L-46 Head Gasket Replacement
Tech Contributor
Joined: Aug 1999
Posts: 14,380
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From: At my Bar drinking and wrenching in Lafayette Colorado
Intentionally building an 11:1 motor for the street, which will require use of race gas, seems like a really bad idea. I would drop the compression as much as possible within reasonable limits of head gasket thickness so the engine can be used on premium pump gas. This isn't 1969 any longer, and the gas situation will keep getting worse. Build the car so it can be used. 10:1 is the max that can be used with pump gas and iron heads. I try to limit the iron head performance engines I build to about 9.75:1, and make up the power with aggressive timing curves. This allows use of 93 ocrtane pump gas so the car can be used and enjoyed.
Lars
Lars
Le Mans Master
Joined: Sep 2001
Posts: 7,739
Likes: 630
From: Unreconstructed, South Carolina
Seem OP isn't building ... but seems he's simply freshening heads on existing L46.
If he were building, I'd suggest a reverse-dome piston and keep a tight quench.
Seems OP is comfortable w/ his supply of 110 gas.
If he were building, I'd suggest a reverse-dome piston and keep a tight quench.
Seems OP is comfortable w/ his supply of 110 gas.
Burning Brakes
Joined: Aug 2007
Posts: 897
Likes: 246
From: Green Valley Ca
Thread Starter
Intermediate
Joined: Apr 2017
Posts: 30
Likes: 2
I run a 50/50 mix of Cam2 and 93 octane. With the timing @ 12 BTDC it really runs great. Jackson is correct, I'm just freshening up the heads.I could go with a thicker head gasket instead of the .015 steel shim.
The heads won't be back from the shop for two weeks and I haven't ordered the gasket set yet. What gasket thickness would put me at 10:1 ? and what would the HP loss be ?
Thanks
The heads won't be back from the shop for two weeks and I haven't ordered the gasket set yet. What gasket thickness would put me at 10:1 ? and what would the HP loss be ?
Thanks
Le Mans Master
Joined: Mar 2004
Posts: 7,502
Likes: 1,510
From: Little Rock AR
I would still keep the .015" gasket so the quench will stay at .040" That is the optimal target to shoot for. We are assuming here that his factory pistons are .025" down in the bore at TDC. It would be good to verify. This engine was already running well before the.008" head cut was in play. No need to get away from a setup that was already satisfactory.
Just for reference - I run a 10.4 CR L-46 350/350 setup with stock cam, .015" steel shim gasket, iron heads and pump 93 - runs great all day. Never tried using 91 but maybe I should give it a go.
Just for reference - I run a 10.4 CR L-46 350/350 setup with stock cam, .015" steel shim gasket, iron heads and pump 93 - runs great all day. Never tried using 91 but maybe I should give it a go.
Last edited by stingr69; Jun 28, 2019 at 08:57 AM.
Burning Brakes
Joined: Aug 2007
Posts: 897
Likes: 246
From: Green Valley Ca
I would still keep the .015" gasket so the quench will stay at .040" That is the optimal target to shoot for. We are assuming here that his factory pistons are .025" down in the bore at TDC. It would be good to verify. This engine was already running well before the.008" head cut was in play. No need to get away from a setup that was already satisfactory.
Just for reference - I run a 10.4 CR L-46 350/350 setup with stock cam, .015" steel shim gasket, iron heads and pump 93 - runs great all day. Never tried using 91 but maybe I should give it a go.
Just for reference - I run a 10.4 CR L-46 350/350 setup with stock cam, .015" steel shim gasket, iron heads and pump 93 - runs great all day. Never tried using 91 but maybe I should give it a go.
stingr69
Do you have the factory spec TRW pistons in your motor, My 1970 L46, 10.4:1 .035 quench with aggressive timing runs fine on 91.
Le Mans Master
Joined: Mar 2004
Posts: 7,502
Likes: 1,510
From: Little Rock AR
I just finished building a 355 engine using some low mileage factory L-46 heads. The build thread is on this web site. These heads were rebuilt and checked for cc's and they came out way above 64cc's. The factory cuts the chamber walls when they open up the intake valve area and the difference in chamber volume is significant.
Burning Brakes
Joined: Aug 2007
Posts: 897
Likes: 246
From: Green Valley Ca
I just finished building a 355 engine using some low mileage factory L-46 heads. The build thread is on this web site. These heads were rebuilt and checked for cc's and they came out way above 64cc's. The factory cuts the chamber walls when they open up the intake valve area and the difference in chamber volume is significant.[/QUOTE]
My 186’s CC’d 64.7 - 65.0
My 186’s CC’d 64.7 - 65.0
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Race Director
Joined: Jul 2015
Posts: 13,082
Likes: 3,399
From: SW Florida.
you can cc your heads for about 10 bucks. piece of plexi with a 3/8 hole drilled off to 1 side.and you need a big syringe. walmart flavor shooter or they make 2-stroke oil-gas mix measuring syringes. grease plexi and stick it over chamber. fill chamber with water from syringe. you find what your heads really are, not a spec that is 50 years old. wallace racing is a pretty good CR calculator.
Pro
Joined: May 2016
Posts: 708
Likes: 150
From: Minnesota
The L46 cam is <0.500 lift so as stated there should be no clearance issues. No reason not to clean up and reuse the original head bolts. Since they are taking .008 off the heads, I’d also go to a thicker replacement gasket to keep that compression down. You can get multilayers or Permatorque (Felpro) that range from 0.025”-0.040” so measure what came out and adjust accordingly.
