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If you experiment with the IMRC opening rpm, you can also find that sweet spot between long-runner (low-rpm) and short-runner (high-rpm) transition.
Typically for short runner/long runner transitions you simply run each on the dyno and right where the power bands crossover that's when you switch. This could just as easily be done with virtual dyno, no dyno rental required.
 

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That is precisely what I was getting at. Not all engine/trans combinations will have the exact cross-over point. So, dyno running and finding where your particular crossover happens (to me) makes a bit more sense versus a 'close enough' point.

Then again, these are just street engines..............
 

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Discussion Starter · #23 · (Edited)
And yeah, open info is good info.

If you are porting, pay attention to the short-side floor area. Be gentle and smoothly reshape it to take the harsh turn out of it (this applies to both intake and exhaust sides). Teardrop the intake port splitter (think leading edge of an airfoil) to improve transition from the throat to the valve. As to opening the bowl area directly above the valve seat, DO NOT go more than 90%, as you want meat there for a good (minimum 3-angle, but for all-out, 5-angle) valve job. Believe it or not, the most positive difference in flow will be made by just that valve job. On the exhaust side, raise the port roof slightly (to match whatever header/manifold you use) and fill the floor the same amount (air flow wants to stick to the roof, and has been known to stall/revert in the lower right corner). This, in effect, is raising the port for a more direct/smoother line out for the airflow to follow. I have done this on 4.6L DOHC heads with success.
As to unshrouding the valves; very good idea but you have to keep the cylinder bore (not the head gasket bore diameter) in mind. That will dictate how much you can potentially remove to unshroud. Pay attention to the shape of your cut, as it shouldn't be harsh. Any removed material in the chamber will drop compression (so keep in mind how many CC's you remove). Some can be regained by shaving the head or using higher compression pistons.

Again, unless you really want to slow incoming air, DO NOT port-match the intake unless you have opened up the upper intake and this will merely align/keep the port velocity moving. Unless your engine has been modded for more low-end torque, losing any velocity down low will make the car very sluggish (even with a larger throttle body) as port velocity isn't aiding in cylinder-filling. The trick is to experiment with throttle body size until you find the one that doesn't kill low-end and hangs on further into the rpm band (just like carburation, there is too big).

What are your overall plans/goals for the engine? Will it see boost? Will you be revving the piss out of it all the time? Auto or stick car? Final drive ratio and tire size? Believe it or not, this all needs to be considered when modifying the engine.

TQ x RPM /5252 = HP
Any change to torque has a greater effect oh HP than RPM does. Higher RPM moves the HP band up.
Missed the last part of your post.

Overall goals are a torquey street engine. I like some neck snap in my cars.

No boost plans at this time although I've contemplated it seriously and, knowing me, will eventually get there but for now I'm trying to keep it N/A. Don't need 5-0 flipping a bitch because they heard the blow off valve go off as they passed me going the other way!o_O:LOL:

Street motor so no need to high rev outside of normal OEM spec but if I'm going to do some head work a set of higher revving springs/valve train upgrades may not be a bad idea.

Manual stock G5M although I have an '03 trans I pulled from the yard waiting for an Mfactory LSD that I want to drop into the wagon. Current trans grinds 3rd gear telling me 3/4 fork is probably bent at the shift tab.. I need to get up to speed on some of the other things I can do to improve performance/durability of the trans. From what I've read their good up to around 200hp in stock mode. Right now my butt dyno is telling me with the bolt ons I have I'm probably pushing around 150 hp at the crank. Final drive ratio I'm assuming is 4.10 since the trans in the car was out of a 2000 ZX2. Running a 205/45/17 tire.

John
 

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....... Overall goals are a torquey street engine. I like some neck snap in my cars. ....................................
Play with ignition timing advance. But advance ignition timing via mechanical means. The computers are just too conservative to go that route. That 1.9L SOHC engine had an actual attitude when the ignition timing was (accidentally) advanced by mechanical means. Mechanical valve timing remained unaltered.

May be achievable by physically shifting the crank sensor on the clock-face. You'll have to devise and craft a jig.
 

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If you will be driving it in pretty much the factory rev range, concentrate more on bowl work leading up to the valve, unshroud the valves, and mill the head the needed amount to recoup the increase in combustion chamber volume due to the un-shrouding effort. You can profile the intake runner split to remove the harsh cut (which leads to barrier air disruption) and valve guide trimming to help the air flow along the roof past that guide and into the rear of the port bowl. Look at the exhaust port and see how it aligns with your manifold/header. If you have a little more headroom in the exhaust manifold/header, move the exhaust port roof as close to that profile as possible. The exhaust floor can be built up (if needed) to create a small 'reversion dam' to keep the exhaust gas from slowing/re-entering the exhaust port (colliding with the next exhaust cycle pulse from that cylinder).

Advancing timing 2*-6* will help, as will being able to adjust intake/exhaust cam timing separately (allowing further adjustments to tailor lobe overlap and move your overall torque curve). Also, if you have means to wire in an RPM switch, you can do a dyno run and see where long-runner to short-runner transition happens, and start playing with the rpm at which that happens (long runners promote low-end torque while short runners promote higher-rpm horsepower).

I am gathering parts to do a 2.0L ZETEC/5spd/Turbo build for my '95, and will be wiring in an rpm switch or two so that I can tune certain aspects of the engine manually. Doing a bit of research, and having built other small-displacement engine before, I will apply that which I know and have learned to the build (unless gas prices keep increasing; in which case the 1.9L gets a refresh!).
 
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