Opinions on L48 aluminum head upgrade
01-07-2018, 11:57 AM
#1
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Opinions on L48 aluminum head upgrade
So I have been saving up some money to finally spend some money on some aluminum heads for my 74 L48. This engine is not stock so heads would be one of the last big upgrades I can do to the engine before having to redo the bottom end.
Current engine mods:
Holley 670 SA
Edelbrock Performer EPS 2701
MSD Pro Billet Ignition
Crane 274H06, 218int/218ex at 050, 274int/274ex, .450/.450, 106 lobe sep.
Hooker 1 5/8 headers w/ e. cutouts
The aluminum heads I've been looking at are Trick Flow Super 23 175cc heads. https://www.summitracing.com/parts/tfs-30310002 . My plan was to get these heads since they have a small combustion chamber at 56cc which would help to raise my compression, and since they are 175cc heads they would make slightly more bottom end torque than heads at 195cc or higher. My plan for a head gasket was to use a Fel Pro 1094 at .015in compressed thickness. This combined with the 56cc heads and the 12cc stock dished pistons would result in good quench and a calculated 10.37:1 compression ratio, which is far better than the less than 8.5:1 factory rating. But I am assuming from the bottom end being 44 years old, it has lost some compression over the years so I'm thinking I would probably be around 10:1 compression.
I am asking for your guys' opinions and suggestions over my plans before I start thinking about ordering anything. I am no expert over this stuff, I am just learning about compression and head stuff so let me know if there is anything I should know about. This car a 4 speed, stock gears, car show/weekend cruiser but I still want fun, reliable power. As the car sits right now, it runs great but I think new heads would make it 10x better than with the factory smog heads. I'm hoping for at least 10:1 compression for the power and the crisp sound that it produces with a cam, showing up a car shows with the cutouts open, I gotta set first impressions with a powerful sound. If I do get these heads I plan on using 1.6 roller rockers to bring the .450/.450 lift on the cam to around .480/.480.
Also, what kind of power do you think the car would be making with these heads and my current specs?
Thanks for all the help
Current engine mods:
Holley 670 SA
Edelbrock Performer EPS 2701
MSD Pro Billet Ignition
Crane 274H06, 218int/218ex at 050, 274int/274ex, .450/.450, 106 lobe sep.
Hooker 1 5/8 headers w/ e. cutouts
The aluminum heads I've been looking at are Trick Flow Super 23 175cc heads. https://www.summitracing.com/parts/tfs-30310002 . My plan was to get these heads since they have a small combustion chamber at 56cc which would help to raise my compression, and since they are 175cc heads they would make slightly more bottom end torque than heads at 195cc or higher. My plan for a head gasket was to use a Fel Pro 1094 at .015in compressed thickness. This combined with the 56cc heads and the 12cc stock dished pistons would result in good quench and a calculated 10.37:1 compression ratio, which is far better than the less than 8.5:1 factory rating. But I am assuming from the bottom end being 44 years old, it has lost some compression over the years so I'm thinking I would probably be around 10:1 compression.
I am asking for your guys' opinions and suggestions over my plans before I start thinking about ordering anything. I am no expert over this stuff, I am just learning about compression and head stuff so let me know if there is anything I should know about. This car a 4 speed, stock gears, car show/weekend cruiser but I still want fun, reliable power. As the car sits right now, it runs great but I think new heads would make it 10x better than with the factory smog heads. I'm hoping for at least 10:1 compression for the power and the crisp sound that it produces with a cam, showing up a car shows with the cutouts open, I gotta set first impressions with a powerful sound. If I do get these heads I plan on using 1.6 roller rockers to bring the .450/.450 lift on the cam to around .480/.480.
Also, what kind of power do you think the car would be making with these heads and my current specs?
Thanks for all the help
01-07-2018, 12:23 PM
#2
Le Mans Master
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The one thing that caught my eye is your algebra. If you have a 450 lift now, you will not have 480 w/ 1.6 rockers. Take the base lobe of the cam and multiply by 1.6.
That new ratio can cause problems in some builds because of the awkward geometry, strain on the valvesprings, valveguides, etc. Some dyno test have shown little to no gain with 1.6 anyway. If you wanted 480+ lift, buying the correct cam would be in your favor instead of using a crutch to get there. Might want to rethink this.
