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Author Topic: Fox 35 hemi head  (Read 5868 times)

Offline Dennis Toth

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Fox 35 hemi head
« on: November 21, 2014, 02:48:44 PM »
Guys,
I have a couple to the hemi heads for the Fox 35 and was wondering if anyone has used them for stunt and if so did you use it stock or add head shims to reduce the compression?

At first I thought the hemi head would have higher compression and would cause issues with the 4-2-4 run. Thinking about it, the hemi head shape may allow the engine to run at the higher compression than the stock Fox wedge head and still hold a 4-2-4 (this was one of the mods the Big Jim Greenway did on the ST 60's).

What has been your experience with these heads?

Best,          DennisT
« Last Edit: October 29, 2016, 07:56:55 PM by Dennis Toth »

Offline kenneth cook

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Re: Fox 35 hemi head
« Reply #1 on: November 21, 2014, 03:04:41 PM »
            Dennis, I found that starting becomes a bit problematic with the Fox hemi-head.  Others have produced hemi heads for the .35.  My stock heads yield much faster starts. I did away with the head gaskets and lapped the top of the sleeve flat on a piece of glass and just used the button directly on the liner. Use caution to align the button properly with the baffle on the piston. The stuffer backplate does more for the engine opposed to the Fox hemi head. Just my experiences with it. Ken

Offline Jim Kraft

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Re: Fox 35 hemi head
« Reply #2 on: November 21, 2014, 03:51:15 PM »
I have run three of them and just used one regular Fox gasket on all of them. They all seem to run fine with a little difference from stock. The 4-2 is much the same except they seem to kick in harder in the 2, at least for me, and probably put out a little more power all the way around. I still think the old Fox flat head is the most consistant running though. As said above there are other hemi heads besides Fox that may run better. I have one that Marvin Denny reworked from a stock Fox that runs extremely well, but they all work.
Jim Kraft

Offline Dennis Toth

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Re: Fox 35 hemi head
« Reply #3 on: November 21, 2014, 04:03:07 PM »
Jim,
What fuel are you running and what plug?

Best,        DennisT

Offline Jim Kraft

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Re: Fox 35 hemi head
« Reply #4 on: November 21, 2014, 06:44:51 PM »
Dennis; I am running mostly Sig 25% castor 5% nitro fuel with Thunderbolt long R/C plugs.
Jim Kraft

Offline Dennis Toth

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Re: Fox 35 hemi head
« Reply #5 on: November 21, 2014, 06:59:15 PM »
Jim,
Are you running a muffler? What prop?

With the muffler I found that I needed to use either a 9x6 old top flite or a 10x5 to keep the heat down and prevent pre-ignition.

Best,       DennisT

Offline Dennis Toth

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Re: Fox 35 hemi head
« Reply #6 on: December 06, 2014, 01:12:00 PM »
OK, went flying with the El D, I have the hemi-head with two head gaskets. I am running a 10x5 old TF prop,  muffler and 7% N, 27% (50/50)oil, long Fox R/C plug. First flight was a bit lean. Second flight got it fairly close, it started out just about perfect but near the end got lean. Looking it over once I got home I found one of the tank kick-out shims worked its way out and the tank was flat against the outside fuse. This causes some of the lean run. I'm thinking I want to go back to the original Fox head with one extra head gasket. This was the original setup I started with, it worked pretty good. Then I got information overload and started looking for more power so I took out the extra head gasket, yada, yada, yada. Anyway, that didn't work, got pre-ignition crackling and have now completed the circle.

Best,          DennisT
« Last Edit: October 29, 2016, 08:04:20 PM by Dennis Toth »

Offline Dennis Toth

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Re: Fox 35 hemi head
« Reply #7 on: December 11, 2014, 08:24:13 PM »
Anyone know if the hemi head with a couple extra head gaskets runs better than the standard head? From what I've read the hemi head should be able to handle higher compression and still run a reasonable 4-2-4?

