Do you know the chamber size of your current 5.3 heads? Stock is about 61.5cc. A set of stock 5.3 heads on an LS1/LS6 block will net you about 10.8:1 compression. That is high, but if you run a big cam, you could probably get by with it. If you heads have a smaller chamber, then its a higher CR.

I think a LS1 swap is a good idea. Less weight, more power, and probably cooler running.

 

When my heads were ported, they told me that they wouldn't mill them that much because I would have too high of a CR. I didn't ask how much they were milled, but I guess it wasn't much. Aren't several F-bodies runing ported 5.3 heads? What CR would be too high?

I'm hoping I could do this since its cheaper than the stroker I want to build. I'm still going to do it but, will take my time and do it right.

 

are you going for a forced induction aplication if so use the 6.o heads if not use the 5.3 that were worked with a cam


marc

 

Basically, the 5.3 trucks have a 9.5:1 compression ratio from the factory, while the LS1 has a 10:1 CR. The 5.3 has dished pistons to reduce the CR while the LS1 has flat tops. With higher compression, you have to run higher grade fuel to prevent detonation. 10.5:1 would be a good CR, that is what an LS6 is. When you go with a bigger cam (more duration), the added overlap drops the cylinder pressure some. So with higher compression and a bigger cam, it will even out. Car guys can get the CR up over 11:1 with a big cam. But for a truck, even with a bigger cam, I'd keep the comression down some. I'd go no more than 10.8:1 and would prefer 10.5 or a little lower. You could have some issues with the heavy vehicle under low rpm engine load with higher compresion.

Did the porters polish the chamber on your 5.3 heads? If so, that could drop your CR enough to run them with no problems. If not, just have the chambers opened up just a little and you'll be fine. I think the LS1 is a good option until you are ready for the stroker.

 

The chambers were polished but, I would still like to match them to the slightly larger bore. The cam I have now is 216/220 duration, would this be enough or should I go for more, like a 220/224? Will I be able to re-use my flex plate or will I have some issues as far as being able to use my Yank 3000?

Redaddiction-I don't plan on going FI, that gets too expensive for me right now and takes away the sleeper look under the hood. Maybe someday, I would like to boosted application.

 

Yank 3000 is great and the same flexplate works fine. You should have no issues.

Depending on what valve springs you have, you could go with a little biger cam. Typically with a larger cam, you give up low end and gain upper rpm power. So the cam you have might be just right. Or I should say that it might not be worth the monet to change it.

 

One the F-body guys is selling an LS6 short block. I'm thinking of buying it but can't decide if I should. I have a pair of completely stock 6.0 heads, stock 5.3 heads, and a set of stage III 5.3 heads I could use. Not sure how well the ported heads will work, any opinions? Should I get this short block? If I go ahead with this, I'll have a complete 5.3 long block w/18K miles I could sell, would anyone be interested?