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horsepower,displacement,dog's breakfast

Use this forum to discuss small engines, and the equipment or machinery that they power. This is the main section for any technical help posts and related questions.

horsepower,displacement,dog's breakfast

Postby 38racing » Sun Oct 28, 2018 5:43 pm

The 50" deck Zero turn that I'm rebuilding from fire damage had a 691 cc (42 ci) tecumseh vtwin on it. Since shroud burned I don't know exact model or stickered HP. I'm hoping that I can restore it but I'm currently waiting on back ordered gaskets. I've been looking at options. I have a 17.5 briggs 31 series that may run ok but that seems a bit small. One option is to swap it with the briggs Vtwin on my mtd since I plan to use mtd for snowblower only. Funny though I think that mower unit is labelled 18.5 HP although engine is same as our church unit labelled 20 HP. But they say there is no replacement for displacement so how about a 42 ci opposed twin? But the HP on them varies starting at 14 hp and maybe up to 20. So I was looking at some JD mowers at Lowes. Both had briggs vtwins of 743 cc (IIRC) but one was 22 HP and the the other 25 HP. Now I see this HF vtwin of just 703 cc but rated 25 HP.
https://www.harborfreight.com/engines-g ... 62879.html
Dog's breakfast as my Dad would say.
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Re: horsepower,displacement,dog's breakfast

Postby creia » Sun Oct 28, 2018 7:13 pm

You have your specs off a little bit for the engine in the link you provided. :) It is 708cc (not 703) and rated at 22 HP (not 25). I cannot tell you about the compatibility of this particular engine for your use, however, my son and I DO have experience with these HF engines- they are the real deal. We have had (2) of the 212cc, 6.5 HP engines I can tell you that they were (surprisingly) well made and performed VERY well! (We even "modified" 8-) both of them with performance upgrades and revved them a "fair amount" over 3,600 rpm) :o Finally, at only $ 100.00 for a brand new 6.5 HP engine (we waited until they were on sale) they were a very good VALUE. These engines were every bit of the 6.5 HP that they were advertised/rated. Now, that being said, the CHALLENGE will be when you need (OEM) parts for future repairs- "GOOD LUCK" with that!! For the professional service techs on this forum that is no doubt reason enough not to install HF engines on your customer's equipment. :bricks: Now, before any of you accuse me of being a China-made engine (only) lover, I will remind you that all of my previous posts on this forum have been our "bread and butter" engines, namely the old (American Made) Briggs and Tecumseh flatheads from the 1960s and 1970s which we truly love. :usa:
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Re: horsepower,displacement,dog's breakfast

Postby bgsengine » Sun Oct 28, 2018 9:47 pm

Not to mention , Displacement does not have any direct translation to horsepower.. or Gross Torque.. Horsepower can be a function of torque and RPM (or both).. while it is true you need more displacement to develop more power, you can't really directly translate CC or CID to HP. Example - Briggs L-head 326432 16 HP engine - 32 CID displacement .. compared to a 21 HP 31Q777 (31 CID) - the specs can be varied by changing RPM , governor sensitivity, carburetion and air flow, and even ignition timing, without ever changing the displacement , so you can't really compare a 708cc to a 641cc fairly - depending on how they are set up, you might actually get more HP out of the smaller displacement... You could probably do just fine with a 420000 or 440000 series Briggs Intek V-Twin and get comparable (or better) performance to what the original was... probably best to get highest rated HP you can in the model series.. if it's too much (LOL right?) it can always be "tuned back" to reduced power....
How poor are they who have not patience. What wound did ever heal, but by degrees? - Iago (Othello Act II, Scene 3)
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Re: horsepower,displacement,dog's breakfast

Postby creia » Sun Oct 28, 2018 10:35 pm

bgsengine wrote:Not to mention , Displacement does not have any direct translation to horsepower.. or Gross Torque.. Horsepower can be a function of torque and RPM (or both).. while it is true you need more displacement to develop more power, you can't really directly translate CC or CID to HP. Example - Briggs L-head 326432 16 HP engine - 32 CID displacement .. compared to a 21 HP 31Q777 (31 CID) - the specs can be varied by changing RPM , governor sensitivity, carburetion and air flow, and even ignition timing, without ever changing the displacement , so you can't really compare a 708cc to a 641cc fairly - depending on how they are set up, you might actually get more HP out of the smaller displacement... You could probably do just fine with a 420000 or 440000 series Briggs Intek V-Twin and get comparable (or better) performance to what the original was... probably best to get highest rated HP you can in the model series.. if it's too much (LOL right?) it can always be "tuned back" to reduced power....


