When you click on links to various merchants on this site and make a purchase, this can result in this site earning a commission. Affiliate programs and affiliations include, but are not limited to, the eBay Partner Network.
Hi everybody,
I have been owning a 94 FD3S in JDM Type R trim since late 2015 and thought to introduce it here so you can be aware of how an FD can be tuned to run on an alternative fuel such as Liquid Petroleum Gas. The car as is at the moment is having an engine rebuild due to evidence of a failing water seal, and so I will be updating a build thread as an ongoing project with plans to put a few upgrades in once the engine block itself is restored.
So why have it run on gas? I knew about a relatively stock car that was converted early 2015 with an add-on LPG conversion kit that enabled the car to run with two fuel options, and it was done purely as an experiment to test whether there were any discernible benefits to running on this fuel. Critics would argue that from a performance standpoint, vaporised LPG that is injected from conventional vaporised sequential injection kits combust with less available joules of energy per cubic volume than liquid petrol. From a dyno reading there is certainly a difference in peak torque and having done a 4th gear pull on both types of fuel, the readings as shown below certainly reflects that trend:
When converted to torque at flywheel, you are looking at a peak torque difference of around 15ftlbs of torque short compared to petrol. Ignore the peak rpm by the way, the dyno reading is not really synced with the correct engine revs very well... And I understand the dip curve on transition is drastic to say the least, due mainly to boost creep at the primary turbo because of wide open exhaust to a stock waste gate. This will be rectified in the rebuild for sure.
Without a tuneable ECU, the fuel delivery and throttle response would also be less refined due to the temperature and pressure changes that the LPG ECU needs to compensate for which the normal petrol fuelling system does not need to recalculate. However, a custom ECU will be able to iron out the foibles and now the car does not feel any different to petrol power delivery throughout the rev range. Fuel pressure for LPG is regulated by a reducer which is fixed to the bulkhead left to the brake servo, and in a twins engine bay, makes the labyrinth of parts more like an amazon jungle of fuel pipes snaking on top of the stock intake piping.
Combustion temperatures will increase as LPG burns hotter than petrol, so heat extraction had to be modified from stock, with 50:50 meth and water injection kit from AEM installed to the stock elbow towards the throttle body mainly to cool the air charge down as much as possible before intake manifold.
Having a resonated mid pipe and ceramic coated down pipe certainly helps get the hot exhaust out before it havocs on intake temperatures, plus the turbos spool up quickly as a result.
Now to the benefits. So from a performance standpoint, the main benefits of LPG would be better emissions, cleaner burning of fuel, no contamination of engine oil and the safety net of higher octane rating. As LPG takes a lot of heat and ignition spark to combust, ignition timing can be advanced, and boost raised to quite appreciable levels provided you have the cooling support to keep pre ignition and knock in check. Carbon build up on the housings and rotors will also decrease to nominal levels and combined with water injection, is reduced even further.
From a financial standpoint, of course you are making over half the savings on fuel bills alone and in an RX7 rotary that is certainly a plus! Being dual fuel, it will start on petrol to warm the car up etc and means you can use the petrol tank should gas eventually run out. The LPG sequential injection will actually send fuel signals to the petrol injectors to run at a fuel duty of something like 15% to help cool and lubricate slightly the fuel mixture so it is useful to have some pre mixed petrol at the same time.
Since owning the car, I have added in a few bits aside from the 3 inch exhaust straight from turbo back. These include a new Re-Amemiya D-Spec shifter, extra wire grounding, under driving the alternator and water pump, brake booster stopper, and new brake lines, discs and pads. Everything else is pretty much stock otherwise. Power levels are at about as new levels with the mods mentioned. As for the rebuild, I will start a new thread if recommended. Meanwhile, enjoy a few more pictures of the car, thanks for your time guys.
Last edited by jeff_fohlen90; 04-28-17 at 09:23 PM.
Thanks, I heard you have an FB which you are installing a turbo to a 12A? My best advice is for you to consult those who have done such conversions from what is originally an NA design with suiting compression ratios and the like. 12As are actually more reliable in the long run over the turbo'd 13Bs due to less excess heat from a set of blowers.
My long term plan is to upgrade the vaporised system to a liquid one, for reduced fuel / air ratio complexities inherent with vaporised gas combustion and more power and efficiency as a result of the cooling effect by vaporising liquid in the intake as opposed to a gaseous substance.
When that can happen, I will post on a build thread to inform how that goes.
04-28-17, 06:14 PM
Welcome Silver FD
