Big cams, OE manifold, way down on power.
Discussion
One for our resident feral cat to get his teeth into maybe 
Sorry, a bit of a long one, i'll split it into two short/long sections for the knowledgeable/patient and snowflake/Millenials.
Short story/question:
From a power perspective only is there any reason why and how smaller cams would give more top end power than 'big' ones in conjunction with a modern convoluted plastic OEM manifold?
Is it just my exhaust cam which is too long on duration, would a shorter duration one give more top end?
Long story:
Basically I've come from a turbo background, but am now going the other way and getting my head around N/A engines. I'm building up my knowledge base by starting at the bottom and adding bits on to see what does what.
I make some of the parts myself and bolt them on, they can be used on other iterations too so it's not like i'm throwing thousands at it then putting the parts in the bin when they don't work.
Car is a 1 ton track car.
The engine i'm working with is a reasonably modern (mid noughties), 2.3ltr 16v. Port injection, single VVT now removed.
The spec so far is:
12:1 CR working with 99 Ron
Mild porting to the already excellent head.
OE valves 30 and 35mm
Inlet cam of 12mm and 276 @ .1mm
Ex cam of 11 and 302 @ .1 (Yes I know)
Both intake and inlet valves are 3mm open at TDC so plenty of overlap, as you can imagine it ticks over like a POS at 1200-1500rpm. I do have angles jotted down if needed.
4 - 1 manifold, 1.8"/45mm externally going into a 60mm exit merge then to a 3" exhaust. (hoping that some venturi effect happens here!), it's an 'off-the-shelf' mani hence 60mm exit.
The inlet manifold is really the only thing which remains untouched, TB is 60mm. It has two sets of runners and i'm going to call them long and short, but in reality and interestingly what the internal runner flaps do is change it from 4 long runners to all 8 (4 short, 4 long) open. Original manifold runner control strategy was; short - long - short throughout the rev range. We call this IMRC.
Long runners are approx 16", short are 12" + port length, neither is straight, both curl round a bit.
It's been mapped twice:
Red lines are first session, green is second session.
Second session was with the ex cam retarded more, it was 2mm open at TDC, is now 3mm like the inlet. Also it was with a 3" exhaust, red run was with 60mm. Sorry for mixing my units. Much of those gains in the 5000 to 6500 region were actually from playing with the IMRC.
As you can see we did make some large improvements in one part of the range, but it still flatlines at high rpm and gives almost the same max output. In it's original road going format the engine puts out about 163bhp. I do have the WHP graph too.
Initially it appears to be the manifold which is the problem from 6k onwards.
Fuelling isn't an issue.
Would a smaller cam and less overlap give more peak power and if so, how or why? It's been suggested it would based on measured manifold pressure, this is the bit i'm struggling to understand, as I see it now I've done everything to create a 250bhp engine, but the manifold is strangling it as it's too restrictive and the pipe lengths are wrong. I know separate TBs are the way to go and ultimately that is what it will get once i've been through everything else.
You might wonder why i've done XY & Z, but there are generally good explanations for this.
My next move is to fab up a simplified inlet manifold with short straight runners, a plenum, the OE 60mm TB and keep the cams or maybe fit some smaller cams with this manifold, but as per above, cams i'm not sure about.
After that will be the more expensive route of ITBs.
Any useful input appreciated.
Sorry, a bit of a long one, i'll split it into two short/long sections for the knowledgeable/patient and snowflake/Millenials.
Short story/question:
From a power perspective only is there any reason why and how smaller cams would give more top end power than 'big' ones in conjunction with a modern convoluted plastic OEM manifold?
Is it just my exhaust cam which is too long on duration, would a shorter duration one give more top end?
Long story:
Basically I've come from a turbo background, but am now going the other way and getting my head around N/A engines. I'm building up my knowledge base by starting at the bottom and adding bits on to see what does what.
I make some of the parts myself and bolt them on, they can be used on other iterations too so it's not like i'm throwing thousands at it then putting the parts in the bin when they don't work.
Car is a 1 ton track car.
The engine i'm working with is a reasonably modern (mid noughties), 2.3ltr 16v. Port injection, single VVT now removed.
The spec so far is:
12:1 CR working with 99 Ron
Mild porting to the already excellent head.
