[adamo]

Hello everybody I have a question if anyone wants to answer. I have a 69 gto. It has a 428 with 270+cfm 722 heads. It has a old faithful cam with Crower solid rollers. Has a sd performance real ram air IV cnc style ported intake. Max a lite connecting rods with je pistons. 10.5 compression. 4 speed M22w with 3.73 gears. The headers are 1 7/8” Indian adventures headers with 3.5” slip on collectors and a 3” exhaust with x pipe and dynomax ultra flow mufflers. Just wondering if changing to a 3” slip on collector would pick me up some torque? My thinking is first of all the exhaust slows down a bit in the large 3” collector them reduces abruptly to the 3” exhaust. Wouldn’t the stranger flow from the 3” collector to 3” pipes work better? Idk. The car works great but you know how it goes. Can never leave these cars alone.

[Skip Fix]

I would bet not much difference. With the exhaust/intake ratio of RAIV heads (85%) and the fact the exhaust side flow as good backwards as out anything that reduces velocity will hurt you. My RAIV 400 picked up going to 1 3/4' headers vs the 2" Hookers and resolved the mild reversion issue I had and being only barely responsive the jet changes. I had 3' front system into 3' mufflers and 2/5 exhaust pipes.

Added a 'reverse split cam and picked up even more! But most folks here disagree that should have worked. 242/236 @ 0.050

[25stevem]

There is two ways to gain torque.

1) if you want more off idle torque, then you need headers with longer primary tubes then what you have now.

2) The best way to get a gain in torque from the mid range on up along with a good hp gain will be by converting your headers with what’s called a Merge collector of the diameter that your using now.

Merge type collectors due to the higher level of vacuum that they make produce a higher level of VE across a wider rpm range then any standard type collector ever could regardless of size.

[Formulajones]

Originally Posted by adamo

Hello everybody I have a question if anyone wants to answer. I have a 69 gto. It has a 428 with 270+cfm 722 heads. It has a old faithful cam with Crower solid rollers. Has a sd performance real ram air IV cnc style ported intake. Max a lite connecting rods with je pistons. 10.5 compression. 4 speed M22w with 3.73 gears. The headers are 1 7/8” Indian adventures headers with 3.5” slip on collectors and a 3” exhaust with x pipe and dynomax ultra flow mufflers. Just wondering if changing to a 3” slip on collector would pick me up some torque? My thinking is first of all the exhaust slows down a bit in the large 3” collector them reduces abruptly to the 3” exhaust. Wouldn’t the stranger flow from the 3” collector to 3” pipes work better? Idk. The car works great but you know how it goes. Can never leave these cars alone.

The worst thing you can do on an exhaust system is to quickly reduce it from the collector size to the exhaust size.

You can do it one of 2 ways. What you have described, removing the slip on 3 1/2" collector and switching to a 3" to match the exhaust diameter. Assuming your engine likes a 3" collector...

Or.....leave the 3 1/2" collector, change the X to a Dr. Gas setup with 3 1/2" inlets and 3" outlets. That way the exhaust piping is the same as the collector and it's not reduced until the "X". Doing it this way shows gains over just simply installing a cheap reducer to mate up to the exhaust system.
Of course more money and work redoing the exhaust in front of the X crossover.

If the 3" slip on collectors aren't overly expensive it's a rather simple change and probably the route I would try since you have that option. 3 1/2" collectors that are not slip on, I use the other method mentioned.

[grandam1979]

I like what you have now I wouldn’t mess with it much.

[Formulas]

if your timing curve and low speed carb mixture isnt optimum your low end torque output will suffer

your build level is at the point where these things should be looked at and tweeked to find power vrs assuming over the counter or 1969 carburation or timing curves will suffice
if you havnt worked them already