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This gorgeous Gentian Blue GT4 was sent to DeMan Motorsport at 1,100 miles in 2021. The full 4.5 liter engine conversion was performed with a total of 565 HP as the result. Much has been said / written about this extraordinary and expensive process. In a word it's... INCREDIBLE! A complete brute and sounds like a Porsche Messerschmitt.
The vehicle was originally commissioned with cat-less headers. Upon obtaining the vehicle last year I immediately spent $6,500 installing new SOUL headers with German made HJS catalytic converters. The emissions system is happy and compliant. I also had Porsche of Chesterfield Valley perform a service on the vehicle using the correct Motul 8200 oil specified by Rick DeMan. I changed the spark plugs with OEM parts at the same time following the Porsche 4 year recommendation. A new AGM battery was installed in the last month and the car sits on a battery tender in my garage.
A very well equipped GT4 it features a PDK transmission, 18-way Sport Seats Plus, Bose, LED PDLS headlights, Leather & Race Tex Interior w/ Silver Stiching, and numerous other options listed.
The car is in immaculate condition with zero issues. It has never been on track although easily could with some DOT 4 brake fluid and an appropriate track alignment.
The vehicle is priced to sell. Its current cost is a fraction of what it would take to replicate and frankly is close to what an extremely low mileage stock GT4 without the $50k+ spent on the beast of an engine. With respect, please do not contact me with wholesale offers.
I welcome comments other than in regards to things that can’t (not would I…) change, i.e. transmission choice. A few of the rabid manual-only crowd seem intent on running posts in to an argumentative ditch. Please not here. For what it’s worth the PDK is utter magic with this engine.
Last edited by 5senna5; Apr 20, 2026 at 12:02 PM.
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Hi, thanks! Yes its a LOT of car for the money.
It is currently running the 98 octane tune that DeMan was installing in 2021. I contacted Rick when I got the vehicle at 1,800 miles to make sure and he confirmed. I also contacted M-Engineering to see if it had been remote tuned to 91 or 93 octane, which it hadn't. I intially thought it was a given that I would change it over however, it runs SO well that adding the BOOSTane Professional octane boost is literally zero trouble. A 32oz can costs $33, a pack of 12 6oz glass bottles off Amazon is $11. One can fills over six bottles and each (5oz filled) bottle changes a full tank of 15 gallons from 93 octane to 98 octane. It's not a daily driver of course so after doing it a few times I lost all interest in spending thousands of dollars to simply not have to. Adding one 5oz bottle of BOOSTane Professional to your DeMan 4.5 engine's gas tank before fill-up is the definition of a First-World-Problem.
I see you put catted headers on -- decatting is a deliberate choice for running this high of a concentration of MMT. did Soul have any opinions on the matter?
related, how are the plugs and o2 sensors faring? the maintenance interval for the plugs is going to be drastically reduced due to the MMT deposition.
I see you put catted headers on -- decatting is a deliberate choice for running this high of a concentration of MMT. did Soul have any opinions on the matter?
related, how are the plugs and o2 sensors faring? the maintenance interval for the plugs is going to be drastically reduced due to the MMT deposition.
I ran that by Rick, the Soul headers use the same (crazy expensive) 200 cell HJS German made converters that would have been installed during the original build had the customer opted to do so. The tune is the same 98 octane version with our without. The short answer is no, the 98 tune has no detrimental effect on the catted headers. The vehicle passes all readiness monitors for emissions with zero codes or out of range performance. Rick also specified that the maintenance schedule does not vary from a stock GT4 other than the use of Motul 8200 oil. Using an excessive amount of octane booster to bring it up way over 98 could cause plug fowling, however 98 octane is readily available in Europe at the pump and it's simply not an issue with this engine. I changed the plugs due to the 4 year interval specified by Porsche to prevent seizing in the block.
When you say 98 octane, do you mean 98RON ? Or 98 AKI? Mentioning Europe implies RON. 98RON is like 93AKI. We use the AKI scale in the US.
How'd the plugs look when you replaced them? Was the orange buildup there, and was it velvety?
No, I'm not speaking in RON, the highest at the pump in Europe is 102 with 100 widely available, the US AKI equivalent is 97-98
The plugs looked perfect when I took them out. This engine is running exactly as it was designed and intended to by DeMan Motorsports.
There are zero issues with it, the plugs, the converters, the O2 sensors, converter efficiency, etc....
Any idea if the car can be tuned for our Ca. 91 octane? Would obviously need to run an octane booster as well.
Yes, absolutely it can be tuned to run on 91 without octane boost. Both M-Engineering and COBB via Rick DeMan can make that happen. Matt Farah of the YouTube channel The Smoking Tire has a DeMan 4.5 Spyder that was running the same 98 octane tune as mine. (In CA) He has a few videos covering his later switch to the M-Engineering 91 octane tune for California gas.
The engine conversion was done 4.5 years ago, only 1,300 miles have been put on since, 600 from my ownership. Porsche themselves don’t warranty new cars beyond 4 years. Any warranty that the original owner had on the 4.5 engine is over. These conversions are not sold on warranty coverage strength. The engine is tremendously over-built for street use. It’d be about the last thing I’d have any concern with.
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