Heymow - Lawnmower Racing Forum

Engine Help => Briggs Flathead => Topic started by: Ace726 on February 28, 2017, 05:52:52 pm

Title: 18hp Oppy running Alky (engine, intake and ignition)
Post by: Ace726 on February 28, 2017, 05:52:52 pm
So I'm partway through building my oppy to run alcohol and I've found myself questioning some of the expenses on certain components if they are absolutely necessary.
First off im not going cheap on the build, I just want to be sure I'm justified in every expense. I already have the Arc rods, and Im ordering mod 28 pistons, wrist pins this friday. Arc billet flywheel is on the list. I am using an MSD ignition/coils with an Tillotson HL-360D Carb and custom intake (for the side draft conversion).
My questionable items are not so much major break points but more a question of performance. I'm on a bit of a time crunch as our test/tune track day is May 7th.  The biggest thing is the cam, I can see how much of an improvement the different lift would be but is it needed? has anyone every lobed or broke the stock cam? If I get a cam it'll be about 250 shipped and I'll end up reinforcing the rest of the valvetrain on it, I.E. bronze valve guides, Stainless valves stock size, stronger valve springs and billet keepers not to mention the addition machine cost if the heads need relief cuts. I believe the lift on the new cam would be around .360. I know it'll be a big power difference but how strong is the stock cam?

P.S. this is NOT just a cam thread, it's for the engine build. more questions to come as it progresses.
Title: Re: 18hp Oppy running Alky (engine, intake and ignition)
Post by: redline on February 28, 2017, 08:02:15 pm
The cam is the "brain" of the engine, as it allows air/fuel in and out and also determines when.
If your going all out on the engine, but letting it breathe with the stock cam, thats like putting a Geo Metro engine in a Ferrari.
This is in regard to engines in general, not the oppy, as anyone who knows me, knows I have no use for the boat anchor.
.360 lift? That's not much...What cam are you looking to get?
Title: Re: 18hp Oppy running Alky (engine, intake and ignition)
Post by: BIG AL 202 on March 01, 2017, 08:06:24 am
Alky? no organization I know of will let you run that. As for a cam people have had real good luck with the "rooster grind" from Isky cams.
Title: Re: 18hp Oppy running Alky (engine, intake and ignition)
Post by: Ace726 on March 01, 2017, 05:10:38 pm
@redline I'm using the "boat anchor" because it's what I've got, I'd rather spend 2,500 on the entire machine than spend the same amount on a stock new engine and suddenly i've spent 5k on the build. As for the cam, I'm not looking to go more than .050 over stock lift (I thought stock lift was around .320) because as you know alcohol requires much more compression so I don't have much clearance on the heads to work with. I'm looking at a cam from Mike with precision cams.

@BIG AL There is an affiliated organization near me that uses the stabil rules as "guidelines" for their own, because of that they created their own class of Outlaws (we call it FX) where the tech rules are much more lenient on things like engine origin, fuel type, tire size/type and overall cubic centimeters (max 1000cc). The rooster grind is a lift of .410 which is too much for the high compression heads. As for Tim Isky, I've tried to get a hold of him multiple times to see what other grinds are available but no luck.
Title: Re: 18hp Oppy running Alky (engine, intake and ignition)
Post by: Ace726 on March 01, 2017, 05:17:24 pm
Here is the mower I started the build with, I built and ran it last season as a super mod (their version of FXT). season before that it was a modified.

www.heymow.com/index.php/topic,31256.0.html



Title: Re: 18hp Oppy running Alky (engine, intake and ignition)
Post by: BIG AL 202 on March 01, 2017, 05:57:26 pm
If you don't get the flow you are defeating the purpose of using alky. You will never get the compression ratio very high on a flathead. You will get your power from flow, and the cam gets the flow going! The cam has more going on other than lift.
Title: Re: 18hp Oppy running Alky (engine, intake and ignition)
Post by: Ace726 on March 01, 2017, 08:13:28 pm
Ok, seems I've got more research to do. I will post more updates once I get more parts.
Title: Re: 18hp Oppy running Alky (engine, intake and ignition)
Post by: berthyd on March 01, 2017, 08:17:31 pm
Alcohol had about half the BTU content of gasoline, meaning theoretically you need to burn twice as much alky to equal the power of gasoline. Alky is generally used in racing because of its octane rating, around 110, and because it burns cooler.

Given the need to pass more alky through the engine compared to gasoline, one might assume a more aggressive cam would be necessary to achieve this result. Don't care what cam theory someone subscribes to (lift vs. duration), it's clear you need a reground cam.

