boost and camshafts
Discussion
Hey all, probably a newbie question - I know boosted cars have a different cam profile to n/a cars - but how much difference will it make in the real world?
To put it into context - i have a mk1 fiesta with a 1.6 crossflow i built myself. wanting to stick with n/a and the time I went with 1300 pistons (raises the compression) full head work, and a piper 300 (broadly equiv to 244 kent cams).
I've since been toying with fiting a low pressure turbo to raise the game - am i dicing with death on the high comp, and am i wasting my time thanks to the overlap on the cam?
Pull the engine and sell it in favour of a zetec turbo?
Bearing in mind everything is cheap, cheap, home built - and so I am not looking for perfection - just more power
Cheers for any help!
To put it into context - i have a mk1 fiesta with a 1.6 crossflow i built myself. wanting to stick with n/a and the time I went with 1300 pistons (raises the compression) full head work, and a piper 300 (broadly equiv to 244 kent cams).
I've since been toying with fiting a low pressure turbo to raise the game - am i dicing with death on the high comp, and am i wasting my time thanks to the overlap on the cam?
Pull the engine and sell it in favour of a zetec turbo?
Bearing in mind everything is cheap, cheap, home built - and so I am not looking for perfection - just more power
Cheers for any help!
cheers both.
i know n/a stock cams work ok with turbo - but the more 'wild' cams have more overlap and i understood that the boost would 'leak' so to speak?
Is it this 'leak' that'll reduce the life? Damage the valve seal? - or am i just going to waste fuel through the exhaust - and end up with lots of popping from the exhaust
happy to be corrected
i know n/a stock cams work ok with turbo - but the more 'wild' cams have more overlap and i understood that the boost would 'leak' so to speak?
Is it this 'leak' that'll reduce the life? Damage the valve seal? - or am i just going to waste fuel through the exhaust - and end up with lots of popping from the exhaust
happy to be corrected
beedz said:
cheers both.
i know n/a stock cams work ok with turbo - but the more 'wild' cams have more overlap and i understood that the boost would 'leak' so to speak?
Is it this 'leak' that'll reduce the life? Damage the valve seal? - or am i just going to waste fuel through the exhaust - and end up with lots of popping from the exhaust
happy to be corrected
For a low boost setup and retaining highish CR, just stick with the cam you have. Ensure turbine back pressure is kept low and it'll still work well in the mid-upper rpm ranges.i know n/a stock cams work ok with turbo - but the more 'wild' cams have more overlap and i understood that the boost would 'leak' so to speak?
Is it this 'leak' that'll reduce the life? Damage the valve seal? - or am i just going to waste fuel through the exhaust - and end up with lots of popping from the exhaust
happy to be corrected
For more boost, then no a wilder cam is definitely not the way to go unless it is a more dedicated race build, even then not a n/a wild profile.
beedz said:
ok jimbob - is that from fuel getting into the exhaust?
basically yes. though, if you could run efi and tune it so that fuel isn't injected until after the exhaust valve has closed you'd be good. the incoming charge air would help expel most/if not all of the residual exhaust gases and help cool the exhaust valve and seat.I take it you are running carbs?
I agree with what stevieturbo says to an extent, just my opinion, but if you could revert back to a more standard cam profile I think it would be advisable.
I would advise a boost limit of about 5-6 psi to start with and see how it performs. Your main concerns are going to be detonation and air/fuel ratio.
5-6psi shouldnt pose any real issues, especially with the bigger cam.
But with big cams and a turbo as said, you'll lose loads at the bottom end, for less gain up top.
When it comes to turbos, milder cams just work superbly.
Many OEM turbo setups will use a n/a profile, or very close to it for that reason.
As you're referring to an ancient engine, I'll make a direct comparison.
19 years ago I had a turbocharged Mini. Head, cam, big turbo lots of boost etc etc.
Originally the turbo used the basic metro camshaft. An Upgrade was the MG metro, but still very mild.
I had a Kent 286 profile lying about so tried it. It's a great n/a profile.
On the turbo engine it was terrible. Absolutely no power below 4000rpm, although around 5k it picked up and pulled hard to 8000rpm.
However, it was definitely no faster than the milder cam which idled super smooth and you could pull 4th gear from tickover. The big cam just destroyed the car. The mild/standard cams and later slightly upgraded cam would still happily rev to over 7k. So they had a wider power band, in a much more usable area, and in general were far more drivable in every respect. The big cam really offered nothing except more rpm's
But that was a 100% n/a profile. That isnt to say a longer duration race profile ground with LSA and valve events more appropriate to turbo usage wouldnt work much better
Although that was with an old SU carb and welded dizzy.
So a more modern setup with proper fuel control and ignition control would probably work a lot better.
But yes you would be better fitting a milder camshaft, or better again your second option, just doing a Zetec turbo.
But with big cams and a turbo as said, you'll lose loads at the bottom end, for less gain up top.
When it comes to turbos, milder cams just work superbly.
Many OEM turbo setups will use a n/a profile, or very close to it for that reason.
As you're referring to an ancient engine, I'll make a direct comparison.
19 years ago I had a turbocharged Mini. Head, cam, big turbo lots of boost etc etc.
Originally the turbo used the basic metro camshaft. An Upgrade was the MG metro, but still very mild.
I had a Kent 286 profile lying about so tried it. It's a great n/a profile.
On the turbo engine it was terrible. Absolutely no power below 4000rpm, although around 5k it picked up and pulled hard to 8000rpm.
However, it was definitely no faster than the milder cam which idled super smooth and you could pull 4th gear from tickover. The big cam just destroyed the car. The mild/standard cams and later slightly upgraded cam would still happily rev to over 7k. So they had a wider power band, in a much more usable area, and in general were far more drivable in every respect. The big cam really offered nothing except more rpm's
But that was a 100% n/a profile. That isnt to say a longer duration race profile ground with LSA and valve events more appropriate to turbo usage wouldnt work much better
Although that was with an old SU carb and welded dizzy.
So a more modern setup with proper fuel control and ignition control would probably work a lot better.
But yes you would be better fitting a milder camshaft, or better again your second option, just doing a Zetec turbo.
Edited by stevieturbo on Sunday 26th May 10:05
cheers guys, really appreciate it. i'll either lift the xflow, or stick with the n/a. either that or flog the car once it's on the road again and look for something in turbo flavour already
I expected it to be a bad idea, but really useful to understand, and hear other's experiences.
I expected it to be a bad idea, but really useful to understand, and hear other's experiences.
beedz said:
cheers guys, really appreciate it. i'll either lift the xflow, or stick with the n/a. either that or flog the car once it's on the road again and look for something in turbo flavour already
I expected it to be a bad idea, but really useful to understand, and hear other's experiences.
it's not really a bad idea. IMO, when chasing more power nothing is a bad idea until AFTER it's blown up I expected it to be a bad idea, but really useful to understand, and hear other's experiences.
Boosted engine like lower compression so you can stuff more boost in befor detonation (pinking)
Radical cams have more overlap which looses boost so good cams for boosted engines prevent less overlap i.e.standard profiles.
On the Pinto engine there are low duration high lift profiles that would work well.
Another point to concider is that boosted engines now need more attention to the exhaust valves and ports than a normily aspirated as that is where the flow will suffer
Radical cams have more overlap which looses boost so good cams for boosted engines prevent less overlap i.e.standard profiles.
On the Pinto engine there are low duration high lift profiles that would work well.
Another point to concider is that boosted engines now need more attention to the exhaust valves and ports than a normily aspirated as that is where the flow will suffer
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