So opening the port timing earlier does create more overlap....correct?

 

The factory manifolds suck for increased output. Unfortunately, most people dont know that, and the few who do, dont have the resources to design and build one.Yes, so does late closing exhaust port.

 

Don't be confusing turbocharged setups with n/a ones. Completly different ballgame...

 

Ok, so lets say your porting a Turbo'ed motor for maximum torque, which way would you port it?



Same question for N/A ?

 

OMFG I have been preaching this with ridicule for the past year. And you mean to tell me there is finally someone in the world that is not stuck hiding there information in a closest that actually understands this! I am speechless.



People this thread is full of hidden secrets book mark it now!!!



Oh yea and this is also on contingence of NA mostly as 1revvin7 said exactly, turbo setup for forced induction VE is completely different!

 

max torque when? a stock gsl-se makes 20.5nm@3000 rpms, a MFR 12A PP engine, setup to the factory specs makes, 22nm@8000rpms. big difference between the 2

 

For the same power output, it's the opposite.



A low overlap engine would need to close the intake ports VERY late in order to be able to have enough port open-time to make power. This kills the low end.



A high overlap engine can close the intake ports fairly early, enhancing midrange power at the expense of top end. This is not necessarily a bad thing. Not very pleasant to drive at part throttle, though.



Of course, if some is good, more is better, so people make their bridge and peripheral ports with late port closing like a huge street port, concentrating the power at the top end of the range. It is not the overlap that is causing the poor low-end performance, it is the late closing.

 

naaaa, the stock manifolds are fine for increased power. they're just not all that friendly for changing your peak rpm power output unless you get pretty hefty with the porting.





can you explain that a little better? all the bridgeports i've done have all made peak power above 8k rpm.



and with the overlap vs. rpm issue, why wouldn't a cleaner charge help out low end torque?

 

This is mostly because of the manifold. Also a bridge has a constant overlap so more closing is needed for a cleaner charge.

 

Let's say I want to build an engine for best low to mid RPM torque, let's say it's for a baja bug, and let's say the engine is an old style 4 port 13B with 1st gen RX-7 12A side plates and J-spec rotor housings with late opening, late closing exhaust ports (same as GSL-SE exhaust timing as far as I know).



I'd like to know whether I should open the intake ports sooner, or just leave them totally stock.



I believe the exhaust ports, with their late closing (compared to 12As and early 13Bs) will add enough overlap so I don't need to touch the intake ports, other than to clean out the casting flash and some hard 90° edges inside. The late opening will allow the exhaust gasses to push against the rotors a little longer. I hope this combination will produce as much or nearly as much low end torque as a genuine GSL-SE, only without the complicated EFI manifolds and wiring.



Part throttle must be smooth, and low to mid RPM responsiveness is very important. High RPM power is unimportant. VW trannies don't like high RPM and high powered situations anyway.



Most people don't think of rotaries as viable powerplants for bajas due to less low end torque than comparable piston engines. Porting, as the best way to increase power output on an NA rotary, only reinforces this attitude. Stock and ported rotaries do ok in street driven beetles, sure, but when low end grunt is needed, like in off-road situations, the rotary takes a back seat to really huge VW engines (1900+) and water cooled 4 cylinders like the new popular ecotech swap.



My goal is to show people a rotary can be a viable powerplant in a baja. I think I can accomplish this with a little help from you guys.