Fixing the SSR with Chamber or CSA.

68corvette · Post by **68corvette** » Wed May 30, 2007 7:19 am

I tried to search but could not find any topics about this.

There are some heads like new sbc LT1 or LS1 which have relatively abrupt shortside radius and they have tendecy to separate with higher depressions on flowbench.

LT1 is really easy to screw up in flowbench if stock valve size is used, after you port everything to work nice and then jus a little open the combustion chamber so that more flow goes over the valve and you have instantly major separation problem on higher lifts.

Do you think that its ok to fix the SS problems by blocking the longside flow so that you can get better pressure distribution over valve or is this more like a band aid just to get things look good and then I'll have problems on live engine?

Then I have seen some CNC ported LS1 heads which have also flowed pretty well to .5" and then separates, that good compared to stock which stalls after .3" with 32"h2o depression.
That CNC ported head had also really abrupt SSR and it seemed like it was not widened (casting flashes still in corners of ssr apex), just cleaned up all over, new seat work and it was enlarged from stock ~0.975"x2.525" to cnc ~1.025"x2.65"
stock flowed 221cfm@0.6"@28"h2o and cnc ported 275cfm@0.5"@28"h2o.
the flow was ~same or little worse on CNC from 0-0.3" lift range and CNC head had also 2.02" intake valve.

I recently ported a pair of LS6 heads and they had also separation problems starting from 0.4" at stock form, max flow was 252cfm@0.48"@28"h2o.
I first cleaned the port with stock valves and gaine ~11cfm@0.5" and max 266cfm@0.56".
then I enlarged the CSA and got 282cfm@0.55".
2.02 valve gave 292cfm@0.6" and valve bottomed..
So this head really liked larger than required CSA.
It really seems like band aid to me.. but I did not find any better solution without ruining the SSR and low lift numbers to get stable high lift flow.

/Marko

Procision-Auto · Post by **Procision-Auto** » Thu Jun 21, 2007 8:35 am

This fell down to the 3rd page and seems like someone here could answer it. A little bump for you...

68corvette · Post by **68corvette** » Thu Jun 21, 2007 2:49 pm

Maby if I try to elaborate this a little by my self someone wakes up =)

I think that "blocking" the flow with combustion chamber to make the port work is more acceptable as it just creates better pressure distribution over valve, though well done port should not need it to cure separation?
I think that pressure distribution wont change so much with higher depression and might work pretty well in living engine too if ssr is done "righ" and it wont makre depression manometer to freak when measuring with 28" or higher depression.

Enlarging the port seems more like customer fooling with flow numbers to me and I think that it is just band aid to make the port speed to go down and allow the flow to go over the shortside without separation. In live engine the intake speed will be higher again and separation will show up. Here comes the velocity probe handy and I believe that the velocity profile / engine VE% / port CSA are important and if CSA if too small from the start its acceptable to enlarge the runners, but I think it wont cure the problem if it exist with smaller CSA.
Its obvious that some shapes like raising the roof may create better angle to SSR and even with floor filled the flow wont separate.

I just wanted to know how you PROs feel about these things =)

CSA creates flow numbers and there are many head desings that are really happy with large cross section area in flowbench but VE% will really suck in dyno. Especially some large bore small stroke engines with allready well sized ports like Opel CIH etc. but thats another topic about FPS and VE%..

-Marko

talon · Post by **talon** » Thu Jun 21, 2007 2:50 pm

Hello 68

can you, for lack of a better word, toss the air up a little over the SSR by creating a little depression just B4 the apex of the SSR and blend it in back towards the port entry. Maybe .015-.02 deep. I may be talking out a orifice that was not designed for talking

Jim

Post by **ou812** » Thu Jun 21, 2007 10:53 pm

It all depends on what your doing with the engine as to whether or not you need the port to hang on at higher lifts/depressions.
If you are going to say build a sb chevy, hyd roller cam with .630 lift at the valve, then because it's rpm limited and lift limited, a port that stalls at .600 lift but flows really good up to it with good port speed, will make more power in it's usable power range.
If you have a 7500rpm sb chevy that has a solid roller cam that lifts .730 at the valve, then you would want to help that port out as much as possible by concentrating your work around the .500-.600 lift range and push the stall point past the .600 lift point.
I wouldn't try blocking the air in a port, but you may be able to manipulate it...that usually requires adding epoxy and reshaping.
I do that sometimes when the customer is up for the cost!!

Brian

Joe Mendelis · Post by **Joe Mendelis** » Thu Jun 21, 2007 11:11 pm

Marko, I know exactly what you are saying. Loading the port with the chamber definitely works on some heads. LS heads are very sensitive to the chamber. I still haven't seen an LS6 head back up at a lower lift with more depression. I have tried it on all of my heads and it doesn't make a difference in the lift they back up at. There are things you can do to the SSR without laying it back that will pick the high numbers up a ton, and make the head go a lot further up the lift curve. The wrong valve job and chamber can make a smooth 320 CFM head a turbulent 305 CFM head. Do not ever make the cylinder wall side of the chamber on an LS6 head go beyond the bore line. That is the biggest killer on those things. In other words, don't make the chamber wall steeper than 90* or it wil kill it. If it doesn't, the short turn is probably mowed down and the port is gigantic.

Next time you have a port stall on the bench, play with the orifice. They are very touchy on LS heads. You can see .100 more lift and 20 CFM by doing the orifice properly

SWB · Post by **SWB** » Wed Jul 18, 2007 1:44 am

Joe Mendelis wrote: Next time you have a port stall on the bench, play with the orifice. They are very touchy on LS heads. You can see .100 more lift and 20 CFM by doing the orifice properly

Joe,

What's the orifice you're talking about?

Thanks,

SWB

V Remian · Post by **V Remian** » Wed Jul 18, 2007 1:15 pm

My interpretation would be "radiused entry" based on my limited experience.

68corvette · Post by **68corvette** » Wed Jul 18, 2007 1:40 pm

I tought so also.. I have seen this with some well flowing 23deg sbc heads which are pushrod area restricted to lose more than 20cfm with clay and they need really large radius to not to separate at the entry.

ported LS6 port with stock CSA had similar issues and SSR separation problems, larger CSA "fixed" both.

automotive breath · Post by **automotive breath** » Wed Jul 18, 2007 10:32 pm

In another thread Joe says this about the orifice:

Joe Mendelis wrote: ... I would flow at higher drops if you have an extremely good orifice. Using
clay except to seal the orifice to the head will give you inconsistency. Fill the
injector boss with clay straight to the termination of the orifice. If you have
your valve job right you will have an absolute minimum of 270CFM by .550
on a 3.900 bore. Don't flow on a bore that isn't what you will run. As soon
as you put that thing on a bigger bore it unloads that part of the valve and
will back up sooner...

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