OutdoorKing Repair Forum Forums Restoring, Customising and Modifying Tech Talk briggs piston

hi everyone. i have a 450 series 148cc briggs with a broken inlet manifold. it has a round port instead of the square, retangular one. can anyone tell me if other models had them, everything iv'e found here has the square type thanks

I belive a lot of the chinese made briuggs motors of the 3-4hp range had the manifold you describe, I have found them on newer sprint 375's and on the classic 37 i just ruined.

Micka, if the 450 is supposed to signify something like 4.5 hp, and it is a side-valve Briggs with fixed ignition timing, it can't be 148 cc (9 cubic inches). It would be at least 11 cubic inches (180 cc).

i wouldnt belive the 450 series would be 4.5hp I think at one point they changed the designation to a torque figure

http://www.briggsandstratton.com/engines/push-mower/detail/?series=450+Series&id=%7B68BC1FA5-2AC4-4F13-84BB-D9B82E6D22CD%7D

4.50 ftlb of torque....

Interesting, Joe. If it maintained that torque of 4.5 lb ft up to its maximum speed of 3,000 rpm (which it wouldn't of course) it would be 2.6 hp. That thing is too puny to run an 18" push mower, unless you mow every week to keep the grass short and the power requirement down. Maybe you could use it for one of those central Australian golf courses, made up of bare earth except for the black tar "greens".

The (3.75hp) 45 series I had on the 22" MTD was way underpowered for the size of the machine. Since I put the (5hp) 625 series engine on, it actually works really well.
I now have 2 x dead 45 series donks, 1 with a bent crankshaft, and one that just died after being "dusted" by the poorly designed air cleaner. Need to start stripping some for parts to make room in the shed

PS. My understanding of it is; 4.5 ft/lbs @ 3060 rpm - 3.75 hp @ 3600 rpm.

hi Igor54, yep this one was dusted too

Micka,
I'll have a look at mine in the morning & see what shape the port is - I wonder if it's a China/USA difference in manufacture, or perhaps something to improve airflow to give a torque boost?

Igor, if your 625 has 6.25 lb ft of torque, and maintains it up to the maximum speed of 3,000 rpm, it would have 3.6 hp rather than 5. (That is still a major improvement on 2.6 hp, of course.) I suspect B&S may be gradually changing to a system of names that comes a bit closer to complying with "truth in advertising" standards where they exist (Australia has some of the toughest ones around. Australian law (the Trade Practices Act) has required that only net horsepower be advertised ever since that Act was introduced some decades ago). You might care to read these:
http://www.newsinferno.com/legal-news/lawsuit-alleges-lawnmower-horsepower-fraud/

http://www.yourlawyer.com/topics/overview/Lawnmower_Horsepower_Fraud

I notice that B&S quote SAE J1940 in their advertising. J1940 still allows gross HP to be quoted instead of net HP, plus according to the internet B&S still tests their engines at 3,600 rpm even though they govern the vertical shaft ones to lower speeds than that. B&S is currently advertising both gross torque and gross horsepower:
http://www.briggsandstratton.com/engines/push-mower/detail/?series=550+Series&id={7AF24CC0-43AB-42CB-8282-4CE6C538D6D6}
"*All power levels are stated gross torque per SAE J1940 as rated by Briggs & Stratton.
*All power levels are stated gross horsepower per SAE J1940 as rated by Briggs & Stratton."

http://www.toro.com/home/mowers/recycler/20066.html
"*The gross torque of this engine was laboratory rated by the engine manufacturer in accordance with SAE J1940. As configured to meet safety, emission, and operating requirements, the actual engine horsepower on this class of lawn mower will be significantly lower."

Gross power and torque can be measured without air cleaner and muffler. If J1940 follows other SAE power testing standards, they can also be measured with mixture and spark timing optimised rather than being controlled by the carburetor and magneto. Given B&S's fixed ignition timing, this could make a large difference. Some other remarkable tricks are also permitted for gross measurements.

The formula for calculating horsepower is 2 times pi times RPM times torque, divided by 33,000. Because 2 times pi divided by 33,000 is 1 divided by 5252, you can calculate horsepower as RPM times torque (in lb ft), divided by 5252.

Generally, square intake ports are used for low to medium speed engines because they may improve torque in that speed range. Round ports tend to suit high speed engines such as modern motorcycles (not mobile air compressors of the Harley breed) and racing engines. However a much more important factor is the size of the port, and the size of the intake valve. In this case the main factor is likely to be which is easier and cheaper to make. As a wild guess, when B&S was getting ready to move engine manufacturing to China it redesigned the products to suit today's market.

Grumpy. You are a very interesting man.


I think i might have learnt something.

But still, bugger Briggs to hell for the new confusing engine series.

But i can tell you that the old 12 series OHV goes awesome compared to the side valve. What a monster.


