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To date we have not done any remote work; i have a gentleman's agreement with the other shop in the country that does this conversion in the northeast to not sell the 4.0L bits and i am holding true to it. My X51 file alone has probably 100 hours in it making the car look and drive like stock as if it were born that way. Some of my greatest IP is in AJW45's X51 4.0L file and to this day DeMan and i still share informaiton. To be honest, one of the biggest reasons we are still around is because people send their cars to us from all over to have this done. If i partner up with a shop, my fear is that it will cannibalize our own business potential. It still happens...customers will call and take my quote with the parts list and take it to their local shop to have other work done and they try and pay me a consulting fee but i end up spending more time on the phone helping them and the customer always circles back and says "you would have charged me less to do the job better and i should have just come to you!" It's easy to tell when someone does this and tries to retrofit the X51 themselves because i get a call asking why their car doesn't run smoothly and then i say "sorry about your luck."
I use a very simple 12.5% drivetrain loss number to come up with 489 crank horsepower and 361 lb/ft. What's crazy is that my Dynojet runs always always always read lower than everyone else's because i'm in the hot Florida sun outside where it's humid and Dynojets are heart breakers that don't pump out ambiguously large numbers. The intake air temps on this run were 99F. This car on an indoor dyno in the northeast sucking 70F air running better gas would be another 15rwhp - 20rwhp stronger than this. The fact that it's running 91 octane and still made this number astonished me. I was expecting 420 and would have been happy with that but to get closer to 430 made my day!
That's the entire idea behind this conversion. Trying to put a 991 GT3 motor in this car would cost over $100K in electronics, engine work, bodywork, etc. Moving sump tanks and making things fit would be a nightmare.
I use a number of about 12.5%. So I think we are at 490/360 crank. I've used this same number since 2004 - i always dyno in 5th because it's as close to 1:1 as we can get with this transmission.
Agreed! I wanted to put the Clubsport up there to give it some perspective because it's a known entity. The Clubsport makes MAYBE 5rwhp more than a stock GT4 because at the end of the day, that's what it is. It's running stock filters, stock intake, stock exhaust (except for the slightly better flowing cats); the only difference is the race gas. It's awesome when you chime in because you always support this product because you have one and you love it. I can market all day long but there's nothing better than customer testimonial. Rick and I share so much information - you're driving the same thing we are dynoing. I'm glad you're loving it.
I think that's the thing that really impressed me. We could make a lot more power if we weren't running 91 octane but it does me no good to tune this car even on 93 and send it back to LA like that. This car was always about 5 - 7 rwhp less than the others because i had to literally go to the pump and put 91 in it which i never ever do. This car on 98 octane would be insane, especially without the humidity. No wonder the owner loves it; i was hesitant that he would be imrpessed because he also owns a turbo McLaren but he loves the high revving NA motor. The data though is just as you said...peak vs. peak is substantial but because of how much power the stock GT4 intake bits lose at 7K RPM, over 7K there's a massive difference. 62lb/ft of torque at 7300 RPM is ridiculous in my opinion. These motors are easy to make power with but getting torque from them has been like getting blood from a stone; X51 + 4.0L is awesome at achieving this!
Yes. The car came back for some intake work to try and achieve some power gains and I made the decision to send the X51 heads out to my engine builder to have them opened up just like we did on our 2013 race motors. While the X51 heads are advertised as already being CNC ported, we did more intake porting and substantial exhaust porting to match everything up. I think that the porting was worth about 15rwhp. The car was originally a Boxster Spyder that showed up here to have the X51 kit installed (intake manifold, cams and heads) and the 4.0L bits (crank, rods and pistons). It went to California for 2 years and then came back for the porting and to have some ECU work done. I wanted to look at the engine and i wanted to dyno it to make sure it was a strong as it was the day it left and it was but now it's even stronger.
