HKS install

35 posts in this topic

Posted

Well, engine is sitting in the Fox on the alum plate. Carbs are about 2" too high so maybe new intake manifolds to move the carbs. Plus a few other things that will have to be modified such as exhaust pipes, oil cooler, 2" prop extension added, and the list goes on. Maybe time to do some soul searching if I want to go thru all this or throw in the towel.

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Posted


Don't quite understand how carbs can be so high Allen.  Is that with a round Kitfox cowl?  I know Mike Ricketts had a couple of bumps on his cowl for the carbs, but that was on an Avid cowl which is way lower then the Kitfox one.  Wonder how much higher your mount holds the engine then the mount I had for the HKS I had.  My mount was made by the same guy who made Mike's mount.  JImChuk

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Posted (edited)

My cowl is the NSI Subaru cowl and the mount is the standard 503/582 mount I got from TJay.  My prop hub sets about 2" below center of the round opening. My cowl is about 8-10" longer than the standard cowl for a model 2. According to Chris Hatin of HKS the intakes are standard carbon steel and I am guessing that no length requirements are recommended, since the intakes are just a travel tube for the mixture, unless they are longer than a two week payday. Look at the cowling length of the nose bowl and one can see the extra length. Disregard the engine and prop, the old Hirth.

Brand New Fox 005.JPG

Edited by Allen Sutphin

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Posted (edited)


I can say from experience messing with intakes can do real funny things to your egt's. Nothing you cant master but usually takes a few tries and lots of attention grabbing test flying.

Man that is a sharp looking airplane.

Edited by TJay

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Posted (edited)

True, intakes can cause strange things to happen. If one gets carried away with length, uneven flow or some other weird adaptation. I only need a straight intake tube instead of a 180 degree bend so not that difficult to do. As far as mine looking good, after seeing yours and how good it looks, I take that as a gold compliment.

Edited by Allen Sutphin
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Posted (edited)

Hi Allen,  I'm guessing your gearbox turns down.  Here is the HKS I had along with the motor mount I got with it.  You can see how low the engine sits, that's why I wondered how your carbs could get in the way.  I had to get different intake manifolds that position the carbs up high above the cylinders.  The guy who built the mount built it with those intakes in mind.  I had the horizontal intakes on my engine and there was a motor mount tube in the way on each side.  To get it running, I reversed them and that put the carbs outside the cylinders.  It was just a temporary fix.   I did build some straight manifolds, but they were just for testing purposes.  What ever you do for the intakes, I think the carbs should end up as close to level as you can while in flight.  JImChuk

PS  just added the last two pictures showing the intakes that go horizontal.  That may be an option for you.   I found a guy who wanted my style, and I traded his for mine.  

Photo0599.jpg

Photo0600.jpg

Photo0601.jpg

Edited by 1avidflyer

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Posted (edited)

Will try to get a couple pictures today. Need to do some more head scratching or other body parts. Maybe set the carbs and filters in position as a 912 has them.

Edited by Allen Sutphin

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Posted

Some pictures of the HKS trial fit. Then I took the carbs off. New manifolds might do the trick.

HKS 700E 001.JPG

HKS 700E 003.JPG

HKS 700E 004.JPG

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Posted

Looks like you only need an inch or so.  Modify the mount???  That might give a bit more clearance on the ends of the cylinders as well.  JImChuk

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Posted

I considered that but that would drop the engine even lower. Plus there are 2 brackets that mount on top of the carbs to mount the cables which raise it another inch. Got myself a plan (haven't we all heard that) for new intake manifolds which put the carbs in the same position as they are on a 912 which is to the rear. They will be shorter and straighter than the stock manifolds but shouldn't cause a problem. A couple air scoops on the side would provide airflow if needed. Better than on top which blocks the view even more. One problem at a time. More will arise, I am sure. I did weigh the engine minus exhaust and oil cooler and it was 110 lbs. So it will be pretty close the advertised weight of 121 lbs.

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Posted (edited)

Allen, have you checked on the HKS-engines forum? Maybe you need to sign up to be able to view the photo albums, but there are many examples of engine mount configurations. Pics of a Kitfox similar to yours are shown in folders 'GB Kitfox' and 'MNFlyer' - he also has written many posts on that forum in the past and there is a lot of other info on there. He also mounted the engine with gearbox in down position and used the optional HKS horizontal intakes. A downside of this configuration is the lack of space to position the oil cooler at the front of the engine mount (as can be done with the gearbox flipped up), so he mounted it under the fuselage. The pics also show his home made cylinder cooling baffles.

https://groups.io/g/HKS-engines/photos

https://groups.io/g/HKS-engines/album?id=50924

https://groups.io/g/HKS-engines/album?id=49199

There is some commentary on that forum about not shortening the intake manifolds too much, due to pressure pulse influences. One guy made some short stub intakes (red colored in pic below) but the performance was reduced so he cut original intakes to create an s shape.

