So what are you Guys reving your 2.5L's to?

[Loudexploder]

Ok I had to bring this post back from the dead, but for good reason. There has been some good information come about in the last 12 years. The 2.5s do like to rev and it has nothing to do with the rod ratio. This is my 2.5 stock bottom end, ported head, intake, header, and custom spec'd cam.. This thing loves the High rpms.. This is 6 psi / 11 psi / 15 psi

[GLHS60]

Agreed, nothing to do with rod ratio but breathing.

I've found retarding stock cams helps move the power band to higher RPM.

Thanks
Randy

[cordes]

Thanks for the graph. That is some serious action for 15psi to say the least.

[Loudexploder]

Thanks for the graph. That is some serious action for 15psi to say the least.

Yessir, made 410 on 24 psi. Again that was with the stock bottom end. Have not had it back on the dyno with the built bottom end, but the increase in compression made a HUGE difference. I would guess and say 450+ on 24lbs.

[chromguy]

Yessir, made 410 on 24 psi. Again that was with the stock bottom end. Have not had it back on the dyno with the built bottom end, but the increase in compression made a HUGE difference. I would guess and say 450+ on 24lbs.

What did you increase the compression to??

[Loudexploder]

What did you increase the compression to??

I just bumped it to 9.3:1

I wanted to be around 10-10.5 but didnt want to wait on custom pistons


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[tryingbe]

What fuel did you use?

[Loudexploder]

What fuel did you use?

E85


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[chromguy]

I just bumped it to 9.3:1

I wanted to be around 10-10.5 but didnt want to wait on custom pistons


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Ah so it is now an interference engine but that is AOK.
increased mine but still wanted to stay non-interference, for now

So you are at 9.3:1 including chamber port?

[Loudexploder]

Ah so it is now an interference engine but that is AOK.
increased mine but still wanted to stay non-interference, for now

So you are at 9.3:1 including chamber port?

Im not sure if it is an interference engine or not as I havent checked that, but Id venture to say it was even before the new motor. The cam im using has a long duration and mid 500 lift which i think would cause interference.

The 9.3:1 is static compression, measured from bore, stroke, deck height, piston dish volume, chamber volume, and gasket thickness.


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[Ondonti]

While I used to take these tech articles seriously, nothing I've seen in winning engine combinations for drag racing has supported these claims. They specifically make claims about Drag racers wanting 1.8 rod ratios.

Real advice about 4 cylinder power production is, obtain as much displacement as possible without having the bottom end scatter at up to 12,000 rpms. Some boosted combinations do better with lower rpms, probably because the rods get way too beefy vs a 12,000 rpm N/A combination.

The idea that long stroke side loads the cylinder enough to hurt power production is wack. The pistons would all be wrecked in half a pass. Yes, rod ratio matters for the longevity of a road course or time attack car. Rod material quality has also improved over the last 3 decades.

http://www.minimopar.net/perf/longrodengine.html