Wow, I dont think that is going to work so good. I mean, how much bigger do you have to go to shroud the valves? a 2.00" valve on the stock 4.8/5.3 valve has to be deshrouded to work and even then, it is still pretty shrouded in there. Did you tell the guy that was doing your heads that this was for a 3.78" bore and not a 3.90" bore like on the 5.7"s? If you did, then I really dont think this guy has a clue as to what he is working with. Not to try to **** you off or anything, but I would expect your truck to be a real dog without the nitrous. Good luck man, keep us updated on how it works out for you.

 

ok ok. it is jay at absolute speed. he has done heads for a lot of people here on the board that are very satisfied with his work. i told him exactly what i had and my plans. i found an email that he sent me with his opinion. 2.00 and 1.57 is what they are going to be. he said that it would be set up perfect for the nos and the cam and rockers i am running. now that i have it right. what do you think.

 

the stock valve sizes on a 5.3l head is 1.89 int, and 1.55 exh, so youre saying that with a 3.78 bore i shouldnt go bigger that a 2.0 valve? im just curious since vhp said that a 2.05 int valve would be good, but i dont think they knew i had a 5.3l.

 

nah hes sayin smaller than 2.0

well. darnit. i meant yes. hes saying stay smaller than a 2.00 valve

 

Here is a pictur of a 2.00" intake and 1.55" exhaust valve in a stock bore 5.3 head. Notice how close the valve is to the side of the chamber wall. This is how big your bore is on your engine. There is not a lot of room for air to get by there. If you open the chamber up more then you are making an area for air to collide on the side of the bore wall. Just think about it like this you have a 3.78" bore. Add the valve sizes up and you get 3.57" now subtract 3.57 from 3.78. That is .210 thousandths. Divide that by three. That is the approximate space you would have between the cylinder walls and between the valves themselves (equally). You end up with around .007 thousandths clearance with a 2.00" intake valve, 1.57" exhaust valve on a 3.78" bore. Get a feeler gauge and look at how much .007 thousandths is. There is a lot of shrouding going on there.

 

Wow, great picture Wess. I'm startin to see eye to eye with you now. Seems shrouding would really take affect with those size valves on such a small bore like we have. Am I wrong?

If some of you guys are lost by the word shrouding. Look at the pic. See how close the cylinder wall is to the outside edges (left and right) of the valves. This can limit airflow.

 

im doing some research and all im getting is 5.3l heads have 1.89 int valves stock,http://www.smokemup.com/tech/ls1.php whick means that an upgrade to 2.0's would be a good idea, or maybe some shaved 6.0l heads.

 

Does valve size have an affect on velocity?

Hink,

Thats a helpful site.
The 6L's have a 4 inch bore compared to our 3.78. So, the 6.0L heads might not be your best option.

 

Here is some more info by Brian Tooley The owner of TEA Cylinder heads:

https://ls1tech.com/forums/showthread.php?t=145060

If you have a 3.90" bore engine then a 6.0L head does not flow like a LS6 head due to the air coming out into the as cast 4.00" size chamber of the 6.0L casting and then hitting the top of the bore, inducing turbulence. This and the fact that a 6.0L casting is 70cc and only yields about 9.5:1 compression is why PP decided to weld the castings they have to the smaller bore. Take my Stg 2.5 LS6 heads, on a 4.00 bore they flow 325 @ .600" on a 3.90" they still flow 320 @ .600", the same program in a 6.0L head flowed 324 @ .600" but on a 3.90" bore they only flowed 309 @ .600", all of this was flowed in house on our bench. So you can see how having the chamber diameter bigger then the bore hurts the airflow.

If you have a 4.00" or bigger bore engine then it doesn't make sense to weld up the chambers to the smaller diameter, just to have to port it out to 4.00" diameter where it needs to be. If a head can be milled a small amount to achieve a desired compression ratio then that is the way to go. So in short, get some 6.0L heads, we have new cores for $400 a pair, and mill them .018" to get to the 67cc that you need. There will be no problems milling these heads this amount, we mill practically every head we do at least this much. And it doesn't make sense to buy LS6 heads only to have to port the chambers out to a 4.00" bore and try to make them 67cc. Hope this helps.


https://ls1tech.com/forums/showthread.php?t=138650

They will sorta fit but not give accurate numbers. If you plan on running a set of heads on a 3.90" bore then flow it on a 3.90" bore.

For example
our Stg 2.5 6.0L/LS6 intake program on a LS6 head with the stock 3.90" bore chamber flows 325 @.600" on a 4.00" bore and 320 on a 3.90" bore- only a loss of 5cfm

The 6.0L head with the same exact everything flows 324 @ .600" on the 4.00" bore but only 309 @ .600" on the 3.90"- a loss of 15 cfm

so you can see if you flow a head with a chamber that is bigger then the bore you flow it on then it is very ditrimental to the flow, so you may not get the full answer if you port and flow LS1 heads on a 4.00" bore fixture. Hope this helps. Brian

https://ls1tech.com/forums/showthread.php?t=126951

If the chambers are not properly opened up to the 3.900" bore (they are 3.800" stock) a 2.00" valve would be too big. We do these with anywhere from a 2.02-2.05 intake and a 1.55-1.57 exhaust. My car went 9's on the spray with just a 2.02 and the stock exhaust valves of 1.55

We do the CNC porting of these heads at around $699 per pair, that includes the entire intake port, exhaust port and combustion chamber. Hope this helps.
__________________
http://www.totalengineairflow.com



__________________
http://www.totalengineairflow.com

 

Reaper,

The set Allan is working for you now, did he suggest stock valve diameter, or was that your choice?

Thanks,

Kyle