Bob.

Interesting points, Grumpy. (I meant to reply to this post a while back, but life gets in the way, doesn't it)

Using that formula gives you a "snapshot" of one point in the rev range, not an overall indication of available horsepower. Both hp and torque work in curves rather than straight lines. Stationary engines are very different to auto engines in regard to the shape of the torque and power curves, as well as the intersecting points.

Many of the older side-valve engines had a much flatter torque curve than some of the new ohv engines. Given equal amounts of torque, a flatter curve means a much more flexible engine, able to maintain power under load as the revs drop.
This is why B&S (and others) have such a wide range of engines available - a mower engine will have a different torque curve requirement than, say, one destined for a grain auger.

One of a number of findings made by Direct Connection (the Mopar factory performance group) in the "muscle car" era, was that simply lengthening the intake manifold could have a marked effect on the amount of torque available at lower rpm.

In the case of my 625, the horsepower is nowhere near maximum at the same rpm that torque peaks. It is quite possibly only producing 3.6 hp at that point. The hp keeps climbing as the revs rise (to 3600), whilst the torque peaks at 3060 rpm, then drops away.

An engine that peaks both torque and hp at the same rpm would be extremely limited in its application - as soon as the engine came under load, the power would "fall off a cliff" and the engine would stall very rapidly.

Mack's range of Maxidyne engines are a good example of hp/torque applications. The little (237hp) motor was revolutionary in the early/mid 1960's. 237hp at around 2000 rpm, but maximum torque (906 ft/lbs if I remember right) delivered at 1200 rpm. Most of the other Mack engines of the time (Thermodyne's etc) had to be kept in a fairly narrow rev range to work well (shifting down at around 1750 rpm), hence the need for the 18 speed "quad-box" transmission. Maxidyne engines were mated with a 5 speed for highway use, and a 6 speed (extra low crawler gear) for severe duty. I have personally pulled road trains (up to 70 tons) with a 237 Maxidyne - an amazing engine!

Large books have been written regarding relationships between hp & torque in all sorts of applications. I suppose we could (over)simplify the subject, by saying that the 625 series is a much better engine for my usage, than the 45 series.

Igor, manufacturers of most everyday engines would like to try to achieve a flat torque curve (the same torque at all engine speeds) because this gives the most flexible engine response, and very high power at high speeds. In practice you can't though, unless you cheat (turbocharge, and use a controlled waste-gate to control the intake pressure to give the torque curve you want). This chart shows the power and torque curves for the Honda GV100, a 97 cc side valve engine with a compression ratio of 5.6 to one:



As you can see, it has maximum torque at 2,900 RPM and over 80% of maximum torque throughout the published speed range. You can also see that at the maximum governed speed of equivalent (side valve, 6:1 compression) B&S vertical crankshaft engines - that is, 3,000 rpm - it has less than 1.6 "recommended" horsepower. Don't you like Honda's way of hinting that the "maximum" (i.e. gross) horsepower line might not actually be achievable in practice for an installed engine?

With regard to your 45 and 625 B&S engines, you had proved that the 45 had insufficient performance, so a 39% increase in power and torque was bound to be beneficial. The actual power of the engines is less important than whether or not they can do the job you need to do.

With regard to the OHV and OHC mower engines, in practice they normally have much higher compression ratios than the side valve ones (8:1 instead of 6:1). This results in a need for different design criteria for camshaft, ports and valves, all aimed at getting more useful power at maximum governed speed combined with lower fuel consumption, compared with a side valve engine. One reason contractors just about always use OHV or OHC mowers is the much, much lower fuel consumption. The offsetting disadvantage is greater cost and complexity, plus a need for more precision in service operations.

4500 rpm from a side-valve single! That thing would be buzzing like a bee

If I could get those revs out of my Royal Enfield, I wouldn't need a Katana for drag-racing!

igor, my vastly modified side valve Austin Big 7 (1937 manufacture) achieved 6,500 rpm with standard valve springs. The bouncing valves did make marks on the cylinder head, though. (The only valve train modification apart from bigger valves was lightened, reshaped tappets.)

In principle, a side valve engine can achieve higher rpm than a pushrod engine, because even after you put in ultra-strong valve springs, the main mechanical limitation is still valve bounce, and the side valve has less weight in the valve train (no pushrod or rocker). Of course they scavenge very poorly and have very long flame front travel distances, so they aren't likely to produce much power at high speed, and there is seldom any reason to try for it. I notice the ride-on mower racers take their side valve B&S engines to 6,500, but I don't suppose they expect an engine life of more than three or four minutes. Those aluminium rods seem to be able to achieve remarkable things, if you can only lubricate the big-end bearings, and the racing guys seem to make some modifications in that area.

It all reinforces my view that thrown rods in B&S engines are nearly always caused by lack of oil.