Straight vs Merge Collector

[RDY4WAR]

I have a set of 1-3/4" headers with 3" straight collectors on a stock long block '93 LT1.

220493046_1016587722494610_3240050265982150910_n.jpg

Would any power gains be seen going to a 2-1/2" to 3" merge collector like this?

10302_WEBL.jpg

This is a max effort 1/4-mile car looking for every little bit I can get. It's open headers with short turndowns.

1993 5.7L LT1
Stock 10.4 compression
Stock cam (202/207 @ .050", 116.5 LSA)
Stock heads
1.7 rockers (.509"/.524" lift)
52mm TB
Ram air sealed to bumper
E85 fuel

...plus a lot of "free up" mods like electric WP, 7qt Moroso pan, crankcase evac, etc...

TH350 w/ 9" 4000 stall
4.10 rear gear with 28x9 PBRs
Peak hp @ 5200-5400, shifting at 5800, crossing at 6200-6300

Any thoughts on 2-1/2" vs 3" collector for this setup? Thanks.

[BOOT]

I've always herd most common headers should have 2.5" collectors but 3" sells. Still only the track will give you the best answer.

[Walter R. Malik]

I have a set of 1-3/4" headers with 3" straight collectors on a stock long block '93 LT1.

220493046_1016587722494610_3240050265982150910_n.jpg

Would any power gains be seen going to a 2-1/2" to 3" merge collector like this?

10302_WEBL.jpg

This is a max effort 1/4-mile car looking for every little bit I can get. It's open headers with short turndowns.

1993 5.7L LT1
Stock 10.4 compression
Stock cam (202/207 @ .050", 116.5 LSA)
Stock heads
1.7 rockers (.509"/.524" lift)
52mm TB
Ram air sealed to bumper
E85 fuel

...plus a lot of "free up" mods like electric WP, 7qt Moroso pan, crankcase evac, etc...

TH350 w/ 9" 4000 stall
4.10 rear gear with 28x9 PBRs
Peak hp @ 5200-5400, shifting at 5800, crossing at 6200-6300

Any thoughts on 2-1/2" vs 3" collector for this setup? Thanks.

Usually a merge collector will help some at a certain RPM range. If that is not in the range you want, it won't make much difference from a straight collector of the correct size..

[77cruiser]

You'll have to experiment with collector extensions.

[RDY4WAR]

Thanks. I'll stick with what I have for now, play with extensions to see what it likes, and go from there.

What about the crankcase evac? Could the higher velocity from that 2.5" merge help draw harder on the crankcase?

[Walter R. Malik]

What about the crankcase evac? Could the higher velocity from that 2.5" merge help draw harder on the crankcase?

It could ...

[Bryan Maloney]

Merge collectors can greatly improve power below peak torque in some applications.
We once saw 24 lb/ft down low, 8 lb/ft at peak torque, with no loss of top end power. This was on a 423 hp restrictor plate engine. I believe most street engines would benefit from utilizing them, especially heavy vehicles with tall gearing.

On the evacuation system, I've thought about drilling a series of small holes around the merge collector, just slightly downstream of the venturi, and then welding a sleeve around the collector to create a chamber. Kind of like an annular booster instead of the typical crude tube hanging into the collector.

[steve cowan]

i like questions like this thread offers,so many "WHAT IF''
alot of us are limited due to packaging in the engine bay and this limits us from sizing correctly for the application.
have you looked at Pipemax ??
not sure if Larry would have enough data for your application but something might trigger a thought.
i would think sizing to be the most important for where you want the exhaust pulse to land
EG- @TDC on overlap or where ever you think it might help.
i hope this thread kicks off be nice to learn something new

[steve cowan]

You'll have to experiment with collector extensions.

Jim,
on those neat headers that you built,have you ever had time to play with collectors at all??

[RDY4WAR]

Merge collectors can greatly improve power below peak torque in some applications.
We once saw 24 lb/ft down low, 8 lb/ft at peak torque, with no loss of top end power. This was on a 423 hp restrictor plate engine. I believe most street engines would benefit from utilizing them, especially heavy vehicles with tall gearing.

On the evacuation system, I've thought about drilling a series of small holes around the merge collector, just slightly downstream of the venturi, and then welding a sleeve around the collector to create a chamber. Kind of like an annular booster instead of the typical crude tube hanging into the collector.

Nice gains though not really relevant here. The car never sees peak torque at any point, much less below that.

I like that idea of an annular booster. Could be overkill, but still has a wheel turning in my head.

i like questions like this thread offers,so many "WHAT IF''
alot of us are limited due to packaging in the engine bay and this limits us from sizing correctly for the application.
have you looked at Pipemax ??
not sure if Larry would have enough data for your application but something might trigger a thought.
i would think sizing to be the most important for where you want the exhaust pulse to land
EG- @TDC on overlap or where ever you think it might help.
i hope this thread kicks off be nice to learn something new

I have an older version of Pipemax. It said 1-3/4" primaries at 34" long. Mine are horribly uneven with the shortest at 26" and longest at 40". If I average them all together, I get 33-3/4" which is pretty close. The collectors it said should be 2-3/4 to 3" by about 20" long. I have an extension on these headers now based on that spec.

[skinny z]

...

[skinny z]

...

[77cruiser]

You'll have to experiment with collector extensions.

Jim,
on those neat headers that you built,have you ever had time to play with collectors at all??

No I haven't I've only been to the track 4 times with the car.

[MadBill]

...I like that idea of an annular booster. Could be overkill, but still has a wheel turning in my head...

A design by a Speed Talker whose name I have forgotten was mentioned and pictured in one of David Vizard's books a few years back. It used a curved pipe from the check valve, entered the (merge) collector upstream of the throat and ran coaxially, ending at the throat. I forget the vacuum number obtained, but it was well above any conventional exhaust-driven design; maybe even well enough so to work with mufflers.

[RDY4WAR]

...I like that idea of an annular booster. Could be overkill, but still has a wheel turning in my head...

A design by a Speed Talker whose name I have forgotten was mentioned and pictured in one of David Vizard's books a few years back. It used a curved pipe from the check valve, entered the (merge) collector upstream of the throat and ran coaxially, ending at the throat. I forget the vacuum number obtained, but it was well above any conventional exhaust-driven design; maybe even well enough so to work with mufflers.

I found that thread. The location looks logical. I wonder if the same effect would be seen by placing the tube from above at a 45° angle with the exit ending up about the same spot?