Using a longer duration cam in a blown engine.
Discussion
I have a 1340 mini engine with a 286 cam (kent) (270/290deg) in it. It has no head and I was going to bung a BMW 16V head on it but my spare money is not sufficient to get it done pronto. So, I was looking at the idea of putting my Eaton M45 blower on it to give it some juice.
I'm well familiar with how to set up a blown engine running a usual cam and I was curious how running a longer cam is going to influence the whole thing. As I sold my race head, I will be using a normal head with normal rockers which will calm things down a bit. I plan to scoop out the chambers using a mill and leave the ports alone.
So, running a N/A engine, you need a higher CR to make the best of a long cam as well as some more advance. So I am curious about how having a longer cam would compare to a shorter cam with the blower.
As the car is a 1966, emissions aren't a problem and I understand that blowby will happen at low revs. I plan to give the blower a ratio to give me a theoretical 10PSI.
It will be blow through and I was wondering if the needle which worked for the N/A engine will be OK assuming the carb is boost sensitive.
Can we have a discussion about how long cams influence the engine under boost and how it differs to a shorter cam.
I virtually know the Vizard big bible and have a fair few supercharger books, none of which give any info.
NB:- Standard dizzy welded up and no intercooler. Cr will be about 8.5:1
The idea behind this being that I bung it together and flash it up. Machining work is free!
I'm well familiar with how to set up a blown engine running a usual cam and I was curious how running a longer cam is going to influence the whole thing. As I sold my race head, I will be using a normal head with normal rockers which will calm things down a bit. I plan to scoop out the chambers using a mill and leave the ports alone.
So, running a N/A engine, you need a higher CR to make the best of a long cam as well as some more advance. So I am curious about how having a longer cam would compare to a shorter cam with the blower.
As the car is a 1966, emissions aren't a problem and I understand that blowby will happen at low revs. I plan to give the blower a ratio to give me a theoretical 10PSI.
It will be blow through and I was wondering if the needle which worked for the N/A engine will be OK assuming the carb is boost sensitive.
Can we have a discussion about how long cams influence the engine under boost and how it differs to a shorter cam.
I virtually know the Vizard big bible and have a fair few supercharger books, none of which give any info.
NB:- Standard dizzy welded up and no intercooler. Cr will be about 8.5:1
The idea behind this being that I bung it together and flash it up. Machining work is free!
Dont worry about the cam, and dont worry about boost bleed off. If you think that is a problem, spin the blower faster, or get a bigger one 
In reality...worst that will happen, is that it will use too much fuel. I dont think it will affect its ability to make power.
Fit mapped ignition. Welded dizzy is crude, but you can get away with it better when you have easy control over boost ( ie turbo )
I personally hate messing about with combustion chamber shapes....I sure as hell wouldnt be messing with the Mini's chamber, although some of the turbo guys seem to be having no problems with this..
The needle will most definately need work. Dont think for one second it will be ok.
I wouldnt go any bigger than that though with a camshaft. It might be worth trying that cam, but with a wider LSA
In reality...worst that will happen, is that it will use too much fuel. I dont think it will affect its ability to make power.
Fit mapped ignition. Welded dizzy is crude, but you can get away with it better when you have easy control over boost ( ie turbo )
I personally hate messing about with combustion chamber shapes....I sure as hell wouldnt be messing with the Mini's chamber, although some of the turbo guys seem to be having no problems with this..
The needle will most definately need work. Dont think for one second it will be ok.
I wouldnt go any bigger than that though with a camshaft. It might be worth trying that cam, but with a wider LSA
Mapped ignition is a grand idea but the name of the game is bunging together what I have now with the minimum work. With higher boosts, the beaked chamber loses some of it's beakyness as the charge gets around it quicker. Getting rid of it seems like the way to go. Again, what I plan to do is to measure the piston dish (squish) and then set the head up in the mill and cut the thing out circular. I should be able to keep the valves in if I make up some blocks to shim the thing out so it clears the table. That's the idea. I was going to go the megasquirt/jolt way with the BMW head but I am a tad more skint now.
