Tuneup differences between Fat and Fuel heads

Discussion in 'PSI Superchargers Tech Questions' started by greenracing, Apr 9, 2019.

  1. greenracing

    greenracing Member

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    Has anyone moved between Fuel heads and Fat heads on a blown alcohol setup and has a ballpark difference for timing and fuel? I've got a safe starting point for a Fat head setup and am putting together a Fuel headed motor with the 176cc camber heads. I'm assuming I can use more timing on the Fuel heads - I'm thinking around 30 would be safe, maybe 32 max? Will the Fuel heads use less fuel, or does the big chamber and more timing require similar fuel?

    Thanks!
     
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  2. KENNETH JORDAN

    KENNETH JORDAN New Member

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  3. bruce mullins

    bruce mullins Top Dragster

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    keep your timing under 28.
     
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  4. greenracing

    greenracing Member

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    thanks Bruce!
     
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  5. quickcut

    quickcut Member

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    Anyone else have any input to this ??
     
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  6. turbo69camaro

    turbo69camaro Member

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    Save yourself a ton on money and tail chasing .Get hooked up with Will hanna,Mike @ rage ,Randy Anderson,ETC and get your fuel system set up and flowed they will get you in the ballpark
     
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  7. Soldierboy0098

    Soldierboy0098 Active Member

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    On alky Fatheads max of 26 but it depends on your compression ratio for how much you will need to babysit the timing. Fuel heads like more timing because of the big chamber size. I have seen between 32 and 38 on a fuel head but they do not like high rpm's because the pistons weigh a ton.

    Also Turbo is correct for the $800 to flow a fuel system your money way ahead in getting it flowed as they will give you a good starting tuneup, flow your jets, and this usually includes one trip to the local track to help tweak it.

    Hope this helps,
    Trev
     
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  8. John byob

    John byob Member

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    Trevor who mills fuel pistons down to take weight off of them. Met a racer years ago he took 200 grams of each blower piston fr his motor? Thx
     
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  9. Soldierboy0098

    Soldierboy0098 Active Member

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    Not sure on that one, I know people who mill the domes to get the compression down but the only people I can think of is the piston company for CP. They do a lot of lightening but not sure on a fuel head deal.

    https://www.cp-carrillo.com/pt-3507-pistons.html

    Hope that helps,
    Trev
     
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  10. Will Hanna

    Will Hanna We put the 'inside' in Top Alcohol
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    I have found (was educated is more proper) the timing is relative to the bore size. Bigger bore = more timing. This is comparing fat head to fat head type of deal.

    Now the fuel head has more flame travel, so it needs more timing to start the burn a little earlier.

    You will hear of people running timing numbers well into the 30's with fuel heads. Most (not all) of that comes from the way these motors used to be ran before we got 44 amp mags. With the big chamber and weak ignition, it needed a lot of lead and a hot cylinder head to combust the mixture. Now we have an arc welder, so we don't need to start the burn as early and don't need 200+ head temp to help preignite the burn.
     
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  11. Outlaw Funnycar

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    We run the old dart 96 fuel heads. I put between 34-38° of timing with a 4.5 amp Mallory. 526 with 14-71hh mert. Runs 4.0s no sweat and will run 3.70s-3.60s if I want it to. Shift at 8k launch at 5k
     
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    promodracer and KENNETH JORDAN like this.
  12. John byob

    John byob Member

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    Trevor found a guy who takes 200 grams off each piston. Think he charges 200 t 300. Not sure why piston makers don’t look into this?
     
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  13. John byob

    John byob Member

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    PS if anybody out there has old fuel heads with rockers and valve covers manifold and wants to go to fat heads. I have a set of AJ fat heads with valve covers and stands but no ROCKERS that I would trade if anybody is interested thx
     
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  14. James2

    James2 Member

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    Thinking of going this route instead of building my BBC since I have more hemi stuff. What kind of pump/gallons do I need? Just shooting for a low HP deal to get some seat time in my street car. But gonna use the parts that I have: 170cc heads, 4.187x4.500 with my low compression big pump/mag long block. 14-71 roots.
     
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  15. aj481x

    aj481x Member

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    Still available?
     
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  16. promodracer

    promodracer Member

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    I would say start at 30 degrees, then 32degrees and 5 steps fatter on main jet. if ok another 2 degrees advance to 34 degrees and 5 steps fatter on main jet.
     
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  17. 1320metalman

    1320metalman Member

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    Had Conway setup our fuel system on a AJ 5 fuel head (200cc) at 10.5:1 comp and a 296°, cam, C rotor.

    We started at 100 over on the 4000lb Inertia wheel dyno. Then stopped at 105 over by end.

    I bought that OLD double gear waterman pump like someone told me Janis used to run on his stuff, cuz u can easily change gears to get the GPM. It used sprint car pump gears but its out of production w/a pic still on Mayers website last i looked..

    Tom said he did not know how much more fuel but it likely needed bout +15% more than a fathead 97/100cc head.

    This was later sorta confirmed by a guy i know who ran a 200cc fuel head on a 14/71 hi helix car and said when he tuned the fuel & grid like a fat head it would not run well..
    Needs more fuel & cant pull a bunch of timing out w/an auto trans car on line, like a fathead can deal with.

    We started at 20.5 gpm on Watermans flow bench as my 14/71 colleage said later..
    u better have at least 19 or 20 gpm.. he was correct as well from a yr at track learning.

    Now the timing goes against some other comments above, but its what worked for us.

    We started out at Conway's setting the mag pickup at 28° lead total,
    & he said of course too chk it on startup do to all MSD grids varying up to 4°.

    He was correct on that as well.. we started at 23° for short bursts and it did fine below 6k rpms to chk pressures and plugs for safety..

    bumped it to 26° and that was great till about 7500 rpms it appeared.