OE valves 30 and 35mm
Inlet cam of 12mm and 276 @ .1mm
Ex cam of 11 and 302 @ .1 (Yes I know)
Both intake and inlet valves are 3mm open at TDC so plenty of overlap, as you can imagine it ticks over like a POS at 1200-1500rpm. I do have angles jotted down if needed.
4 - 1 manifold, 1.8"/45mm externally going into a 60mm exit merge then to a 3" exhaust. (hoping that some venturi effect happens here!), it's an 'off-the-shelf' mani hence 60mm exit.
The inlet manifold is really the only thing which remains untouched, TB is 60mm. It has two sets of runners and i'm going to call them long and short, but in reality and interestingly what the internal runner flaps do is change it from 4 long runners to all 8 (4 short, 4 long) open. Original manifold runner control strategy was; short - long - short throughout the rev range. We call this IMRC.
Long runners are approx 16", short are 12" + port length, neither is straight, both curl round a bit.
It's been mapped twice:
Red lines are first session, green is second session.
Second session was with the ex cam retarded more, it was 2mm open at TDC, is now 3mm like the inlet. Also it was with a 3" exhaust, red run was with 60mm. Sorry for mixing my units. Much of those gains in the 5000 to 6500 region were actually from playing with the IMRC.
As you can see we did make some large improvements in one part of the range, but it still flatlines at high rpm and gives almost the same max output. In it's original road going format the engine puts out about 163bhp. I do have the WHP graph too.
Initially it appears to be the manifold which is the problem from 6k onwards.
Fuelling isn't an issue.
Would a smaller cam and less overlap give more peak power and if so, how or why? It's been suggested it would based on measured manifold pressure, this is the bit i'm struggling to understand, as I see it now I've done everything to create a 250bhp engine, but the manifold is strangling it as it's too restrictive and the pipe lengths are wrong. I know separate TBs are the way to go and ultimately that is what it will get once i've been through everything else.
You might wonder why i've done XY & Z, but there are generally good explanations for this.
My next move is to fab up a simplified inlet manifold with short straight runners, a plenum, the OE 60mm TB and keep the cams or maybe fit some smaller cams with this manifold, but as per above, cams i'm not sure about.
After that will be the more expensive route of ITBs.
Any useful input appreciated.
What engine exactly and pics of the manifold would help. Bore/Stroke? Cam open and closing timing.
The exhaust cam is probably a bit strong.
IME of the BMW S14B25 2.5lt 4cyl, 95/87mm bore stroke, it generally wants more intake cam than exhaust. My engine has 292deg @ 0.1mm intake and 284deg @ 0.1mm with 4.5/3.5mm lift at TDC. It idles rock solid at 950rpm and I can pull away in 2nd without touching the throttle.
Other things to consider are that as cams get more aggressive, the more sensitive the engine is to intake and exhaust length.
But in this case, I think much too much exhaust cam.
The exhaust cam is probably a bit strong.
IME of the BMW S14B25 2.5lt 4cyl, 95/87mm bore stroke, it generally wants more intake cam than exhaust. My engine has 292deg @ 0.1mm intake and 284deg @ 0.1mm with 4.5/3.5mm lift at TDC. It idles rock solid at 950rpm and I can pull away in 2nd without touching the throttle.
Other things to consider are that as cams get more aggressive, the more sensitive the engine is to intake and exhaust length.
But in this case, I think much too much exhaust cam.
stevesingo said:
What engine exactly and pics of the manifold would help. Bore/Stroke? Cam open and closing timing.
The exhaust cam is probably a bit strong.
IME of the BMW S14B25 2.5lt 4cyl, 95/87mm bore stroke, it generally wants more intake cam than exhaust. My engine has 292deg @ 0.1mm intake and 284deg @ 0.1mm with 4.5/3.5mm lift at TDC. It idles rock solid at 950rpm and I can pull away in 2nd without touching the throttle.
Other things to consider are that as cams get more aggressive, the more sensitive the engine is to intake and exhaust length.
But in this case, I think much too much exhaust cam.
Yes I agree, it was designed by computer, flies in the face of conventional wisdom and is probably wrong, but that's how I arrived at it. Whilst it's unsurprisingly causing idle issues, I don't know for sure if it's lowering the top end power, that's the issue, you are probably running ITBs? Valvetronic, VVT?The exhaust cam is probably a bit strong.