Some people have minimised the height of the throttle/ cold start cables by rerouting them... I'll try attaching pics below. 

Screenshot_2020-06-27-10-52-29-09.png

IMG_20200627_105447.jpg

Screenshot_2020-06-27-11-03-50-81.png

IMG_20200627_110532.jpg

Edited by pedro10012000
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Posted

Didn't know there was a group on HKS's. Thanks!

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Posted

My intakes won't quite be that short (as the red ones) but a little shorter than the long curved ones. And a slight S curve to them. The oil cooler has room to live under the engine mount and I generally wrap all my exhaust pipes with heat wrap to lessen the heat in the cowl. I generally stay away from some online sites due to negative comments about everything that someone is using or trying.  Very few negative comments on this group though, which is one reason its a great group to be on. Most are very supportive! There are a few model 4 Foxes flying with a 503 so a model 2 should do fine with an HKS. I am not looking for nosebleed performance.

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Posted

Yes Allen, I understand your experience with some forums! The HKS one is barely active but people still watch and make useful comments.

What prop are you planning to use? Some flyers have been disappointed using smaller 3 blade props (eg that they may have switched across from a 503 or 582) and have got much better performance from 2 blade props of about 70" or greater. Your 3.47 ratio gear box seems the preferred option, and the longer props perform better on the wide, round Kitfox' cowl. 

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Posted

Have a 70" Warp Drive 2 blade hanging on the wall. Correct rotation, just need a 2" prop extension to make it fit. Could possibly go with a 72" if I had to. The oil cooler will fit good right in front with a couple custom made brackets.

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Posted

Did join the HKS engine group. A lot of information on there as well. And seen Jim Chuk's name on there as well.

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Posted

Yep, I'm a member there.  I joined it after I got the HKS I had. Mostly was looking for info about the engine.    JImChuk

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Posted

Allen, on the HKS forum there is a 'files' section that has a few good docs, eg a list provided by HKS of compatible sparkplugs.  Also for your interest, have you seen this video of Mike Ricketts flying his hks Avid... maybe some inspiration for you. He has a few other videos on Vimeo and YouTube. You'll see his solution to fitting the carbs within the cowls was to create cowl bumps

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Posted

Pedro, thanks for the heads up on the HKS group. Yes, I've seen the video and looked at the files section. Just about got the new intakes made. Waiting on some materials from Aircraft Spruce to finish them. I don't need anymore stuff blocking the view over the nose. A couple air scoops on the sides to help feed air to the carbs should help. Intake/oil cooler situation just about worked out. Next on to the exhaust and to do some minor modification to make it fit. A pet peeve of mine is cutting up a good cowling and sticking stuff on the outside instead of taking the time to make everything fit inside.  I understand that sometimes its unavoidable and have to do it. No offense to anyone but I kind of take performance opinions with a grain of salt. Different people have different opinions on what they expect to get from a certain engine. Factory horsepower numbers can be misleading depending on how they were acquired. A proper gearbox/prop combination can make or break an engine reputation. In the end, if a pilot is satisfied with his aircraft and the way it performs, then I am tickled to death for him. Take the same aircraft and let another pilot fly it and all of a sudden its a dog. We pilots can be a funny breed sometimes! On looks along, the HKS is a neat looking little engine and even connected and flyable it is a clean looking engine. Some engines look like a can of worms with all the hoses, wires, and sensors.

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Posted


I watched the video Allen and think you better keep plugging away looks like your gonna have a nice airplane for putting around.

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Posted

Putting around the general area is what the Kitfox is for and my style in my older years. Its funny how the perception of performance differs between pilots of airplane types. Talk to a group of RV pilots and builders and performance is all about speed. Talk to a group of Avid?Fox pilots and performance is about take off and landing distance. Talk to an old pilot and he's just happy to fly! And yes, I'll keep plugging away just for the fact that I have to know what it will do. May be disappointed or elated, either way, its a learning experience. Some of my past learning experiences have been costly.

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Posted

I would guess you will get at least as good of performance with your Kitfox as Mike did with his Avid.  The extra 2' of wing on the Kitfox should help some in climb also.  And his fuel burn numbers are really great.  Imagine just burning a couple of gallons an hour for that nice evening flight.  Keep at it Allen.  You will like it I'm guessing.  JImChuk

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Posted

Naturally progress isn't moving along fast enough. Too many things to try to keep up with this summer. Did discuss the engine change with the local FSDO. Said it wasn't a major change and all that was needed was a log entry and new W&B and carry on phase 1 for 5 hours.

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Posted

Well it fits with the oil cooler and oil tank mounted. Now on to making new intakes.

HKS 700E 001.JPG

HKS 700E 002.JPG

HKS 700E 003.JPG

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Posted


That looks great

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