Calculating manifold header size.
Discussion
stevesingo said:
I don't know how it is calculated but, an S14 (E30M3) has 50bhp per cylinder and they have a 45mm primary. Folks running 70bhp per cylinder are using 50mm (Evo2 manifold).
Steve
Steve
but those are blown engines which is slightly different from the AJP which is a NA 4.5ltr, even so, really large primaries in turbo's is not necessarily good either. Put it his way in NA form the latter is enough to flow nearly 160hp per cylinder. I would proffer in this NA application both would lose torque with primaries that large in a 4-2-1 system. David H said:
HarryW said:
stevesingo said:
I don't know how it is calculated but, an S14 (E30M3) has 50bhp per cylinder and they have a 45mm primary. Folks running 70bhp per cylinder are using 50mm (Evo2 manifold).
but those are blown engines
OK E30, I was on Nissan 200SX's there
Edited by HarryW on Sunday 3rd June 23:05
now this is not very scientific, more based on previous experience........50bhp per cylinder will not require anything near the sizes suggested above.....do not fall into the "bigger is better trap" for that sort of power you should not go bigger that 1.5" pipe OD (38mm)......the bigger you go, the slower the gas velocity will be......the smaller you go, the faster the gas velocity will be.....50bhp per cylinder is very mild......as a guide a 270bhp BTCC engine only uses 1.75" OD primary pipes (44.5mm)......quite why you would need 45-50mm OD primary pipes is beyond me, your wasting your time with that size when in the 50bhp per cylinder region
Edited by knighty on Tuesday 5th June 13:33
knighty said:
now this is not very scientific, more based on previous experience........50bhp per cylinder will not require anything near the sizes suggested above.....do not fall into the "bigger is better trap" for that sort of power you should not go bigger that 1.5" pipe OD (38mm)......the bigger you go, the slower the gas velocity will be......the smaller you go, the faster the gas velocity will be.....50bhp per cylinder is very mild......as a guide a 270bhp BTCC engine only uses 1.75" OD primary pipes (44.5mm)......quite why you would need 45-50mm OD primary pipes is beyond me, your wasting your time with that size when in the 50bhp per cylinder region
Edited by knighty on Tuesday 5th June 13:33
so for a 2x4 pot Cerb engine that (1.75"
would flow 540hp with no issue, even FIA GT cars run 1.75" primaries, feck knows what an E30 thinks its doing .tbh if you do the maths 1.25" would flow 50hp with a little to spare, but doesn't take into account bends.
Not heard from the OP yet, any thoughts or just fishing
HarryW said:
knighty said:
now this is not very scientific, more based on previous experience........50bhp per cylinder will not require anything near the sizes suggested above.....do not fall into the "bigger is better trap" for that sort of power you should not go bigger that 1.5" pipe OD (38mm)......the bigger you go, the slower the gas velocity will be......the smaller you go, the faster the gas velocity will be.....50bhp per cylinder is very mild......as a guide a 270bhp BTCC engine only uses 1.75" OD primary pipes (44.5mm)......quite why you would need 45-50mm OD primary pipes is beyond me, your wasting your time with that size when in the 50bhp per cylinder region
Edited by knighty on Tuesday 5th June 13:33
so for a 2x4 pot Cerb engine that (1.75" would flow 540hp with no issue, even FIA GT cars run 1.75" primaries, feck knows what an E30 thinks its doing .tbh if you do the maths 1.25" would flow 50hp with a little to spare, but doesn't take into account bends.
The BMW S14 header may be the size is for homologation reasons. The s14 is over square , has a large valve area and has relatively short exhaust cam duration and I think this may be a contributing factor, i.e a short opening window per cycle will require a higher peak flow.
Steve
I think we are all going off topic a bit.....in the original post is said this
for the record, good 4cyl BTCC engines have a small bore, typically 83mm, for long stroke and good torque....but they are dead now, its gone the ETCC route, but I suspect they will follow the same trend
The AJP Griff said:
How do you do this please?Lets assume it's a flat plane crank V8 with 50bhp per cylinder.
if thats the case, then thats a 400bhp V8, and I still stand by what I said....1-1/2" primary OD.....possibly 1-5/8" at a pushfor the record, good 4cyl BTCC engines have a small bore, typically 83mm, for long stroke and good torque....but they are dead now, its gone the ETCC route, but I suspect they will follow the same trend
knighty said:
I think we are all going off topic a bit.....in the original post is said this
for the record, good 4cyl BTCC engines have a small bore, typically 83mm, for long stroke and good torque....but they are dead now, its gone the ETCC route, but I suspect they will follow the same trend
1 1/4 & 1 5/8 are exactly the sizes TVR used with the orignal AJP installation on the Cerb (4.2 & 4.5) The AJP Griff said:
How do you do this please?Lets assume it's a flat plane crank V8 with 50bhp per cylinder.
if thats the case, then thats a 400bhp V8, and I still stand by what I said....1-1/2" primary OD.....possibly 1-5/8" at a pushfor the record, good 4cyl BTCC engines have a small bore, typically 83mm, for long stroke and good torque....but they are dead now, its gone the ETCC route, but I suspect they will follow the same trend
trackcar said:
I've just written a 2 page article for Sprint magazine on cerbera exhausts, the main point in there being that the std cerbera manifolds are not as bad as they look.
Agree they perform surprisingly well. The JP replacements will give you, after much work, at least +10 across the board though. Which is why unless they need replacing then it is not an early modification on the hp/£ scaleometer list. However a lot of earlier cars the manifolds are falling apart and there is no real cost effective replacement apart from the JP ones. Do you know if the orignals are still avialable and for how much afaik they are a similar price .re teh griff, Joolz if you are going bespoke on this I would seriuosly condider Tuscan routing with a matched long primary 4-1 system
.nice to hear the boys at TVR knew what they were doing.....as I said above, bigger is slow, smaller is faster......its very easy to fall into the bigger is better trap, only for your car to drive like a dog.
