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Daytona engine rebuild - how many HPs would you expect?

Discussion in 'Vintage (thru 365 GTC4)' started by Italian Tuneup, May 6, 2020.

  1. Italian Tuneup

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    My Daytona engine is in the process of a complete rebuild. At the end it will be bench tested.

    Everything has been made to original specification. No high compression pistons or hotter cams.

    It´s a euro spec engine.

    How many HPs would you expect?
     
  2. Smiles

    Smiles Moderator
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    9.3:1 compression ratio?

    No more than 350 bhp.

    Matt
     
  3. Italian Tuneup

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    Yes standard compression but with forged pistons and new rods.
     
  4. Smiles

    Smiles Moderator
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    Neither gets you more horsepower.

    Matt
     
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  5. gcalex

    gcalex Karting

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    If we are talking about a bench dyno, I've seen a curve (claimed "stock", but possibly jetted in some way) that went into the 370 range, but dynos are notoriously variable, so I would not get too hung-up on the exact figure.

    Did they dyno the engine before they tore it apart? That comparison would be the real thing that would be telling..

    If not, perhaps they have some curves of other engines that they have done, so that you could see that things were at least typical for their shop.
     
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  6. Smiles

    Smiles Moderator
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    Although there was a reason for rebuilding the thing.

    Matt
     
  7. gcalex

    gcalex Karting

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    Well, yes, if it had failed in some big way, then yeah, "before" might not be so interesting... :)
     
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  8. Italian Tuneup

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    Yes they have a bench dyno with a separate control room (don´t know the correct english term for this setup)

    They did and do a lot of vintage Ferrari engines and will not rebuild your engine without testing on a dyno. So they have a lot of curves from stock and race Ferrari engines.
     
  9. TTR

    TTR Formula 3
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    Stefan, IIRC, pre-rebuild dyno testing was not a reasonable option in your case...

    ... besides, the HP/Torque will be whatever it is and probably sufficient.

    P.S. Would you mind sending me an email or PM about the discovery of "the cause" ?
     
  10. Edward 96GTS

    Edward 96GTS F1 Rookie
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    be sure to dyno with air filter box and air filter box off. there will be a difference.
    also suggest testing with premium fuel and again with 100 or 110 octane racing fuel.
     
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  11. westextifosi

    westextifosi Karting
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    How much difference would you expect to see using 110 race gas given 9.3:1 compression?
     
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  12. Edward 96GTS

    Edward 96GTS F1 Rookie
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    its not the comp ratio that matters, its the ethanol vs non ethanol. here in cali we only have 91 octane w/ 10% ethanol and 100/110 octane race fuel(non ethanol) as options.
     
  13. Wheels1

    Wheels1 F1 Rookie
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    Do you really want them to rev the nuts of your newly rebuilt engine? sure test it and run it in a little but I would give it 500 miles or more before revving it so much.
     
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  14. westextifosi

    westextifosi Karting
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  15. Edward 96GTS

    Edward 96GTS F1 Rookie
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    every good engine shop dynos a fresh engine.
    if it breaks let it break while in their hands. also good way to check for leaks.
     
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  16. gcalex

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    As noted already, it is probably better to have the engine spin a bearing while still in the shop... :)

    But also, doing a few dyno-pulls is also the best way to check/tune the set-up of the engine, and it is a lot easier to do that sort of thing on a bench dyno, than on a rolling road dyno...
     
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  17. DWR46

    DWR46 Formula 3
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    This entire discussion may be fun to talk about, but it is absolutely useless. Like the saying "statistics don't lie, but statisticians do", dyno's give real numbers, but dyno operators lie all the time. If you tell me how much power you want your engine to make on the dyno, I can guarantee I can get the dyno to give you that number. It is all about the "correction factor". Every dyno should be calibrated before a motor is tested. The operator inputs the ambient temperature, engine air inlet temperature (carb air temp), fuel specific gravity, barometric pressure and other variables. All this data becomes the "correction factor" which converts the raw torque and bhp readings to a "standard" number. This number provides consistency and allows for the normal variances in weather, etc.

    By manipulating these numbers, a dyno operator can cause the results to vary widely and produce whatever power he desires. For example, we purchased a 275 Comp Car that had a "special" motor. The dyno sheets that accompanied the engine showed 404 bhp at 8,400 rpm. That would be a "very stout" 275. Upon careful examination of the dyno sheets, i noticed a "strange" correction factor was used. In specific, the barometric pressure was very low. Actually it was similar to that found in the eye of a hurricane. I checked with the airport in the town where the dyno was located and asked them for the pressure on the day of the dyno test and, you guessed it, the actual pressure was MUCH higher ( Milwaukee, WI doesn't have many hurricanes). When we pulled the engine and ran it on our dyno, it made 348 bhp, still a VERY STRONG 275, but no where close to the "reported" results.

    All the above illustrates is that dynos are only good for ONE THING, comparing and evaluating changes back-to-back. You can make a carburetion or cam timing change and then make another "pull" and the dyno will tell you instantly if the motor liked it or not. Obviously, testing fresh engines on the dyno is much easier then installing them in a car and then finding all the water and oil leaks.

    With the above said, absolute power and torque numbers can have some relevance IF the dyno operator always sets up the runs conservatively and accurately with his Correction Factor inputs. Still different dynos will give widely ranging results. Trying to compare engine outputs from different dynos is truly apples and oranges. It just cannot be done with any reliability.

    With all that said, my GUESS is the gentleman's Daytona motor should be considered a success if an conservative and correctly set up dyno shows anywhere from 320-350 bhp.

    As to breaking-in motors before dyno testing. We get the motor running, make initial timing and carburetion adjustments, and run the engine at varying rpm (up to about 3,500) for 30 minutes and then commence the power tests. We run as many tests (pulls) as required to test all the various ignition and fuel combinations as well as sometimes cam timing changes. These can be a few a 6-8 pulls with engines we are familiar with, to over 20 pulls ( you think you are going to wear out the motor on the dyno) with engines that we have a lot of variables to investigate. In EVERY case over the last 30 years, we have ended the day with at least 10-15% more power than we started, thanks to being able to evaluate each change quickly on the dyno.
     
  18. Ak Jim

    Ak Jim F1 Rookie
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    I could just imagine a pre-rebuild dyno test where the engine drops a sodium filled exhaust valve during the test.
     
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  19. TTR

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    No different than dropping one while driving.
    Well, come to think of it, actually dropping one while driving could result to more severe consequences.
     
  20. Terra

    Terra Formula 3
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    Isn't the stock compression ratio 8.8:1 ? (both for Euro version and US)
     
  21. TTR

    TTR Formula 3
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    I thought U.S. spec. is 8.8 and Euro 9.3, but having never actually measured either myself, can't say for sure. I did (and measured) one with 10.0.
     
  22. christc

    christc Karting

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    Pre not post...!
    Fully agree. I would not want to test an engine of unknown state before a rebuild on full load on a test bench. To many unknowns. Post rebuild any time. It is the best way to check if you succeeded in having a healthy engine.
     
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  23. TTR

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    Oops, perhaps I shouldn’t have revealed that, as it may give someone an idea that I actually don’t know anything about vintage cars, let alone 365 GTB/4s. :oops:
     
  24. Terra

    Terra Formula 3
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    I'm fairly certain US and Euro Daytona all have identical pistons (and compression ratios). Aside from the differences in emissions equipment and exhaust systems, I believe the only thing major mechanical difference are some slight changes to the carburation.
     
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  25. DWR46

    DWR46 Formula 3
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    Terra Is correct. Same pistons per Parts Catalog, and 8.8 to 1 compression per Factory Build Sheets.
     
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