Groovin' Honda CVCC head suggestions - Fuelly Forums
Go Back   Fuelly Forums > Tech, Troubleshooting and Repair > Experiments, Modifications and DIY
Search Today's Posts Mark Forums Read
Thread Tools Display Modes
Old 02-07-2008, 02:26 AM   #1
Registered Member
Join Date: Jul 2007
Posts: 280
Country: United States
Groovin' Honda CVCC head suggestions

Ok, so I really wanted to post this on but the admin has not replied to me in over a week and they're image verification script it broken so you can register a new name and they keep making my name 'inactive' with no explanation of how to fix that or what that even means (ARGG!).

But that aside, I've seen a few CRX posts and some grooving posts and figured I'd take suggestions. If you think this would be better in a different forum (other than experiment) let me know, I was unsure.

Anyway, I have an '87 Honda CRX and like all first gens it's a CVCC engine (if you don't know what that is look here, it's quite awesome: My question is if grooves can even help and where to put them. I worry about them actually hurting by squishing too much of the lean mixture into the spot that's supposed to be rich.

Now here's a link to pictures of my head since they're all kind of relevant and no login in required and I didn't want to spam this forum with pictures:

And here's the head:
And here's my proposal/thoughts:
Ok, 6 and 7 are fairly common and probably won't give much gains since the piston is dished anyway, should I bother?
I like the idea of the two smaller grooves, 4 and 5 but it's hard to angle them toward the spark plug hole and I'm not sure they're really necessary.
The CVCC hole is right where I'd normally like to groove, but the ignition will some from this hole, so I think 1 and 2 to propogate the flame along the cylinder wall is a very good idea, I'm just worried about it also compressing too much air into the prechamber and leaning out the mixture there.
Now, number 3, should I even bother? Should I direct it toward the small hole or toward the main chamber. I think flame/ignition will come from both holes and I can't go too deep or I'll hit the prechamber.

My first goal is to increase the compression from the stock 9.2:1 to about 10.5:1. I've seen a member on Honda swap (using the EFI Si though) that said it worked well there and I think with the CVCC it should be fine, but I'd like to groove just incase and improve flame propogation if I can.

Ideally I'd like to keep the prechamber as rich as it needs to be and be able to lean out the main charge on the fly. If my flame propogation is good it seems that extra lean (as long as it doesn't 'knock') will simply produce less power and leave more air in the exhaust, there should be no worry of it not igniting (I love this head design).

I'm not sure if it has an O2 sensor though and that might mess things up as it adjust in the carb somehow (I've had a few 80s 'electronic carb' type cars). Eventually I'd like to have it using about half the gas and igniting and getting hot very quickly and then directly injecting water and using steam explossion as my energy transfer method to the pistons (similar to Crower/6-cycle but different and very hard on a budget of $50 ).

But that's all for the future, for now, any groove suggestions or ideas of how far is too far for high compression (I'm just planing head for now). And as a second thought, how much work (new pistons/etc) would it take to reach 13-15:1 compression and run E85?

itjstagame is offline   Reply With Quote
Old 02-07-2008, 03:29 AM   #2
Registered Member
GasSavers_Erik's Avatar
Join Date: Nov 2006
Posts: 1,027
Country: United States
I have an 87 1.5 CVCC as well.

You are right to be cautious about possibly cutting a groove that will mess things up. I'm sure a lot of engineering research went into designing the pre/post combustion chambers. I think that all cuts except the 1 and 2 cuts would be pretty safe to do without the risk of messing things up.

I just wanted to share 2 things:

1. Be sure to use the reinforced Felpro head gasket. Our engines are bad about crushing the head gasket between cylinders 2 and 3 (it happened to me last summer) and the felpro replacement is reinforced here. The first sign that the head gasket is crushed it that it will no longer suck coolant back up into the radiator from the overflow bottle, and then things get worse from there- cyclical overheating etc.

2. You can adjust the angle of the rich barrel's throttle valve in relation to the main throttle valve. If you take off teh air cleaner, on the drivers side of the carb, there is a screw with yellow paint on it that can be used to adjust the ratio of rich to lean mix (by tilting the tiny precumbustion butterfly valve more or less open). My engine runs well with the rich valve almost completely closed (closed at idle- it opens up as you pull the throttle cable). I have been meaning to test my mileage at different settings but I seem to be doing well as it is so I have left it alone since I changed it

You should definitely have an oxygen sensor in your manifold- this is tied in to a crude computer that adjusts the mixture via a vacuum bleed (not an electric solenoid like on some electronic mixture controlled carbs). The electric solenoid on the back of the carb is an idle shut off solenoid to prevent dieseling.