1-1/4" eh!....cripes, now that is small!.....but it obviously worked, I missed your reference to 1.25" being up to the job of 50bhp/cyl in your other post......we are obviously on the same line of thought ;-)
1-1/4" eh!....cripes, now that is small!.....but it obviously worked, I missed your reference to 1.25" being up to the job of 50bhp/cyl in your other post......we are obviously on the same line of thought ;-)
Edited by knighty on Wednesday 6th June 15:47
HarryW said:
Not heard from the OP yet, any thoughts or just fishing
My initial thoughts were to make them as small as possible,then a few people i talked to who's opinion i respect,said to go big so i was totally confused!My problem is that i cant afford to try two or three different sizes of course,and the way this thread has gone hasn't really helped me decide,either.Some interesting thought's though folks,so thanks to all for the contributions
not helped?.....yes it has!......rule number 1.....stay well away from 1-3/4"......for 50bhp per cylinder, I honestly believe 1-1/2" will be fine.....if you go much above 50bhp per cyl go 1-5/8".....I'm not a great fan of 4-1 systems, as they are not kind to the mid-range performance...... on a 4cyl my experience has taught me go for 4-2-1, which give good mid and top end performance, couple cyls 1&2 then 3&4 then into 1, go for a long primary, and short secondary, look at a good K-series pipe as fitted to a highly tuned elise, they are pushing 200bhp on 1-1/2 primary OD.......you will struggle to find anyone who stocks 1-5/8" in the UK, as its a rare size, but someone like Hayward and Scott will probably do it......do not go too big on the primary pipe OD otherwise you will lose ALL mid-range performance, and this is where you use the engine the most......even on a race track - believe it or not.
knighty said:
not helped?.....yes it has!......rule number 1.....stay well away from 1-3/4"......for 50bhp per cylinder, I honestly believe 1-1/2" will be fine.....if you go much above 50bhp per cyl go 1-5/8".....I'm not a great fan of 4-1 systems, as they are not kind to the mid-range performance...... on a 4cyl my experience has taught me go for 4-2-1, which give good mid and top end performance, couple cyls 1&2 then 3&4 then into 1, go for a long primary, and short secondary, look at a good K-series pipe as fitted to a highly tuned elise, they are pushing 200bhp on 1-1/2 primary OD.......you will struggle to find anyone who stocks 1-5/8" in the UK, as its a rare size, but someone like Hayward and Scott will probably do it......do not go too big on the primary pipe OD otherwise you will lose ALL mid-range performance, and this is where you use the engine the most......even on a race track - believe it or not.
If you use vizards rules of thumb then 1 1/2" straight pipe will flow around 90hp without restriction. Agree 1 5/8" can be done but you'd be surprised how much more difficult it becomes to accomdate each step up in size and still fit it in the package.
Are you sure about linking the right cylinders there, on the AJP flat plane V8 (2x4pots) its 1&3 2&4 if you want to get the pulse tuning up and running
HarryW said:
knighty said:
not helped?.....yes it has!......rule number 1.....stay well away from 1-3/4"......for 50bhp per cylinder, I honestly believe 1-1/2" will be fine.....if you go much above 50bhp per cyl go 1-5/8".....I'm not a great fan of 4-1 systems, as they are not kind to the mid-range performance...... on a 4cyl my experience has taught me go for 4-2-1, which give good mid and top end performance, couple cyls 1&2 then 3&4 then into 1, go for a long primary, and short secondary, look at a good K-series pipe as fitted to a highly tuned elise, they are pushing 200bhp on 1-1/2 primary OD.......you will struggle to find anyone who stocks 1-5/8" in the UK, as its a rare size, but someone like Hayward and Scott will probably do it......do not go too big on the primary pipe OD otherwise you will lose ALL mid-range performance, and this is where you use the engine the most......even on a race track - believe it or not.
If you use vizards rules of thumb then 1 1/2" straight pipe will flow around 90hp without restriction. Agree 1 5/8" can be done but you'd be surprised how much more difficult it becomes to accomdate each step up in size and still fit it in the package.
Are you sure about linking the right cylinders there, on the AJP flat plane V8 (2x4pots) its 1&3 2&4 if you want to get the pulse tuning up and running
trackcar said:
HarryW said:
knighty said:
not helped?.....yes it has!......rule number 1.....stay well away from 1-3/4"......for 50bhp per cylinder, I honestly believe 1-1/2" will be fine.....if you go much above 50bhp per cyl go 1-5/8".....I'm not a great fan of 4-1 systems, as they are not kind to the mid-range performance...... on a 4cyl my experience has taught me go for 4-2-1, which give good mid and top end performance, couple cyls 1&2 then 3&4 then into 1, go for a long primary, and short secondary, look at a good K-series pipe as fitted to a highly tuned elise, they are pushing 200bhp on 1-1/2 primary OD.......you will struggle to find anyone who stocks 1-5/8" in the UK, as its a rare size, but someone like Hayward and Scott will probably do it......do not go too big on the primary pipe OD otherwise you will lose ALL mid-range performance, and this is where you use the engine the most......even on a race track - believe it or not.
If you use vizards rules of thumb then 1 1/2" straight pipe will flow around 90hp without restriction. Agree 1 5/8" can be done but you'd be surprised how much more difficult it becomes to accomdate each step up in size and still fit it in the package.
Are you sure about linking the right cylinders there, on the AJP flat plane V8 (2x4pots) its ?&? ?&? if you want to get the pulse tuning up and running
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