383 LT4 Piston
Thread Starter
Pro
Joined: Dec 2008
Posts: 512
Likes: 2
From: Denton TX
383 LT4 Piston
Any number of compression calculators will tell you that a 12cc inverted dome piston in a 3.75 Stroke/4.030 Bore/6.00 rod/.0250 deck to piston clearance/.043 compressed head gasket/ 54.4 cc head...will net (stock?) about 10.8 to 1 CR. Now, the big question where is the piston at....I have found only a couple. Anyone use a TRW-LW2617F30? Its a forged piece that seems to fit the specs. You guys building the 383 in an LT4 based engine must have some idea...I hope.
Sam
Sam
Le Mans Master
Joined: Aug 2000
Posts: 8,838
Likes: 31
From: Australia
Some inverted dome 3.75 stroke / 6" pistons
Probe # 12345 10.3 w/ 58 cc head
Ross #99529 (+40) 10.2 w/58 cc
Wiseco #PT009H3 9.9 w/ 58 cc
# PT095H3 10.7 w/58 cc
SRP #138103 10.4 w/ 58cc
Are you committed to a 6" rod?
Probe # 12345 10.3 w/ 58 cc head
Ross #99529 (+40) 10.2 w/58 cc
Wiseco #PT009H3 9.9 w/ 58 cc
# PT095H3 10.7 w/58 cc
SRP #138103 10.4 w/ 58cc
Are you committed to a 6" rod?
Thread Starter
Pro
Joined: Dec 2008
Posts: 512
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From: Denton TX
By the way..thanks for your response very valuable
Le Mans Master
Joined: Aug 2000
Posts: 8,838
Likes: 31
From: Australia
I was told that is only to do with the balance.
I believe the lack of choice with the inverted / 6" pistons is to do with the fact that the 1.20 CH and inverted dome leave little material in the piston crown to play with.
I note most of the above suppliers state not for over 150 NOS shot
I believe the lack of choice with the inverted / 6" pistons is to do with the fact that the 1.20 CH and inverted dome leave little material in the piston crown to play with.
I note most of the above suppliers state not for over 150 NOS shot
Thread Starter
Pro
Joined: Dec 2008
Posts: 512
Likes: 2
From: Denton TX
rodj.
You could be right about the balance issue..My engine guy indicated that it was easier to balance the 6" vs 5.7" setup. The begs another question..is the stock LT4 internally balanced, externally balanced or balanced externally at the rear and internally at the front...anyone know?
You could be right about the balance issue..My engine guy indicated that it was easier to balance the 6" vs 5.7" setup. The begs another question..is the stock LT4 internally balanced, externally balanced or balanced externally at the rear and internally at the front...anyone know?
Le Mans Master
Joined: Aug 2000
Posts: 8,838
Likes: 31
From: Australia
All 1 pce seal RMS (LTX ) engines are factory external balance at rear ; hense the weight on the flexplate.
As a note
the factory considers the crankshaft an "internal" part even though the counterweight on the early 2 pce RMS engines is on the crank flange outside the engine.Some people wrongly claim this makes it a EXT balance
The design change to 1pce seal meant the weight could not be cast on the crank flange so it was added to the flywheel / flexplate which is "external" to the engine
Melting Slicks
Joined: Jun 2000
Posts: 3,215
Likes: 6
From: Tampa Florida
sampaschal: Sounds like you might want to plan the engine before you buy any more parts. Buying before you have a plan is not the ideal way...
383 is more common than a 350 build! Suggest a SBC Engine Mod book for starters.
Another issue with 6.0 rod is an oil support rail for the oil scraper...some feel this makes it difficult to minimize oil consumption. I agree and kept it simple with a 5.7 rod.
Switching rods for a crank that was not designed for that may also mean larger/smaller counterweights???
Good Luck with the build...I have a few details on my site.
383 is more common than a 350 build! Suggest a SBC Engine Mod book for starters.
Another issue with 6.0 rod is an oil support rail for the oil scraper...some feel this makes it difficult to minimize oil consumption. I agree and kept it simple with a 5.7 rod.
Switching rods for a crank that was not designed for that may also mean larger/smaller counterweights???
Good Luck with the build...I have a few details on my site.
Thread Starter
Pro
Joined: Dec 2008
Posts: 512
Likes: 2
From: Denton TX
sampaschal: Sounds like you might want to plan the engine before you buy any more parts. Buying before you have a plan is not the ideal way...
383 is more common than a 350 build! Suggest a SBC Engine Mod book for starters.
Another issue with 6.0 rod is an oil support rail for the oil scraper...some feel this makes it difficult to minimize oil consumption. I agree and kept it simple with a 5.7 rod.
Switching rods for a crank that was not designed for that may also mean larger/smaller counterweights???
Good Luck with the build...I have a few details on my site.
383 is more common than a 350 build! Suggest a SBC Engine Mod book for starters.
Another issue with 6.0 rod is an oil support rail for the oil scraper...some feel this makes it difficult to minimize oil consumption. I agree and kept it simple with a 5.7 rod.
Switching rods for a crank that was not designed for that may also mean larger/smaller counterweights???
Good Luck with the build...I have a few details on my site.
I have built several 383s...just not an LT4 version. although it may seem that I don't have a real plan, sometimes it turns out to be more process than plan. I think we have it
nailed at this point...Sam
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