T5 aly with a 152 polini conversion.

[fastfrog]

Hi folks,
a new topic about my new project: fit a 61mm polini piston in a std aly barrel. Several arguments militate in doing this uncommon conversion:
-The gilardoni's is my favorite barrel of all. Top design, heavenly build and very powerfull when tuned. I think it's better than the ones made by malossi or pinasco (a giladorni too) and the awfull polini.
-Mmw head is avalable for the polini piston.
-65mm conversion looks risky because of the tapered transfer design. 61 mm bore leaves enough meat to keep it safe.
-nikasil relining for a 61 mm bore is still affordable.
-A perfect mild tuning for someone who just needs a fast, reliable and not everybody's engine....
- a 54 mm stroke crank for a std inlet, SI24 (maybe a"E" type to get more torque, T5 air filter, airbox pinasco.
- PEP3 pipe
-21/68 and standard gear ratio

This new engine is intended to replace my previous pinasco 172: a bit too powerfull and noisy....

Begining of the porting job:

[Jack221]

Did I miss something? How did the standard 200 project work out?

This ones looking like is coming on. What kind of rev range are you looking for with this one? Interested in your chosen crank inlet timing and transfer port durations. Are you re you going to get in the barrel and reshape the transfer port roofs or are they ok? Can't quite see in the pictures.

[fastfrog]

Oups! 200 is finished and reframed. Oliver's choice was 160/BE3/125 and 55/160 for the first kickstart yesterday. nice sound and fast throttle response....

for the T5 barrel transfer roof seem ok. But with 3mm less of wall thickness,auxiliary and boost post that both have very slopy roof, will need to be reshaped and a bit reprofiled.
A very mild timing indeed :125/180° and 125/55° for inlet timing. Knowing that it's 120/170° and 120/55° on a std engine.

[Jack221]

what max rpm you expecting from 125/180 on a T5 54mm? Are you putting the secondaries and boost back to the same height as the main transfers or something else? Any reason that you haven't cut the crank a little more? I would think 127/60 to start with.

[fastfrog]

Pmax at 7500 and revs till 8-9000 max.

Anyway I would prefer not to put a packer on. So I can't wait to take my timing with the 54mm crank in place. I said 125° but could be more. 10° or a bit more of overlap sounds ok to me. There is enough meat upon the crank pin to creat a real advanced crank even with an excentric pin. Anyway I don't want to gain timing ATDC. Not interesting at all....

[fastfrog]

...Are you putting the secondaries and boost back to the same height as the main transfers or something else?...

yes I'll need to raise them quite a lot. I'll see If I leave boost port a bit lower....

[Jack221]

yes I'll need to raise them quite a lot. I'll see If I leave boost port a bit lower....

Why would you leave the boost port lower on a T5? What you thinking?

[fastfrog]

Because boost port has a straight stream where main and auxiliary ports are reverse streams. They cover a longer distance before reverve pulse from exhaust hit them back. Boost port stream is sooner "knocking" at exhaust door and could this way been lost before reverse pulse occurs... It's very theorical but i usualy see boost port lower from 3-4° than main/auxiliary port to begin its scavenging job a bit later. Not sure it has a real efficiency on a so primitive Barrel/ exhaust system like the one I want to use.....

[Jack221]

I thought you were thinking that With large mains and secondaries and a good expansion pipe, when the boost port is angled up correctly, it's the initial opening of the boost scavinging flow takes the longer path. I think in this instance increasing the boost duration will suit what you are trying to do better.

[fastfrog]

no real expansion pipe but a pep3. A tuned and powerfull sito+...