IME of the BMW S14B25 2.5lt 4cyl, 95/87mm bore stroke, it generally wants more intake cam than exhaust. My engine has 292deg @ 0.1mm intake and 284deg @ 0.1mm with 4.5/3.5mm lift at TDC. It idles rock solid at 950rpm and I can pull away in 2nd without touching the throttle.
Other things to consider are that as cams get more aggressive, the more sensitive the engine is to intake and exhaust length.
But in this case, I think much too much exhaust cam.
There isn't much to be gained by looking at a manifold like this, not without cutting it into multiple pieces.
Edited by 227bhp on Monday 13th January 21:20
yes big cams can cause reverison issues especially when you have way too much exhaust duration and a primary pipe about of 45mm which is way way too big? the 3" tailpipe is way too big.
there are diminshing returns with cams when you keep OE intake manifold, the 12" runner length and a few inches of port is about right to run 6500-7500 bnut its probably a dogs breakfast inside that compact OE piece
there are diminshing returns with cams when you keep OE intake manifold, the 12" runner length and a few inches of port is about right to run 6500-7500 bnut its probably a dogs breakfast inside that compact OE piece
ex duration is probably not the root cause at the topend at those specs but wont be helping the bottom and midrange.the big ex pipes do cause high rpm reversion as they dont scavenege which causes reversion back up the intake at IVO hurting the cylinder fill thereafter.
most likley inlet side is the root cause, a straighter shot correct length runner would help. how good is the head? what air cleaner is feeding the intake manifiold? often there is improvment when going to a new manifold design when the OE air cleaner assembly is binned
most likley inlet side is the root cause, a straighter shot correct length runner would help. how good is the head? what air cleaner is feeding the intake manifiold? often there is improvment when going to a new manifold design when the OE air cleaner assembly is binned
Edited by Inline__engine on Sunday 12th January 01:24
big...small...whatever either means
Right...wrong....maybe more correct....but who knows.
But the biggest mistake everyone makes with cams...is thinking "bigger" is better. Most modern engines have good head flow, reducing the need or desire for stupid overlap or silly aggressive profiles.
And I'd assume most OEM intakes are not designed with very high rpm use in mind either, if very high is what you're after ? 12" runner is still pretty long.
But big or small....doesnt really cover valve events which are of ultimate importance. Nor does it cover whether lift used...is actually usable or sensible in terms of the head/intake.
Nor what sort of LSA's that have been tried, which can easily be played with on a DOHC setup ( I presume...you dont mention what engine, nor what sort of cam drive )
You say the head is excellent...so has it been flow tested at the lifts involved with the intake manifold attached ?
You mention VVT.....have you retained this, or got rid of it ? And is it proper VVT, or simply off/on 2 position ?
Why not opt for milder more sensible cams and make use of the VVT ?
Vizard did say years ago.....go through cam choices and select the camshaft you want. Then buy/install one stage lower. Pretty much everyone always thinks they need a bigger cam than what in reality is needed.
DOHC gives you more room to play and experiment, as does VVT without going for silly big profiles that often just hurt things more than they help.
And is this engine something unique that there are no tried and tested profiles ?
Right...wrong....maybe more correct....but who knows.
But the biggest mistake everyone makes with cams...is thinking "bigger" is better. Most modern engines have good head flow, reducing the need or desire for stupid overlap or silly aggressive profiles.
And I'd assume most OEM intakes are not designed with very high rpm use in mind either, if very high is what you're after ? 12" runner is still pretty long.
But big or small....doesnt really cover valve events which are of ultimate importance. Nor does it cover whether lift used...is actually usable or sensible in terms of the head/intake.
Nor what sort of LSA's that have been tried, which can easily be played with on a DOHC setup ( I presume...you dont mention what engine, nor what sort of cam drive )
You say the head is excellent...so has it been flow tested at the lifts involved with the intake manifold attached ?
You mention VVT.....have you retained this, or got rid of it ? And is it proper VVT, or simply off/on 2 position ?
Why not opt for milder more sensible cams and make use of the VVT ?