The redpepper racing website folks might know more about the grooves, I was on there a year ago and many of them were still running CVCC motors. I think there are only about 10-15 of us on this site that have CVCC engines and I'm not sure if many of us have done any serious modding like this.

Keep us posted as to what you do and how well it works!

GasSavers_Erik is offline   Reply With Quote
Old 02-07-2008, 06:52 AM   #3
Registered Member
Join Date: Jul 2007
Posts: 280
Country: United States
Yeah well I was hoping for people with thoughts too, because they can't hurt.

Yes, I've yet to post on RPR, not sure they'd care about grooves, but definately a lot of CVCC and 1st gen CRXes.

As for the Felpro, all set there. In fact the 'old' gasket under the head looks brandnew (it was a Felpro put on 3k ago), but I have a brand new one as well that I'll use. Heads off already because timing belt slipped, I was told there was a wobble or bump or something on the cam gear that caused it and it may or may not have been replaced already... I don't see anything but to be safe I'm thinking of getting an adjustable cam, because I want to mill the head a bit and this may throw off my timing miniscully. I've seen one on ebay for $50 (you think that's too cheap and will just destroy my engine?).

As for mixture adjust, are you saying closed on the rich bowl is more lean? And this adjust the full operation, not just the idle circuit? The only other carb experience I have is with my Kawasaki motorcycle and it's A/F screw only affects idle and you have to change needle height for mid/high range A/F.

I haven't honestly checked on the O2 yet, I asked because with making changes and stuff I dont' want the computer to do the 'wrong' thing.

As for the grooves, yeah, the rest seem pretty safe but don't seem like they'll do much either. 3 doesn't seem too safe, the main exhaust (jet) from the prechamber is where 3 is openning in to. It's hard to see but there's a much larger hole (about 3 times the diameter of the 'upper' one) that leads to the prechamber as well. Yes, 1 and 2 worried me about affecting mixtures but also seem like they'll do the most good because they'll help spread out the initial explossion....

I'm really not sure but I'll definately post any results (it'll probably be very slow going), I have a lot of ideas that I want to try.
itjstagame is offline   Reply With Quote
Old 02-07-2008, 01:56 PM   #4
Registered Member
GasSavers_Erik's Avatar
Join Date: Nov 2006
Posts: 1,027
Country: United States
The idle mix screw is under a metal plug on the bottom of the back of the carb (it faces the firewall).

The adjustment I made really just lets less of the extra rich mix into the precombustion chamber, so I assume that means more of the lean mix in the main chamber. So overall, in theory it should average out to be a little leaner.

I would love to find an adjustable cam gear for just $50- but you are right, sometimes you get what you pay for. Might be really good to check the seller's feedback rating. has a webpage that described how to test the CVCC mixture feedback system. Here it is:

I honestly haven't tried it yet though
GasSavers_Erik is offline   Reply With Quote
Old 02-08-2008, 09:44 AM   #5
Registered Member
Join Date: Dec 2007
Posts: 170
Country: United States
The original use for "grooves" (normally called Singh grooves by the after the originator) being machined into the head was to help flame travel around extremely high compression pistons with domes projecting into the combustion chamber.

Where the piston is dished this will make virtually no difference apart from adding some stress raisers to the casting , decreasing the compression ratio and lightening your wallet.

Honda , as most car companies , have engineers dedicated to R&D and yes they are aware of these things as well.

GasSavers_Pete is offline   Reply With Quote
Old 02-22-2008, 03:11 AM   #6
Registered Member
Join Date: Sep 2007
Posts: 22
Country: United States
That's why one should mill the head first -- as I understand it, the chief advantage of the Singh groove is to allow higher compression with lower octane...

GasSavers_Glacial is offline   Reply With Quote

Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off

Similar Threads
Thread Thread Starter Forum Replies Last Post
Coasting down hill Ann General Fuel Topics 13 11-27-2008 06:32 AM
Multiple fillups per day - broken mathrock Fuelly Web Support and Community News 10 09-10-2008 01:02 AM
Heat Pump Hockey4mnhs General Discussion (Off-Topic) 5 10-18-2007 03:46 PM
Ever wonder how wind will effect your mileage? Lots of interesting Prius info krousdb General Fuel Topics 4 02-08-2006 07:49 PM
My paint job saga... with pictures of the finished product Matt Timion General Discussion (Off-Topic) 9 01-04-2006 07:16 PM

Powered by vBadvanced CMPS v3.2.3

All times are GMT -8. The time now is 04:42 PM.

Powered by vBulletin® Version 3.8.8 Beta 1
Copyright ©2000 - 2016, vBulletin Solutions, Inc.