Brian's explanation is clear, concise and RIGHT ON^^^^^^^^^^^
As far as the statement in the OP "But they say there is no replacement for displacement." That is not necessarily true. A Simple illustration to demonstrate my point:
Chevy 396 cu in = 6.5L/375 HP
Chevy 427 cu in = 7.0L/435 HP
Dodge (Demon) 378 cu in = 6.2L/840HP
Granted, this is an extreme example and not to mention that the Demon has a LOT of extra, modern "hi-tech" equipment on it contributing to that added HP, but you get the point.
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Re: horsepower,displacement,dog's breakfast

Postby KE4AVB » Mon Oct 29, 2018 2:07 am

And why would you go with a Chinese that parts are hard to get when go the Briggs 44S977-0032-G1 25 hp 1 inch diameter crankshaft for a little more @$800 with shipping as compare to the $745 for the Predator 22 hp. One note here is that the Briggs does not come with a muffler but most times you needing to use the current any way. Also these are the gross hp rating and actual net is lower. Besides I can the above Briggs for less than the HFT engine with my dealer discount. Even if I was paying the $800 it still a better deal considering I know I can get replacement parts easily instead having to wait on parts from China if they are available. Plus the Briggs warranty is definitely a lot better than the 90 day warranty the HFT has. Don't let the 2 yr part mentioned get you as that is the emissions warranty only and don't cover the rest of the engine.

Now Creia and BGS touched on something else, you must be comparing apples to apples too. I recently changed engines on a MTD Yard Machines 42 cut due power problems. It had on the 310000 series rated at 16.5 hp (mainly because it had a restrictor plate) that would not cut even slightly overgrown grass. I installed a 21hp that I was unable to sell and now it cuts whatever I throw at it including waist high grass; just got to slow down so the deck can clear itself. The only problem is 5/8 belt I had to upgrade the deck to as I keep burning up the 1/2 belts.

Creia back in the early 90's when you could get custom aftermarket parts and didn't have onboard computers fighting you I rebuilt my 79 Malibu 265 small block V-8. Though the use of a mild racing camshaft and variable duration lifters I greatly improved the HP output and increased the fuel mileage at the same time. Plus didn't hurt to install turbo (free flow) muffler. When compared the fuel economy to the before of 16 hwy I was getting 23mpg combined and 31 hwy. I probably could have farther increased the HP if I installed a turbo charger but I already had problems with breaking traction which was why I installed a heavy torsion bar from a Caprice on the rear. I also probably could could have further increase the fuel economy by installing a 200R4 instead of the 700R4 that I installed later that hurt my fuel economy a little; drop to 21 mpg combined. Now I will admit I never put my build on a dynamo so I don't what the actual HP of the build was.
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Re: horsepower,displacement,dog's breakfast

Postby creia » Mon Oct 29, 2018 7:40 am

KE4AVB wrote:Creia back in the early 90's when you could get custom aftermarket parts and didn't have onboard computers fighting you I rebuilt my 79 Malibu 265 small block V-8. Though the use of a mild racing camshaft and variable duration lifters I greatly improved the HP output and increased the fuel mileage at the same time. Plus didn't hurt to install turbo (free flow) muffler. When compared the fuel economy to the before of 16 hwy I was getting 23mpg combined and 31 hwy. I probably could have farther increased the HP if I installed a turbo charger but I already had problems with breaking traction which was why I installed a heavy torsion bar from a Caprice on the rear. I also probably could could have further increase the fuel economy by installing a 200R4 instead of the 700R4 that I installed later that hurt my fuel economy a little; drop to 21 mpg combined. Now I will admit I never put my build on a dynamo so I don't what the actual HP of the build was.


Ahhhhh, you are taking me back to the GOOD OLD DAYS!! :D Does anybody here remember the vehicle performance "doldrums" of the mid 1970's through the 1980s? :x Those were DARK TIMES...
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Re: horsepower,displacement,dog's breakfast

Postby 38racing » Mon Oct 29, 2018 8:10 pm

The ' no replacement for displacement' was just referring to a line I heard commonly in the sixties when guys were bragging about their big engines. I am aware that many factors determine the final power. Reality is I won't find a Briggs 44 series in Canada 25 hp for decent money and no HF up here.
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Re: horsepower,displacement,dog's breakfast

Postby KE4AVB » Tue Oct 30, 2018 7:26 am

I do forget about the exchange rate and all the other added expenses. At least the current exchange of 1.31:1 is not as bad as 1.41:1 Australian rate that deal with every once awhile when I sell part there. Of course shipping is outrageous.

38Racing what is fairly easy to get in Canada that is close to the 25HP range that priced at a fair price?

It is hard to get anything done lately here too with all the crazy stuff coming our government executive branch. Personally it is hitting my business hard with the additional costs here too which I need to pass along to customers. Yes my gross sales per repair is up but the overall sales are the same as customers are putting off repairs or simply just buying the parts off eBay and Amazon then doing the repairs themselves. This has caused me to stop giving free estimates plus I am having to raise my labor rates to offset the higher shipping charges and other overhead.

I have been working Stihl products for years doing most fuel system repairs but with Stihl getting Zama to propriety all the carburetors and parts that Stihl uses it is now nearly impossible to get a reasonable priced carburetor repair kit. The Zama that I had been purchasing around $6 from my Zama distributor are now around $18 at the Stihl shops. On top that my Stihl dealer is now demanding a minimum shipping charge of $20 for anything Stihl that they got to order out of the Stihl warehouse. This make the part I needed yesterday that was 3.23 now 23.23 just to get it and that don't included my markup.

I also have problems with getting many of the aftermarket parts as where companies like Briggs are demanding the distributors no longer sell them if they are for their equipment; not just the new equipment but the older equipment too. I am beginning to hear rumors that Kohler is planning on doing this too. At least I can still get these parts through Amazon vendors.

I got a very bad feeling things are going to get even worse before things improve.
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