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Thread: Modifying the 084 for more horsepower !!

  1. #1
    Super Moderator Corky's Avatar
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    Modifying the 084 for more horsepower !!

    Hi Guys !!
    Since my airboat is ready to hit the water it's time to get this thread going...We have a few options now with members trying different carbs to get away from the original carb's issues...This thread isn't about that...
    It's about some real mods to the engine to gain some horsepower and torque..
    I've already started collecting NOS 084 parts...Why do this when I have a new engine ??? So I can evaluate,measure, identify areas for more HP and then modify those parts while I'm having fun on the water with hopefully no real down time as I go...While keeping the original parts to reinstall if things don't go as planned.. So, short of grenading an engine or making a new hole in the block I can revert back to the original part if need be for another try...

    I'm hoping to involve as many members as I can here in some real world discussion about these mods...

    So far I've got:
    {4} NOS piston/rod assemblies
    {4} NOS jugs
    {4} NOS rod bearing sets
    {2}NOS head assemblies

    I'd like to find an NOS camshaft...And I'll probably buy an NOS crank and bearings also...
    So you can see I'm taking the hunt for horsepower seriously....

    From what I've been reading from different sources the biggest issue with our application is probably going to be keeping the heat down as the hp goes up...We'll see how this goes...If I need to add more gauges to monitor the engine so be it...
    So where do you start with a stock 084?? There's so many ways to gain hp and torque..Reason would dictate to start with simple,easy mods and work our way into some more involved areas as we go...And stick with the golden rule : Only do one mod at a time and evaluate the pros and cons if it with some real world run time..

    Aluminum .120 14' X 76" hull
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    Member Bart's Avatar
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    Re: Modifying the 084 for more horsepower !!

    couple of questions.
    how much would the heads need to be shaved to go from the stock 6.8 to 1 compression. to 8 to 1?
    i am good for asking questions. so here it goes.
    last winter i tore apart my 084 and looked at a lot of things.
    so with my limited knowledge. with shaving the heads. say like 10 thousands. couldn't i shave 10 thousands off the jug and this would do the same thing?

    windage trays? i even found windage trays for the VW motor the other day.

    and has any one dealt with swain tech coatings. trying to manage the heat in the combustion chamber, has been a problem

    these are just a couple of things that i have been looking at doing some time, with my 084, just wondering if anyone else has any thoughts about this

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    Re: Modifying the 084 for more horsepower !!

    Every thing i've read is don't modify the 084 engine. but whose to say it can't be done. i'll be watching this thread closely. have at it.

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    Super Moderator Corky's Avatar
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    Re: Modifying the 084 for more horsepower !!

    Yes, I've read the same thing about modifying them...But why ??? If anyone runs across someone's attempt at modifications feel free to link them so we can see what did or didn't happen..
    Bart, yes it would be much easier to shave the jug than to have the heads milled...But we need to determine exactly what the combustion chamber volume is to begin with so we can hit a certain compression...This would involve CC ing the heads and determine how far down in the hole the piston top is and calculate that volume as well... I need to locate a thread I've read somewhere on an aviation forum that the guy milled the block end of the jug like 40 thousands !!...
    ..........Here's the concerns with some aggressive milling... To keep everyone in the loop I'll speel it out...Pertaining to the heads :Most assume the rocker tip sits in the center of the valve and simply push down on the valve...That's not the case..At rest{no lift} the rocker should be offset to the far side of the valve stem so as the valve opens it actually crosses over the center and at full lift it's on the other side of the valve stem simply because of the geometry making the rocker "shorter as it's angle increases...Now, as you bring the head assembly closer to the block{by milling the head or jug} there will be a point where you'll need a shorter pushrod because the rocker will "run off" the valve and not stay on the valve tip...A shorter pushrod brings the rocker back into alignment to run across the top of the valve through the lift cycle..They make an adjustable pushrod for engine mock-up it has a threaded body or tip so you mill your heads or jugs in this case and then install the adjustable pushrod and run it through the lift cycle then find the length that keeps the rocker on the valve tip evenly from side to side as it swings through its travel then order the length you need...

    Aluminum .120 14' X 76" hull
    Teledyne 4a084-4 engine
    Circle S 1.69:1 reduction
    67" Whirlwind "Razor X" prop



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    Super Moderator Corky's Avatar
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    Re: Modifying the 084 for more horsepower !!

    Ok enough of that book for now.......I'll start a different reply and keep all that to digest separately...Now, on the windage tray...Speaking of books I just bought a book "how to hotrod VW engines"...Why? it's actually has a lot of good info on all these carbs we're all trying to use and those engines aren't all that different in the main scheme of things...I need to determine how the rods are oiled in those VW engines compared to the 084...If we add a windage tray to the 084 are we blocking valuable splashing oil that's lubricating something we're missing ???
    Last edited by Corky; 08-25-2017 at 07:16 PM.

