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In a race motor, has anyone disabled the 4th valve? Dating to the 1970's, I think the CVCC concept was primarily for emissions control. What would happen if you simply set the valve lash very loose so that the 4th valve just sat there and didn't do anything, or maybe removed the rocker arm and put in a spacer in the valve train? Any thoughts would be appreciated, especially from someone who has tried this.
First, I'm not sure either would be legal in IT racing. If you know the design of the CVCC head though, than you know that the CVCC chamber that is fed by that auxillary 4th valve is where the spark plug is located. So if you didn't have that auxillary valve feeding that CVCC chamber, and ultimately the spark plug location, than I can't see how it could possibly be better.
The Si heads (non-CVCC) do not have that auxillary valve or the CVCC chamber and make more power. It's more due to not having that pre-ignition chamber versus not having that extra valve.
What your basically asking is exactly the description of the Canadian 12v cyl. head. Here in Canada, we did get the 12v CVCC head in 1984 but in 85/86/87 the CVCC design was eliminated and the 4th valve chamber was filled in. The Canadian head is sought after by American tuners because of this and it make 2 or 3 more HP (not sure of the exact numbers).
R2 indicates that this might be IT illegal and therefor the Canadian head may be illegal too. It's funny because I know of some Canadian IT CRX's that used to race south of the border without issue.
Somewhat related, I hope. My ITC Honda is a Civic DX. We are rebuilding the engine. I have heard that the Si head is illegal for this car in ITC. Any truth to that?
Plus, we may want to purchase a new head. Any sources besides a Honda dealership or trying to find a mid-mileage one from a salvage yard? Any companies who prep Civic heads for ITC use?
Thanks.
Yes, it is illegal to use that head on a ITC motor since it is used in the soon-to-be-reclassed ITB cars (classed in ITA till the end of the year).
And yes it does make alot more power than the CVCC head.
Also very easy to catch cheaters without pulling the head since the p/n is cast on a visible surface (same is true for illegal Canadian heads).
Both OPM and King Motorsports offer 'IT' cylinder head prep services for these older Honda heads. There are probably others. Any decent, reputable foreign car shop with machining services should be able to go thru your head and skim it, replace the guides, recut the seats to factory specs, and replace the valves/seals. Additionally, what the good prep shops (like the two I listed) will do is port matching, and also legally optimize the valve grind angles in order to make the most power. This is where experience and attention to detail provided by thoses shops payoff. A good, legal valve grind is the biggest key to making good power with those heads.
Boneyards are still the best bet for used heads, but most 'good' heads are snapped up since the motors are 'interference' type and you bend the valves if the timing belt breaks, which usually happens because the car owners don't feel like following the scheduled maintenance, so when they bend the valves, it is usually cheaper to throw a junkyard head on the motor with zero prep vs tearing down a head to replace the damaged valves. If you get lucky, you might find a head with bent valves to be used as a decent core.
Also....DO NOT advance the ignition timing too much!!! You will either get lucky and only melt the spark plugs, or else you'll get screwed and melt the prechamber turning the head into a door stop.
BTW - A tip I learned from the Rivergate guys was to use Champion N2C's (designed for small scooter engines). These have a much, much cooler heat range than the stock NGK plug and they work very well in the CVCC engine and best of all, they are about $0.99 a piece at Wally World http://Forum.ImprovedTouring.com/it/smile.gif The only precaution is that because they are a very cold plug, it's easy to foul the plugs on a very cold, damp morning but they generally clear up once the car has warmed up.
[This message has been edited by Greg Gauper (edited December 06, 2004).]
Thanks Greg.
As for valve grinding, I guess I'll have to look at the GCR again. What do you mean by an illegal value grind? I don't remember seeing this in the GCR - probably there - just might have missed it.
Any advice would be great. I have just completed my rookie season in SCCA, so I'm still pretty green.
I didn't say 'illegal' valve grind... I said 'legal' valve grind. The GCR states all rebuilding/machining must be per factory specs. The factory shop manual specifies a 3-angle valve grind and inludes sketches showing the angles, seat widths, guide placement, etc. The 'go fast' guys know how to cut the seats & valves to meet these specs, yet allow the tolerances to stack up in their favor to make the most power. In reality, the closer you can follow the factory shop manual specs, the more power you will make.
Here are two links to a website that has the manual posted. I posted the two pages that describe the valve grinds:
http://www.redpepperracing.com/technical/8...v-fsm-chap6/aap
http://www.redpepperracing.com/technical/8...v-fsm-chap6/aaq
Like anything else in the engine, you can legally blueprint the motor to the factory specs/tolerances. Another example...you can legally skim the head up to 0.025" but not to excede 0.5 CR point over stock. For this particular Honda engine, you can't take the full 0.025 of the head or else you'll exceed the CR limit. A good shop knows how much they can take off (and no, I don't no how much that is but I'm guessing somewhere around 0.015" or so).
What you are really paying for is the knowledge & experience in knowing when to go to the high side of this tolerance or the low side of that tolerance, in order to get the most power. Like anything, there are usually some tradeoffs. For example, in exchange for more power, your motor might not live to see 100K miles. It might have to be 'freshened up' after 3-5 years of hard racing, depending on how many events you run per season.
[This message has been edited by Greg Gauper (edited December 08, 2004).]