00454sscamaro

what are the effects of say a 1 7/8-2" x3 1/2 header on a ms4 cam and 125 wet shot of nitrous-stock cubes. i wanted to go this big because i want to get some more ci's down the road and i dont want to buy headers twice. so question is why is it not recomended to go that big with headers on a stock cubed motor. the effects it would have? just less low end power? make the motor come to life later?

NoMoreFWD

iTrader: (1)

The size you posted will work well with N2O on stock cubes. I'm sure it will cost a little bottom end power, when your running N/A. With big cubes plans, go with it.

Nate_Taufer

iTrader: (1)

I wouldn't reccomend it. Somebody did a 1-3/4 to 1-7/8 swap on a nitrous 408 and didn't gain the horsepower to justify the torque loss. On a strictly drag motor maybe, but not on a street strip car.

Plus if you have a 1.6" exhaust valve the smaller header will help improve velocity and scavenging.

Nate

CAT3

iTrader: (9)

Lower torque on the bottom and reduced throttle response. Even a non-stepped, straight 1 7/8" header you'll lose over a straight 1 3/4" primary. Stock cubes, I'd get a 1 3/4 stepped to 1 7/8. Just my $.02

00454sscamaro

less throttle response evreywhere or just low end? - under 3k rpm's ?

Spellbound

I bought 1 7/8ths QTP's with the HVMC for a future big cube project and ended up putting them on my stock cubed engine. I think I lucked out into an overall good combination. 90/90, AFR 205's, 229/229 114, Magnflow Cat back(no cut out)
316 ftlbs at 2400 rpms, 372ftlbs at 3500. This is the White car in the sig.

cantdrv65

iTrader: (3)

i dont think it will hurt much, but its not going to help ya either NA.... On the spray Id expect you to gain a little, but again wouldnt bet it would be much.

white2001s10

iTrader: (4)

Depends on what kind of tune you go with.
If you stick with closed-loop operation then yeah you'll probably notice a loss in response and bottom end.

Also keep in mind that the exhaust valve needs to match your exhaust port diameter/header primary as close as possible. A small exhaust valve is not going to be so happy with a large primary. It's a good idea to plan a significantly larger exhaust valve to better match your cubes and exhaust system.

ChucksZ06

iTrader: (9)

They will work great. Hot rod just dynoed a stock ls2 engine and it gained 10 hp going from 1 3/4 to 1 7/8. These engines move a lot of air. No one thinks twice about 2" primaries on a big block chevy that makes 500 hp. Is an lsx engine making 500 hp moving less air than the big block. I do not think so. The lsx is not your fathers small block. Good luck with your selection.

Z28XTC

iTrader: (5)

Get the 1 7/8s, when people say they lose TQ I think they mean over what you would make with 1 3/4s but I think you will still make TQ gains over stock manifolds and lets face it LS1s are not lacking in TQ anyway are they? Do you have nitrous? If so some of the guys on LS1tech have switched to 1 7/8s and gained 20 to 30 more hp on there nitrous dyno runs. Also I have not compared the sound but I bet the 1 7/8s sound better.
This is a hot topic here like the 90/90 on stock cubes topic I say if you are going for more cubes in future go for both you make good gains with both with stock cubes even if its 10 to 20 less than a ported TB,ls6 intake and 1 3/4s but you will make it up when you get your 383,402 0r so.
Also get a ory,pulley and port your T/B and intake and make up the TQ lost in the mean time.

Ed Wright

iTrader: (1)

Also keep in mind that the exhaust valve needs to match your exhaust port diameter/header primary as close as possible. A small exhaust valve is not going to be so happy with a large primary. It's a good idea to plan a significantly larger exhaust valve to better match your cubes and exhaust system.[/QUOTE]

That's one I haven't heard. I have used 2' primaries on manual trans 292" sbc race cars, and picked up over 1 7/8". That's with a 1.6" exhaust valve. Right now I have 1.56" exhaust valves in my old LT1, and it picked up close to 2 mph with 1 7/8" X 3" headers. Much more to it than exhaust valve dia.

chicane

There are many ideas about header pipe sizing. Usually the primary pipe sizing is related to exhaust valve and port size. Header pipe length is dependent on wave tuning (or lack of it). Typically, longer pipes tune for lower r.p.m. power and the shorter pipes favor high r.p.m. power. The collector package is dependent on the number of cylinders, the engine configuration (V-8, inline 6, etc.), firing order and the basic design objectives (interference or independence). The collector outlet size is determined by primary pipe size and exhaust cam timing.