Vizard did say years ago.....go through cam choices and select the camshaft you want. Then buy/install one stage lower. Pretty much everyone always thinks they need a bigger cam than what in reality is needed.
DOHC gives you more room to play and experiment, as does VVT without going for silly big profiles that often just hurt things more than they help.
And is this engine something unique that there are no tried and tested profiles ?
stevieturbo said:
big...small...whatever either means
Right...wrong....maybe more correct....but who knows.
But the biggest mistake everyone makes with cams...is thinking "bigger" is better. Most modern engines have good head flow, reducing the need or desire for stupid overlap or silly aggressive profiles.
And I'd assume most OEM intakes are not designed with very high rpm use in mind either, if very high is what you're after ? 12" runner is still pretty long.
But big or small....doesnt really cover valve events which are of ultimate importance. Nor does it cover whether lift used...is actually usable or sensible in terms of the head/intake.
Nor what sort of LSA's that have been tried, which can easily be played with on a DOHC setup ( I presume...you dont mention what engine, nor what sort of cam drive )
You say the head is excellent...so has it been flow tested at the lifts involved with the intake manifold attached ?
You mention VVT.....have you retained this, or got rid of it ? And is it proper VVT, or simply off/on 2 position ?
Why not opt for milder more sensible cams and make use of the VVT ?
Vizard did say years ago.....go through cam choices and select the camshaft you want. Then buy/install one stage lower. Pretty much everyone always thinks they need a bigger cam than what in reality is needed.
DOHC gives you more room to play and experiment, as does VVT without going for silly big profiles that often just hurt things more than they help.
And is this engine something unique that there are no tried and tested profiles ?
the exhaust only needs to expel what gets in through the inlet so big/small duration is in part with respect to the inlet duration (which is not that large though often catcams stuff is misleading for solid lifter cams if thats what we are dealing with). Right...wrong....maybe more correct....but who knows.
But the biggest mistake everyone makes with cams...is thinking "bigger" is better. Most modern engines have good head flow, reducing the need or desire for stupid overlap or silly aggressive profiles.
And I'd assume most OEM intakes are not designed with very high rpm use in mind either, if very high is what you're after ? 12" runner is still pretty long.
But big or small....doesnt really cover valve events which are of ultimate importance. Nor does it cover whether lift used...is actually usable or sensible in terms of the head/intake.
Nor what sort of LSA's that have been tried, which can easily be played with on a DOHC setup ( I presume...you dont mention what engine, nor what sort of cam drive )
You say the head is excellent...so has it been flow tested at the lifts involved with the intake manifold attached ?
You mention VVT.....have you retained this, or got rid of it ? And is it proper VVT, or simply off/on 2 position ?
Why not opt for milder more sensible cams and make use of the VVT ?
Vizard did say years ago.....go through cam choices and select the camshaft you want. Then buy/install one stage lower. Pretty much everyone always thinks they need a bigger cam than what in reality is needed.
DOHC gives you more room to play and experiment, as does VVT without going for silly big profiles that often just hurt things more than they help.
And is this engine something unique that there are no tried and tested profiles ?
Also for pipe size the magntude of hp determines what big and small mean ....
12" is not a long runner for a engine that peaks around 7000 but a tortuous path doesnt help
for a street engine i'd also retain VVT and choose milder duration but big lift and then use the VVT to make it rpm
The exhaust cam is ridiculous. If a computer program came up with that then it needs scrapping. Much of the combustion power is going straight down the exhaust pipe because the exhaust valves are opening far too early. Same exhaust duration as inlet would be plenty. LCA is way out also. The engine probably needs about 105 degrees timed 3 degrees advanced so 102 ATDC full lift on inlet and 108 BTDC on exhaust with the right cams.
Exhaust manifold is sized for about 260 bhp and should need a 2 1/2" o/d exhaust. 3" is too big.
https://web.archive.org/web/20110918115047/http://...
https://web.archive.org/web/20110903091024/http://...
Inlet cam should suffice for about 100 bhp/litre.
It's pointless speculating about the potential of the plenum system. If you want 100 bhp/litre then fit TBs.
Main problem is lack of torque. 75 ish ft lbs per litre is not very good. Should be over 90 with proper pulse tuning and the right exhaust cam.