Best,         DennisT

Offline RandySmith

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Re: Fox 35 hemi head
« Reply #8 on: December 11, 2014, 09:21:29 PM »
Yes the Hemi head is better, and will run a nice 4/2  while making a little more power, You do not need to run but 1 head shim in my experience , The Smith design Hemi, is a very good head and runs cooler and is 1 piece, has deeper fins, circular cooling and a heat dam to keep the plug hotter

Randy

Offline Dennis Toth

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Re: Fox 35 hemi head
« Reply #9 on: December 12, 2014, 01:21:48 PM »
Randy,
Is that the setup for running the Fox 35 with the muffler? I've opened the stinger up but it still holds some heat and I get a little crackling, seems like I might need one more.

Best,     DennisT

Offline RandySmith

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Re: Fox 35 hemi head
« Reply #10 on: December 13, 2014, 10:02:46 PM »
Randy,
Is that the setup for running the Fox 35 with the muffler? I've opened the stinger up but it still holds some heat and I get a little crackling, seems like I might need one more.

Best,     DennisT

What head?
What muffler
What size spraybar?
What fuel formula?
Hole size in muffler?
Decompressing it will make more heat

You need one more what? gasket?

Randy

Offline Dennis Toth

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Re: Fox 35 hemi head
« Reply #11 on: December 14, 2014, 12:39:45 PM »
Randy,
What I would really like to do is run the stock head, I have a hemi head on it. Running a old Top Flite 10x5. I have your Fox NVA, I want to run the stoke muffler with it drilled out to 3/8", fuel is Sig 5% (2 oz extra Klotz added to the gallon), Sig RC long plug, open uniflow tank.

The engine is clean inside, no binding with the plug out, no slop in the shaft or conrod, excellent compression. The engine runs well but seem to crackle once it unloads. To me that indicates it is pre-igniting, hence why I have been adding head gaskets to retard ignition. What am I missing?

Best,      DennisT
« Last Edit: December 14, 2014, 01:51:13 PM by Dennis Toth »

Offline RandySmith

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Re: Fox 35 hemi head
« Reply #12 on: December 14, 2014, 06:31:14 PM »
Randy,
What I would really like to do is run the stock head, I have a hemi head on it. Running a old Top Flite 10x5. I have your Fox NVA, I want to run the stoke muffler with it drilled out to 3/8", fuel is Sig 5% (2 oz extra Klotz added to the gallon), Sig RC long plug, open uniflow tank.

The engine is clean inside, no binding with the plug out, no slop in the shaft or conrod, excellent compression. The engine runs well but seem to crackle once it unloads. To me that indicates it is pre-igniting, hence why I have been adding head gaskets to retard ignition. What am I missing?

Best,      DennisT

Why don't you try fuel with at least 25% oil, and add 1 extra gasket to your glow plug., This will make the glowplug slightly colder,, or try a cooler plug, like an Enya #4. It is also very easy to  switch to a stock head to see if that helps, by the way FOXes  crackle a lot some times with no ill effects,  What I suggest is to just try a couple of differant setups, run what you like best.

Randy

Offline kenneth cook

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Re: Fox 35 hemi head
« Reply #13 on: December 14, 2014, 10:42:58 PM »
                Dennis, looking over your post I see something here that I feel might be responsible for some of your engine running issues. I never had the need to run additional head gaskets with the hemi-head. I don't run a 4-2-4 or supposed 4-2-4 due to the engine running to slow for me in that mode. I run the engine faster in a wet 2 but what I do see is the fact that your using a Fox r/c long. I've seen more problems with those plugs than anyone plug in particular. They're a spin of the wheel in terms of reliability. They can rob many rpm's over other plugs such as a Thunderbolt r/c long. The posts can leak not too mention fall out. Rpm's drop off immediately when the battery is removed  as well. I would certainly give another plug a try like the Thunderbolt prior to diagnosing engine mishaps with a Fox plug. Ken

Offline YakNine

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Re: Fox 35 hemi head
« Reply #14 on: December 16, 2014, 07:28:16 PM »
One of the guys in my club told me to file a small notch in the button that points to a fin or a head bolt so you can see if it rotates on you when changing a plug. He said that happened to him and he ruined a 40th. Anniversary piston & liner that he had been breaking in very carefully after lapping it and it was shot when the baffle rubbed on the slot in the button. T.J.
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