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Hot Rods 383 chev quad webers falls short on the dyno 200hp 248ftlbs

Discussion in 'The Hokey Ass Message Board' started by mike53merc, Aug 9, 2015.

  1. mike53merc
    Joined: Jul 22, 2009
    Posts: 63

    mike53merc
    Member
    from calgary

    so here goes fellas so I purchased this 383 use verified the crank its a 400 crank and verified it before i purchased by dropping the pan and checking the casting numbers I was given the build sheet (supposed) the cam shaft was changed to the comp cams it has the aftermarket double hump heads ported and cleaned up by the builder I put felpro performance head gaskets and measured 2.02 1.60 on the valves with a caliper so based on the specs of this engine is 200hp 248ftlbs sound right? the webers are 48IDA 37mm chokes f7 emulsion 135 120 mains and 120 65 idle initial timing is 20 and 38 mechanical all in at 3000rpms so any help in this set up is greatly appreciated

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  2. Hmmm. I once had a stock 292 Yblock Ford that had more horses than that. But I will post on here to give your thread a bump.
     
  3. mike53merc
    Joined: Jul 22, 2009
    Posts: 63

    mike53merc
    Member
    from calgary

    I had a stock eagle talon tsi that pulled a bigger number then this but was no where near as fast as this car or as throw you back in your seat I had 383 in 96 that didn't pull as hard as this car does but dynos don't lie do they I've played with 458 Ferrari and stayed beside them from a stand still c6 corvette look like he put his ebrake on so why the low number or is my car just so light it feels and pulls good with only 200hp? The car will lay rubber and chirp in third and will cut sideways when I'm on it in 2nd
     
  4. mike53merc
    Joined: Jul 22, 2009
    Posts: 63

    mike53merc
    Member
    from calgary

    I've taken a lot of my buddies for rides who are blown away with the results who have or have driven in 400 plus hp cars and we can't figure it out before I threw it on the dyno we were sure we were gonna lay 360-400 to the wheels maybe 350 as worst case
     
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  5. You did not post the Air Fuel ratio. It looks to me that it is way to fat on the top end. Please post the air to fuel ratio numbers.
     
  6. mike53merc
    Joined: Jul 22, 2009
    Posts: 63

    mike53merc
    Member
    from calgary

    It's on the dyno image I'm rich as fuck where I make power in the idle circuit then when my main circuit I'm perfect 14 afr and he didn't have the sniffer in until half way into the second pull with electric cutouts open I gained 50ftlbs with the dumps open its at the bottom of the dyno sheet attached
     
  7. mike53merc
    Joined: Jul 22, 2009
    Posts: 63

    mike53merc
    Member
    from calgary

    The way webers work I'm idle circuit until 3000 rpm then my main circuit takes over usually there is a drop on most dynos with webers during this transition but mine is a curve just not a high curve when it transitions
     
  8. Wow....that makes no sense...I had a VW motor with 2 48 Ida's that made that kind of hp..and I ran 40mm vents in mine

    383 stroker small blocks are usually are great motor...

    You got a sync gauge for the carbs, is the linkage working properly, are you getting wide open throttle?
     
  9. mike53merc
    Joined: Jul 22, 2009
    Posts: 63

    mike53merc
    Member
    from calgary

    Oh yah all synced it's not a weber issue I get wot at 6200rpm
     
  10. mike53merc
    Joined: Jul 22, 2009
    Posts: 63

    mike53merc
    Member
    from calgary

    Check me out on Instagram 29roadster666 to see videos of the guy running my car on the dyno and me in my garage at wot there is a difference he wouldn't rev my engine past 5000 cuz he said the horse power was dropping off but I spin this engine 6200 all day long the valves float at 6700
     
  11. mike53merc
    Joined: Jul 22, 2009
    Posts: 63

    mike53merc
    Member
    from calgary

    There is two videos on my Instagram listen to the way I rev and listen to it on the dyno
     
  12. big duece
    Joined: Jul 28, 2008
    Posts: 5,615

    big duece
    Member
    from kansas

    If you know your rich on 0-3000, then go to a F10 60 idle. 37mm choke may not be big enough for that cubic inch. I plan on using 37mm for a .060 327 build. Might try some 40 mm chokes, and 60 idles. Might have to invest in a wide band air/fuel sensor, unless you have unlimited chassis dyno access. The gauge will mount in your cab, and you can see the fuel/air ratio change as you drive.
     
  13. big duece
    Joined: Jul 28, 2008
    Posts: 5,615

    big duece
    Member
    from kansas

    Also, IR intakes like to have cams with more than 110 lobe separation, ideal is 114-115 to prevent reversion at high rpm.
     
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  14. mike53merc
    Joined: Jul 22, 2009
    Posts: 63

    mike53merc
    Member
    from calgary

    I put a 65 in idle in it after I got home car responds the same as the 70 a little leaner but not noticeable and I was planning on going to 42 this winter and ordering 50 for the idle
     
  15. big duece
    Joined: Jul 28, 2008
    Posts: 5,615

    big duece
    Member
    from kansas

    Your trying to move the same amount of air through the 37 choke as you would any other. But the smaller the choke is, the more fuel it will draw naturally. I think going to the 40 and leave your idles close to what you have would be a good starting point. Dont make more than one large change at a time before you can test drive. I have some 40's if you want to borrow on good faith or purchase if they work out.
     