    Aluminum .120 14' X 76" hull
    Teledyne 4a084-4 engine
    Circle S 1.69:1 reduction
    67" Whirlwind "Razor X" prop



  6. #6
    Super Moderator Corky's Avatar
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    Re: Modifying the 084 for more horsepower !!

    For a quick breakdown here's what we're starting with for calculations
    Bore: 3"
    Stroke: 3"
    Compression ratio:6.9 to 1
    Displacement: 84.8 cu in
    Rated continuous net hp: 20 (at) 3600 rpm
    Max hp 33.3 (at) 3600 rpm
    Max torque (at) 2000 rpm; 60.3

    Aluminum .120 14' X 76" hull
    Teledyne 4a084-4 engine
    Circle S 1.69:1 reduction
    67" Whirlwind "Razor X" prop



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    Member yamahaulerG1's Avatar
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    Re: Modifying the 084 for more horsepower !!

    I can tell you those motors are bad about dropping exhaust valve seats when they run a little warm and when you are experimenting they tend to run warm so watch temps carefully. I met a guy in Belleview that said he machined some blocks, I think it was for Chuck, but he said the motors didn't last long. I would ask Chuck about higher compression on those he will probably know.

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    Super Moderator Corky's Avatar
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    Re: Modifying the 084 for more horsepower !!

    Yes, that would make sense with the exhaust valve getting the heat...I think Bart is on the right track with the thermal coatings but I'm thinking A}even that won't protect the valve seat from getting the heat transfer ..B}I wonder if re-staking the seat would hold it in better..Or C}Possibly a bigger exhaust valve to open it up and transfer more heat out of the head ??? Some room for bigger valves...
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    Last edited by Corky; 08-27-2017 at 11:43 PM.

    Aluminum .120 14' X 76" hull
    Teledyne 4a084-4 engine
    Circle S 1.69:1 reduction
    67" Whirlwind "Razor X" prop



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    Administrator Papee's Avatar
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    Re: Modifying the 084 for more horsepower !!

    Quote Originally Posted by yamahaulerG1 View Post
    I can tell you those motors are bad about dropping exhaust valve seats when they run a little warm and when you are experimenting they tend to run warm so watch temps carefully. I met a guy in Belleview that said he machined some blocks, I think it was for Chuck, but he said the motors didn't last long. I would ask Chuck about higher compression on those he will probably know.
    I talked to him a few times on the phone. I think his name was Bill and it's in his user name here.
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    Re: Modifying the 084 for more horsepower !!

    Getting the right fuel mixture is key. I've seen while experimenting big changes in temps depending on the tune. Since I put on the tuned exhaust I've never replaced a plug. They all look good every time I pull them to put new in.
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    Super Moderator Corky's Avatar
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    Re: Modifying the 084 for more horsepower !!

    Quote Originally Posted by Papee View Post
    Getting the right fuel mixture is key. I've seen while experimenting big changes in temps depending on the tune. Since I put on the tuned exhaust I've never replaced a plug. They all look good every time I pull them to put new in.

    And this is exactly what Chuck said when I talked to him today...He's doing better...As well as can be expected in his situation but he still liked to discuss his findings with me...
    His experimenting was limited to the exhaust and intake mods to pull the most out of what was already there he stated..
    Even length intake runners were the most important feature from his carb inductions{mostly mikuni} to see the most gains..
    Any mods to this engine requires you to monitor the plugs and operating temps...The valve seat failures he experienced was from the engine running too lean and overheating the head...
    He also said keep in mind some of the failures he experienced was from modifying a well used engine that customers owned and the engine's had some substantial hours on them and they wanted "just a little more" isn't that how it always is...
    Although he had some jugs milled for higher compression Chuck never got around to installing them to see the gains to be had...He had more than one set done and 2 sets went to Bruce{Circle S reductions} which he never followed up to see how they worked out for him... And he just recently sold his set to someone else to try so he couldn't comment on how well it did or didn't work..
    And as we all know he stated he'd seen a new engine wore out in one season from running lean where the jugs and pistons were shot from overheating/overreving/excessive wear...
    So as we've assumed the A/F needs monitoring closely as the mods are done...
    And there you have what Chuck has to offer with his experience..

    Aluminum .120 14' X 76" hull
    Teledyne 4a084-4 engine
    Circle S 1.69:1 reduction
    67" Whirlwind "Razor X" prop



  12. #12
    Super Moderator Corky's Avatar
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    Re: Modifying the 084 for more horsepower !!

