C5natie

iTrader: (1)

OK, so I know that the 1 3/4 vs 1 7/8 header debate will always continue. Ive seen dynos arguing both sides but I started to look closely at the design of these headers especially those for C5's. I noticed that many C5 owners even those with 376-418ci engines noticed either no gains or very small gains when going to 1 7/8 headers from 1 3/4 while owners of other model vehicles might have noticed more significant gains. Then one thing caught my eye, it seems that most 1 7/8 headers for C5's have much shorter primaries when compared to 1 3/4 headers. The primaries are shorter and go into the collector much earlier. This would choke them up (compared to a 32in primary) and the scavenger effect would suffer robbing them of making potentially more power and especially torque. Maybe this is needed to squeeze the bigger headers in the C5 and through the exhaust tunnel opening and by the batwing oil pan? IDK, what do you guys think?

LG 1/3...TSP is almost an identical design,



Kooks 1 7/8,



TSP 1 3/4, 32in primaries,


ARH 1 7/8 headers. Better design but still shorter primaries vs 1 3/4,

1989GTA

Regarding headers there are four important measurements. Here they are in order of importance.

1. Collector length
2. Collector diameter
3. Primary tube diameter
4. Primary tube length.

You can see the primary tube length is the least important. I believe it will only effect the total torque that is made and we are not talking much. That is why most people ignore the length and focus on what fits in the car with the least restrictions.

On my L92 motor I measured the exhaust ports on the head and at the widest point it was only 1.625". That is the inside diameter of a 1 3/4" tube. The idea is to keep the exhaust gas velocity up so that you get a better tug on the intake side during overlap. That is why on my motor I have decided to use 1 3/4" x 1 7/8" stepped headers. On larger motors I would step those numbers up one size.

By the way on dyno's with the 1 3/4" x 1 7/8" stepped headers they always make in the upper horsepower range when compared to others. Again talking 376" motors and smaller.

C5natie

iTrader: (1)

I agree about the stepped header but I cant find one for a c5

Juicedh22

iTrader: (6)

^^ That is completely crazy and unfounded (suggesting collector length/diameter is 'more' important than primary design)


First and foremost, all the aspects of exhaust manifold design are important and work together. Though suggesting the collector and midpipe are more critical than the primary is asinine.

Primary diameter and primary length have significant impact, this is the first part of the flow. Length and diameter determine how fast the gases move and impact scavenging.

In general:
Longer lengths and smaller diameters shift peak efficiency to lower engine speed
Multiple steps/merges split scavenging wave pulses
Diameter should be large enough to reduce restriction and allow the exhaust gases to flow freely at high velocity, but not so large that the gases slow down and have time to cool and become more dense, creating restriction as well as prevent pulses from stacking.

1989GTA

In your case the 1 3/4" headers would probably give you a little more torque. The 1 7/8" headers would probably give you a little more horsepower.

C5natie

iTrader: (1)

I thought the same since im cam only but im looking at some heads too so idk if it would be best to go with bigger headers then.

1989GTA

In that case I would go with the 1 7/8" headers.

hsvgtsr

So on a 454ci it would be better to have 1 7/8 headers ?

1989GTA

From what I have seen I would go with 2" headers on a 454.

hsvgtsr

Ow well custom headers then
Unless someone knows where I can get a set to fit a ve holden commodore
I think there are company's in oz but the shipping cost are massive to the uk

6D9 Matt

Yeah 454 Id go 2"... Im going to go 1 7/8 with a 416.

Dyno Junkie

I'm using 1 7/8" on a cam only LS3

C5natie

iTrader: (1)

Im sure youre making good power with them but I wonder what a comparison vs 1 3/4 would look like.

Dyno Junkie

Possibly not a lot different!

Pacemaker make 1 3/4" with 3" collector and 1 7/8" with 3 1/2" collector.
I had a set made with 1 7/8" pipes and 3" collector.

dbs1

I can't speak to pacemaker headers, but I did have some 1 3/4" pacesetter headers I ran on my cammed LS1 and then on my 416. They ran well but I changed over to some tsp 1 7/8" and picked up around 15hp. Changed mufflers from a dual in/out magnaflow stock style transverse on my 02 camaro to some bullet style muffs as well as losing the tsp y pipe and single pipe and going to a custom built true dual and gained 30hp. Significant gains.

Dusto

Here you guys check this out back to back comparisons
this is for ve commodore / pontiac G8

http://www.ozgarage.com.au/season2-v...xhaust-comparo

l2mb

i went with 1 3/4 and have been making great power n/a

-TheBandit-

iTrader: (1)

This article has a lot of relevant information:
http://www.popularhotrodding.com/eng...re/0505em_exh/