Tin Indian

Reading all these head posts lately, one would come to the conclusion that many folks are now opting for 5.3 heads over the ported LS1 5.7s. The "TEA" folks really seem to have gone this route. I would bet that at least 2 out of every 3 TEA heads being installed now are 5.3s.

Anyway, with even .035" milled from your 5.7 heads, you will get 10.6 to 1 CR. Do we really need 11.0 to 1 + CR the 5.3 heads will provide since most folks here don't use better that 92 or 93 octane pump gas on a daily basis?

Maybe I am missing something here. Are these ported 5.3 heads flowing better than a set of ported 5.7 (LS1) heads with your standard aftermarket 2.02"/1.57" valves?

Or is it [just] the greater increase in CR that people are now selecting to use the 5.3 heads?

I am going to be purchasing heads soon, so thats why I bring this whole thing up for discussion.

Thanks,
Ron

sited12

Every 1 point in CR is 20 HP. If you can get 11.3 no problem with very slight milling of heads and 11 to 1 with no milling why not get that extra few horsepower. That is the only reason why people get the 5.3 heads. They flow the same as the 5.7 heads.

Tin Indian

Thanks for the info...

Now, we read all the time about folks actually hearing slight detonation and seeing some knock retard when using ATAP during the hot summer months. If some of these cars will detonate with a stock 10.1 to 1 CR on the crap oxygenated pump gas now available, I hate to see how they do with 11.0 + CR.

Hey, I certainly would get a set of 5.3 heads, but I am still not convinced they will work well with 92 octane (Arizona) pump gas in the heat of summer on a daily driver.

Country Boy

iTrader: (24)

I would say that the main reason is you do NOT have to mill the heads for a 10.8:1 compression. The 5.7s, you have to mill them resulting in a smaller P2V clearence. Also the 5.3s exhaust ports flow alot better than the 5.7s. Ive seen big differences on the two. Not sure why, if its size, shape or what.

Tin Indian

Also the 5.3s exhaust ports flow alot better than the 5.7s.

I'm not disagreeing with you at all, but that seems strange since the 5.3 heads have smaller stock valves to begin with compared to 5.7 heads.

QUESTION: Will a 5.3 head accept a set of 2.02"/1.57" valves without installing new larger seats?

I know the 5.7 head uses a stock 2.00"/1.50" set of valves, and the stock seats will only accept 2.02"/1.57" valves. I can't see how the 5.3 heads with smaller stock valves to begin with will take the 2.02"/1.57" without larger seats machined in.

Ron, <img border="0" title="" alt="[Confused]" src="images/icons/confused.gif" />

Hardtop

iTrader: (3)

I went with 4.8's for more compression, and P/V clearance. My car has zero KR with 29-30 degrees timing. Runs great on 93 octane gas. I also got to keep my stock 5.7 heads by suppling the 4.8 cores.

Bruce

justin sutton

4.8's are the same thing as 5.3's.I think I am correct on that.

Country Boy

iTrader: (24)

The 5.3s have the same valves as the 5.7s <img border="0" title="" alt="[Smile]" src="gr_stretch.gif" /> 2.00 I and 1.50 E and yes, they can take a 2.02 valve.

Do you think youre going to notice the extra .02" in valve size? <img border="0" title="" alt="[Confused]" src="images/icons/confused.gif" />

<small>[ November 12, 2002, 07:55 PM: Message edited by: Country Boy ]</small>

Hardtop

iTrader: (3)

</font><blockquote><font size="1" face="Verdana, Helvetica, sans-serif">quote:</font><hr /><font size="2" face="Verdana, Helvetica, sans-serif">Originally posted by justin sutton:
<strong>4.8's are the same thing as 5.3's.I think I am correct on that.</strong></font><hr /></blockquote><font size="2" face="Verdana, Helvetica, sans-serif">They are the same. <img border="0" alt="[cheers]" title="" src="graemlins/gr_cheers.gif" />

Bruce

justin sutton

I thought they were.I dont understand why you don't see more people running the 4.8's also.They should be easy to come by as the 5.3's.

verbs

</font><blockquote><font size="1" face="Verdana, Helvetica, sans-serif">quote:</font><hr /><font size="2" face="Verdana, Helvetica, sans-serif">Originally posted by Kimchee and Rice:
<strong>Hey, I certainly would get a set of 5.3 heads, but I am still not convinced they will work well with 92 octane (Arizona) pump gas in the heat of summer on a daily driver.</strong></font><hr /></blockquote><font size="2" face="Verdana, Helvetica, sans-serif">Hey FYI Ron, we don't have 92 Octane, we have 91 Octane. <img border="0" title="" alt="[Sad]" src="gr_sad.gif" />

That's the main reason I opted for a lower 10.8:1 compression ratio with my heads/cam.

Tin Indian

verbs ....

My bad... Jeeze, thats even worse. Well, I think I will just stay with ported 5.7s and .035" mill. Also, with a .035" mill and a smallish TR-220, I can't see that P to V clearance would be of any concern at all.
________________________________________________

Got this from another thread:

"Milling 5.7 LS1 heads .035” will decrease the stock 67.3cc chamber volume to approx 63cc
This will yield a 10.7 to 1 compression ratio when the stock GM .052" thick graphite head gaskets are used".

