Dyno tuning vs tried and true?
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  1. #1
    Fellow Frogger!
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    Dyno tuning vs tried and true?

    OK ok,

    I realise there a plenty of people for and against, but I am after a 'realistic' opinion anyway-on dyno tuning.

    My 1647cc motor with twin sidedraught dellortos badly needs a tune -. I have checked out all the jet sizes/air bleeds etc when I first bought the carbs and they should work on this motor just fine. It has a bad hesitation off idle- coughs/splutters then goes like a b....std!

    I have had to replace the O2 sensor in the exhaust as my mixture meter wasn't much good with a dud one! This will allow me to see if it's running rich or not.

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    I am thinking of biting the bullet and getting someone to 'power tune' it on a dyno and fiddle the fuel and spark to get it just right. However my previous experience with a dyno operator was charge first - do the job (with an apprentice) later!

    I am thinking it might be better to get another company, where the guy is into race cars (raced beemers at Bathurst even- those old black JPS ones?!) etc to do it- altho' he doesn't have a dyno, because I trust the guy.

    Thoughts anyone?

    Ben

  2. #2
    Budding Architect ???? pugrambo's Avatar
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    when you say it dies off idle is that under heavy acceleration ?
    does it die and cough when you just sit there and blip the throttle ?
    what size chokes/venturis are in the carbs ?
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  3. #3
    Fellow Frogger!
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    It all depends how much experience the guy with the dyno has. Take your car to a guy who's not very good and you're pouring money down the drain (they charge by the hour, and tuning can sometimes take alot of hours). Take it to someone who knows what they're doing and it can make a world of difference to the car. Unfortunately there seems to be way too many guys who fall into the first category. Sam's Performance in Padstow, is one of the few guys in Sydney who falls into the later category, and the fact that his dyno is usually booked out a month or so in advance, demonstrates this. Moral of the story is to look for a dyno guy who's workshop is booked out because there's usually a good reason for it.

  4. #4
    Fellow Frogger! MYT205's Avatar
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    I must agree with the comments about Sam's Performance. For quite a few years in a row they have had cars that have won the NA 4 & 6 cyl classes in HP Heroes at Summernats.

    Dyno time can be expensive, but is worth it in the right hands.

  5. #5
    Fellow Frogger!
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    ummm,
    yeah I'll have to pull a few bits off it - I wrote them all down when I first got it- but wouldn't you know I have lost the bit of paper now!

    As for the hesitation, you can rev the motor when not in gear and it doesn't bog - it just revs. However on the road you have to accelerate slowly to get smooth acceleration, if you dump it, it bogs down then gets up and boogies.

    Hope that explains it a bit better?

    Cheers Ben

  6. #6
    1000+ Posts tekkie's Avatar
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    Renault17:
    ummm,
    As for the hesitation, you can rev the motor when not in gear and it doesn't bog - it just revs. However on the road you have to accelerate slowly to get smooth acceleration, if you dump it, it bogs down then gets up and boogies.

    Hope that explains it a bit better?

    Cheers Ben
    Sounds like accelerator pump(s) dumping a bit much into the cylinders. once the revs build up the engine happily accepts the extra fuel. I used to have triple SU's on my Torry (washing out my mouth now) and once tuned the engine was joy to rev, before tuning tough it had symptoms not dissimillar to what you are describing. good luck
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  7. #7
    1000+ Posts Damien Gardner's Avatar
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    Two possibilities spring to mind with regards to your tuning, back in the '70's i had a similar fault with twin SU's on an R8 the first was the carbs were unbalanced airflow wise and secondly there was no oil in the dash pots this caused pistons to lift to quickly & load the motor. i've had no experience with Delorto's however if they are configured like the SU's this could be looked at.
    In regards to the Dyno question the quality of the vehicle tuning with either method depends on the competence of the operator, my experience in having found a Brilliant mechanic the tuning is done by sight and ear and the Dyno shows his judgement to be spot on. However i've found with my radically modified car around 90% of Dyno & or conventional operators have the attitude of if it's not in a book it can't be done or just don't want to risk it. Verbal praise is the best advertising for any business. So choose the most highly recomended workshop in your area. Another good rule of thumb is if the business has affiliations with any form of motorsport they'll be looking for best performance for the type of usage of the vehicle.

