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#109130 28/10/20 03:14 PM
Joined: Jul 2018
Posts: 2,085
Likes: 80
Tyler Offline OP
SENIOR TECHNICIAN
Hi all

Since it has been quiet (dead) for a couple of days, I will pose a query

A friend asked me to fix his Briggs quantum 45. He questioned why mine said quantum 50. I told him there is also a quantum 60, 55, 40, 35 and apparently a 30 (though I have never seen one and believe this was dud info.

He said so different CC makes different power? No, all are 190cc. Different max rpm? No, all are around 3200rpm.

Then how the hell do they get double the HP?

Only thing I could say was briggs did get done for HP cheating, but surely not to that degree. Do they strangle them with the carby, or governor system

Its honestly something I never thought about

How do they do it?

This is from a 1990 briggs yearly bulliten I have, and shows some difference in torque curves, but I still would like to know exactly how they do it

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briggs.JPG (90.65 KB, 173 downloads)
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Tyler #109133 28/10/20 04:40 PM
Joined: Dec 2007
Posts: 174
Apprentice level 2
***
Cam profiles would be my guess.

Tyler #109139 28/10/20 08:58 PM
Joined: Jul 2018
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Tyler Offline OP
SENIOR TECHNICIAN
Hi Greg

Could well be

Its just strange how there can be such a huge difference in effectively the same engine

Tyler #109140 29/10/20 12:58 AM
Joined: Jan 2013
Posts: 940
Likes: 18
Moderator
I've always thought it was cam profiles and jet sizing, but that's just an uneducated guess.

Tyler #109141 29/10/20 02:48 AM
Joined: Feb 2006
Posts: 4,675
Likes: 164
SENIOR TECHNICIAN
Maybe a hidden turbo somewhere. Seems hard to believe one engine can have twice the power of another like it.


Ahh, if only victa had kept producing the thumblatch catcher series, they would be in better shape today!
Tyler #109142 29/10/20 03:48 AM
Joined: Jan 2015
Posts: 1,487
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AVB Offline
SENIOR TECHNICIAN
Just as in automobile cam timing, lift, and duration does affect performance. Briggs also would label same engine with different hp ratings even when the engine had the identical specs. This what they and other manufactures got in trouble about here in the USA.

A good example was three opposed engine that came in the shop at the same. There a 18.5, 19.5, and 20.5 hp all with the same model and type numbers.

I also know cam timing does effect hp as I accidentally timed a 12 hp L head years off by one tooth. Boy what an increase in hp I had. I just don't remember if I advanced or delayed it but it is more likely I advanced it a few degrees. So I can personally believe in the increased hp.

Also on some of the larger Briggs they use restrictor plates to limit the hp of a larger engine.

Tyler #109143 29/10/20 06:34 AM
Joined: May 2010
Posts: 304
Likes: 22
Apprentice level 4
I seem to remember Briggs were the subject of a lawsuit regarding Hp ratings.. in the last few years they were generally only labeled with cc's and not hp

Its less of the fact they got 6hp out of a 3hp engine, more so that they got 3hp out of a 6hp engine. Makes production cheap when every part is the same, Massive rip for the customer though when you might have had to pay considerably more for the bigger engine when its identical bar maybe a cam as the small engine.

Again this was an 80's onward thing, part of the poor management that ultimately brought them undone this year

Tyler #109144 29/10/20 08:13 AM
Joined: Jan 2015
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AVB Offline
SENIOR TECHNICIAN
Just a little research show the 4hp and 5hp has different camshafts. Probably other changes but that will require carefully research through the the IPls.

Last edited by AVB; 29/10/20 02:03 PM. Reason: missing word "require"
Tyler #109145 29/10/20 10:21 AM
Joined: Feb 2006
Posts: 4,675
Likes: 164
SENIOR TECHNICIAN
I notice nearly all other vertical pull Briggs I see have 3.5hp labels on them, while my later magnetron model says 3hp, yet it's performance is adequate as far as I can tell, though I have only used it on a light lawn.
Maybe this motor came out as the regulators were clamping down back home.


Ahh, if only victa had kept producing the thumblatch catcher series, they would be in better shape today!
Mowerfreak #109150 29/10/20 04:20 PM
Joined: Dec 2007
Posts: 174
Apprentice level 2
***
I reckon it was an older SAE standard that allowed for HP to be measured with out the air filter and muffler installed.

Tyler #109155 29/10/20 09:38 PM
Joined: Jan 2015
Posts: 1,487
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AVB Offline
SENIOR TECHNICIAN
Yes old standard was deceptive as they able to allow engines coming off the assembly to as little as 85% of the rating label so an engine rated at 4 hp could be as little as 3.4 hp at right the initial start up. Now the new standard is 95% forces them to have tighter specs coming off the assembly as they randomly test engines now to make they meet the specs.

