grocerygetter

iTrader: (2)

Bump the good thread

squalor

iTrader: (3)

I second your bump sir. I have a few questions about the thread though.
On the LG Super Pro, what is a "Fire Cone" ? The Venturi after the 4-1 merge ?
On the Nextel Cup set, I thought shorter primaries work for higher RPM ? Attached is pic of Headman stepped headers. They look like the step from 1.75 to 1.88 is also 7" down from the flange. Is this some sort of physics rule; how did they know where to put the step ?
Are merge collectors made from 3" radius 18* bends like this one ? I saw the youtube video and thought about making my own in mild steel.
How important is it to have correct firing order rotation at the 4-1 Merge collector, as in 1-7-5-3 for driver side and 8-2-6-4 for passenger side ?
How important is it to have the x-pipe close to the collector ?
Lastly, where in the powerband do steps, merges and venturis benefit most, and by how much % ?
Is there a header science thread someone could point me to ?

NemesisC5

In for the education.......

BrntWS6

iTrader: (7)

I've posted this several times on here so some of you may have already seen it. But here is my before and after from switching to 1 7/8" headers on a H/C/I car. Both were Kooks and each was after a tune. Same dyno as well.



20 rwhp
15 rwtq

kinglt-1

iTrader: (26)

I picked up 2 tenths going from 1 3/4 hookers with Flowmaster CB to Kooks 1 7/8 with Kooks TD's on a bolton car. Was I expecting huge gains...no. I did it to get rid of the rasp and compliment my 3800 stall. Doing this also future proofed my exhaust setup for future mods.

Tsp also has dyno proven results of their 1 7/8 picking up 8-9whp over their 1 3/4 LT's on a basically stock LS1. So I guess it all depends on the setup and header design.

FMX05

iTrader: (3)

Outside of the header designs being completely different...


1 7/8" headers might be having a hard time trying to suck more air through an apparently unported LS7 intake at high RPM... If the intake is the restriction it might not matter what size your header primaries are. In order to move more air at high RPM to see the gain you were expecting you must first pull more air in. As other people have said in the less exotic design of an F-body header the gains of 1 7/8 above 5000rpm are pretty well documented. The low RPM loss has a lot to do with the exhaust port on the particular head in question. Some show a large loss, others do not. It's all about the combo. Look at the power the guy with the LS7 powered Monte Carlo is making with a sheet metal intake and 1 7/8" to 2" to 2 1/8" 4" collector headers.

Build the combo to put power where you want it. There are endless possibilities.

Zfan

Flowmaster mufflers are very restrictive and do not flow for crap.

01ssreda4

iTrader: (96)

I forgot about this gem.

redbird555

iTrader: (14)

A flowmaster isnt losing anything over stock and really isnt all that terrible. A muffler swap wont gain you 2 mph in the 1/4.

Lets also not forget that the lg headers are pretty well known to be better in their 1 3/4 configuration the 1 7/8 version commonly loses power over on corvette forum on smaller setups. However thats not the case with any other brand or setup. So again anyone who's buying 1 3/4 hoping for more power and mid range torque over 1 7/8 can keep dreaming.

kinglt-1

iTrader: (26)

fsvaasam

I did 1 7/8 for my stock ls1 engine and its overkill for that, even for mild street use. I lost much torq in low to mid range in butt dyno. I think you should have quite much mods and potential for power to get 1 7/8 justified. My 2 cents.

dr_whigham

iTrader: (49)

Its been proven far too many times that 1 7/8" makes more power even on a completely stock motor. The Vette LG's I can't speak about, as I don't and won't own them.

The "butt dyno" tells us NOTHING.

1989GTA

As some have alluded to in others posts in this thread maybe the 1 3/4" to 1 7/8" stepped headers may be the best. After all the exhaust port in the head is no bigger than 1 5/8" so there is more likely a better transition from the head to a 1 3/4"(1 5/8" ID) primary pipe. Less turbulence equals more exhaust flow.

fsvaasam

It might be so, that 1 7/8 make most peak power on stock engine, but what count the most is average power in my point of view. Im speaking only with my experience, nothing more.

fsvaasam

I think that the "butt dyno" is good, because when you change something and you can feel it when you are driving, defenately something has been changed. Im sure that if small amount of torq is lost somewhere, you cant notice that, but with my modification to change only nothing but stock headers to 1 7/8 i feel immediately its more lazy in lower rpm. Hard to say what amount im losing in there. It pulls little better on hi rpm, but i wouldnt trade it for torq loss what i got now on low rpm. Dont think this is any kind of thruth, only my experience. Im still waiting for tune, so there is still left on table.

redbird555

iTrader: (14)

Changing manifolds to headers will feel lazy in the midrange. That has nothing to do with power. My car felt like it lost its guts after i swapped to my original 1.75 bbks setup. In reality I gained power everywhere and could spin the tires in 2nd gear which never happened before. After I went to 1.875 headers I again felt that it lost a bit but actually gained everywhere again

fsvaasam

You guys could be right. I think my max power is still there where it should be, but im talkin about torq in small throtte openings like normally leaving on traffic lights. There the torq loss is more noticable.

redbird555

iTrader: (14)

again headers will dop that no matter the primary size. the back pressure of the system is largely gone and it will feel like you lost torque but its usually not the case

FMX05

iTrader: (3)

Luckily we don't race at part throttle. A good tune can make a full bolt on car drive pretty close to stock at part throttle. After you cam it there is no turning back. It is going to lose something somewhere.

quickvert1

the long tubes from lg are the bomb..its not the header size..lgs 1 3/4 is an old borla design w really long tubes there 1 7/8 less powerful headers are shorter tubes
i make 914 rwhp w the tiny lg/borla 1 3/4 and 2.75" collector