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  8. #8
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    I actually found my 604 used to bog down if you planted the foot and found that it had too much fuel going in on idle i backed off the idle mixture and that helped a stack

  9. #9
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    Hi Ben,

    If the pump jet is either too big or too small it can cause the problem you describe. However, it's quite hard to work out whether the problem is that the jet's too big, unless you work with Dell'Ortos all the time. Therefore, the best way is to start with a too small jet and work up in jet sizes until the hesitation disappears. This is where a good dyno tuner is invaluable, but of course you need a stock of jets. In fact, where the engine is modified to a unique spec. you really have to dyno tune it.

    However, there's a screw adjustment for the pump stroke underneath the carb in the middle, that operates on the pump arm (the one that goes to the middle of the diaphragm, under a housing retained by four screws). This is what pumps the fuel through the pump jet, and the only function of this and the jet is to prevent hesitation on putting your foot down.

    If you screw the adjustor upwards, it causes the pump to have a longer stroke, and it will pump more fuel. If this helps, you'll know the jet is too small. Vice versa, it may indicate the jet is too big. Don't know how obvious it'll be though...

    Good luck

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  10. #10
    Fellow Frogger!
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    Hey Guys,

    went to a mechanic the other day and had a chat to him- he charges NZ $50-100 for a basic tune- plus parts - this includes time on the dyno. He seemed very straight-up and on to it too. He also has his own race car and does various cars for guys in the same car club I belong too. He has all the spare jets in stock (cheap too he tells me) and he thought from the look and listen that it was running a little lean if anything. I have since had the car running on the open road with the mixture meter running and it is just that -it stays mainly on the first two LED's and there are aout 9-10 of them- the first two indicate a lean mixture.

    So I've booked it in - I'll let you know how I get on!

    Cheers Ben

  11. #11
    Fellow Frogger!
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    Umm,
    just found all the specs for the jets in the carbs, amazing what you can find when you have a clean up!

    It has;
    * 34mm chokes
    * 777.2 emulsion tubes
    * 135 main jets
    * 200 air correctors
    * 7850.2 idle jets

    The webpage that I was using said that for a modified Pinto on twin 40's it should have;

    * 34mm chokes
    * 145 main jets
    * 7772.6 emulsions
    * 180 air correctors
    * 7850.2 idle jets
    * 40 pump jets???
    * 7848.1 aux vents (have no idea what this is though?!)

    Thus I figured that with the slightly modified 1647cc motor I wouldn't be too far off- anyway at least now I have the numbers to give to the tuner.

    Ben

  12. #12
    Fellow Frogger!
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    Sorry that should have read 7772.1 emulsion tubes not 777.2!

    Cheers Ben

  13. #13
    Fellow Frogger!
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    Hi all,
    thought you might like to know the result.

    He found a faulty coil, crap in the carb filters, altered the timing and set the points. Checked all the float levels, jets and chokes nad then ran it on the dyno. Then he altered the emulsion tube settings one level to 7772.1 adn it ran up clean as on the dyno with around anothre 3-4 kw.

    Now the disappointing part- it had a peak power output of 52kw!! So at the wheels factoring in a 33% drivetrain loss for FWD- it comes to around 93hp. Yet in the manuals it was s'posed to make 104hp (code 843 motor) and I would have thought the carbs would have added another 20hp- perhaps a tad too ambitious. I was feeling rather glum until he mentioned that hsi RS1600 escort(with a single downdraught weber) has 42kw at the treads....

    Do these figures sound about right- it doesn't really worry me- as it goes well- and at least it had more than that Escort!!

    Cheers Ben

  14. #14
    Fellow Frogger!
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    Ben,

    Don't worry, that's a fine wheel horsepower figure. Yes, it means your are probably producing ninety something REAL horsepower at the flywheel, but this is equivalent to over 100 "manufacturer" horsepower (i.e. the numbers you see quoted by manufacturers). Very few cars ever have the same REAL horsepower level as their "manufacturer" horsepower level. Very few factory standard "130hp" Pug 205 1.9 litre GTI's make more than 120-125 REAL horsepower.

    Also I think the 104hp motor is 104 SAE horsepower. I think the DIN "manufacturer" horsepower figure is something like 95hp (i.e. maybe 85 REAL horsepower), so you've probably gained 10% over stock by adding the side draught carbs (you've now got as much REAL horsepower as the "manufacturer" DIN horsepower figure).

    Dave

    <small>[ 16 July 2002, 07:50 PM: Message edited by: fiveohs ]</small>

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