Update: A better solution might be the Comps 1.52 rockers. Gives you a little more lift w/o the strains of 1.6
That new ratio can cause problems in some builds because of the awkward geometry, strain on the valvesprings, valveguides, etc. Some dyno test have shown little to no gain with 1.6 anyway. If you wanted 480+ lift, buying the correct cam would be in your favor instead of using a crutch to get there. Might want to rethink this.
Update: A better solution might be the Comps 1.52 rockers. Gives you a little more lift w/o the strains of 1.6
Last edited by HeadsU.P.; 01-07-2018 at 12:50 PM.
01-07-2018, 12:27 PM
#3
.450/1.5*1.6=.480
01-07-2018, 12:49 PM
#4
Le Mans Master
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01-07-2018, 02:10 PM
#5
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St. Jude Donor '22
a little high comp ratio.
44 years is not the issue but miles are.
what is the quench at .015?
remember, cast pistons.
what are future plans?
you might go for a 9.5 ish C/R
to possibly save the low block?
then later when the bottom gets a new setup start pushing 10 plus?
either way, good luck
44 years is not the issue but miles are.
what is the quench at .015?
remember, cast pistons.
what are future plans?
you might go for a 9.5 ish C/R
to possibly save the low block?
then later when the bottom gets a new setup start pushing 10 plus?
either way, good luck
01-07-2018, 02:16 PM
#6
Race Director
1.5 rockers are 1.52. Now you're talking about redoing the bottom end at some point. Doing what to it? Leaving it as a 350? Then the small chambered heads are acceptable. If you're going to go 383 like just about everybody does you need to buy heads that are big enough for that displacement so you don't have to buy them twice. Better to have slightly lazy engine now then to have $1,500 worth of heads with chambers that are too small later and you're also then stuck with this Pistons. Are you going to have too much compression if you put flat pistons in it when you rebuild the bottom in. You need to seriously think about your time frame before you do anything to the bottom end of that engine and what it's going to be. Before you go by heads.
Last edited by derekderek; 01-07-2018 at 02:26 PM.
01-07-2018, 02:51 PM
#7
Le Mans Master
I got a couple thoughts on your plans. Take it or leave it up to you.
Bumping the compression that much with no other changes could give you several challenges.
one is that the ring seal is not likely good enough to take that bump in compression without becoming an oil burner.
second is that you still are dealing with the stock dish pistons that offer no quench pad on the piston top.
so any kind of quench with that piston top design is questionable.
Take a look at the piston top design in this thread. Note the lack of any kind of quench pad. They are also pretty limited on max HP production due to the cast aluminum construction. Hypers would better if you're looking to be north of 350 HP.
https://www.corvetteforum.com/forums...mber-size.html
Check post #31 for the measured CC of the L-48 piston.
Now look at this type of dish piston. The flat area is a quench pad promoting both heat transfer and turbulence to the air fuel mixture making detonation much less likely, particuarly at higher CR's.
https://goo.gl/images/K7Urs7
The con rod and main rod bearings may need refreshing at least. No telling what their condition is unless you've replaced them or changed them yourself.
106 is a pretty narrow LSA for a 350. You could probably benefit from a high stall converter, even in it's present configuration. Do you have much vacuum right now? If someones got it idling good with that LSA and that low of a CR then they've done well. That cam has 62* of overlap. Quite a bit for a street car.
I happen to agree with getting the lift as high as you can, at least with more CR than it's current config. More lift more air and fuel in. I use 1.6RR just for this reason. My lift is .549 at the valve. No detrimental effects on the valve train.
However this will effectively increase your overlap a little and may be detrimental to it's ability to idle. If CR is increased though then it will behave better, more vacuum and power will come on sooner than with it's current CR.
The minimum recommended CR for that cam is 8.75. Stock the L-48 is about 7.7 measured, vs the 8.5 advertised.
Bumping the compression that much with no other changes could give you several challenges.
one is that the ring seal is not likely good enough to take that bump in compression without becoming an oil burner.
second is that you still are dealing with the stock dish pistons that offer no quench pad on the piston top.
so any kind of quench with that piston top design is questionable.
Take a look at the piston top design in this thread. Note the lack of any kind of quench pad. They are also pretty limited on max HP production due to the cast aluminum construction. Hypers would better if you're looking to be north of 350 HP.
https://www.corvetteforum.com/forums...mber-size.html
Check post #31 for the measured CC of the L-48 piston.
