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Head comparison VTEC vs. Non VTEC

Posted 06-18-2004 at 04:14 PM by Jacksont001

Hey TI!
My latest installment in my ongoing battle to educate the masses is the side by side comparison of the VTEC and NON-VTEC heads.

I will be walking you through as I disassemble these heads and illustrate some key differences and similarities between the two.

NO Jokes on the Mugen Valve cover, it is what I had laying around and I used it to illustrate a point.

The heads I used were a b16a Head, and a B18a head. The b16a and type-r heads are identical in construction, and similar to the B18c1 GSR heads.
The b18a and b18b heads are Identical in construction as well.

Yes I know all the heads run different cam profiles, but thatís not important here, and is covered by other articles in depth.

Side by side
B16a and B18a


Notice the bolt patterns for the Valve cover, 8 bolts (7ft lb.) hold on the VTEC valve covers


The Non-VTEC covers are held on by 7, three in the center and two on either side


The patterns are completely different and this is why you cannot swap covers between the two types of heads.

Upon removal of the covers we see the VTEC heads have an oiling tube covering the cam retainers (more on that in a moment)


The Non-VTEC cams are held in by 12 retainers, six per side


Here is a side-by-side of the two with the oil passages removed.
Notice the VTEC head uses 5/side cam retainers vice the 6/side used by the non-VTEC.


Closer inspection to illustrate the difference in width and construction.


Non VTEC retainers are held in by two 10mm bolts


VTEC retainers are held in by 4 12mm bolts, two on ether side of the cams.
If you didnít notice already the VTEC retainers straddle both cams.


Bolt Differences


Looking at the centerline of the cams, I noticed the VTEC head was actually TALLER than the non VTEC one!
I took a shot to point out the differences in height and the fact the H2O passages and sensors are in different spots. Additional note, the water neck on the heads are NOT interchangeable. The opening and bolt holes are slightly different and will not work.


The difference in inches


How does this effect the timing belt? good question.
Since the ports are the same distance relative to the Deck, you can swap exhaust manifolds, but the cams are definitely higher up on the VTEC motors.
Perhaps it is the reason that there are different timing belts between the two, besides the number of teeth on the coolant pump.

Now that we see the differences in the retainers, lets talk about some things that will save you a LOT of money when upgrading your cams.

OILING those suckas!

The VTEC heads have a very complicated, but effective, oiling system that lubes the journals and each lobe on the head.













The non-VTEC cam oiling system is less complex. This is due to a lower Redline and much simpler valvetrain.
Oil is forced through the head and into one side of each retainer.



The opening is larger than the bolt so oil can flow around the bolt. Since the bolt-head blocks off the top, the oil is forced out the jets on either side.


This spray hits the cam lobes and the side of the cam journal.
Since the retainer and journal are narrow, the oil wash on either side is sufficient to keep them lubed.

Timing those cams

This info is very useful if you don't have a helms, or are helping a buddy change cams with a different head than yours.

The timing holes in the VTEC cams will align with one of the two holes in the center of the Oil tubes.


The Non VTEC cams timing holes are located right next to the cam gear


The cams are easy to identify as well


ROCKER ARM DIFFERENCES

Probably the #1 most noticable and misunderstood (by Neophytes) aspect of the valvetrain system is the difference in the rocker arms.

The VTEC system uses 3 rockerarms per side per cylinder. The rocker arms are mounted on a tube that runs thru each and holds them in place. The actual operation is described in the "all about VTEC" article


It is important to note that both valves for the cylinder are side by side, with the Lost Motion Assembly between them.

In the Non-VTEC head, the cam journal sits in between the valves.


The only thing that actually holds the Rockerarms down is the pressure from the Cams when torqued down to specs.
The ball bearing sits in pressurized oil and the hook holds on to the valve stem.

Note: when changing out cams, these little suckers can jump off and wedge themselves in between the springs.

Side by side of the two


Notice the lash adjustments are made at different points, GOOD to know!


Combustion and Cooling

This next section is pretty much self-explanitory. the key differences are intake valve size, cooling port openings and oil drain back holes

B16a and b18a


Closer


Oil drain holes are larger on the VTEC heads


VTEC Combustion chamber. Note the larger 33mm intake valves and the 28mm exhaust valves


Non-VTEC Combustion chamber. Note the smaller 31mm intake valves and the 28mm exhaust valves


Hopefully this explains why you need the right headgasket when doing head swaps.

As we sailors say, Any port in a storm!

Okay time for the MAIN event... this is where the heads really make money.

As has been covered in numerous articles, there is some science to making ports flow thier best based on the target powerband. As has been covered before in other threads, the b18/b20 heads do not perform well above 6000 rpm, but do great at the lower ranges.

We also know that the Exhaust manifolds are very similar between models and all have the same bolt patterns.

With that stated lets get into it!

B16 exhaust ports dimensions:





B18 exhaust port dimensions





As you can see the ports are nearly identical, which goes to show there may be room to improve on the exhaust ports in the N/A B18a/b if you can believe the theory of making them smaller to increse flow velocity. If you turbo, they are just fine.

And now the moment everyone is waiting for....



B16 intake ports




B18a intake ports




Eureka!!!! that right there shows why the heads stop performing after 6000.
Heavy portwork will allow them to flow better, but you still have issues with the integrity of the valvetrain at high speeds. It MUST be reinforced or else you will pay the concequences.

Of course we all know about the rod ratio, but that's a whole other story.
[*]If you care to discuss this article please feel free to post in this thread.
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  1. Old Comment
    nice article
    permalink
    Posted 01-16-2012 at 01:16 PM by adecorzo adecorzo is offline
 

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