Ron, (Originally from Phoenix)

_______________________________________________

<small>[ November 12, 2002, 10:32 PM: Message edited by: Kimchee and Rice ]</small>

Jason99T/A

iTrader: (21)

</font><blockquote><font size="1" face="Verdana, Helvetica, sans-serif">quote:</font><hr /><font size="2" face="Verdana, Helvetica, sans-serif">Originally posted by Country Boy:
<strong>The 5.3s have the same valves as the 5.7s <img border="0" title="" alt="[Smile]" src="gr_stretch.gif" /> 2.00 I and 1.50 E and yes, they can take a 2.02 valve.
</strong></font><hr /></blockquote><font size="2" face="Verdana, Helvetica, sans-serif">stock 5.7l valve size: 2.00/1.55
stock 5.3l valve size: 1.89/1.55

Both will accept a 2.02/1.57 without changing the seats out.

From what I have seen, there is VERY little difference in flow numbers between these two heads after porting.

The main reason for using the 4.8/5.3l truck heads is for the added compression they give for the very minimal amount of material taken off the deck surface. This helps quite a bit when trying to fit a big duration cam with stock pistons.

One Monkey

Kimchee and Rice!! what you run for compression have a Relation for the cams you use. The compression you are familia with is "static compression" wich dose not have a real meaning.

(This is not exact just too explain.)

A 220/220 cam in a 10.1:1 compression car would
have the same actrul compression as say a 230/230
with 11.5:1 there bouth would be able too run on 93.

AS you move up the RPM band you can increase compression also... again the cams will get larger.

So I can have a car with a 240/240 duration with 12.5:1 compression. running on 93. and have no problem, But If I was too put a stock cam back in.. Caboom!!!!

Some of the people is going with the 5.3 because that's what everyone else is doing.. some because they wanted the extra compression, and some because there don't want too mill the head for cause of PV issues.

5.7 and 5.3 has the same types of ports flow #s are equal
hope it help.

verbs

</font><blockquote><font size="1" face="Verdana, Helvetica, sans-serif">quote:</font><hr /><font size="2" face="Verdana, Helvetica, sans-serif">Originally posted by One Monkey:
<strong>A 220/220 cam in a 10.1:1 compression car would
have the same actrul compression as say a 230/230
with 11.5:1 there bouth would be able too run on 93.

AS you move up the RPM band you can increase compression also... again the cams will get larger. </strong></font><hr /></blockquote><font size="2" face="Verdana, Helvetica, sans-serif">So are you saying that either Ron needs to play it safe with a 10.4:1 compression or something like that with a smaller 220/220 cam, or being that I have a much bigger cam, I can afford to go to say 11.3:1 compression even on 91 octane and 100+ degree summers?

Tin Indian

"One Monkey" makes sense here. Come to think about it, I have heard that before.

Long duration cams will make less dynamic (for lack of a better word) compression, due to the fact that the valves are closed for a shorter period of time. That may be an over- simplification of it, but I think you get my point.

Soooooo, your right, verbs. Your bigger cam can take more static compression than my smaller cam. Where you may detonate at 11.0 to 1, I may at 10.7 to 1

I'm sure there is a formula, but I would bet the stock cam with 10.1 CR yields about the same dynamic (cyl pressure) compression as a 220 with maybe 10.5 CR. And maybe about the same as a 227 cam with some where around 11.0 CR

Ron, <img border="0" alt="[cheers]" title="" src="graemlins/gr_cheers.gif" />

ls1290

iTrader: (20)

</font><blockquote><font size="1" face="Verdana, Helvetica, sans-serif">quote:</font><hr /><font size="2" face="Verdana, Helvetica, sans-serif">Originally posted by One Monkey:
[QB.... But If I was too put a stock cam back in.. Caboom!!!![/QB]</font><hr /></blockquote><font size="2" face="Verdana, Helvetica, sans-serif">If you run higher octane fuel, you should be ok. Running a stock cam with 12.5:1 compression would take at least 100 octane fuel.

Slowhawk

iTrader: (12)

Bigger Cams have more overlap which bleeds more cylinder pressure.That's why if your running a bigger Cam it is better to bump the compression.The reason peopl run the 5.3's is because the chamber is smaller,so minimul machining is needed for the higher compression and you save some P/V clearence for the bigger Cam.

Richard@WCCH

iTrader: (3)

Ron, IMO it would be safer to go with slightly less compression given the warmer climate you are driving in. An oil pan full of broken pistons WILL ruin your day.......... <img border="0" title="" alt="[Eek!]" src="gr_eek2.gif" />
Good luck with whatever you decide,
Richard <img border="0" title="" alt="[Smile]" src="gr_stretch.gif" />

verbs

</font><blockquote><font size="1" face="Verdana, Helvetica, sans-serif">quote:</font><hr /><font size="2" face="Verdana, Helvetica, sans-serif">Originally posted by Kimchee and Rice:
<strong>Soooooo, your right, verbs. Your bigger cam can take more static compression than my smaller cam. Where you may detonate at 11.0 to 1, I may at 10.7 to 1

</strong></font><hr /></blockquote><font size="2" face="Verdana, Helvetica, sans-serif">I personally would like to see you try out 10.8:1 yourself, because if you don't detonate, then I may try 11.3:1 <img border="0" alt="[devil]" title="" src="graemlins/gr_devil.gif" />

I have had no detonation problems myself, even in August (at 110 degrees) with the engine as hot as 230 degrees in rush hour traffic....

<img border="0" alt="[guns]" title="" src="graemlins/gr_guns.gif" /> FTRA in the summer

<small>[ November 13, 2002, 11:47 AM: Message edited by: verbs ]</small>