Good morning guys question running a 9901 /40121 on my 4btt and its Ok but just don't seem to have the right power I'm looking for its good but not perfect what pipe/manifold combo would you guys suggest I'm running it in a MBX 7r and on a big/medium size track.

I mean what are you looking for? More bottom? More top? What carb insert are you running?

All arounds better performance id say I'm just asking what are the suggested pipes and manifolds guys are using also a bit more fuel milage running 6.5 insert its one of the pre broken in engines as well it runs good i guess I'm looking for a bit more top end as it seems to not be peaking out like my p5s do with the 9901

I mean you a trying to make a much tamer 4 port run like a hotter 5 port.

id personally run a p5 with a 9886/41021 for a quicker engine. if you were stuck on novarossi anyways lol

you could try a 9886 pipe on your 4btts

First try the 8mm venturi, if that doesn't do it try a 41001 manifold with the 9901.

6.5 insert and a 41021 manifold...no wonder you have no top end..... swap the manifold to a 41001 or a 41033..then go to a 8 mm inserts, as well remove the brass shim from under the button...will be like a whole new engine

Thanks also I know fuel milage depends a lot on throttle finger but with the 8 mm venturi won't that hinder fuel milage as well? what other pipe could i try with that manifold ?

Well do you want power or mileage. You can't really have both with a 4 port imo. Like I said earlier. The p5 is very punchy whereas a 4btts was specifically designed to be mellowed and smooth so it will not feel the same.

Manifold is more critical then pipe.... the 41021 is quite long and because of that it doesn't work well on the top end ... The bigger inserts do use a little more fuel, but not so much that it cause you issues, especially if your finding issues with your current lack of top end...

I like the engine it just seems to be held back on top end with the current pipe manifold set up ill try manifold and insert best way i can explain it wasn't the tune the tune was good it just seemed like it wasn't peaking like it should on the front straight if that makes sense

Shorter the header = better top end

Longer header = better bitten end grunt

That should help you find the middle of the road. I agree header is more important than pipe.

It is the combo you run, 9901/41021 will only give good bottom n mid range, imo no top end. 2096/41021 give good bottom n top end. I personally will only run 41033/2096 on 4btt,or efra 2058 for better overall power

086 9886 or 2096 I don't care what drake says I do not like the 9901 with any of my header choices on my btt. 2096 with 021 header is smooth and will easily do ten minute pits,086 or 9886 you will loose runtime but gain an equal or greater amount of power

Just as a heads up Amain is having a sale on the new P5XLT-16!

Good Afternoon,

I have a Rex Legend 7 and noticed recently I've been getting a lot of flame outs and the engine wouldn't hold a tune. It felt like the pinch is completely gone and probably needs a pinch but wanted to confirm this is worth pinching or just get a new engine. here are some internal pics, also wondering why there is a golden hey on all the internals and if the piston is still good, it's slightly rough.

https://lh6.googleusercontent.com/-C...821_095008.jpg

https://lh4.googleusercontent.com/-2...821_095028.jpg

https://lh4.googleusercontent.com/-O...821_095031.jpg

https://lh4.googleusercontent.com/-i...821_095039.jpg