Re: Merge collectors
 

Pretty much an over-simplification but the car won't be responsive to timing or jet changes.
If the combo can handle it, open up the exhaust lash and make a run.

Re: Merge collectors
 

Been out of racing for about 15 yrs but I can remember when we changed from our Stahl headers (2 inch) to a Davis step header (2,1 7/8,1 3/4). Didn't see much gain until we added an 18 inch extension on the collector. Really brought it to life.

What was it trying to tell me???

Re: Merge collectors
 

Billy is dead on,you can't seem to get it rich enough. You'll be putting jet in that makes no sense, loosening the exhaust lash and picking up shows the exhaust is pulling unburn
,ed fuel out on overlap,

Re: Merge collectors
 

The topic of lean rear cylinders is what drove my question. We haven't even run the motor yet, not looking for gains, just don't want to go backwards. Headers are nothing special...straight 2" primaries about 40" length. Last year we made some fixes (new fuel pump) and added 13" to the collectors and picked up 2 tenths. I suspect much was from the exhaust. But everything is bigger now, with lots of other changes with same basic induction. We'll probably put straight 4" collectors on to start. FYI this is not for my stocker. It's a bracket motor built with a lot of S/S technology.

Re: Merge collectors
 

Mine is very responsive to timing changes, likes to run richer than some others. I talked to Jere Stahl quite a while, twice when I ordered mine. Always used his stuff on my old "Jr Stockers". Tried to order a set from him when I make it a race car. At that time they had no jig for the LT1 Camaro/Firebird. Whoever I talked to then told me they could build a set for me if I wanted to bring my car there. York, PA is a long drive from Oklahoma. Talking to Bobby Warren a couple years later, I learned he had taken his there to have a set built, so they now had a jig.
Jere had me fax him my dyno data (both steped & straight 1 7/8" headers) and engine specs. I told him I had tried my friend's merge collectors at the track, and what I found.
Jere told me he saw no way it would like the 1 3/4" to 1 7/8" steps, he said the non-step 1 7/8" should be right, and it MAY like 1 7/8" to 2" steps. He didn't see it liking merge collectors, either.
I tried backing the ex lash off with both styles collectors, didn't like it. I have not tried less than 4 degree int/ex duration split @.050". Less than 3 at .200" lift. Tried wider lobe centers, even with more gear. Dyno liked it, short times suffered. Back half about the same. May need a 7" converter with that cam? Don't know. The normal cam did not like one at all.

Re: Merge collectors
 

Quick question, and I know this may be more complicated than this, but as a generic rule of thumb would you need a better scavenging header setup for a cam with more or less overlap?

assume generally the same cam specs for a cam with 80 degrees overlap compared to one with say 70 degrees. only change being lobe separation. you you need more scavenging going to the smaller overlap to be as efficient?

Re: Merge collectors
 

If you measure the port on the LT1 head, last time I checked, 1 5/8 tube covered the port. The reason you see no change is the header isnt even working at this point....13/4 and 1 7/8 are way too big... proven many times over... you guys are not talking to Calvin Elston obviously....

my proven $.02... race track and dyno

Re: Merge collectors
 

Two header gurus told me steps are what I need, one even talking three steps, (with a 1 5/8" first step) but THE master header builder, (IMHO), Jere Stahl, (knew Jere from Jr Stocker days. Happily he remembered me) told me what it should like after I sent him all the data he asked for, and it agreed what I had found on Patterson's dyno, and (since we don't race Dynos) A-B-A testing during a track rental test session.
More to header fabrication & layout than I realized. My 1 7/8" Stahl headers (one of the very last set they built) are a full MPH faster than my old 1 7/8" Hedman Hustlers, which were on the dyno. And, I can get all my spark plugs out. Haven't been back on the dyno with the Stahl headers.
I just went back and looked, I typed the correct numbers in: 1 3/4" to 1 7/8". I cut a pattern, like cutting a gasket, and sent it to Jere, he had his guys water jet (I think) cut a set of flanges for the 1 3/4" tubes, for my Stahl bolt pattern on my aluminum adaptor plates. So they were centered correctly.
Elston is one I have not talked to.
Btw, Sir, who are you?

Re: Merge collectors
 

http://www.speedtalk.com/forum/viewtopic.php?p=75639

start reading here. lots to learn about the correct header before any of you should consider merge collectors....every winter there is a new thread it and it dies the same way.... this winter, lets start with Calvin and maybe we can convince him to swing in the forum and educate people....

Re: Merge collectors
 

I tested what Jere Stahl recommended. It was faster. Good enough for me.
Thanks.