Heads questions
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Joined: May 2020
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Heads questions
Hey all just picked up a set of 243’s for my car and cleaned em up, did some light porting and polished also the valves. My question is about lapping. What grit to use to start and finish? They look decent with a little pitting just in exhaust valves but I want to do this right. Input Appreciated
Le Mans Master
Joined: Aug 2005
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From: CA.
St. Jude Donor '13-'14-'15
I would not gamble ---Take your heads to an expert and have them look them over--
PS I added STOCK 243's to my 98 C5 and on the dyno --it made 12 more RWHP !! so it is a great mod
I would also recommend
Doing the LS6 PCV system swap as the LS1 PCV system sucks and ingests lots if oil vapor into your combustion chambers
Installing a LS6 intake manifold ( good for another 10-12 RWHP)
PS I added STOCK 243's to my 98 C5 and on the dyno --it made 12 more RWHP !! so it is a great mod
I would also recommend
Doing the LS6 PCV system swap as the LS1 PCV system sucks and ingests lots if oil vapor into your combustion chambers
Installing a LS6 intake manifold ( good for another 10-12 RWHP)
Race Director
Joined: Oct 2004
Posts: 12,864
Likes: 4,670
I would not gamble ---Take your heads to an expert and have them look them over--
PS I added STOCK 243's to my 98 C5 and on the dyno --it made 12 more RWHP !! so it is a great mod
I would also recommend
Doing the LS6 PCV system swap as the LS1 PCV system sucks and ingests lots if oil vapor into your combustion chambers
Installing a LS6 intake manifold ( good for another 10-12 RWHP)
PS I added STOCK 243's to my 98 C5 and on the dyno --it made 12 more RWHP !! so it is a great mod
I would also recommend
Doing the LS6 PCV system swap as the LS1 PCV system sucks and ingests lots if oil vapor into your combustion chambers
Installing a LS6 intake manifold ( good for another 10-12 RWHP)
Thread Starter
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Joined: May 2020
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I agree and plan on taking em in to be pressure tested and looked over before I install em. I’m doing the heads, intake and tb, along with ls7 lifters, upgraded trunnion bearings, and 80# injectors all at the same time. These vettes are tough fighting the n/a battle LOL I want to boost it but **** 6gs for a supercharger and I can’t see how a turbo would even fit... my tuner said about the same 30-50 whp for a realistic number. Just know it’ll leave me wanting more though because I’m already bored with the mods I’ve done. Oh well at least it’s a healthy addition
Safety Car
Joined: Aug 2011
Posts: 4,454
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From: Portland OR
I would have the surface cut to make sure they are flat and have a good gasket surface.
.003-.005”
Or, .025” to give a nice CR bump.
Of course not if it will be boosted.
Coarse grit is fine. If you can get both, then follow with fine.
A nice proper valve job would be a benefit.
.003-.005”
Or, .025” to give a nice CR bump.
Of course not if it will be boosted.
Coarse grit is fine. If you can get both, then follow with fine.
A nice proper valve job would be a benefit.
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Thread Starter
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Thanks for the input! Yeah I was going to have em done but really want to up my game on engines so figured worse case I lose the 280$ I spent and have to get different heads LOL but hopefully they come out good. I lapped the valves they all look like will have a complete seal. I agree new valves and cut seats would be the best. I’m adding a supercharger later this year so not gonna shave em
Race Director
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Famous head porting guru Jerry Branch once said "You can't trade port volume for port velocity". Even though the LS7 heads I'm now running made around 35hp more on top end than my older AFR CNCd 225 cathedral port heads, my car felt WAY more responsive with the AFR heads. I also got at least 4mpg more. Yeah, I didn't build the motor for gas mileage, but if it's a free windfall in a far more responsive engine, with $4 premium lurking closer by the day, I'd take it every day of the week. If I could've hooked my old combo, I'm certain it would be just as quick, if not quicker, than this motor with the LS7 heads. A lot to be said for cathedral port heads, imho.......
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Yeah these 243’s are cathedral port I’m not sold on the square ports. These will hopefully work well and if not I’ll just put the stick heads back on it. I want throttle response along with power and it responds well right now just thought these will let the cam shine a little better and hopefully put more to the ground. Like I said the blower is coming this year so after that I’m sure I’ll be happy. LOL at least for awhile
Instructor
Joined: Apr 2019
Posts: 138
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From: North Side of Atlanta
I know I'll probably be in the minority here, but I lapped my valves myself using the off-the-shelf lapping compound from the local auto parts store
What we did for my junkyard 243's
What we did for my junkyard 243's
- Spread the compound on the valve where it meets the head.
- Put the valve into the head and turn the head combustion side down.
- Attach the end of the valve into the chuck of a cordless drill (not too tight, don't want to damage the valve stem)
- Run the drill at a medium speed and "seat" the valve over and over. Basically push the valve open, then close it all while spinning it.
- Do the same but spin the drill in the other direction
- Repeat until the sound changes from gritty to smooth. The lapping compound will break down from larger pieces of grit to smaller and smaller until it is just a paste. At that point, it's not very abrasive anymore.
- Clean both surfaces (valve and head) of all of the compound and inspect the valve and head to see if they're both smooth and shiny.
- Put the clean valve back in the clean head and spin it against the seat. It will be completely silent when the seats are mated completely. You should be able to feel the difference between a valve that you haven't done yet and a finished valve by doing this.
Last edited by bradleyss14; Apr 13, 2021 at 11:56 AM.
Safety Car
Joined: Aug 2011
Posts: 4,454
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From: Portland OR
BTW, I do it just like Bradleyss mentioned.
I watched my engine builder reface some of there on his fancy machine. Took a decent cut to remove all the pits. Some were just slightly visible. Said no issue as long as they seal.
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Another way to do this would be to get some fuel line that fits the valve stem tightly. If you can't find something that fits tight enough, used a small hose clamp. Push the line down the stem until it's just above the guide seal area. Now you can rub it back and forth between your hands like a traditional suction cup lapper, difference being you must pull up on the line......
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Cool I’ve heard of the drill method but I ended up using a suction cup tool but the smaller cup for the exhaust valves kept popping off kinda frustrating.. I’ll send a pic of the exhaust valve pits that are left very minimal but maybe I’ll give it another go and get em all out. I used good compound that I ordered online 400,800,1200 was my process and they look consistent and clean so should seal but I’ll check em all before I install the heads