Introducing our latest 9A1 GT4 based engine, the 4.5L GT4.

Check out more discussion on Rennlist:

Review from ajw45 on Rennlist

“The 4.5L is SAVAGE! I got a little time in the development car yesterday and it is one angry GT4! The car is the full package with everything – 4.5L, exhaust, lwfw, short gears, and who knows what else but it is far from stock. The mid-range hit going WOT totally caught me off guard, I cursed, then I held on, then I laughed my *** off after I pulled the next gear and could breathe again. I think if you crossed the old C63 NA AMG v8 with the GT3 engine you’d get something like this – aggressive, motorsporty, and silly fun. It’s not just the power, it’s also the power delivery. The combination of a lwfw, shorter gears, and the torque everywhere 4.5L makes for insane throttle response and a sharp smack of G forces when you get into the gas. Where the 3.8L makes power with an elastic surging kind of feel, this is shockingly immediate and abrupt, you get into the throttle and you don’t get pushed into the seat, you get smacked in the face. Sure the 4.5L car with that set-up and tune the new fastest most powerful GT4 but what really struck me is that car is just oozing character now. The engine is so dominant in the 4.5L that it changes the whole driving experience and turns the GT4 formula on it’s head really. Lots of torque and short gearing has given the GT4 a whole new ridiculous and hilariously hoonable side at street legal speeds like BMW M cars or modern muscle cars. I did 10k miles on my stock 3.8L, have 13k miles now on my 4L X51, test drove a stockish 4.25L, and this ***** out 4.5L development car is a whole new experience. I’ve always been skeptical about mods on performance NA engines but each and every evolution of mods to the 9A1 has really surprised and impressed me. My 4L x51 feels like a totally different engine from the stock 3.8L, stockish feel below 4k rpm but shreds from 5k-8k rpm. The 4.25L car felt like the 3.8L but, well, way bigger with massive mid-range torque like a small V8 for some serious shove. The 4.5L with X51 and GT3 bits feels like a whole different engine again, the torque curve feels flatter than both the 4L X51 and the 4.25L so there is just more power available everywhere and an exciting ramp to redline which comes so so much faster with more power and short gears. No doubt in my mind this is also a way more exciting and aggressive powertrain set-up than a stock 991.2 GT3 manual which is revvy and responsive but a little gutless and you need to ride the revs vs being able to drop the torque hammer of the 4.5L. Without sounding like too much of a fanboy, as exciting as the new 4L in the 718 is, I think the 9A1 in the 981 is still the engine to have. The 718 race cars are still racing the 3.8L, the new intake mods give it more power than the street 4L, and it is approved for racing in the 718 for the next few years with no plans to switch to the 4L. Given the next Boxtser/Cayman gen will be all electric or hybrid, the 4L will likely never get raced and we’ll never see a GT3 engine or any 500hp+ ICE in a Cayman from Porsche. On the other hand, the 3.8L 9A1 has been race tested and not only has there been a lot of effort put in developing and maintaining it by race teams, it still has another few years of continued development by race teams going forward in the 718 GT4. I think for anyone that’s found the GT4 engine a little lacking, this is going to bring more smiles and laughs than an upgrade to a 718 GT4.”

Below are a few pictures of the development process, pistons, intake adapters as well as some shinny engine hardware parts to drool over.