Finally, red/green lines on the graph is not very f'ing helpful to someone who is red/green colourblind!
Exhaust manifold is sized for about 260 bhp and should need a 2 1/2" o/d exhaust. 3" is too big.
https://web.archive.org/web/20110918115047/http://...
https://web.archive.org/web/20110903091024/http://...
Inlet cam should suffice for about 100 bhp/litre.
It's pointless speculating about the potential of the plenum system. If you want 100 bhp/litre then fit TBs.
Main problem is lack of torque. 75 ish ft lbs per litre is not very good. Should be over 90 with proper pulse tuning and the right exhaust cam.
Finally, red/green lines on the graph is not very f'ing helpful to someone who is red/green colourblind!
DeadCatWalking said:
The exhaust cam is ridiculous. If a computer program came up with that then it needs scrapping. Much of the combustion power is going straight down the exhaust pipe because the exhaust valves are opening far too early. Same exhaust duration as inlet would be plenty. LCA is way out also. The engine probably needs about 105 degrees timed 3 degrees advanced so 102 ATDC full lift on inlet and 108 BTDC on exhaust with the right cams.
I agree and moreover, after suspecting it was wrong I now have proof so will get my money back.So you think the ex cam is actually losing power?
If it is i'll get another, the 11mm lift matches the springs, I can go to 12mm and change the springs if it would be worth it, but not sure an extra 1mm would do much on the exhaust.
DeadCatWalking said:
Exhaust manifold is sized for about 260 bhp and should need a 2 1/2" o/d exhaust. 3" is too big.
https://web.archive.org/web/20110918115047/http://...
https://web.archive.org/web/20110903091024/http://...
The exhaust is debatable and others would disagree. As I see it it's not costing me power, it was done so it couldn't be suspected of holding the engine back.https://web.archive.org/web/20110918115047/http://...
https://web.archive.org/web/20110903091024/http://...
DeadCatWalking said:
Inlet cam should suffice for about 100 bhp/litre.
It's pointless speculating about the potential of the plenum system. If you want 100 bhp/litre then fit TBs.
It's pointless speculating about the potential of the plenum system. If you want 100 bhp/litre then fit TBs.
As outlined there is a halfway house here, it would be interesting to see what a better design of manifold brings to the party. What I didn't say was that is has drive by wire (electronic throttle), so a lot to be lost and a lot of money to be found to get rid of it.
DeadCatWalking said:
Main problem is lack of torque. 75 ish ft lbs per litre is not very good. Should be over 90 with proper pulse tuning and the right exhaust cam.
Ok, as per above, i'll get another cam.227bhp said:
Yes I agree, it was designed by computer, flies in the face of conventional wisdom and is probably wrong, but that's how I arrived at it. Whilst it's unsurprisingly causing idle issues, I don't know for sure if it's lowering the top end power, that's the issue.
Bore is 87.5 and Stroke 94 so a completely different long stroke compared to yours, but you are probably running ITBs? Valvetronic, VVT?
There isn't much to be gained by looking at a manifold like this, not without cutting it into multiple pieces:
No VTT, but I do have ITBs, but in regard to idle quality, this should not be a differentiator. My EMS uses TPS for load calculation. What are you using? MAP and MAF can suffer at low rpm with long duration cams.Bore is 87.5 and Stroke 94 so a completely different long stroke compared to yours, but you are probably running ITBs? Valvetronic, VVT?
There isn't much to be gained by looking at a manifold like this, not without cutting it into multiple pieces:
WHat is the origin of the engine. There maybe schematic images of the intake online however moot that may be. Just get to TBs.
Something else to consider is a validity of the dyno result. When I built my engine and tuned it, the result was somewhat disappointing (based on similar spec engines), to the point where I began to question it.
I ended up doing a BSFC calculation from the injector pulse width, flow rate and rpm and ended up with a BSFC in the region of 0.635lb/hp-hr. I either had the worst BMW S14 ever built or something was amiss. A trip to another dyno which was used by someone with a similar engine build was less disappointing and in line with expectations.
Edited by stevesingo on Sunday 12th January 10:33
227bhp said:
So you think the ex cam is actually losing power?
Which bit of "Much of the combustion power is going straight down the exhaust pipe" was unclear?My best guess is that exhaust cam is costing 10-20 bhp.
