carbed lq4 with ls3 heads
08-22-2014, 10:18 AM
#1
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carbed lq4 with ls3 heads Well I decided to go with the ls3 heads instead of 243 heads. But know my question is for the people that have combos like this is how big of camshaft can I put in here without have to flycut the pistons which I might end up doing but would like to try to stay away from doing it. I saw a build on here were a guy used the tsp 233 239 cam and seemed to do pretty well? thanks for any info
08-22-2014, 03:33 PM
#3
This is a really common question. This is a topic that I am going to address further in the carbureted LS camshaft sticky. In order to answer this question, the first thing you will have to know is your "valve drop" measurement. This is detailed in this post:
https://ls1tech.com/forums/18356789-post4.html
Here is the piece of that post that is relevant:
Valve Drop
The object of measuring valve drop is to determine how far a valve can open before it touches the piston while that piston is at top dead center in the cylinder. Knowing this figure is the only way one can estimate piston-to-valve clearance without actually measuring an assembled engine. Furthermore, knowing this allows engine builders to determine which camshafts might fit in a given engine without further modification. There are two ways to measure valve drop. Actual valve drop (assembled) and estimated valve drop (not assembled).
If you will measure your valve drop to 3 decimal places in inches, you can do a pretty good job of estimating what cams will fit.
https://ls1tech.com/forums/18356789-post4.html
Here is the piece of that post that is relevant:
Valve Drop
The object of measuring valve drop is to determine how far a valve can open before it touches the piston while that piston is at top dead center in the cylinder. Knowing this figure is the only way one can estimate piston-to-valve clearance without actually measuring an assembled engine. Furthermore, knowing this allows engine builders to determine which camshafts might fit in a given engine without further modification. There are two ways to measure valve drop. Actual valve drop (assembled) and estimated valve drop (not assembled).
Actual (assembled) Valve Drop
The most fool proof way is to measure valve drop in an assembled engine. Just rotate the crank until the the piston is at top dead center and then lower the valve until it touches the piston. Whatever that distance is, that is your valve drop. Do this for both intake and exhaust valves as they are most often different.
Estimated (unassembled) Valve Drop
You can also estimate valve drop while the cylinder head is not on the engine. For this start by placing the cylinder head on a flat surface and lower the valve until it touches the surface in which the head rests. This measurement of how far the valve "drops" is your cylinder head valve drop. Next measure your piston to deck height relationship. Most LS engines have a positive deck(between .005" to .008" is most often reported by builders). Next measure the thickness of your head gasket. The formula looks something like this: Cylinder head valve drop + head gasket thickness - positive deck height = valve drop. this is very accurate for an engine equipped with flat top pistons. Here is an example:
.155" + .051" - .007" = .199"
Again, do this for both intake and exhaust valves as they are most often different. Also, engines with dome pistons or dished pistons might better be done assembled as it is difficult to account for the different piston surface shapes using this method.
The most fool proof way is to measure valve drop in an assembled engine. Just rotate the crank until the the piston is at top dead center and then lower the valve until it touches the piston. Whatever that distance is, that is your valve drop. Do this for both intake and exhaust valves as they are most often different.
Estimated (unassembled) Valve Drop
You can also estimate valve drop while the cylinder head is not on the engine. For this start by placing the cylinder head on a flat surface and lower the valve until it touches the surface in which the head rests. This measurement of how far the valve "drops" is your cylinder head valve drop. Next measure your piston to deck height relationship. Most LS engines have a positive deck(between .005" to .008" is most often reported by builders). Next measure the thickness of your head gasket. The formula looks something like this: Cylinder head valve drop + head gasket thickness - positive deck height = valve drop. this is very accurate for an engine equipped with flat top pistons. Here is an example:
.155" + .051" - .007" = .199"
Again, do this for both intake and exhaust valves as they are most often different. Also, engines with dome pistons or dished pistons might better be done assembled as it is difficult to account for the different piston surface shapes using this method.
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08-22-2014, 07:38 PM
#8
10 Second Club
SpeedTiggers way is the way I did a lot of SBC's and it works.
239/247 here and .050 off the heads plus fly-cut.
Since you're looking at LS3/L92 heads....I would just do the cuts and get it over with
239/247 here and .050 off the heads plus fly-cut.
Since you're looking at LS3/L92 heads....I would just do the cuts and get it over with
08-22-2014, 08:30 PM
#10
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Gonna have converter built for it but would like to stay around 4000 but plan on bracket racing it and doing some street driven also have victor Jr intake
08-22-2014, 10:23 PM
#14
lindy tools has a nice cutter that they rent out. here is what i had to do with my LS2 to fit my cam. I would lend you mine, but it's too small for that gigantico ls3 valve. this is how mine looked before hitting them with a 3m rolec pad to smooth out the cut and take the edge off the lips.
08-22-2014, 10:26 PM
#16
yes. pull all valves and use the valve guide as a guide for the cutter with a drill. the cutter has a stop on it. you set the depth of your cut using shims.
it was important to use my heads for the cut instead of a stocker since i have trick flows that put the valve at a different angle.
it was important to use my heads for the cut instead of a stocker since i have trick flows that put the valve at a different angle.
08-24-2014, 04:29 PM
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3pedals taught me this simple trick as well. Works great!!!! 3pedals is a do-it-yourself genius!