Race Director
Joined: Jul 2015
Posts: 13,082
Likes: 3,399
From: SW Florida.
looks like flat pistons with 4 cc of valve relief. .016 in the hole 4.125 dia gasket bore .015 gasket gets 11 to 1. .041 gasket gets you a point back to 9.9:1. oh yeah. decked .008. 10.13;1. and with .041 blue felpro gaskets you don't meed heads decked. previous question. power loss with CR loss. 4% a point from 7 to 9. 3% 9 to 10. 2% a point from 10 up to truly unreasonable.
Last edited by derekderek; Jun 28, 2019 at 07:29 PM.
Tech Contributor
Joined: Aug 1999
Posts: 14,380
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From: At my Bar drinking and wrenching in Lafayette Colorado
Lars
Last edited by lars; Jun 28, 2019 at 10:48 PM.
Le Mans Master
Joined: Sep 2001
Posts: 7,739
Likes: 630
From: Unreconstructed, South Carolina
Aw shucks ... go ahead and put thick head gaskets on it ... both Fel-Pro and Chevy have 'em in 0.051" ...
... that'll add some 8.334cc - 7.257cc More than a 3.245cc shim does ...
... that should Drop CR from about 11:1 to some 9.95:1 - 10.08:1 ...
... while robbing much of the Quench's desirable, anti-Knock effect.
... that'll add some 8.334cc - 7.257cc More than a 3.245cc shim does ...
... that should Drop CR from about 11:1 to some 9.95:1 - 10.08:1 ...
... while robbing much of the Quench's desirable, anti-Knock effect.
Le Mans Master
Joined: Mar 2004
Posts: 7,502
Likes: 1,510
From: Little Rock AR
Aw shucks ... go ahead and put thick head gaskets on it ... both Fel-Pro and Chevy have 'em in 0.051" ...
... that'll add some 8.334cc - 7.257cc More than a 3.245cc shim does ...
... that should Drop CR from about 11:1 to some 9.95:1 - 10.08:1 ...
... while robbing much of the Quench's desirable, anti-Knock effect.
... that'll add some 8.334cc - 7.257cc More than a 3.245cc shim does ...
... that should Drop CR from about 11:1 to some 9.95:1 - 10.08:1 ...
... while robbing much of the Quench's desirable, anti-Knock effect.
Anybody here ever "over cam" an engine? why does it feel lazy?
How about the difference between an L-82 and an L-46???? Same cam, same stroke, just less compression. How about just rip out the L-46 and drop an L-82 in there? Anybody want to go there? I doubt it. Do people actually pay more for L-82's over those "undesirable" L-46 engines???? Nopes.
As was pointed out above - Reducing the compression ratio would only have a small reduction on peak HP at wide open throttle.......but the part throttle "feel" is not to be ignored. You will loose torque from idle to red line when you drop C/R.
Le Mans Master
Joined: Sep 2001
Posts: 7,739
Likes: 630
From: Unreconstructed, South Carolina
Also, if OP's heads are milled 0.008", he'll Lose about 1.45cc Volume (raising CR) But ...
... But he may Gain some Volume (lowering CR) if his valves recede when re-seating them.
... But he may Gain some Volume (lowering CR) if his valves recede when re-seating them.
Thread Starter
Intermediate
Joined: Apr 2017
Posts: 30
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Well,.. Here's a new twist on the head rebuild. While the heads are out at the shop I'm re tapping the block head bolt threads. Cleaning and inspecting the bores. They all look fine. No ridges and no gouging. the pistons do not have any carbon build up. I pulled a few lifters to inspect the cam lobes and lifter base. so far everything looks good. on #4 the lifter base is concave with slight heat discoloring and a wear pattern that suggest it's not rotating within in the bore. On the #4 cam lobe I can see even wear with lines across the entire lobe. Not good.. Questions: Keeping everything stock on this engine, what cam is the best replacement choice. An OEM L-46 ? Also, Can I replace the cam without removing the hood ?
Thanks again for all of your help. Great forum.
Thanks again for all of your help. Great forum.
Le Mans Master
Joined: Mar 2004
Posts: 7,502
Likes: 1,510
From: Little Rock AR
You need a new cam and lifters. Probably a timing chain set.
Other people will toss out cam advice. Big can of worms to sort out there. I picked the stock one to put in mine. Your results may vary.
Other people will toss out cam advice. Big can of worms to sort out there. I picked the stock one to put in mine. Your results may vary.
Le Mans Master
Joined: Sep 2001
Posts: 7,739
Likes: 630
From: Unreconstructed, South Carolina
Other than head rebuild ... what's your budget for remainder?
Before you go further ... get # 1 piston itself at TDC; then verify the zero on damper-timing tab agrees with piston.
You'll need to lay the radiator & support forward (if not remove them). You MAY be able to do the job with hood in place? ... but it'll make the the job much harder ...
... I suggest remove hood. Also remove fan, water pump, damper & timing cover.
Before you go further ... get # 1 piston itself at TDC; then verify the zero on damper-timing tab agrees with piston.
You'll need to lay the radiator & support forward (if not remove them). You MAY be able to do the job with hood in place? ... but it'll make the the job much harder ...
... I suggest remove hood. Also remove fan, water pump, damper & timing cover.