Also as Greg point out the gross hp was before options were added which lower hp even more down to a net hp rating. Even the ft-lb torque is a little deceptive as it doesn't cover the worst case loads but at least gives you the expected power band rating.

Tyler #109156 29/10/20 11:32 PM
Joined: Jul 2018
Posts: 2,085
Likes: 80
Tyler Offline OP
SENIOR TECHNICIAN
Thanks guys, I will pass this on. Its amazing they can nearly double the horsepower (or as Nath says, probably halve it) with such simple changes (or at least they said they doubled the horsepower.

I would really like to put a few older models on a 'dyno' and really see how much they lied

Plus, as Greg said, we all know what happened to holden's quoted power/torque levels around the time of the HJ/LH and HX/LX when they went from no filter, fan or exhaust to fully assembled.

The quoted HP fell off a cliff

Tyler #109592 05/12/20 07:11 AM
Joined: Dec 2007
Posts: 174
Apprentice level 2
***
Interesting I have just procured a Super four 50 with a 5hp I/C and it feels to have a better torque curve than the XTS 50 which is the 190 cc Quantum. It can't be just displacement being a 205cc v 190cc or were the I/C deliberately designed with a flat curve to maximise their attractiveness.

Tyler #109597 06/12/20 12:21 AM
Joined: Jan 2015
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AVB Offline
SENIOR TECHNICIAN
I look at this this way. About 15 yrs ago I rebuilt a Chevy 265 cu in V8. It was basically the same cu in afterwards with only four changes but these changes made a world of difference.

What I changed was the stock camshaft to a mild racing cam, duration and lift profile changes. Along with variable duration lifters. Then I free flowed the exhaust by changing to a turbo muffler.

I gained greater torque at takeoff and better slightly better fuel economy. Then I went one step further and switch from the stock 350 transmission to a 350C with locking torque convertor. That when went from the factory 16 mpg combined to nearly 23 mpg combined.

The end results just shows how just a few minor/major changes can really affect an engine power curve and hp even the cu in never changes.

Tyler #109600 06/12/20 02:38 PM
Joined: Feb 2006
Posts: 4,675
Likes: 164
SENIOR TECHNICIAN
There's so many more variables with a car engine over a single cylinder mower engine I'd imagine, with much more scope for gains, but I get the example.


Ahh, if only victa had kept producing the thumblatch catcher series, they would be in better shape today!
Tyler #109604 07/12/20 12:49 AM
Joined: Jan 2015
Posts: 1,487
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AVB Offline
SENIOR TECHNICIAN
Yes I understand that but a slight timing change on the single cylinder can make a world difference. I know as I intentionally miss timed an old Briggs 12 hp L head years ago on a personal mower and seen fairly larger apparent HP gain. Just don't remember if advance a tooth or delay it a tooth on the camshaft timing.

Tyler #109609 07/12/20 10:50 AM
Joined: Jul 2018
Posts: 2,085
Likes: 80
Tyler Offline OP
SENIOR TECHNICIAN
This is for car engines, but idea is the same

https://help.summitracing.com/app/answers/detail/a_id/4706/~/advancing-%2F-retarding-a-camshaft

I would guess advanced 1 tooth

Tyler #109628 08/12/20 08:37 PM
Joined: Feb 2006
Posts: 4,675
Likes: 164
SENIOR TECHNICIAN
Gave my sole Briggs a spin today. The SuperSwift mower had a missing throttle knob so threw on a Victa style one.
Also added an extra pair of blades.

Attached Images
IMG_20201208_195953-1000x564.jpg (120.16 KB, 67 downloads)
IMG_20201208_200208-1000x564.jpg (91.71 KB, 67 downloads)
IMG_20201208_200242-1000x564.jpg (106.48 KB, 67 downloads)
IMG_20201208_200311-1000x564.jpg (64.29 KB, 67 downloads)
IMG_20201208_205436-1000x564.jpg (50.49 KB, 68 downloads)

Ahh, if only victa had kept producing the thumblatch catcher series, they would be in better shape today!
Tyler #109631 09/12/20 01:06 AM
Joined: Jul 2018
Posts: 2,085
Likes: 80
Tyler Offline OP
SENIOR TECHNICIAN
MF, goes to show the HP of the engine is irrelevant to a degree; having a big blade disc spinning around gives more power

Tyler #109632 09/12/20 01:12 AM
Joined: Jan 2015
Posts: 1,487
Likes: 23
AVB Offline
SENIOR TECHNICIAN
Originally Posted by Tyler
This is for car engines, but idea is the same

https://help.summitracing.com/app/answers/detail/a_id/4706/~/advancing-%2F-retarding-a-camshaft

I would guess advanced 1 tooth
Now that would explain things and actually be useful too for later mods.

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