Tuning with tri-y headers

[my69396]

Wanting to know if there is a difference in the tune when going from 4 into 1 step headers to a tri-y step header?

[Pedigo Perf]

Did you change the cam too?

[Greg Hill]

I can tell you from personal experience the camshaft can make a big difference with tri-y's. The stock eliminator racers who use tri-y's and have found et have worked with cams. Also the dyno will not tell the tale.

[Jim Caughlin]

As a header builder, I tell people to not go with tri y headers unless they have they are very serious about putting the time into making them work. Tri y's are a lot tougher to tune. Also, it's very easy to mess up on the sizing with bad effects. In a word, tri y's are not for the faint hearted. Plan on building more than one set if you really want to make them work.

Jim Caughlin
SS 6019

[REGGIE WINKLES]

When I switched to Tri-y headers I had to richen the carb as they like more fuel. My car is a stick which may vary from auto trans car. Those headers were worth about .05 overall after tuning on my application. 4-7 swap cams will not work with Tri-y's. They really pick up the 1/8 time, not so much on the top end of 1/4 tracks. Overall they are an improvement, but for my 2 cents I would say they perform much better on auto trans cars than with the stick. I don't know for sure, but have heard anywhere from .10 to .12 on auto trans car. Hope this helps.

[James L Miller]

Originally Posted by REGGIE WINKLES

4-7 swap cams will not work with Tri-y's.

I would think that would depend on the cylinder pairing. In the old days I think Tr-Ys were developed to get away from the 5-7 firing order so they would pair 1&5 and 3&7 together or something like that. I'm not familiar with the new Tr-Y headers. How do they pair them now?

[Alan Roehrich]

Tri-Y or 4-2-1 headers are almost certainly going to require a major cam change in order to make them work. If not, you were almost certainly running the wrong cam for 4 into 1 headers. It's the same as going to one or two step 4 into 1 headers and a merge collector from regular 4 into 1 headers and a regular connector. The header change creates an entirely different scavenge cycle, that's why you use them. When you make a radical change in your scavenge cycle, you need to change the cam, unless you had the wrong cam to begin with.

If you improve your scavenge cycle by any real amount, you should be creating an over scavenge with your 4 into 1 header designed cam. So you basically just pull a big part of your intake charge out the exhaust, wasting it. To take advantage of the improved scavenge cycle, you reduce the exhaust lobe and/or spread the LSA out to prevent an over scavenge condition. In some cases you can even increase your intake lobe to take advantage of reducing your exhaust lobe and/or spreading the LSA.

[older racer]

Originally Posted by Alan Roehrich

Tri-Y or 4-2-1 headers are almost certainly going to require a major cam change in order to make them work. If not, you were almost certainly running the wrong cam for 4 into 1 headers. It's the same as going to one or two step 4 into 1 headers and a merge collector from regular 4 into 1 headers and a regular connector. The header change creates an entirely different scavenge cycle, that's why you use them. When you make a radical change in your scavenge cycle, you need to change the cam, unless you had the wrong cam to begin with.

If you improve your scavenge cycle by any real amount, you should be creating an over scavenge with your 4 into 1 header designed cam. So you basically just pull a big part of your intake charge out the exhaust, wasting it. To take advantage of the improved scavenge cycle, you reduce the exhaust lobe and/or spread the LSA out to prevent an over scavenge condition. In some cases you can even increase your intake lobe to take advantage of reducing your exhaust lobe and/or spreading the LSA.

question? how much shorter should the ex lobe be? 10 deg @.050

[Alan Roehrich]

Originally Posted by older racer

question? how much shorter should the ex lobe be? 10 deg @.050

There is no answer for that question, it is way too broad.

An example would be a combination that has a relatively large and lazy exhaust port, usually having 4 into 1 headers on the large side. A properly designed and built Tri-Y header, with merges at both Y's and on the final exit, could allow 6-8 degrees off of the exhaust lobe at 0.050", as well as an increase in the LSA of 2 degrees. That could allow 2-4 degrees more intake lobe.

This is something that requires very serious dyno testing, as well as track testing. There is no shortcut, none. Unless you find a person with an identical combination that has done all the work and is willing to share. It's a really nice guy that will share the results of spending $10K and 80 hours or more to find a tenth.

As discussed in a thread about merge collectors, Tri-Y headers are another one of those things that should be a "near end of development" endeavor for a given combination. You can probably find cheaper and easier tenths in your combination, unless you've been flogging it seriously for ten years.

Probably one of the smartest guys on this is Larry Meaux, the developer of PipeMax software, he is a cylinder head guy, who has a flow bench, a dyno, and an incredible love for this stuff. Larry will be the first to tell you that once you get past the first steps of correct length and diameter sizing on headers and collectors, 99.9% of all racers will quit working and spending money. They won't even spend the time or money to find what can be had with merge collectors.

You often need a significant cam change just for one or two step headers and merge collectors. One of our engines, for example, will suddenly use 20 cfm more air above 6400 RPM, yet lose 12HP, when we switch to one step headers and a semi merge collector. As such, we know we have a serious over scavenge condition. We did not have time for a new camshaft, and given that we gained a ton of torque, we had to skip the cam change. We broke it before we had time to get back to the cam. But I now know we need 4 degrees less exhaust at 0.050", and 1-2 degrees more LSA. We also know we can run 2 more degrees at 0.050" on the intake, to compensate for a weak intake port we can't fix on these heads.