High compression 5.3
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Launching!
Joined: Aug 2012
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From: harrisville R.I
High compression 5.3 This winter I plan on turning my 4.8 into a high compression 5.3. I read about this a while ago. For those that don't know how it's done, I am putting a 5.3 crank and connecting rods with my 4.8 flat top pistons into my 4.8 and will have a high comp 5.3, Now why i'm posting this is i'm wondering if anyone else has done this and if so, how did you like the results. Thank you very much in advance.
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There were a few other changes, but the L33 had 0cc flat tops vs. the LM4's -6.7cc dished pistons for instance. The heads and cams were different as well, so pistons are part of the gain...but it would give you an idea of where you stood vs. a LR4.
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Yes just a bit of lift. If anyone is looking for it, we reference the RPO code articles at Summit Racing's Customer service page all the time.
https://help.summitracing.com/app/results/kw/lm7/page/1 has some of LM7 Specs and
https://help.summitracing.com/app/results/kw/l33/page/1 has some links to L33 materials as a for instance.
Casting numbers, chamber volumes and other specs are there too.
https://help.summitracing.com/app/results/kw/lm7/page/1 has some of LM7 Specs and
https://help.summitracing.com/app/results/kw/l33/page/1 has some links to L33 materials as a for instance.
Casting numbers, chamber volumes and other specs are there too.
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If your wondering about an increase in power with just compression alone, prolly 8-10ish across the board. You however will find more power in increasing your stroke as well. I never dyno’d this, so just guessing.
I just recently built a 5.3 flat-topped piston engine. Have been working on swapping this engine into a '70 C-10 truck. Was able to start it today! It has a mild cam, and stock heads with a valve job-guides, seals, seats & valves cut for 5 angle, and mild porting work done by me.
I won't be able to post back and tell you how well it runs though until I get the exhaust installed. I can tell you that it seems to rev much faster off idle than my LQ9-370 engine with 220/224 cam. This little 5.3L wants to scream as soon as you give it a little nudge of the throttle. It "seems" a little more snappy off-idle.
As said above-flat-tops in a 5.3L has been done not dozens, but THOUSANDS of times, if not hundreds of thousands of times. One thing I will tell you though is that you need to measure your piston height in relation to the deck. The after-market flat-top pistons will actually sit down in the bore, whereas using TRUE GM 4.8 pistons will stick out of the block several thousands. SO, if you are running budget after-market flat-tops, and they are down in the bore a few thousands, you will not gain ANYTHING as compared to using real GM pistons that extend out of the block which will give you a little bump in compression. You can find real GM 4.8L pistons on E-bay all the time. I used real GM 4.8L pistons in my 5.3 and they extend out of the block a little over .007" of an inch. My pistons came with the correct GM part #'s on them-and were twice the cost of the budget after-market flat tops. The after-market flat-tops are designed to be able to work with blocks that have been decked so that they don't stick out of the bore... Just food for thought. If you have your piston part #, you can check your piston crown height compared to piston pin location and figure you out *approximately* where the piston will fall in relation to deck height.
I won't be able to post back and tell you how well it runs though until I get the exhaust installed. I can tell you that it seems to rev much faster off idle than my LQ9-370 engine with 220/224 cam. This little 5.3L wants to scream as soon as you give it a little nudge of the throttle. It "seems" a little more snappy off-idle.
As said above-flat-tops in a 5.3L has been done not dozens, but THOUSANDS of times, if not hundreds of thousands of times. One thing I will tell you though is that you need to measure your piston height in relation to the deck. The after-market flat-top pistons will actually sit down in the bore, whereas using TRUE GM 4.8 pistons will stick out of the block several thousands. SO, if you are running budget after-market flat-tops, and they are down in the bore a few thousands, you will not gain ANYTHING as compared to using real GM pistons that extend out of the block which will give you a little bump in compression. You can find real GM 4.8L pistons on E-bay all the time. I used real GM 4.8L pistons in my 5.3 and they extend out of the block a little over .007" of an inch. My pistons came with the correct GM part #'s on them-and were twice the cost of the budget after-market flat tops. The after-market flat-tops are designed to be able to work with blocks that have been decked so that they don't stick out of the bore... Just food for thought. If you have your piston part #, you can check your piston crown height compared to piston pin location and figure you out *approximately* where the piston will fall in relation to deck height.
Thread Starter
Launching!
Joined: Aug 2012
Posts: 203
Likes: 2
From: harrisville R.I
I just recently built a 5.3 flat-topped piston engine. Have been working on swapping this engine into a '70 C-10 truck. Was able to start it today! It has a mild cam, and stock heads with a valve job-guides, seals, seats & valves cut for 5 angle, and mild porting work done by me.
I won't be able to post back and tell you how well it runs though until I get the exhaust installed. I can tell you that it seems to rev much faster off idle than my LQ9-370 engine with 220/224 cam. This little 5.3L wants to scream as soon as you give it a little nudge of the throttle. It "seems" a little more snappy off-idle.
