The GRP's, both the 21 and 28, have had tuning issues. On some that were returned there was air leaking from the exhaust port going around to the side bypass chamber on the sleeve. Low RPM tuning provided frustrating results, newer versions that had the smaller restrictors seem better - 'read': better tolerance on the maching of the block.
P3's would offen advance the timing too much but would definitely improve performance. The stock plugs are simply too cold for the engine. P4's were a better match, however the ease of tuning with a standard head button AKA GO or Novarossi, made the engine run like a mid range Novarossi - which is what it basically is.
Although our local track has been great in supporting them, I'm going back to the diehard long live Novarossi's. Even Truhe and Drake had inconsintent Flameouts which are not as frequent now. In another year I think Manufacturing will have tighter tolerances now that initial demand has weaned a bit.

I'm not meaning to start an arguement, just stating my experience.

I run OS P3 have never (knock on wood) flamed out during a race unless my tune was off because f'd around with the needles more than necessary. My engine holds a tune very well now that I have found it's sweet spot. Like previously mentioned you only need to adjust LSN an hour or two.

Spdjunky you have pm....not flaming ya just a question

Hey guys, I have tried most of you guys telling me about glow plugs, tuning and all that... it was ALL WRONG!!!

Adam Drake told me that it was supposed to be running at 250-267 temp after break in. for a few tanks about half gallons, it will start to cool down better. Also, OS p4 glow plugs does not work on this mill at all. it lost alot of top end power. So use C4 plugs from GRP or even PLUS 4. I ran at JBRL race over the weekend, it was way so smooth and wow great overall performance.

So I am not baggin or anything on some guys who were trying. But I want to thanks and let you all know this. I am looking foward to keep running this mill, i love it. after running V-Specs.. But I have to admit that V-Spec is a little ROUGH at bottom end. The GRP mill is very fast throttle response.

Oh yeah I want to add this, I broke in the motor idling 4 tanks, and no more than half throttle about 3-4 more tanks going straight with big turns oval like laps.

i am not at all certain of what you just said, but i think you are saying that Adam told you that this motor is to run at 250+, and that is OK/Normal? BUT will cool down "some" after break in?

I find that VERY hard to believe. I have been in pit lane when Adam has brought his car in after a main, and his came in at 190, and was telling his pit guy that it seemed to be lean bogging a bit.

I dont know. Just seems odd to me. I will stick with the temps, mine seems to be running good at. That is normally about 180-190, occasionally hitting the 202 mark, if running low on fuel. That is just MY experience.

As for glow plugs, the GRP 6 is just too cold. The GRP 4 is a good one, and the OS P4 has been working well for me. I have yet to try the P3, because I have not had any issues with the P4 yet.

I guess, to each thier own. I dont know that anyone is "wrong". They are saying what is working for them. If someone else has the hot ticket, and you feel safe with that, then I say "run it"! Let us know how it all works out.

depends on what temp gun you use, if you are using exergen it will show up around 190 but is realisticly its running 240, which is were this motor likes to run

I do use the Exergen gauge. Maybe that is the difference? Which temp guage is recommended to get the realistic temp of this, or any engine?

I spent quit a bit of $$ on this gauge, so if there is a more accurate gauge, and hopefully cheaper, I may want to switch.

Personally, I dont tune just to temp. I do like to have something that is as accurate as can be though.

The exergen gauge is excellent, probably the best. The only problem is that many others do read 10-40 degrees higher.

I agree...when temped with anExergen, it will read 190-210 or so....any of the other temp guns could very well be showing much lower or much higher....my Raytek (a good temp gun) would show about 230 or so at the same time my buddy's Exergen showed 195...also, GRP 4 plugs are the ones I used with no issues. This mill definately runs cooler then other mills..kind of like a Radical (they ran cool as well)

the problem with the exergen on the grp is that it dosent get down the hole at all, the exergen is the best gun you can buy, but the grp hole is small, when i use any other style of temp gun on my engine it comes up with 240, if i use the exergen on the block right under the head its 240 also, its just the design of the head that dosent allow it to get accurate reading

funny how my $20 duratrax or what ever brand it is consistently temps mine at 185 to 190 when I'm on a good tune...

i agree. All guns are not created equal, but that is another thread.

I guess the bottom line is, the GRP is an awsome running engine (IMHO), no matter what gauge your using as a reference. I think we all agree that the GRP6 plug is too cold (in most cases), and that the GR4 (or some other hotter type plug) works better, and that everyone has thier own idea, as to what works best for them.

Well, I wasnt even trying to be rude and say wrong like it was personal. Just that I was trying almost every ways that everybody else recommened in here until after Adam finally said something to my pit guy about the mill tuning. My pit guy just had it setup wrong, did what other guy told me in the PM.. and it didnt work, was way way too fat, ran at 170.. the odd thing is when after i broke it in and had it run on ground after 4 tanks idle breakin.. it ran at 210 about.. then on the track next day it shows it runs at 160-170.. and was really fat. went lean, at 210 it still runs like its fat.. and it did sounded fat.. so adam said to go for 250-260.. then it ran really good, we didnt change the tuning until my B main, it ran at 210.

Yep i think my binding prob could have been the fuel, but it could have been an adjustment i made also.

I put a little larger ball cup on the ball link witch allowed it to move a little freer than the losi one and also got the engine up to temp where it would bind then adjusted the linkage while it was hot and now its bind free, still binds a little at wide open, but allot better. But also changed fuel at the same time so that could be it also.

In terms of plugs, my C4 that i used for for break in has died at the 4ltr mark, is that good or bad?

Dont have any more GRP plugs atm so im having to use OS's. Put a P3 in it witch lasted 2 tanks then a OS hot plug witch is on its way out, they seem to be dieing under rich conditions with this engine, they seem to be alright if the engine is running under high performance lean conditions.

Also stuck a Jp-3 pipe on the engine and wow was the stock 2053 suffocating this engine, it breaths allot better now.