I have a 94 Z28.. thought my car would have non-561's right? WRONG. hehe.. I remember that my motor was rebuilt in 97. Guess whats on my car.. 561's.. What kind of CFM is out there for max port 561???

 

FWIW.. i forgot to mention that the heads will have 2.00/1.56 Valves...

 

one last thing.. am i crazy for taking the heads off with my hooker LT's still IN the car?

 

Supposedly these have the least potential, but the most flow (Impy flow) stock for stock. 1993 has the most meat on the heads. My ported 94s I think peaked 279 on the intake @ 600, with parts of the head .035" so without breaking something there wasn't really any more in them.

 

As far as stock they do flow about 10 cfm betteron the intake and exhaust. I posted some #'s a few months back in a post called "561 flow #'s" or something like that.

Basically the heads are thinner and can not have as much removed from them as the other heads. The roof is not as thick and the area behind the shortside is not as thick so you can not widen as much or lay back as much when going with larger valves. With a stock valve they are fine.

The reason that they flow better seems to be the shortsides. The intake and exhaust ports seem to be the same other that that and when you port them you do not have to do much in these areas but "un touched" they are better. After porting they wind up the same with stock valves and with larger valves I can actually get better #'s from the other castings on the intake but the exhaust ports end up the same.


NightTrain66

 

i knew you would post in here mr elliot .. do you think my 561's will be ok to port out though?

 

I recently ran into the same problem with the 561's on my 97 LT1. It just so happened my we had a set of non 561 95 LT1 heads lying around in the shop. So after mixed reviews of people ideas on this board we decided to test them ourselves. Now one thing that we already agree with is there is more material on the NON 561's to be ported which we were uncertain if it would gain any performance over the 561's since they are supposed to flow better. So off to the flowbench we went. Both heads in stock form ( stock ports , stock valves )

This was done an a flowbench unit at 28" of H20

lift 643's lift 561's
Intake Exhaust Intake Exhaust
.100-- -67 ---47 --63 --46
.200- -121 --90 --120 --93
.300- -170 --120 --170 --121
.400- -205 --139 --198 --142
.500- -206 --147 --201 --150
.600- -205 --150 --202 --154

From our tests they actually flow worse on the intake side than the older 643 castings but flow better on the exhaust side.

Which if you look at it as a flow ratio the 561's flow 3% better than the older 643's. Now Nights #'s conflict with ours, his show better intake flow. I do not know why, It could be our location
(South Florida) was cool and not humid at all at the time, maybe it was our techniqe, maybe it was user error. We used totaly stock heads however they were cleaned, hottanked and painted. But this is just a general idea here.

We chose to go with the 643 castings and got about 265CFM with 2.00 race valves.

 

here are the last 561's that i tested and some non-561's.
---------561-------------------other--------
lift------Int.----Ex---Int----Ex
.100----59----42----59----42
.200---115----84---110---79
.300---172---120---169---115
.400---213---142---206---135
.450---223---149---213---141
.500---221---155---210---144
.550---218---157---210---144

I do have a 4.155 bore instead of a 4.030 but I would think that would help the low lift #'s more than anything???? I also use a 1/2 clay lip on the intake port and no pipe on exhaust. These heads are used but have been cleaned. They both had stock valve jobs with ???,??? miles on them and that is how I flow all of the heads BEFORE porting. These #'s might vary by 5 cfm plus or minus on all of the LT1's that I have tested but they seem pretty inline with what I normally see. The 561's are alot less common so I have only tested 7 or 8 sets since knowing that there was a diff in them. These 561 #'s are the best I have seen from any of them.

Tripin, it seems that our benches might put out diff. #'s unless you are not testing with a clay funnel on the intake port. On my bench I usually get 275 or so with larger valves and 260-265 with stock valves. Your bench shows a stock LT1 head at 204 and mine says 213 so the "after porting" #'s would be diff as well. The only way to know for sure would be to flow the SAME head on both benches and compare.

I guess to answer his question, 260-265 or so with stock valves and 270 or so with larger valves according to MY BENCH, but then again my bench shows a stock LT1 at 210-215 as well.


NightTrain66

 

I used a 1/2 lip of clay on the Flowbench as well. Totaly stock everything. I used a hot washer ( kinda like a big dishwasher for engine parts, I call it the Dishwasher ) then threw it into the Oven at 600F ( not home oven, the Engine block oven in the shop)
then threw on one stock intake and one stock exhaust valve from when we tore the heads down. Maybe the cleaning caused it to be a little roguher. I have no clue, maybe one of our Flowbenches is off. GM claims 207 CFM @ 28inches on the NON 561 heads.

 

I dunno, the 561's I put on the bench peaked 11-12cfm higher & reasonably close to what a stock LT4 does. Can't remember the exact figures though.. don't really care what it does stock .

99.9% of people aren't going to max out a casting anyway. Getting the first big jump is easy, but finding the last 12-15cfm is much more difficult, and IMO most of the time, the real restriction is in the abilities of the person working it.

If it were mine, I wouldn't worry about it. Hell, people with less experience may end up getting more out of the 561's, so it may be a good thing .

 

Well we ported the 643 castings heads so much that we had to epoxy the outside of the intake runner ports because the vertical walls were paper thin ! we fell thru on a 2 areas ( not by much, just a tiny pinhole sized hole on 2 intake runners) so we had to tach weld it. these things were hogged out to the MAX ! No doubt about it.

 

Ahh, dont go saying that! Then all those people with heads that flow 289 on the intake side are going to question reality.

 

I dunno what to tell people.. everyone claims they get 290 or that their bench is low. Argue it all you want, but there's only so much material to get XXX crossectional area from... so at 28", you're only going to get so much air through the damned thing.

Of course I can make our bench say anything I want... it just wouldn't be honest.

Whaddever, tell people the truth and they get upset and call you an *** for giving them a clue. Rip them off and they love you, gotta love it - all people want is to race flowbenches, not dynos, seems backwards to Phil, but oh well, people are odd

 

Well Im not talking about the gasket surface area, just the outside portion on the intake side. Its hard to expalin without a picture but basically if your looking at the intake port, stick your finger in about an inch. This area is where it got ported really thin.
I dotn think we are going to see 289CFM out of the intake side. I belive 265-275cfm would be more realistic.