Slo-MTX4

iTrader: (1)

Hace you timed a Ielasi GP9 or GP9R?

Roelof

No, havn't one seen yet. I have seen a VS05 which is 2104 based. It is just an 2104 with a 2 degee wider crankshaft opening.

To be honest, I do not think the Ielasi will be far off from other 2104 based engines.

invrtd

iTrader: (29)

Still wondering if anyone has tried one in a GT since it's a 5 port?
Also wondering for mileage/runtime is a 2115 or 2069 better?

Roelof

As I did mention before it would not surprise me that the 5 port R21 is the same as the GT but olny with a different head and carburator, its timings are in between the onroad and offroad models. As I have seen people using real onroad engines but also buggy engines in a GT it will work for sure.

invrtd

iTrader: (29)

I was thinking the same thing. I may just order a piston/rod/sleeve kit for R21 and put it in my R2103 once it's worn out. I have several offroad OS motors so I can get the head and carb off of to test in GT.

Roelof

You can always rotate the carburator but then the idle screw can be on a difficult spot.

wichitafc98

iTrader: (47)

the r21 doesn't have a much torque as the gt engine. The gt cars are heavier than the 1/8 onroad cars

rc_hydro

I've measured an R1 5 port GT engine;
exhaust port = 184 degrees
transfer ports = 126 degrees
29 degrees blow-down.

• Chrome was still present in top of all liner ports and the piston did not appear to have any signs of modification via decking, and no liner shim was present.
• The exhaust port plus sub exhaust ports width was the full width of the bore, a lot of overlap to transfer ports.
• No sub port induction at TDC, port closed.
• Crank 220 duration, closing at 70. Note - The crankshaft (DLC coated) open and close sides had been ground upon exposing steel prior to me receiving this engine so cant say if its OS timing or aftermarket. I suspect the latter.
• Bowl volume in head = 0.15cc, angled squish, dished piston.

I have not yet measured a 2104 to compare, but figured someone else may have and can use my numbers as a reference. I have measured NR Mito GT5/17 and Mephisto GT5 also, they both have higher transfer and exhaust port numbers.

As you can see by the numbers above, its not as low timed as a buggy engine but not as high strung as many on road engines. 184 degrees exhaust with 29 blow-down, coupled with the bowl volume all point to being built for more torque - which makes sense for a 3.5kg GT.

Roelof

So to my measuring language the exhausst is at 92 degrees (2 degree higher than the 5-port R21 I have neasured), a same transfer of 63 and the total opening of 220 seems the same as with the 5 port onroad R21 but shifted 5 degrees like the XZ-B in my list.

Regarding the measured numbers by rc_hydro the exhaust of the GT is 2 degree higher together with the same transfer and the same crank window but shifted for a better RPM range/response I would say the 5-port onroad R21 has more torque although it will not differ much.
I wonder how you did come to that statement

invrtd

iTrader: (29)

If the crank is showing silver color, then it might have had the timing adjusted. I am not home to pull any of the cranks from my DLC coated OS engines. Figuring $175 for R21 piston/rod/sleeve kit vs $450 for new GT motor. Only thing I think the new GT motor has the newest carb that is supposed to get a little better run time? But that is all on trigger pull and exhaust pipe and header too. I am still not seeing how anyone is doing 7 min on a GT motor according to IFMAR GT regs for engines. Did they enforce that at the 2020 GT worlds?

Byronf1

I tried R21 on my GT, and works really nice, has good torque and top speed, the runtime I am getting 7min, but my pipe and header is not helping with that,

Roelof

As I would expect. Makes me even wonder more on what base wichitafc98 made his statement.

rc_hydro

Hi ByronF1,
Which pipe and header you are running on your R21 / SRX8TQ?
I run same chassis & I've so far tested the R21 with Hipex S48 manifold and 2108 pipe, 19/24 pinions and 58/63 spurs. Felt very strong low end, and very smooth transition but not a super high rpm. I didn't do a timed run to check fuel consumption. I'd dare say this combo will do 7 minutes comfortably. I'm planning to try the NR 41032 manifold and different pipes on it soon.

invrtd

iTrader: (29)

7 min is unheard of where I race. I am running 032 header and 9886 and only getting about 4:45. And most other racers are only getting about 5min. But I am running on a large track. I know the 9886 is a gas hog. Will have to do some testing with 2015 when I get back home with maybe an OS 70mm header. Will also test OS 70mm header with 2060 since I have that pipe too. I am running HB GT with OS XZ-b engine right now. Will be moving to GT specific engine when I get back and thinking the R21 is a good option since I don't run GT all the time. I did read on OS web page the newest OS GT engine got the new 22E carb that is advertised to get better run time.

rc_hydro

Long track with sustained full throttle use and a high rpm setup will use more fuel than tracks with shorter straights. Perhaps look into changing your gear ratios to smaller spurs if you can when you test with the 2060 and OS header. It will shift the power band lower than the 41032 / 9886 combo. (kinder on the rod too!). This will make more difference to fuel economy than the carb. The engine and pipe dictate how much fuel it needs.