View Full Version : Help ls3 block 4.125 bore 4.070 Heads issue


mohammed_k81
04-04-2012, 12:50 AM
Hi I have an ls3 Block using a crank 4.125 and piston 4.070 Rod 6.125

Can I install ls7 heads or is the piston to small I canít seem to find threads about this topic and understand

If I canít use ls7 heads please someone provide me with link to best ls3 heads.

mohammed_k81
04-04-2012, 01:27 AM
So my Bore is 4.070 my stroke is 4.125 rods 6.125 Cubic 429.33

People tell you I cant use ls7 and should just get the PRC Aftermarket LS3 250cc CNC Cylinder Heads from texas speed?

A_VAS
04-05-2012, 03:12 PM
you can use a LS7 head yes, if you drop down to smaller exhaust valve size.

N2OBaby
04-05-2012, 04:45 PM
Hot Rod mag built a resleaved LS3 block to 468 cid and they got good results from LS3 & aftermarket LS3 heads this maybe an option.

87silverbullet
04-05-2012, 09:03 PM
you can use a LS7 head yes, if you drop down to smaller exhaust valve size.

I wouldn't even try dealing with the hassle of trying to get a smaller exhaust valve in an LS7 head. Changing to a smaller valve would work but it would more than likely mess with the efficiency of the head. It wouldn't release the full potential of a motor of the size of the OP.

Hot Rod mag built a resleaved LS3 block to 468 cid and they got good results from LS3 & aftermarket LS3 heads this maybe an option.

I wouldn't consider an LS3 head for a motor that size. My friend has a full weight GTO that comes in at 3800lbs he has an LSX block 451 in it that had LS3 ported heads on it. It ran 10.80's on motor he pulled them off and ran a set of LS7's on it and gained 3 tenths just from the head swap. The cam is a mild 23x/24x duration cam.

Will it work and make power? Yes.

Can it be better with a set of LS7 heads? Yes.

To the OP Texas-Speed also makes a set of small bore LS7 heads for applications just like yours. It is designed for 4.060 bore and larger.

Here is the link to them on TSP website.
http://texas-speed.com/p-1236-prc-ls7x-265cc-70l-cnc-heads.aspx

Here is a thread with alot of pics on it.
http://ls1tech.com/forums/generation-iv-internal-engine/1521427-tsp-prc-265cc-ls7-heads-min-4-060-bore.html

DietCoke
04-05-2012, 10:08 PM
I have TSP's small LS7x heads on my car. 429ci LS3 4.07 Bore * 4.125 stroke with a mamofied fast ls7 intake. Car runs great.

mohammed_k81
04-08-2012, 12:15 AM
So may goal is 441 ci with after market ls7 heads everyone thanks for the support

87silverbullet
04-08-2012, 08:29 AM
Hi I have an ls3 Block using a crank 4.125 and piston 4.070 Rod 6.125

Can I install ls7 heads or is the piston to small I canít seem to find threads about this topic and understand

If I canít use ls7 heads please someone provide me with link to best ls3 heads.

So my Bore is 4.070 my stroke is 4.125 rods 6.125 Cubic 429.33

People tell you I cant use ls7 and should just get the PRC Aftermarket LS3 250cc CNC Cylinder Heads from texas speed?

So may goal is 441 ci with after market ls7 heads everyone thanks for the support

Wait,wait,wait....stop. Your first post is mumbo jumbo. Your second post you say your bore is 4.070 and your stroke is 4.125 and comes in at 429 cubes. So I post the LS7 head that you can use on that smaller bore to feed your motor.

Now in your third post you say you are going 441. You can't get 441 from an LS3 block unless you are going to run some crazy stroke above 4.125 which I wouldn't recommend. 441's are usually made from LS7 blocks using a 4.125 crank. Then with the larger bore of the LS7 block you are able to use an LS7 head with the stock size valves which in turn opens up more options for you.

My question is, what are you going with? 429? 441? LS7 block? LS3 block?

mohammed_k81
04-09-2012, 09:57 AM
Wait,wait,wait....stop. Your first post is mumbo jumbo. Your second post you say your bore is 4.070 and your stroke is 4.125 and comes in at 429 cubes. So I post the LS7 head that you can use on that smaller bore to feed your motor.

Now in your third post you say you are going 441. You can't get 441 from an LS3 block unless you are going to run some crazy stroke above 4.125 which I wouldn't recommend. 441's are usually made from LS7 blocks using a 4.125 crank. Then with the larger bore of the LS7 block you are able to use an LS7 head with the stock size valves which in turn opens up more options for you.

My question is, what are you going with? 429? 441? LS7 block? LS3 block?


Sorry what I mean is I have decided to upgrade my current engine which is an ls3 429, what I will do is sleeve it and increase the bore piston size to 4.125 so that I can use LS7 heads and gain maximum hp because I will not be using Nos.



I am looking to get the most HP possible NA

A_VAS
04-10-2012, 01:21 PM
I wouldn't even try dealing with the hassle of trying to get a smaller exhaust valve in an LS7 head. Changing to a smaller valve would work but it would more than likely mess with the efficiency of the head. It wouldn't release the full potential of a motor of the size of the OP.


maybe what's perceived as a hassle for some is easy for others who know

87silverbullet
04-11-2012, 10:40 AM
Yes, but then you do all that work just to get an LS7 head on a motor that makes the same power as a ported LS3. Now that is what I call a hassle