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WHAT SIZE HEADERS TO GET ON A CAMMED L98 WITH HARROP 2300FDFI

Frosty005

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Hi after some help from people that have done testing etc with headers …. Currently have a L98 with cam etc with 310 rwk….. exhaust currently a 3” system with Magna flow mufflers on the rear and VF HSV headers …. I’m getting a Harrop 2300 fdfi fitted soon and am in a dilemma on which size manta headers I’m going to put on …. Everyone I’ve talked to including performance workshops and other people that have supercharges recommend to go with the 1 7/8” over the 1 3/4 “ but the very well renowned and trusted workshop fitting the charger are saying go the 1 3/4 “ …. Now what I’m worried about is if I did go the 1 7/8 will it be considerably louder than the 1 3/4 “ ? I have also heard you loose a little power down low with the 1 7/8” headers but seeing though it’s going to be charged if that will be a problem anyway ? And also I was thinking as I’m running 3.7 gears and manual that Loosing a little down low may help with not getting to much wheel spin and may be a better choice …. So ultimately my main concern is if the 1 7/8” headers are going to be to loud or much louder than the 1 3/4 “ …… any advice or experience to help point in the right direction will be appreciated
 

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You won’t need to worry about a lack of power mate, it will make plenty!!
Mine is just a baby Magnusson, small cam with 1 3/4” and the torque is mean, your setup will be nuts with any gearing and will not have grip on the street if you mash it anyway!
I would go with the shops recommended combo.
Good luck with build, it’ll be killer.
 

07GTS

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with the blower u have to get the exhaust out, 1-7/8 will be fine if u don't have any already but if u have the 1-3/4 now and ur not after all out power will be fine, u will have more then enough torque either way
 

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I think after the headers is where loudness is exacerbated not cross section of header primary. The main thing is velocity and efficiency which equates to torque spread.
As you get to 360-370 rwkw the velocity through 1 3/4” is too high with catted full exhaust. But that is screaming at peak revs, not likely 99% of the time with 370 / 740 Nm at rears.
Performance wise 1 3/4” and velocity is good for exhaust resonance tuning. Smallest that fits the exhaust gas is good engineering.
Noise level same theoretically but too low velocity with large CSA can boom around cat back in driving modes like un-boosted low load cruise, back off, highway etc. you run risk of being stuck with hard to tune out resonance (drone), which should not be a part of a modern performance equation.
 
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Pollushon

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There's plenty of side by side testing of 3/4 vs 7/8 with boost. Also speaking from experience I would definitely go the 7/8. Scavenging becomes less relevant when you're force feeding

Edit - I didn't notice any difference in noise. It was friggin loud before and it was friggin loud after. I have older ears too
 
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Frosty005

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You won’t need to worry about a lack of power mate, it will make plenty!!
Mine is just a baby Magnusson, small cam with 1 3/4” and the torque is mean, your setup will be nuts with any gearing and will not have grip on the street if you mash it anyway!
I would go with the shops recommended combo.
Good luck with build, it’ll be killer.
Thanks for your feedback
 

Frosty005

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There's plenty of side by side testing of 3/4 vs 7/8 with boost. Also speaking from experience I would definitely go the 7/8. Scavenging becomes less relevant when you're force feeding

Edit - I didn't notice any difference in noise. It was friggin loud before and it was friggin loud after. I have older ears too
Thanks for your feedback
 

Frosty005

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I think after the headers is where loudness is exacerbated not cross section of header primary. The main thing is velocity and efficiency which equates to torque spread.
As you get to 360-370 rwkw the velocity through 1 3/4” is too high with catted full exhaust. But that is screaming at peak revs, not likely 99% of the time with 370 / 740 Nm at rears.
Performance wise 1 3/4” and velocity is good for exhaust resonance tuning. Smallest that fits the exhaust gas is good engineering.
Noise level same theoretically but too low velocity with large CSA can boom around cat back in driving modes like un-boosted low load cruise, back off, highway etc. you run risk of being stuck with hard to tune out resonance (drone), which should not be a part of a modern performance equation.
Thanks for your feedback
 

Frosty005

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There's plenty of side by side testing of 3/4 vs 7/8 with boost. Also speaking from experience I would definitely go the 7/8. Scavenging becomes less relevant when you're force feeding

Edit - I didn't notice any difference in noise. It was friggin loud before and it was friggin loud after. I have older ears too
Thanks for your feedback
 

Immortality

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There's plenty of side by side testing of 3/4 vs 7/8 with boost. Also speaking from experience I would definitely go the 7/8. Scavenging becomes less relevant when you're force feeding

Edit - I didn't notice any difference in noise. It was friggin loud before and it was friggin loud after. I have older ears too

Exactly, I need to be able to hear my engine running, the older I get the louder my exhaust requirements are. I friggin hate electric cars because I can't hear em.
 
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