Exhaust system design is a balancing act between many complex events and their timing. Even with the best compromise of exhaust pipe diameter and length, the collector outlet sizing can make or break the best design. The bottom line on any exhaust system design is to create the best, most useful power curve. All theory aside, the final judgement is how the engine likes the exhaust tuning on the dyno and on the track.

For more detail on the specifics of header theory read ‘The Scientific Design of Exhaust and Intake Systems' by Phillip H. Smith’.

In a limited explaination, the size will effect where your peak numbers will be produced. From lets say, 1 3/4" to 1 7/8" or the latter to 2.0" it will shift your peak hp production up in the rpm bandwidth. For instance, if you made 400hp at 6000rpm with the 1 3/4" and you changed to the 1 7/8" it would bump it up to 400hp but at 6500 to 6750rpm.

You will sacrifice low speed throttle response and scrub some low speed torque production..... and will most likely gain a few hp, since hp is a function of torque at higher rpm.

Z28XTC

iTrader: (5)

chicane,but when you say scrub low end TQ you mean slightly less than 1 3/4s not less than stock manifolds as 1 7/8s will make more low down TQ than stock manifolds.

chicane

Please refine you question, it is contrary in various ways.

One, I doubt that an 1 7/8" primary header will make more low speed torque from the mere pressure vessel volume alone on a stock cube build. Unless the header primary length was 28+ inches or longer. Can you make more than the stock manifold.... ??.... sure, but it is going to be with the addition of other parts being changed. But not by themselves.

Two, when dealing with primary tube diameter (without changing anything else), your hp and torque production will trade directions in peak numbers when going from one diameter to another, within the respects of proper primary sizing to valve diameter. Going to a bigger primary size will net you peak hp and torque numbers higher in the curve and you will most likely pick up a few more hp, but scrub a few ftlbs of torque.

Z28XTC

iTrader: (5)

Sorry if that was a bit hard to understand but what i was trying to ask was will 1 7/8s make more low down TQ than stock exhaust manifolds and stock cubes?
And what extra parts would be needed if it cant do it by themselves?

00454sscamaro

^i think hes saying different types of headers just move the power around.. sounds very true, considering i cant gain hp throughtout the powerband going with aftermarket exhaust with my yz450f (or i cant gain anywhere without loosing power somwhere else), just move where all the power is being made. so these ones im considering, will be top end oriented. ^ i do have nitrous (125 wet) , i just havent installed it yet. i have a ud pulley, a ewp, ported tb,ms4 cam(not installed yet) etc. i was going to make this system a true dual system with x pipe when i get the headers, the only thing im still debating in the type of setup is if im going to put high flow cats on too.

Ed Wright

iTrader: (1)

Buy this guy's Pipemax software, the best I have seen for header design. Also has some freebies throw in. (power calculations, etc.) Not expensive, and well worth it.

http://www.maxracesoftware dot com

Z28XTC

iTrader: (5)

Can someone answer my last question?Will 1 7/8s make more Low end TQ than stock exhaust manifolds?

white2001s10

iTrader: (4)

Depends on two things really.
1. torque at what VE or throttle opening?
2. where you draw the line for low end?

There's a big difference between cruising down the highway at a steady 1800 RPM, and being WOT at 3500 RPM.

With a properly set up car most people would get quite a bit more power WOT and increased performance with the 1 7/8" pipes over stock ...however drivability could still suffer a bit.

Z28XTC

iTrader: (5)

I am putting on mine next week and I will tell everyone how it goes.