Making some kick ass pipes for 2nd gen commodore

[vs manta 218Participant Vs hsv manta View build HERE Member since: March 2, 2015 Posts: 796]

Ok so I’m making some custom extractors for my blowen 355

 

iv got a DIY kit from difilippo, iv got a holden engine flanges in 1 3/4 that I will port out

 

if I can I’m goin to put some slits in 2 inch pipes and taper them down slightly so they clear the extractor bolts and run full 2 inch 4 Into 1 with a 3.5 inch collector

 

so my questions are, I’m running LS ecu with 2 O2 sensors, how far down the pipes should these be and does it matter witch way they face ( upside down or right way up)

Iv got a wide band and that goes at the collector

I have EGT, how close to head ports should this be ?

 

And also Iv got 2 3.5 inch moroso spiral mufflers that I’ll be fitting straight after the 3.5 inch cats along side the gear box, are there any pros and cons of having these mufflers before the x pipe ??

 

After these it will tapper down to 3 inch where it will connect to my existing exhaust pictured below

 

??

[VRSenator065Participant Adelaide SAVR Senator LSx454 1960 Kombi (project) 1921 Nash Hot Rod (future project) View build HERE Member since: February 17, 2015 Posts: 5 777]

Ok deleted the other thread mate, play on

[VRSenator065Participant Adelaide SAVR Senator LSx454 1960 Kombi (project) 1921 Nash Hot Rod (future project) View build HERE Member since: February 17, 2015 Posts: 5 777]

Btw looking forward to following this, take heaps of pics

[delcowizzidParticipant View build HERE Member since: March 2, 2015 Posts: 13]

Isn’t this centrifugal charged the last thing you want to do is cripple your low rpm torque production with way to big primaries and collectors

[vs manta 218Participant Vs hsv manta View build HERE Member since: March 2, 2015 Posts: 796]

What do you declare as low down torque ?

I dont get boost till 3000rpm and has no power below that so not after torque below that rpm

having 1 7/8 for first 8-10 inches then 2 inch after that is what quite a few have said would be about the perfect size for 800-1000 hp and leaves me room for down the track if I go a torque power block and throw all I can at it

 

this is entire set up was not built for low torque, it’s all mid range to top end power

 

I was also advised by Daren him self and others to go with 3.5 inch collectors over 3 inch running this power level

[vs manta 218Participant Vs hsv manta View build HERE Member since: March 2, 2015 Posts: 796]

What size would you suggest delco wizard for this sort of power between 3000-7000 rpm ??

 

And nd can anyone tell me how far down the pipes the LS O2 sensors like to be ??

And how close a EGT sensor should be to head port ?

[delcowizzidParticipant View build HERE Member since: March 2, 2015 Posts: 13]

Length will play a big roll short and small diameter can sometimes give the best of both worlds for both torque and hp.to big you may loose 30+ft/lb of torque below 4500 rpm and only gain 5hp at peak making the car slower by a lot.2″ upwards with 3.5 collectors is 540 bigblock teratory. Egt within 1″ of head o2’s closer to stock ls1 distance from port will make your learning to tune easier

[vs manta 218Participant Vs hsv manta View build HERE Member since: March 2, 2015 Posts: 796]

If I was building a street user engine I would agree but myn is not street user

it’s a rip tearing off it’s head high reving engine

 

have a look at my dyno graph, that is 6500rpm at the top dot and this was the 4th power run and still blowing black smoke so it should make power till 7000rpm

 

all my torque is up in the rpm range so that’s where Im focusing on

 

I’m not interested in the area lower 4000rpm, it just is what it is down there

 

all my calulations point to 1.9 or 2 inch primary’s in about 34 inch length

 

getting this length right is where I’m goin to spend all my effort, And from what I can gather using 1 7/8 inch for first 8 inches and 2 inch the rest of the way seams to suit this best

 

I haven’t seen collectors yet but I hope the have a bit of a choke down then back to 3.5 inch and if they don’t I might modify them so they do

 

I’m not in any way doubting you this is just what I have found in my reshearce

 

im interested in knowing what you think would be the optimum size for this type of combo

 

and thank you very much for 1 inch info and O2 position same as factory exhaust manifold on a ls1

 

[VRSenator065Participant Adelaide SAVR Senator LSx454 1960 Kombi (project) 1921 Nash Hot Rod (future project) View build HERE Member since: February 17, 2015 Posts: 5 777]

Does seem larger def is not always better.  I currently have 1 3/4″ on my 454 (NA).  When I was speaking to Jake Bain about doing heads/custom cam/headers etc as a package he ran the numbers through his design software and he said he could maybe make the 1.75″ headers work.  I def would lose on ultimate, but not necessarily that much, of course 1 7/8″ would be better and he thought 2″ was maybe borderline too big.  I guess that backs up Delcowizzid is saying (as expected).  But does yours being forced induction change that?  I always thought (maybe wrongly) that with NA you wanted/needed to be very particular about runner length and diameter, but with FI its more about getting it out, so you can pump the next charge in, so going slightly larger in diameter is better.  But is that not right?