Hi John (@BGB Motorsports)
i have just entered a purchase agreement for a 4.0L X51 (from a German friend who is now getting the 4.5L from the states) for my 981 spyder, it will come in in march 21, so I am reading this thread and all your other info for inspiration and pre-ownership happiness Thanks for sharing your insights and information - I always recommend you and Rick to any fellow fb group/forum members that live in the states.
i wanted to get your professional opinion on my new/used motor (it comes from a 991.1 gts with x51, just keeping the x51 heads, using a finely balanced 991 s crankshaft and increasing the stroke so it has 3998 ccm (4.0L) - bolt ons will be race/sport headers with 100cell HJS cats custom build from a shop that is building OE quality headers for racecars, throttle body from gt3, 991s plenum, PSE exhaust + fabspeed x-pipe tips. the ECU mapping/tune will be done more in favor of low/mid-range torque - i am estimating 450-460 HP at the crank (conservatively i hope). As it comes into a 981 Spyder I am not getting a lightweight flywheel - car will be doing 3 DEs a year and lots of b-roads/alpine roads.
I have some questions in regards to the motor:
1) am I missing much from not having the 718 CS intake?
2) the 718 CS intake seems to be the more popular choice than keeping the x51 intake bits (as they need to be programmed) - what is your opinion on that?
3) taking this well running motor to 4.25L or so would be a good choice or risky? if good choice what would be the way to go about it? or stay at 4.0L and do additional head porting?
4) am I missing any other bolt-ons or other mods for a road focused 981 Spyder?
5) using 93 Oct (US norm) gas - what do you believe could be a good HP result?
of course the same questions go out to the other forum members as well - especially the 4.0, 4.25 and 4.5L owners.
Last edited by Martin Anders; 11-13-2020 at 10:16 AM.
Reason: clarity + tagging John
Sorry to intrude but my question to you is why go through the trouble of cracking the engine to convert to 4.0L when you can make it worth it and do 4.5L?
Sorry to intrude but my question to you is why go through the trouble of cracking the engine to convert to 4.0L when you can make it worth it and do 4.5L?
all good - i am getting a good deal on the already completed 4.0 x51 from a friend who is now getting the 4.5l - so most likely no cracking it open again.
all good - i am getting a good deal on the already completed 4.0 x51 from a friend who is now getting the 4.5l - so most likely no cracking it open again.
5) being able to use 98/100 octane fuel all over Germany and 95 when going to Italy - what do you think a realistic HP goal should be?
Just to lend clarity on octane—North America uses AKI aka (RON+MON)/2 for our octane rating, so when US/Canadian folks here talk about 91, 93, and 98 those are equivalent—respectively—to approx. 96, 98, and 102 in RON numbers. I'm sure everyone here is more than well versed, but I figured I'd drop that in for our UK & continental Europe friends that might be flummoxed by our weird fuel ratings.
Sorry to intrude but my question to you is why go through the trouble of cracking the engine to convert to 4.0L when you can make it worth it and do 4.5L?
Follow-up.. why not go lighter on flywheel to make it more lively?
4.5l actually makes the ltfw more friendly thanks to the extras low end grunt. Very streetable.
would love to have a 4.5l one day - for now 4.0l x51 is what i can realistically afford (if i would start from scratch i would do 4.5l or just bolt ons actually due to budget)
lwfw i am skipping for the spyder - for gt4 would put it in - as more race car and less cruiser/road racer (porsche only puts the lwfw in the RS and option only for R afaik)
Just to lend clarity on octane—North America uses AKI aka (RON+MON)/2 for our octane rating, so when US/Canadian folks here talk about 91, 93, and 98 those are equivalent—respectively—to approx. 96, 98, and 102 in RON numbers. I'm sure everyone here is more than well versed, but I figured I'd drop that in for our UK & continental Europe friends that might be flummoxed by our weird fuel ratings.
thank you - i actually did not know - no i do - thank you for the education we get 93us/98eu at almost every fuel station, and 98/102 at 70% of stations - with the right tune the difference could be 5% more HP or less?
guys, a friend is looking for a gt4 engine case / cylinder block / crank case as a spare part for an engine conversion - ideally from a seller in the US. 9A110193883 is the part number - anybody selling one or know how to get one? @BGB Motorsports maybe?
10-01-2020, 12:24 PM
Thanks for sharing your insights and information - I always recommend you and Rick to any fellow fb group/forum members that live in the states.