    Quote Originally Posted by yamahaulerG1 View Post
    I I met a guy in Belleview that said he machined some blocks, I think it was for Chuck, but he said the motors didn't last long. I would ask Chuck about higher compression on those he will probably know.
    The key wording is "machined the blocks"...And that would make sense..Think about it : If you machine the block's jug mating area you now have the ability to simply buy a new jug without the cost of additional machining as you wear them out... I'd really like to know what he did and what type of failure was experienced..

    Aluminum .120 14' X 76" hull
    Teledyne 4a084-4 engine
    Circle S 1.69:1 reduction
    67" Whirlwind "Razor X" prop



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    Member Bart's Avatar
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    Re: Modifying the 084 for more horsepower !!

    here is some food for thought,

    I came across this info. the other day while looking for parts and pieces among other things......
    this was on the G503.com forum talking about the differences in the between the 2A042 generator and the A042 mule motors.
    all this time I have always thought more compression = more horse power.

    But for the 2a042 motors it is completely opposite,
    the 2A042 generator is listed at 10 hp with 6.9 to 1 with 145 psi compression
    the A042 mule is listed at 14 hp with a 6.1 to 1 with 125 psi compression.

    the A042 motor has a lot more low end torque, but if you ran it at full rpm for hours on end, like the 2A042 generator, it would not hold up to well.

    another thing that had been noted was the type of rings used on the piston
    there are a couple of options cast iron, or chrome.
    on most of the pistons that are for sale on ebay & other places come with cast iron rings. these tend wear out the cylinder walls in the 1500 hours of service.
    I just measured mine, 3 of mine were at 3.003, at the center of the stroke. where the max limit is 2.995, maybe that is where I have been having so much fun with tuning my motor??

    he have found out if you use chrome rings there is virtually no wear on the cylinder walls.. just replace the rings and a light hone.

    there is a lot more information that you might be able to gather, and see if it works for you.
    I visited with the author. found out that he has been wrenching on these motors for over 40 years. and he was okay with me posting his information that he has put out there.
    this information can be found at
    https://forums.g503.com/viewtopic.php?f=148&t=262382

  14. #14
    Super Moderator Corky's Avatar
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    Re: Modifying the 084 for more horsepower !!

    Great info.. I'll have to look to see just what I've got for pistons and jug sizes... I know the cast rings will seat quicker and the chrome rings tend to break in slower...

    Aluminum .120 14' X 76" hull
    Teledyne 4a084-4 engine
    Circle S 1.69:1 reduction
    67" Whirlwind "Razor X" prop



  15. #15
    Member Bart's Avatar
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    Re: Modifying the 084 for more horsepower !!

    I know what you mean, I have looked at the specs for this motor and and seen where that pistons are numbered A,B,C, & D. and there was a gain of .0005 for each number, but never gave it much thought...
    until now, as I have found out. it doesn't do a person much good, to put all the bells and whistles on, or mod mine like I have done if I don't take care of the basics.
    as for matching the pistons to the same cylinder, that might be an impossible task. if they need replaced, we are kind of at the mercy of what is available.
    the main thing is you don't want to put a "D" piston with a "A" cylinder, there is not enough clearance for the thermal expansion of the piston skirt. It will score the cylinder walls
    looking at what I have on hand, all the pistons on the 084 and the 042 that I have in pieces, they all have chrome rings for both the top and middle slots.
    I measured the 042 cylinders and there is no wear. I am thinking that perhaps my 084 was re-ringed at one time. I know I was not the first to open it up. but the damage to 3 of the walls was already done...
    so I have 3 cylinders & pistons that are good to go. just a slight hone and new rings. I did come across a fellow that sends the piston and cylinder to a shop and has them fitted. specifically to each other.. I am thinking of going that route for my last one.
    even though there was some wear on rod bearings. the journals all were between 1.4975 and 1.4978. but if needed the same person sells undersized rod bearings also.
    so at the moment, I am in the waiting period for more freight to show up. so I can start putting this motor back together. and hopefully with the basics done and taken care of I might be able to see how this mod I am doing really works...

  16. #16
    Super Moderator Corky's Avatar
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    Re: Modifying the 084 for more horsepower !!

    Well, rather than grenade my NOS engine on the airboat I bought a used engine to play with..I'm going to give this one the once over,freshen it up and probably install some performance enhancements... Here's the lucky contestant..
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    Last edited by Corky; 11-04-2019 at 12:24 AM.

    Aluminum .120 14' X 76" hull
    Teledyne 4a084-4 engine
    Circle S 1.69:1 reduction
    67" Whirlwind "Razor X" prop



  17. #17
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    Re: Modifying the 084 for more horsepower !!

    Quote Originally Posted by Corky View Post
    Well, rather than grenade my NOS engine on the airboat I bought a used engine to play with..I'm going to give this one the once over,freshen it up and probably install some performance enhancements... Here's the lucky contestant..
    Any thoughts on what method you might use to document changes in performance or HP, as you are going forward?

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