Now look at this type of dish piston. The flat area is a quench pad promoting both heat transfer and turbulence to the air fuel mixture making detonation much less likely, particuarly at higher CR's.
https://goo.gl/images/K7Urs7
The con rod and main rod bearings may need refreshing at least. No telling what their condition is unless you've replaced them or changed them yourself.
106 is a pretty narrow LSA for a 350. You could probably benefit from a high stall converter, even in it's present configuration. Do you have much vacuum right now? If someones got it idling good with that LSA and that low of a CR then they've done well. That cam has 62* of overlap. Quite a bit for a street car.
I happen to agree with getting the lift as high as you can, at least with more CR than it's current config. More lift more air and fuel in. I use 1.6RR just for this reason. My lift is .549 at the valve. No detrimental effects on the valve train.
However this will effectively increase your overlap a little and may be detrimental to it's ability to idle. If CR is increased though then it will behave better, more vacuum and power will come on sooner than with it's current CR.
The minimum recommended CR for that cam is 8.75. Stock the L-48 is about 7.7 measured, vs the 8.5 advertised.
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BakedPotato65 (01-09-2018)
01-07-2018, 03:22 PM
#8
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St. Jude Donor '22
good write up ^^
baked, personally I would do the bottom end
first. then you can make better decisions and
only deal with top side stuff as time and money
become avail.
or, do as previous poster says,
baked, personally I would do the bottom end
first. then you can make better decisions and
only deal with top side stuff as time and money
become avail.
or, do as previous poster says,
01-07-2018, 03:26 PM
#9
If you are not changing the rings its a roll of the dice. In my case I added 58cc L98 heads to a 55k ZQ3 bottom end to get near 11:1 CR (OEM is spec'ed @ 10.25:1). When I pulled the heads I noticed a couple of pretty good scratches in two of the cylinder walls and almost pulled the whole engine, but after thinking about it I proceeded anyway. So far no oil burning or other issues.
Last edited by Dynra Rockets; 01-07-2018 at 03:30 PM.
01-07-2018, 03:43 PM
#10
Le Mans Master
Member Since: Aug 2017
Location: Cool Northern Michigan
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No, 1.52 are 1.52 rockers because they are after-market not GM. Research has shown that 1.5s are actually 1.4 something.
01-07-2018, 04:46 PM
#11
Race Director
01-07-2018, 05:47 PM
#12
Advanced
Thread Starter
I got a couple thoughts on your plans. Take it or leave it up to you.
Bumping the compression that much with no other changes could give you several challenges.
one is that the ring seal is not likely good enough to take that bump in compression without becoming an oil burner.
second is that you still are dealing with the stock dish pistons that offer no quench pad on the piston top.
so any kind of quench with that piston top design is questionable.
Take a look at the piston top design in this thread. Note the lack of any kind of quench pad. They are also pretty limited on max HP production due to the cast aluminum construction. Hypers would better if you're looking to be north of 350 HP.
https://www.corvetteforum.com/forums...mber-size.html
Check post #31 for the measured CC of the L-48 piston.
Now look at this type of dish piston. The flat area is a quench pad promoting both heat transfer and turbulence to the air fuel mixture making detonation much less likely, particuarly at higher CR's.
https://goo.gl/images/K7Urs7
The con rod and main rod bearings may need refreshing at least. No telling what their condition is unless you've replaced them or changed them yourself.
106 is a pretty narrow LSA for a 350. You could probably benefit from a high stall converter, even in it's present configuration. Do you have much vacuum right now? If someones got it idling good with that LSA and that low of a CR then they've done well. That cam has 62* of overlap. Quite a bit for a street car.
I happen to agree with getting the lift as high as you can, at least with more CR than it's current config. More lift more air and fuel in. I use 1.6RR just for this reason. My lift is .549 at the valve. No detrimental effects on the valve train.
However this will effectively increase your overlap a little and may be detrimental to it's ability to idle. If CR is increased though then it will behave better, more vacuum and power will come on sooner than with it's current CR.
The minimum recommended CR for that cam is 8.75. Stock the L-48 is about 7.7 measured, vs the 8.5 advertised.
Bumping the compression that much with no other changes could give you several challenges.
one is that the ring seal is not likely good enough to take that bump in compression without becoming an oil burner.
second is that you still are dealing with the stock dish pistons that offer no quench pad on the piston top.
so any kind of quench with that piston top design is questionable.