As said above-flat-tops in a 5.3L has been done not dozens, but THOUSANDS of times, if not hundreds of thousands of times. One thing I will tell you though is that you need to measure your piston height in relation to the deck. The after-market flat-top pistons will actually sit down in the bore, whereas using TRUE GM 4.8 pistons will stick out of the block several thousands. SO, if you are running budget after-market flat-tops, and they are down in the bore a few thousands, you will not gain ANYTHING as compared to using real GM pistons that extend out of the block which will give you a little bump in compression. You can find real GM 4.8L pistons on E-bay all the time. I used real GM 4.8L pistons in my 5.3 and they extend out of the block a little over .007" of an inch. My pistons came with the correct GM part #'s on them-and were twice the cost of the budget after-market flat tops. The after-market flat-tops are designed to be able to work with blocks that have been decked so that they don't stick out of the bore... Just food for thought. If you have your piston part #, you can check your piston crown height compared to piston pin location and figure you out *approximately* where the piston will fall in relation to deck height.
I won't be able to post back and tell you how well it runs though until I get the exhaust installed. I can tell you that it seems to rev much faster off idle than my LQ9-370 engine with 220/224 cam. This little 5.3L wants to scream as soon as you give it a little nudge of the throttle. It "seems" a little more snappy off-idle.
As said above-flat-tops in a 5.3L has been done not dozens, but THOUSANDS of times, if not hundreds of thousands of times. One thing I will tell you though is that you need to measure your piston height in relation to the deck. The after-market flat-top pistons will actually sit down in the bore, whereas using TRUE GM 4.8 pistons will stick out of the block several thousands. SO, if you are running budget after-market flat-tops, and they are down in the bore a few thousands, you will not gain ANYTHING as compared to using real GM pistons that extend out of the block which will give you a little bump in compression. You can find real GM 4.8L pistons on E-bay all the time. I used real GM 4.8L pistons in my 5.3 and they extend out of the block a little over .007" of an inch. My pistons came with the correct GM part #'s on them-and were twice the cost of the budget after-market flat tops. The after-market flat-tops are designed to be able to work with blocks that have been decked so that they don't stick out of the bore... Just food for thought. If you have your piston part #, you can check your piston crown height compared to piston pin location and figure you out *approximately* where the piston will fall in relation to deck height.
Thread Starter
Launching!
Joined: Aug 2012
Posts: 203
Likes: 2
From: harrisville R.I
Hello Che70velle I appreciate you getting back to me. I am increasing the stroke. Mine is a 4.8 and i'm adding 5.3 connecting rods and crank. i'm just using the 4.8 pistons. i'll let you know next spring just what i noticed. I didn't mention my car is a 74 mgb weighing about 2300 lbs.
It'll work out great. You'll end up with a 10.5:1 325 in a 2300 lb car!
That is if you're using 61.5 cc truck heads and not 799 truck heads.
Like said above it will be a 5.3 with an increase in compression. So it'll give you a small bump in power and tq vs a stock 5.3, but nothing big.
If you're that far into it, you should consider boring it out to at least 3.9 to run a stock LS1 piston, it wont cost all that much and you'll increase cubes and compression. If you do this with 61.5 cc heads you'll be at 11:1, with 799/243 heads you'll be around 10.5
An 11:1 347 sounds like fun too
That is if you're using 61.5 cc truck heads and not 799 truck heads.
Like said above it will be a 5.3 with an increase in compression. So it'll give you a small bump in power and tq vs a stock 5.3, but nothing big.
If you're that far into it, you should consider boring it out to at least 3.9 to run a stock LS1 piston, it wont cost all that much and you'll increase cubes and compression. If you do this with 61.5 cc heads you'll be at 11:1, with 799/243 heads you'll be around 10.5
An 11:1 347 sounds like fun too
Hello Che70velle I appreciate you getting back to me. I am increasing the stroke. Mine is a 4.8 and i'm adding 5.3 connecting rods and crank. i'm just using the 4.8 pistons. i'll let you know next spring just what i noticed. I didn't mention my car is a 74 mgb weighing about 2300 lbs.
Still in the planning stages for a 5.3 alcohol build but on the fence as to leaving it stock bore and stroke to save some $$ for other parts. I'm not sure what heads I want to run on it either but thinking the stock 862's for the compression bump but get them ported and machined for the 2.00" valves but that's more $$. I have the 241's from my LS1 and a set of 243's that look to have been milled 0.01. I'm thinking scrap the LS6 intake idea and run the Victor Jr./ MSD 6LS with a nice carburetor.
I sent you a pm with different piston and rod weights did that info help , if you have any questions lmk.
Thread Starter
Launching!
Joined: Aug 2012
Posts: 203
Likes: 2
From: harrisville R.I
Thread Starter
Launching!
Joined: Aug 2012
Posts: 203
Likes: 2
From: harrisville R.I
Just what do i need besides boring it out. I know i'll need the pistons. And can I use the crank I just bought. It is out of a 2001 surburban 5.3. Thanks in advance.