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  16. mike53merc
    Joined: Jul 22, 2009
    Posts: 63

    mike53merc
    Member
    from calgary

    The issue isn't really the carbs yah they run rich but they wouldn't account for the low dyno number unless his rpm on his dyno wasn't reading the same as what my tach reads when he was running it my car sounded maybe 45-4800 rpm but on the dyno sheet he spins it to almost 5500 when I get on it it sounds like an f1car can a dynos tach read different then a vehicle tach you can see the main circuit should make more power then the idle circuit taper off and be on the down slope as soon as it hits the main circuit as you can see in the graph where when I drive it I don't start making real power till I hit 3000 rpm the car does 45mph in 1st at 5500 and I cruise around in second the car
     
  17. Sometimes with dynos, like doctors, you need a second opinion..............................
     
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  18. big duece
    Joined: Jul 28, 2008
    Posts: 5,615

    big duece
    Member
    from kansas

    Was h.p. ever checked at the flywheel? You will loose 15% or more at the wheels.
     
  19. mike53merc
    Joined: Jul 22, 2009
    Posts: 63

    mike53merc
    Member
    from calgary

    No i didn't want to dyno until my webers were close to being functional and then getting an afr sniff so I can be close to jet closer to where I need to be optimal the price of the Jets and emulsion tubes and chokes are not cheap as you know but 230hp I just had a buddy and based off of sound compared to the video where my tach reads 4500 rpm and where his dyno reads 5500 and when I take it to 5500 there is a huge difference I think his dyno and my tach are reading different so I'm guessing he let off in the transition circuit with the dip in power on his way up as webers usually show I have a couple hours booked on the 20th I'll post the results when I get them and I'm running my car not the dyno guy at this location that's the only thing either my tach is reading wrong or his is who knows
     
  20. big duece
    Joined: Jul 28, 2008
    Posts: 5,615

    big duece
    Member
    from kansas

    Looking forward to seeing more results, keep the thread posted.
     
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  21. models916
    Joined: Apr 19, 2012
    Posts: 380

    models916
    Member

    Chassis dyno needs the final gear ratio correction added in to be even close. Some chassis software is used to only show improvement from run to run. I was in contest years ago at a automotive school. Dyno operator asked what gear I had in the back. I told him 3:76. I really have a 4:56. Dyno read something like 600 hp to the wheels and I got top number for the day.
     
  22. Splinter
    Joined: May 14, 2005
    Posts: 1,113

    Splinter
    Member

    What is your fuel pressure? Webers are super sensitive to pressure, and you may be getting rich because of too much pump. And if you are dropping off like that at higher revs, how is your ignition system? Any broken counterweight springs?
     
  23. Dyno Operators are like accountants, any good one can fudge the numbers. Like stated above, a chassis dyno needs a whole bunch of correction factors to accurately calculate engine horsepower. Other things like transmission and torque convertor type can play a big role as well. What type of transmission and / or torque convertor are you running? If the torque convertor or clutch is slipping, that will really screw up the numbers, and don't even get me going on what a CVT does to chassis dyno numbers.

    Do you have the actual data file from the run? It would be interesting to see the measured wheel drum torque and rpm numbers.
     
  24. Ole don
    Joined: Dec 16, 2005
    Posts: 2,915

    Ole don
    Member

    I had three tachometers in the Y block before I found one that worked right. The one I settled on was an Autometer.
    It may be hard to do in a roadster, but my tachs would fall off after about six hours of continuous freeway driving.
     
  25. mike53merc
    Joined: Jul 22, 2009
    Posts: 63

    mike53merc
    Member
    from calgary

    Fuel pressure is 2.5psi its not an issue with the webers I'm running 351 trutrac posi he did the dyno pull in third with an m20 4 speed
     
  26. mike53merc
    Joined: Jul 22, 2009
    Posts: 63

    mike53merc
    Member
    from calgary

    Well redid the dyno and 215hp and 325ftlbs I guess time for some better flowing heads and a new cam shaft laying down 325ftlbs at 2500rpms isn't bad I will upload the dyno data when I am at my computer later on did 6 pulls with consistent numbers
     
  27. porknbeaner
    Joined: Sep 12, 2003
    Posts: 41,135

    porknbeaner
    Member

    Hmmmmn a 280 horse 383. Nope don't sound right at all. I got a 400+ horse 355 running a single 4.

    There is a reason that all the real racers went to a 2x4 or a single 4 on a carbureted car. The multiple carbs look neat and that is about where it stops for most builders a 2x4 or a single is way easier to tune and build HP. In the late '60s I was running trips on my 312 and when I went to a 2x4 I dropped 2 tenths off my time before I started tuning it. the 3 deuce intake was well tuned ( to the point of working the runners and the plenum) but the 2x4 made more zot. After tuning the 2x4 we got the old heap to run consistent low 12s ( like in 12.01 low 12s). You may consider a single 4 or a pair f them in place of your pipe organ intake.
     
  28. 51box
    Joined: Aug 31, 2005
    Posts: 791

    51box
    Member
    from MA

    Dyno numbers don't really mean much, different brands different correction factors etc. they are more of a tuning device. Take it to the track, only way to show true power. MPH doesn't lie.
     
  29. porknbeaner
    Joined: Sep 12, 2003
    Posts: 41,135

    porknbeaner
    Member

    Absolutely correct. I one for sure that you can take the same car to 4 different chassis dynos and get 4 different results. That said the dyno shouldn't be that far off you can buy a target motor that makes 280 horse.

    If the OP is not a tuner he needs to loose those Webbers or keep a tuner on retainer. If a man is not one to tinker then a simple setup is king.
     
  30. saltflats
    Joined: Aug 14, 2007
    Posts: 9,561

    saltflats
    Member
    from Missouri

    If he making the pulls in third gear you will have a number drop because of the power loss in the tranny.
    Need to try it in 4th.
     

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