• This reply was modified 9 years, 7 months ago by  VRSenator065.

[cava454Moderator 93 VR BT1 View build HERE Member since: February 20, 2015 Posts: 2 390]

Being manual u will go faster by keeping that “down low power”

 

stalled auto. Bigger is better

[vs manta 218Participant Vs hsv manta View build HERE Member since: March 2, 2015 Posts: 796]

From what i can gather its calulation between peak torque at what rpm and CI of engine

Peak torque been at

4700rpm in 355comes is about 1 7/8

3600 rpm or below 355 is more like 1 3/4 and can go even less if its peak torque is at 2500 rpm and

 

A 304 engine would be less again

 

My torque climbs all the way to 6000rpm and is still on the rise

A 355 peak torque been 5000 + comes in at a fly hair less then 2 inch and over 5200 rpm is 2 inch and higher continues getting bigger

 

The same 3600 rpm in 454 would be more like 1 7/8

 

But yours gary hits torque at 2200 so 1 7/8 will be big and may benefit more from 1 3/4

 

If you go bigger cam and raise the torque line then the bigger pipes will work more effictevly

 

Correct me if im wrong as this is just what iv been able to gather

[vs manta 218Participant Vs hsv manta View build HERE Member since: March 2, 2015 Posts: 796]

Thats the absolute bare baisics

 

Its gets a hell of a lot more complercited then that

[vs manta 218Participant Vs hsv manta View build HERE Member since: March 2, 2015 Posts: 796]

And as gary says i to believe it takes a step up for F/I set ups as what iv found out that I put above is for N/A set up

 

But still after others oppions on what they would use and why running a set up like this

[VRSenator065Participant Adelaide SAVR Senator LSx454 1960 Kombi (project) 1921 Nash Hot Rod (future project) View build HERE Member since: February 17, 2015 Posts: 5 777]

Yea as I understand it pretty much as you have described is the go.  Just remember it really isn’t a  single purpose race car, so for example you don’t have straight through pipes, so its going to be a bit of a compromise.  Maybe the engine builders could help with suggestions?  I mean realistically you are going to be talking the difference between mental and insane, so your on a win-win anyways

• This reply was modified 9 years, 7 months ago by  VRSenator065.

[vs manta 218Participant Vs hsv manta View build HERE Member since: March 2, 2015 Posts: 796]

They recommend 1 7/8 for my engine in N/A form but can just cope on 1 3/4 and have a engine with 555hp over the gold pro my is based from with 525hp and that one needs 1 7/8 as a minium

 

Add boost and i have no idea lol

 

2 inch is just such a nice number though lol

[VRSenator065Participant Adelaide SAVR Senator LSx454 1960 Kombi (project) 1921 Nash Hot Rod (future project) View build HERE Member since: February 17, 2015 Posts: 5 777]

I would go 2″. That’s what my guts tells me anyways. I remember talking to an old school guy many years ago about exhaust valve size. He said, “make it big, get that shit out of there”. Not exactly elegant but you get what he means

• This reply was modified 9 years, 7 months ago by  VRSenator065.

[Anonymous View build HERE Member since: January 1, 1970 Posts: 0]

Personally I’d start the bigger pipe a couple of inches off the ports so the 1st bend is 2″ but that’s just me…

[vs manta 218Participant Vs hsv manta View build HERE Member since: March 2, 2015 Posts: 796]

Yeah it’s what my gut tells me to Gary

 

Ij  are you saying run a 1 7/8 for just the first straight about 35mm/ 1.5 inch or so and get the 2 inch bend on it there  ??

 

This is the main part I haven’t made up my mind on yet unless some one comes up with some hard evidence these are to big but I’m certainly not finding any

 

I have thought about running some cuts maybe 4 down about 30 mm on a 2 inch pipe and flaring it down a little just so I can get my extractor bolts in and that in it’s self would act as a scavenge  type thing or like you say a smaller pipe just a inch or 2 or make the first bend 1 7/8 something less then 8 inches I would imagine

[Anonymous View build HERE Member since: January 1, 1970 Posts: 0]

I’d probably roll up 8x cones to go from whatever you can fit on the ports to 2″ Pete, this has proven to work well on Turbo dump pipes as it allows the Gases to expand quickly and can help a bit with scavenging.

ARP Studs with 12 point small nuts will help here as well.

[vs manta 218Participant Vs hsv manta View build HERE Member since: March 2, 2015 Posts: 796]

Absolute legend 

 

best idea ever

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