2.5" dia Exhaust - Effect on hight spec build

[Evogone]

Interesting result on the rollers today in the Rallycar.

Origional build mapping showed 228bhp 182lb/ft with 2" diam exhaust, Peak about 7k, went on 3 different occasion and was withing 1/2bhp..

Full 2.5" exhaust fitted and full top end rebuild (everything the same inc. timing) the map needed a few tweeks as a result of the exhaust. Its now eliminated some of the bumps in the torque curve but in essance the exhaust just moved the torque curve 500rpm higher but after 6k held the torque curve longer before dropping off. Now the power is still climing after 7.5k where previously is was dropping off. Results where 243bhp @ 7800rpm torque 180ft/lb. We even backed the timing back a little and were conserative due to using pump fuel.

Cliokongen had a very similar effect on his ITB engine which is similar spec (slightly lower cr and milder cams) with the exhaust. He also modified his manifold to have the mating down pipe of 2.5" dia to match the exhaust. This is the next step for me the back to the rollers but conclusion is if you have a high spec build then 2.5" exhaust is a must...

Before everyone says figures are rubbish, these are all on the same rollers so the step change is the important aspect rather than the absolute figures BUT these rollers are hub rollers and read very consistantly and are very accurate based on lots of feedback. Although did have one scare when the fuel pressure dropped on one run but was due to the exhaust boiling the fuel up due to not air getting to it.!! covered the exhaust and was fine after that.

Car goes very well, at the last event a guy came across whos was running a Millington engined Mk2 freshly built by Melvin Evans and said F@*% thought i would catch you up on the straight but couldnt, was well impress with the car.

Hopefully cars all OK for the next round of the championship for the Promenade stages 7/8th September on New Brighton sea front, great event with night time super special stages on the Friday.

[cliokongen]

Excellent result! Well done...
The difference is about the same as we found on my engine going from 2" to 2,5"

Michael

[dave17]

Think you guys need to take a look at mine, Did you ever start your own firm Evogone?

Dave

[Evogone]

We have the facility to look at it if you want......the same person who rebuilt mine would be the one looking at it etc. Havent set up EVOgone"sport" LOL but this guy has his own facility etc.

PM with info im sure we can help you out with any issues you have.

[zmaster2k]

thats an almost unbelievable difference...

top marks

[Coops]

nice work, good to see some power similar to the old rally spec maxi's coming out of the home n/a builds

[cliokongen]

Evo... Just realise - We have very similar results.
Yours: 243bhp @ 7800rpm torque 180ft/lb
Mine: 241bhp @ 7537rpm torque 179ft/lb @ 6261rpm
Yours is higher compression than mine i believe (mine is 11.2 to 1)

I can only imagine how much fun that car is as it is a properly built car - remember seeing it when Yozzasport had it.
And you have improved it a lot i believe!

Remember to post some videos of the next race!

Michael

[Wobba]

I may have imagined it, but I think I lost power but had more readily available torque when I swapped back to a Mongoose from the 2.5" Oreca.

The trouble is, the Oreca was just too loud for normal road use. I couldn't even hear the ITB's at full chat. Much prefer the sound now and it pisses less people off.

Sure, maybe I will go back to it at a later date, but for me right now the exhaust is fine. Even though I use a Supersprint manifold I do believe it could be a bigger bore for better gains. Any suggestions, please let me know.

Great results by the way.

[Evogone]

Put the ORECA one back on a just get a bigger back box fitted. The origional one was too small plus mine had no silencing material left after a couple of events.!!!

You will need a tweek of the map with changing the exhaust though.

[dave17]

I may have imagined it, but I think I lost power but had more readily available torque when I swapped back to a Mongoose from the 2.5" Oreca.

The trouble is, the Oreca was just too loud for normal road use. I couldn't even hear the ITB's at full chat. Much prefer the sound now and it pisses less people off.

Sure, maybe I will go back to it at a later date, but for me right now the exhaust is fine. Even though I use a Supersprint manifold I do believe it could be a bigger bore for better gains. Any suggestions, please let me know.

Great results by the way.

Would your ORECA 2.5 be for sale by any chance?


Thanks
Dave