Take a look at the piston top design in this thread. Note the lack of any kind of quench pad. They are also pretty limited on max HP production due to the cast aluminum construction. Hypers would better if you're looking to be north of 350 HP.
https://www.corvetteforum.com/forums...mber-size.html
Check post #31 for the measured CC of the L-48 piston.
Now look at this type of dish piston. The flat area is a quench pad promoting both heat transfer and turbulence to the air fuel mixture making detonation much less likely, particuarly at higher CR's.
https://goo.gl/images/K7Urs7
The con rod and main rod bearings may need refreshing at least. No telling what their condition is unless you've replaced them or changed them yourself.
106 is a pretty narrow LSA for a 350. You could probably benefit from a high stall converter, even in it's present configuration. Do you have much vacuum right now? If someones got it idling good with that LSA and that low of a CR then they've done well. That cam has 62* of overlap. Quite a bit for a street car.
I happen to agree with getting the lift as high as you can, at least with more CR than it's current config. More lift more air and fuel in. I use 1.6RR just for this reason. My lift is .549 at the valve. No detrimental effects on the valve train.
However this will effectively increase your overlap a little and may be detrimental to it's ability to idle. If CR is increased though then it will behave better, more vacuum and power will come on sooner than with it's current CR.
The minimum recommended CR for that cam is 8.75. Stock the L-48 is about 7.7 measured, vs the 8.5 advertised.
01-07-2018, 06:02 PM
#13
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Thread Starter
Video of engine running with knocking: https://photos.app.goo.gl/oksf4VujsJ4U2l832
01-07-2018, 06:21 PM
#14
Having the bottom end exposed without a pan on would not cause it (assuming you don't have a giant dust storm blowing in your garage). I've had my pan off for several months before.
01-07-2018, 06:25 PM
#15
Advanced
Thread Starter
Ok well that is reassuring, it didn't really make sense to me if that was the cause of it anyway. The car ran perfect before I even touched the oil pan gasket, just leaked. I did replace the timing chain with the pan off, but I don't think that would cause the sound I am getting.
01-07-2018, 06:28 PM
#16
Le Mans Master
Doing something with the bottom end makes good sense. I think the higher compression would blow right by the rings.
Look on racing junk .com I know guys that have gotten some nice stuff cheap, but some have gotten junk too so be careful.
Look on racing junk .com I know guys that have gotten some nice stuff cheap, but some have gotten junk too so be careful.
01-07-2018, 09:30 PM
#17
Le Mans Master
Take a look at Ohio Crankshaft- I've not looked at SBC stuff, but they have some really good deals on BB short blocks. A "you build it" option that cuts some decent size bucks off the cost. And they're on the west side of Ohio- Might even save you some shipping depending on where you are.
Last edited by TimAT; 01-07-2018 at 09:31 PM.
01-07-2018, 10:04 PM
#18
Melting Slicks
Well, it looks like I'm going to be spending the money I had saved for heads on a new block and bottom end... 3 days ago I replaced the oil pan gasket for the second time and today I started the engine affter letting the rtv dry, it sounds like it is about to die. It's making a horrible bottom end knocking/ticking noise which I don't understand why it is. I changed the oil pan gasket in about 45 minutes so none of the bottom end was exposed for long. However the first time I replaced the gasket about 2 weeks ago, the pan was off the engine for about a week because it was too cold to go out and work on it (didn't have a heater for the garage yet). When I started the engine 2 weeks ago it ticked a little but it went away as oil circulated. Now today when I started it, it's giving me a death knock and I'm too scared to let it run to see if oil isn't getting somewhere. I have 50-60lbs of oil pressure so I know oil is getting circulated. I don't if it's the colder weather today (38 degrees) or if something happened the first time the engine ticked and now it's showing even more or what. But I guess I'm just gonna look into getting a new engine to build and hopefully get done before car show season is here.
Video of engine running with knocking: https://photos.app.goo.gl/oksf4VujsJ4U2l832
Video of engine running with knocking: https://photos.app.goo.gl/oksf4VujsJ4U2l832
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BakedPotato65 (01-09-2018)
01-09-2018, 12:36 PM
#19
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Thread Starter
Remove the sheet metal shield on the bottom of the bellhousing and try running it again. It sounds to me like the shield may be hitting the crank. Since you had the pan off you may have disturbed something down there. I have had this happen and it sounds terrible, but it might be an easy fix. Good luck.