227bhp said:
The exhaust is debatable and others would disagree. As I see it it's not costing me power, it was done so it couldn't be suspected of holding the engine back.
How dare you disagree with me or quote pretenders to my throne who do! I am a tuning god. Overly large exhausts (both manifolds and systems) almost always cost power and more importantly torque. Read the articles again.Manifolds are more important than systems but both can hurt if oversized.
if you want an engine sim then use ENGMOD4T and the new version of pipemax.
this engine looks like it was designed based on 2V/cyl push rod engines meant for drag racing.....
if you tell us
bore
stroke
rod length
cylinder head inlet valve size and flow
cylinder head exaust valve size and flow
type of characteristcs you want, street, race, plus powerband etc
can run some basic numbers
throwing some stuff at pipemax with guestimations suggested a duration in the order of ~230-235 at 1.0mm for both inlet and exhaust for a 250hp engine goal. and primary of 1-5/8" and 2-3/8" tailpipe
this engine looks like it was designed based on 2V/cyl push rod engines meant for drag racing.....
if you tell us
bore
stroke
rod length
cylinder head inlet valve size and flow
cylinder head exaust valve size and flow
type of characteristcs you want, street, race, plus powerband etc
can run some basic numbers
throwing some stuff at pipemax with guestimations suggested a duration in the order of ~230-235 at 1.0mm for both inlet and exhaust for a 250hp engine goal. and primary of 1-5/8" and 2-3/8" tailpipe
Edited by Inline__engine on Sunday 12th January 10:48
stevesingo said:
227bhp said:
Yes I agree, it was designed by computer, flies in the face of conventional wisdom and is probably wrong, but that's how I arrived at it. Whilst it's unsurprisingly causing idle issues, I don't know for sure if it's lowering the top end power, that's the issue.
Bore is 87.5 and Stroke 94 so a completely different long stroke compared to yours, but you are probably running ITBs? Valvetronic, VVT?
There isn't much to be gained by looking at a manifold like this, not without cutting it into multiple pieces:
No VTT, but I do have ITBs, but in regard to idle quality, this should not be a differentiator. My EMS uses TPS for load calculation. What are you using? MAP and MAF can suffer at low rpm with long duration cams.Bore is 87.5 and Stroke 94 so a completely different long stroke compared to yours, but you are probably running ITBs? Valvetronic, VVT?
There isn't much to be gained by looking at a manifold like this, not without cutting it into multiple pieces:
WHat is the origin of the engine. There maybe schematic images of the intake online however moot that may be. Just get to TBs.
As per my last post If I ditch the DBW throttle i'll lose everything else it brings to the party, i'll take it one step at a time.
It isn't all about the end result, it's about the journey too.
Inline__engine said:
if you want an engine sim then use ENGMOD4T and the new version of pipemax.
this engine looks like it was designed based on 2V/cyl push rod engines meant for drag racing.....
if you tell us
bore
stroke
rod length
cylinder head inlet valve size and flow
cylinder head exaust valve size and flow
type of characteristcs you want, street, race, plus powerband etc
can run some basic numbers
I have the latest Pipemax now, it's very hard work and also has bugs in it. I'm hoping to get my head around it soon.this engine looks like it was designed based on 2V/cyl push rod engines meant for drag racing.....
if you tell us
bore
stroke
rod length
cylinder head inlet valve size and flow
cylinder head exaust valve size and flow
type of characteristcs you want, street, race, plus powerband etc
can run some basic numbers
The problem with a lot of these programs is they depend on the paying customer to iron out the faults for them!
227bhp said:
I have the latest Pipemax now, it's very hard work and also has bugs in it. I'm hoping to get my head around it soon.
The problem with a lot of these programs is they depend on the paying customer to iron out the faults for them!
i just ran some numbers after i found most info except head flow. no bugs foundThe problem with a lot of these programs is they depend on the paying customer to iron out the faults for them!
what engine is this?
throwing some stuff at pipemax with guestimations suggested a duration in the order of ~230-235 at 1.0mm for both inlet and exhaust for a 250hp engine goal. and primary of 1-5/8" and 2-3/8" tailpipe. this means for something 180bhp currently its way out to lunch.
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