed me the difference between my cold air intake with the solid cover I had and the cold air intake with a K&N lid: 2.5 hp and 6 ft/lb of torque improvement.

Then a major setback: The fuse for the electric fan had dropped down onto the header tube and melted the fuse, resulting in a boil-over. I replace the fuse and they cooled it down with special cooling applied to the intake.

Once cooled, the final pull results were 292.6 hp and 327 ft-lbs of torque with the cold air intake and K&N cleaner and lid ON. It drives like I expected it to. The drive home in the rain was kinda’ fun because I could break the rear end loose so easily. Great throttle response, and a ssmmoooooth torque curve that’s nearly flat in the 3200-4200 rpm range, with hp that flattens out at 5000 rpm. The A/F was stayed in the 13-14 range, but still with a rise to 14 just before the secondaries opened, a drop to just above 13, and then a return to about 13.5 until about 5000 rpm where it reached 14.

If you figure my driveline accounts for 15%-25% loss from flywheel to rear wheel, then the engine is exceeding the GM rating – about 344-390 hp.

So, there’s the data on a GM 350 HO Deluxe crate after some tuning and a true dual exhaust for those of you who have been wondering.

BKbroiler

Nice writeup. Just a question on your math:
292.6 x 1.15 = 336.5
292.6 x 1.25 = 365.8
Right?

10caipirinhas

Good write up. Thanks !!

mikejpss

Excellent post and valuable info for my motor exchange later this year.
Question- you mentioned the "Deluxe" crate - can I assume you bought the package deal that included the intake and carb-ready to run right out of the crate? If so, how does your intake work in relation to the hood closure? does it fit? any mods to make the hood close?
Thanks for your input.

SanDiegoPaul

Wow great numbers and similar to my 383! I need to put a larger cam in mine to get the rest of the ponies out of it. I'm only showing about 30HP more with similar torque numbers.

LFZ

Great review for a great engine..thanks for sharing.

Roughrider

Thanks for the post. I have a 350HO in one of my cars (an Avanti...not a Vette). It has Edelbrock RPM electronic fuel injection and a Mallory electronic distributor designed specifically for the Edelbrock EFI. It runs through a 2 1/2" dual exhaust with Magnaflow mufflers.

I'm very happy with how it runs...it can smoke the tires in at least the first two gears in 700R4 tranny. Maybe one day I'll get the car on a dyno to see what it's actually putting out, but I can say the engine puts out more power than I can use.

Priya

I would think with a 4 speed the driveline loss would be closer to 15% than 25%.

MakoShark72

NEVER!!! OK, you can tell your wife that , we're not buying it!!!!

MN80Vette

You're right. I had a spreadsheet I was using for a bunch of estimates over the past 2 years and didn't watch what copied formulas were really referencing.

MN80Vette

I researched estimated dyno loss here on the C3 forums. Estimated losses for manual transmission were 15, 20, 22, 23, and 25%. Since I don't have actual hp at the crank, I just used the lowest and the highest estimated loss. The range is accurate enough for me.

Kipring

I thought it would be:

At the Wheels HP = Engine HP * (1-Drive Train Loss)

So it would be: 292.6 = x * (1 - .15) = 344.24

and: 292.6 = x * (1 - .25) = 390.133

I think MN80Vette had it right on the money.

phildawg19

BKbroiler

Kipring - The numbers do work out using your formula. I just don't get it intuitively. If rear wheel HP is what is actually measured on the dyno, and the assumption is that there is 15% loss thru the drivetrain, why wouldn't you just add 15% to RWHP to get flywheel HP?

MN80Vette

Yep, I have the package deal that is almost ready to run right out of the crate. The stock '80 dual snorkel does not fit, so you need to work something else out. You will need a 1 1/2" drop base if you go with a standard 14x3 air cleaner under stock low-rise hoods. I was drawing hot air from inside the engine compartment until I fab'd my own cold air intake that draws air from ahead of the radiator. The dome down the center of the hood is the top of the intake duct.

Here is a picture of it when I finished it but before dyno day. Since then I replaced the chrome Chevrolet lid with a K&N lid as it had for the final dyno run last Saturday:

Kipring

Because

15 % of 292 is 43

while

15% of 344 is 51.6
or
15% of 390 is 58.5

Send me a PM if you still need some help. I'll be glad to help ya out, don't wanna hijack the thread any more than we have.

MySpiritOfAmerica

good write up! helped me a lot

Roughrider

That's my story and I'm stickin' to it!

toddalin

Because you loose 15% of the engine horsepower as opposed to 15% of the rear wheel horsepower.

ajrothm

Interesting thread......Nice job on fine tuning that car and getting it up to its potential.....I still think you could go up on the jetting, get the AFR in the mid to upper 12s and make a little more power.....if its not shown on the dyno, it WILL show on the track...


As for the numbers....I get:

292 / .75 = 389.33

292 / .85 = 343.52


I think the 343hp number would be pretty accurate assuming the chasis dyno readings are accurate....

I dynoed my dad's ZZ4(355hp rating) in a 59' and that one was tuned pretty well also....It netted 261 rwhp but that was running a mechanical fan and going through a M22 and 9" Ford(power sapper)....

261 / .75 = 348hp...... Pretty close