Menu toggle

4.25L GT4 Upgrade

Author
ralphmusic
PCGB Member
  • Total Posts : 14221
  • Joined: 2009/03/06 20:11:58
  • Status: online
ralphmusic PCGB Member
2019/04/12 08:53:58 (permalink)

4.25L GT4 Upgrade

Shamelessly copied from BGB's post on rennlist
 
QUOTE:
After several setbacks and a shipping mishap that sidelined us yet another month, the strongest Cayman/Boxster engine conversion we have ever executed is now complete. We owe an enormous amount of thanks to the car's owner for his patience. We have never ever ever ever had a car in our shop this for as long as this car has been here. We had a miscue with our machine shop and then UPS dropped something and then it seemed like 1 thing after another when it came to getting our parts in hand. We both began to wonder if this car would ever again be released from solitary confinement! HOWEVER, since apparently good things come to those who wait, we now have this to show for it.

We find it best to do a pre and post dyno analysis because every dyno seems to always read differently and we have to see the gains for ourselves before we release the cars to the customer. I have been going to the dyno more and more frequently with cars with standard bolt-ons because we have seen claims that you can get almost 450hp from a Cayman GT4 with an intake, exhaust and ECU upgrade but we have never been able to reproduce those numbers ourselves when we dyno them. Of the dozen GT4s we have dyno'd with different iterations of exhaust and tune combos from different tuners, they all dyno within 5 hp at or near the 365rwhp number on our Dynojet in town and this car was no different.

The blue line is how the car showed up on our doorstep with aftermarket exhaust, intake and ECU upgrades that were done prior to its arrival, none of which we were involved in selling to the owner. The red line is from today.The car is running 91 octane. The before and after peaks gains are + 80rwhp and + 40 rwlb/ft but at 7K RPM where the Cayman intake begins to starve for air, the numbers are +95rwhp and + 81rwlb/ft. These motors need to breathe and the gains are attributed to the addition of the stroke increase to 4.0L, a further bore increase to 4.25L, the addition of the X51 Power Kit with additional CNC porting and upgrading to the Cargraphic catless race manifold.

The owner was tired of the senseless GT3 bullying that occurs on race tracks across North America and we feel that we have finally leveled the playing field! Per the same 12.5% drivetrain loss number that i have used for the last 15 years, this equates to 506 hp and 383 lb/ft at the crank. At the moment the engine is still relatively new and we therefore did not opt to spin the car over 7600 RPM. When it's broken in and in the hands of the owner, it will be pushed further.
END QUOTE
 


Modified Reg - Asst RS
R15 Devon
12 - RSRTC

3 Replies Related Threads

    Brian_Innes
    PCGB Member
    • Total Posts : 1285
    • Joined: 2012/06/15 17:15:44
    • Status: offline
    Brian_Innes PCGB Member
    Re: 4.25L GT4 Upgrade 2019/04/12 16:16:50 (permalink)
    Ralph,
     
    Interesting.
     
    Impressive power increase.
     
    Why 91 Octane fuel? I wouldn't run a lawn mower on that.
     
    Has the USA not discovered Shell V-Power 99 Ron yet?
     
    Brian

    Nairnshire,
    Highlands
    Previous:
    2007 Cayman 987.1 2.7 Manual.
    2010 Cayman S 987.2 Manual
    2012 Cayman R Manual
    2019 718 Cayman S PDK
    Current:
    2015 Abarth 595 Competizione 180bhp Manual
    718 Cayman GTS PDK

    Motorhead
    PCGB Member
    • Total Posts : 4305
    • Joined: 2011/04/20 12:13:14
    • Status: offline
    Motorhead PCGB Member
    Re: 4.25L GT4 Upgrade 2019/04/12 17:36:10 (permalink)
    Brian,
     
    The US uses a different octane rating system from Europe and most of the rest of the world. We use Research Octane Rating (RON) and Motor Octane Rating (MON) is another more rigourous test method which gives a lower octane number than RON.
     
    The US uses a Pump Octane Number (PON) which is the average of RON and MON - all very complicated..!
     
    98/100 RON equates roughly to 93 PON.
     
    Jeff

    987.2 Cayman S
    North Beds (R10 & R24)
    Brian_Innes
    PCGB Member
    • Total Posts : 1285
    • Joined: 2012/06/15 17:15:44
    • Status: offline
    Brian_Innes PCGB Member
    Re: 4.25L GT4 Upgrade 2019/04/12 18:00:55 (permalink)
    Thanks for the insight on the octane rating Jeff.
     
    Even at my age I'm still learning something new 
     
    Brian
     
     
     
     

    Nairnshire,
    Highlands
    Previous:
    2007 Cayman 987.1 2.7 Manual.
    2010 Cayman S 987.2 Manual
    2012 Cayman R Manual
    2019 718 Cayman S PDK
    Current:
    2015 Abarth 595 Competizione 180bhp Manual
    718 Cayman GTS PDK

    Jump to:

    Posts made and opinions expressed are those of the individual forum members

    Use of the Forum is subject to the Terms and Conditions

    Disclaimer

    The opinions expressed on this site are not necessarily those of the Club, who shall have no liability in respect of them or the accuracy of the content. The Club assumes no responsibility for any effects arising from errors or omissions.

    Porsche Club Great Britain gives no warranties, guarantees or assurances and makes no representations or recommendations regarding any goods or services advertised on this site. It is the responsibility of visitors to satisfy themselves that goods and/or services supplied by any advertiser are bona fide and in no instance can the Porsche Club Great Britain be held responsible.

    When responding to advertisements please ensure that you satisfy yourself of any applicable call charges on numbers not prefixed by usual "landline" STD Codes. Information can be obtained from the operator or the white pages. Before giving out ANY information regarding cars, or any other items for sale, please satisfy yourself that any potential purchaser is bona fide.

    Directors of the Board of Porsche Club GB, Club Office Staff, Register Secretaries and Regional Organisers are often requested by Club members to provide information on matters connected with their cars and other matters referred to in the Club Rules. Such information, advice and assistance provided by such persons is given in good faith and is based on the personal experience and knowledge of the individual concerned.

    Neither Porsche Club GB, nor any of the aforementioned, shall be under any liability in respect of any such information, advice or assistance given to members. Members are advised to consult qualified specialists for information, advice and assistance on matters connected with their cars at all times.

    © 2020 APG vNext Commercial Version 4.6