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Discussion Starter · #1 ·
Hey folks,
This thread is to discuss the technical aspect of the Head differences illustrated in This article
 

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Definetly says a lot about the top end power. Also makes me wonder about the low end power as well.

As I am sure most know by now, the B18B has more lower end torque than the B18C's. I have always figured the key player in this was the stroke, and piston dwell time as a result of the stroke.

However if the ports are that much smaller, I wonder how much of a role that and the TB/IM size factor into that powerband location.

Granted you could easily upgrade to a S2 mani, ITR TB, and open up the ports, but you might be losing the advantage (in my eyes) that the B18B has.... Midrange.

I wonder how experianced headports approach the non-vtec heads in terms of port size. It seems most head porters don't try and OPEN up the ports of the vtec heads, just reshape them. However the nonvtec heads would the same theory apply, or would more airflow be worth the drop in velocity.
 

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Even after having the intake ports machined open, arn't you still in trouble with flow because of the smaller intake valves? Even with agressive cams? I'm totaly new to the b-18...
 

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jojo on Jun/19/04 said:
Even after having the intake ports machined open, arn't you still in trouble with flow because of the smaller intake valves? Even with agressive cams? I'm totaly new to the b-18...
Or would the porting include bigger intake valves?
 

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StyleTEG on Jun/19/04 said:
Granted you could easily upgrade to a S2 mani, ITR TB, and open up the ports, but you might be losing the advantage (in my eyes) that the B18B has.... Midrange.
Ross,
I get what you mean here, but however with these changes would you expand your highend power thus moving your powerband up?

Still new to this and wanting to understand it more
 

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StyleTEG on Jun/20/04 said:
Eh?

With an ls/vtec the head should be fine for the RPMs. The block is what I would worry about.
well, there's probably reasons for the better cam oiling, a cam girdle, an extra cam retainer, and oversized bolts all over.
 

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well, there's probably reasons for the better cam oiling, a cam girdle, an extra cam retainer, and oversized bolts all over.

No doubt. But its easier imo to get the block closer to the vtec blocks than the head.

You can get a block girdle, you can notch the rods to use the wider GSR bearings. Obviously a full build with rods/sleaves/forged pistons would make throwing a rod or cracking a sleave much less of an issue. You can switch to an ITR oil pump, etc, etc. At this point you can get longer rods and pistons with the wrist pin raised.

The only thing you can't do easily is add oil squirters. But Larry at Endyn has mentioned that sometimes he even removes them, because they increase windage and don't always hit the underside of the piston.

Quote: I get what you mean here, but however with these changes would you expand your highend power thus moving your powerband up?

Still new to this and wanting to understand it more
The problem is, once you enlarge all these intake tracks the air is going to travel at a slower rate in the low/mid-range.

Instead of expanding the powerband, it will most likely simply shift it upward.

I guess the best way to figure out how it effects the powerband location is look at some ls/vtec graphs. As obviously those have the larger intake ports and matching IM/TB.
 

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what an awesome write-up man, thx for taking the time to do this.

sounds like it might be good to do something in between the b16 and b18, maybe just enlarge the intake ports 1 or 2mm,

i was wondering if theres a way to measure whether the exhaust ports are tapered as they approach the cylinder. i read that it helps to work on the inside of the exhaust port to make it a more uniform size.
 

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very nice write up. I wonder how you can make the B18b rocker arms stronger, cause they seem pretty weak and when at high RPM's they would not do jack. Ports are easy to alter but rocker arms and overall integreaty of the head is not.
 

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Discussion Starter · #17 ·
T.J.
My concern is not neccisarily the strength of the rocker arms, but the way they are held onto the valves.
All in all the rocker arms contribute to a much lighter valvetrain in the LS heads, but the spring pressure on the bottom and the cam pressure on the top is what holds it in place.
If you were to experience coil bind, there's a possibility the rockerarm can pop off of the valve, and all hell would break loose.

When I was doing the initial teardown of my engine one of those suckers popped off and fell. it wedged itself BETWEEN the springs, and I had to pull the spring/valve just to get the rocker arm out.

So how would you overcome that problem? Careful selection of the springs based on your cams, and target powerband. And staying safely within the rev limits!

Scooby Dooby,
There is a reverse taper, since the exhaust valves are smaller than the exhaust port. I would strongly urge people to leave them alone!!! If you must port out something, widen the exhaust manifold openings 1mm to form an anti-reversion step but that's it. if those ports flow well enough for a 1.8 liter type-r and a 2.0 liter CRV based on thier displacement and rpms (max flow based on engine speed and combustion volume) then the 1.8 liter non vtec is just fine with those ports.

Ross,
You and I agree, the smaller ports give the non-vtec the velocity advantage down low, but kill it up high.


If you don't mind me speculating... I think the Honda Engineers tried to create two different creatures in the 89-92 time frame. both use the same basic design and parts (cost-effective). The b16 (in japan)was a high revving (better rod ratio) little motor and had to make it's power higher in the band. It was given the big ports and valves to do so. The b18 (USA) was designed for a lower powerband and used the smaller ports to help fill the cylinders.

A little while later they figured releasing a larger displacement b16 in the US would boost sales. so they upped the stroke and came out with a b17, using the same ports. Surprised at how well the b17 performend they did testing with a b18 block until they found the best balance between rod/stroke ratio (which effects breathing) and displacement which could still use the same PR3 head as the b16 and b17 had. thus the B18 Vtec motors were born.

Or I could be talking out of my butt.
 

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So I take it enlarging the intake valves is not needed? Like it is on the B-16?

Or porting the intake valves would increase the power in the higher RPMs, or leaving them as is ,the power will remain down low?
 

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Discussion Starter · #19 ·
If you enlarge the intake ports, the valves should be matched to the increase as well, or else they become the bottleneck.
Essentially what you would have done is put a vtec size intake port and valves in a non-vtec motor. those ports don't hit peak VE until the point where the NoN VTEC motor is already at redline. So you could shift the powerband up and theoretically make more power, but you also will kill the VE at the lower RPM range. that results in a loss of torque and power.

one more thing to mention, VTEC vs Non-vtec.
VTEC engines do have bigger ports and valves to give the airflow needed up top. but it has a completely different cam profile for the lower end too! on the smaller lobes you have shorter duration and lower lifts. this "choking" down causes the air velocity to increase and promotes more efficient filling of the cylinder.

NoN-VTEC engines don't have that advantage. so when you make the change in port sizes, it needs to be done with the cam profile in mind, and a realistic expectation of the Idle quality and powerband location.

Big ports and the Equivalent lifts of the VTEC killer cams will idle like crap, bog down low but scream at the top. VTEC is the ability to use the tame cam but have the big nasty cam on standby, waiting for the solenoid to click.
 
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