    Then it liked 28° above the 7400 rpm mark.
    Then we tried 30° up higher..

    We wanted a "bbq" eng combo.. thats when
    (U can cook food between rnds vs fighting bad vlv springs and valve lash movin around..)

    A no/low maintenance eng combo,
    while going easy on rods for longer life (like 35 runs vs 25)

    So we only ran it to a little over 8k and when we backed it up to 26° @ 7500
    & then went to 28° till just north of 8k, it did better..
    w/ 20.5 gpm pump and no bypass jet. Just was blocked off after early pulls.

    are fuel was a touch lean (but still ok)
    down low (below 5000)
    and a touch fat up high (above 7500) but not ridiculasly fat by any means. Nice and safe.

    We had 1450ft of REAL AIR density,
    w/below ave water grains that day.

    105 main & Conway had hat nozzles in the 80s.
    We bumped to 28° @ 7900 and ran it to 8400 on hardest pull.

    Near the end,
    It made PEAK hp at 7900 on the 28°,
    & that was running @ 7600 @26°- then the bump to 28° to 7900. We tried going to 30° after 7900 and that pull was only 2 hp more at peak of 8000rpms...
    Vs -2hp w/-2° (28°again) at 7900 rpms

    ENDED UP with
    0 rpm - @ 20°
    6500 - @ 24°
    6800 - @ 26°
    7500 - @ 26°
    7900 - @ 28°
    That timing combo was DOWN only -2hp
    VS @ the 30° hit at close to 8000 rpms .

    Again.. down -2hp @ 7900 rpms pull of max hp at 28 max.

    We were wiling to give up 2 hp at 100 rpms lower for 2° LESS MAX Timing.

    Was this optimum. QUITE DOUBTFUL.
    were we gonna wear out the dyno...nope.
    Sure...there was prolly more..

    But we were NORTH OF 2850 hp Corrected by a nice amt..
    And that was a good starting point for an entirely new eng combo that was going in a car that wasnt ready for prime time..
    any more hp & torque for a back half car would be a useless starting point.

    Conway said he didnt really hav any data as to what it was gonna want..but knew it needed more pump than a typical 17.5+gpm fathead setup. He had ran sone Walt 175cc heads yrs ago..but never any 200 fuel hds..
    He is in the majors.. we are playing 1A ball here w/our stuff..

    But his 15% more gpm than a fathead suggestion, due to the deep chamber ... valve overlapping fuel losses of unburned but still gotta hav xtra fuel goin thru there opinion,

    Which he said was just unavoidable consequence to our cam and heads...
    cam wasnt bad..just old technology...
    But still followed Stormin Norm's starting point, a 296° duration baseline on his using his Screw.

    Tom was as close to being right on the tune,
    as Columbus was tellin the Queen..
    the Earth is round.

    So yes..hiring a good fuel system guy whos forgot more than most will know
    (myself included) is a huge step towards starting out right on these fuel heads.
    w/a screw anyhow. Prolly roots as well.

    Toms only reservastion was "could we make enuff power" to satisfy ourselves at only
    8000 rpms...??

    He slightly grinned an said
    " that arm will go 9500 if needs too u know"..
    Man of few words, really . But like Norm.
    Who made u drink from a firehose during a consult..(a lot of words)
    ..u be smart to listen to each words of either..
    God rest Norms soul now.. no more advice from Drazy.. What a brilliant guy to learn from he was..or so i found..

    For saying up front he didnt know what it wanted w/C rotor..(Tom)
    he is a heck of a blindfolded dart thrower.
    Thats just experience at work...

    vs our "minds eye" logic of these fuel heads/ diff chamber cc sizes/ and other (fat vs fuel) theorys out there on methanol.

    Based on our dyno results i cant image running much over 30° w/C rotor at nearly any rpm on a fuel head...
    but it does show it wants more lead up high than dwn low..for sure...based on previous pulls early in day..

    (Those who know tom can may say his
    "not knowing tuneup"
    is still better than many who may say ,
    "they know" this fuel head tune.

    Maybe this helps a budget fuel headed screw guys out there.
    The roots deal ran parallel to the fuel headed in many aspects...
    cant say on timing end of it for sure..
    our results i can attest too.

    My colleage w/fuel headed roots seemed to see much the same things after a yr on track of learning, as we did on the big spinnin weight,
    but we did it in a day vs a yr at track..

    (W/Tom "estimating" at what we might want)

    The roots fuel hemi saw nearly the same things we did .. but oerhaps w/the standard drawbks of his roots blower, & fuel head alcohol eng,
    vs what improvements a C screw normally shows..
    lower intake discharge temps..ect

    We were 4.187" bore & 4.500" arm 495".
    Bout 50lbs...dyno boost sensor malfunction at 47psi @ like 7300 on up..
    had we bothered to reboot puter it would hav fixed that based on his past experience of sensor malfunction.. we just forgot too in the rush to keep pullin.

    Left dyno and we made 55 lbs on track 1st time out at 8000,
    but air was a lil better that day..
    bout 1000 ft vs dyno day 1450 DA..

    Thats all we know..and it aint much.
    All This info & $1.00 bill, combined...
    Might get u a cheeseburger somewhere.

    Let us know if u run a fuel head & how it works out.. i realize this is a really old post but race seasons pass qwikly and maybe u havnt ran it yet..
     

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  18. greenracing

    greenracing Member

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    Wow - that's more than a cheeseburger's worth of info there! You're right - seasons pass quickly and I haven't run it yet :)

    I've got the 175cc chamber Brad's so a little smaller chamber, but still a bathtub compared to the fat-head chambers, so everything you're saying still makes sense in my case.

    Very good information - Thanks a lot!
     
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