Bert
Title: Re: 18hp Oppy running Alky (engine, intake and ignition)
Post by: Ace726 on March 01, 2017, 09:55:02 pm
I've used alcohol in other engines before and it will take twice as much as gas with more than an equal power output. As in 20-30% more depending on the application and flow. Also there are other factors that can increase the flow of an engine than just a cam. That's the only reason I brought up the question, it WILL run on alky with the stock cam and run better than gas. It's just not optimized for alky, so considering that I'm getting a cam. Call it an insurance plan for that much more to the wheel......   assuming the drivetrain holds up  :omg:
Title: Re: 18hp Oppy running Alky (engine, intake and ignition)
Post by: PJG56 on March 01, 2017, 11:38:49 pm
So will this be one of those 60HP oppy's running on alcohol when done??
Title: Re: 18hp Oppy running Alky (engine, intake and ignition)
Post by: Ace726 on March 02, 2017, 03:28:14 am
I haven't decided yet lol the ignition setup I'm looking at to reach 9k rpms is close to a grand. Plus if I want maximized intake flow, dual carbs would be great. I haven't decided my budget on the build yet. Anything over 3 grand and I should've just bought a better engine. I've seen some Kohler's claiming to push over 100hp and that's on pump fuel
Title: Re: 18hp Oppy running Alky (engine, intake and ignition)
Post by: BIG AL 202 on March 02, 2017, 08:04:02 am
All I can say is "GOOD LUCK!"
Title: Re: 18hp Oppy running Alky (engine, intake and ignition)
Post by: Ace726 on March 03, 2017, 05:02:58 pm
mod 28 pistons and pins ordered, should be here in a few days. Port and polish this weekend and bake the pistons when they get here. Rods came in today. I've been thinking on the ignition and I've found some mini pulling tractor coils that might work but I'm not going to over complicate things (more things that could break or fail). So buying a new OEM coil and a tach to see just how many rpms it will push. Got a possible lead on a new used isky cam rooster grind, another on the flywheel for a lot cheaper than new. Miked the valves and they are still tight, so gonna get billet keepers and stronger springs.

Anyone have some info on billet lifters???
Title: Re: 18hp Oppy running Alky (engine, intake and ignition)
Post by: PJG56 on March 04, 2017, 07:34:58 am
Stock lifters are fine
Title: Re: 18hp Oppy running Alky (engine, intake and ignition)
Post by: Ace726 on March 08, 2017, 06:19:41 pm
Pistons just came in today, been looking for a skirt coating but no luck. Probably will do the ceramic for the domes too. Only issue is where can I buy the antifriction compound for the skirts? Molykote, Poly Moly, and Cerakote all make it but only sell to a limited number of distributors. I can get them coated both with skirts and domes for 265. Although I have the 120grit aluminum oxide, blaster, and the oven to do the work myself, just can't find the coating. Has Anyone else looked into this or done this themselves?
Title: Re: 18hp Oppy running Alky (engine, intake and ignition)
Post by: Ace726 on March 24, 2017, 07:08:03 pm
So I've got almost everything I need to put it all together and fire it up, gotta finish match porting, a little hone, and carb work this weekend. Got lots of boxes of new parts, all except springs (will be here Monday) and flywheel with hub (for delivery next week sometime). Pictures to come this weekend.
Title: Re: 18hp Oppy running Alky (engine, intake and ignition)
Post by: Ace726 on April 03, 2017, 08:17:39 pm
Sorry for the lack of pictures, but I need some insight here. My valve lash with the isky cam installed is WAY over spec.... Isky calls for .005 hot or cold on the intake and exhaust. My valves are measuring 13, 16, 20, and 21 thousandths. Stock cam valve lash is out of spec too... Calls for 3-5 thou on the intake and 7-9 on the exhaust. My STOCK valves measure 8 on both intake and 9 and 16 on both exhaust. Somebody have stock valve height and stock tappet height???? Don't want any catastrophic failure as I have over $1400 in this engine.
Title: Re: 18hp Oppy running Alky (engine, intake and ignition)
Post by: PJG56 on April 04, 2017, 06:30:38 am
You will have to weld the end of the lifters up,or buy new valves and hope they are long enough.
Title: Re: 18hp Oppy running Alky (engine, intake and ignition)
Post by: Honey Badger on May 04, 2017, 08:30:52 pm
Id like to see this thing in Action. I remember there was an oppy in an FXS out in Iowa a few years back. It looked pretty cool.  If i had time, I would love to try and figure out something like that in an FXS. 
Title: Re: 18hp Oppy running Alky (engine, intake and ignition)
Post by: FlatheadPuller on November 05, 2017, 11:52:02 am
Haven't been on heymow in a long time, that said. Ignition for this doesn't cost a grand. Your looking in the wrong place. Look thru my old build and pictures if there still on here. 2 wire mag pickup, Chrysler ignition module and a gm 3.8 2 post coil will fire anything you feed it. As far as methanol your wasting your time. The ports suck in this engine. I know I've built several. Don't kill it with a ton of compression. Moderate lift with alot of duration will get you what you want. They aren't a big rpm engine.