I heard that VMax used a 286 cam on a race engine with good results, however, he keeps his ideas to himself. I'd put a SPI cam in if I was swapping cams, and 1.5 rockers. The 5 port head is something I'd like to ditch and I have a nice unleaded one from an Auto Metro which I'll cut up. The standard (s size) valves and ports as well as 1.3 rockers should keep the cam as mild as it can be.
I was wondering about how the cam would influence the dynamic CR and how I should skew my timing/cr requirements to the boost.
I heard that VMax used a 286 cam on a race engine with good results, however, he keeps his ideas to himself. I'd put a SPI cam in if I was swapping cams, and 1.5 rockers. The 5 port head is something I'd like to ditch and I have a nice unleaded one from an Auto Metro which I'll cut up. The standard (s size) valves and ports as well as 1.3 rockers should keep the cam as mild as it can be.
I was wondering about how the cam would influence the dynamic CR and how I should skew my timing/cr requirements to the boost.
Each to their own....
The mapped ignition would be money very wisely spent..I wouldnt see it as an option, more a necessity
If going to a better flowing head....even more reason to opt for a wider LSA cam.
I think Mini's run such tight LSA's, due to the poor head design.
As for the chambers....I would still keep the shape the head was designed with. Whilst my mini work is many years ago, I did have 2 cylinder heads modified with opened chambers by a head porter already mentioned, and my car would never perform properly with those heads fitted. Its a long story though....and caused me weeks and weeks of headaches, and money thrown away trying to cure the problems, which turned out to be down to those heads.
But I do know it works for many now...
As for other peoples results...some people's "good" might be bad for others. Good doesnt really mean anything. You would need much more info about Stuarts setup with that cam.
But given the nature of a PD blower, It should almost tame a relatively big cam like that, as airflow is always going the right direction through the engine, with less reliance on scavenging etc. But all the more reason to try one with a wider LSA, to remove a little overlap. But I certainly wouldnt reduce it to nothing.
The mapped ignition would be money very wisely spent..I wouldnt see it as an option, more a necessity
If going to a better flowing head....even more reason to opt for a wider LSA cam.
I think Mini's run such tight LSA's, due to the poor head design.
As for the chambers....I would still keep the shape the head was designed with. Whilst my mini work is many years ago, I did have 2 cylinder heads modified with opened chambers by a head porter already mentioned, and my car would never perform properly with those heads fitted. Its a long story though....and caused me weeks and weeks of headaches, and money thrown away trying to cure the problems, which turned out to be down to those heads.
But I do know it works for many now...
As for other peoples results...some people's "good" might be bad for others. Good doesnt really mean anything. You would need much more info about Stuarts setup with that cam.
But given the nature of a PD blower, It should almost tame a relatively big cam like that, as airflow is always going the right direction through the engine, with less reliance on scavenging etc. But all the more reason to try one with a wider LSA, to remove a little overlap. But I certainly wouldnt reduce it to nothing.
stevieturbo said:
Each to their own....
The mapped ignition would be money very wisely spent..I wouldnt see it as an option, more a necessity
If going to a better flowing head....even more reason to opt for a wider LSA cam.
I think Mini's run such tight LSA's, due to the poor head design.
As for the chambers....I would still keep the shape the head was designed with. Whilst my mini work is many years ago, I did have 2 cylinder heads modified with opened chambers by a head porter already mentioned, and my car would never perform properly with those heads fitted. Its a long story though....and caused me weeks and weeks of headaches, and money thrown away trying to cure the problems, which turned out to be down to those heads.
But I do know it works for many now...
As for other peoples results...some people's "good" might be bad for others. Good doesnt really mean anything. You would need much more info about Stuarts setup with that cam.
But given the nature of a PD blower, It should almost tame a relatively big cam like that, as airflow is always going the right direction through the engine, with less reliance on scavenging etc. But all the more reason to try one with a wider LSA, to remove a little overlap. But I certainly wouldnt reduce it to nothing.
Harry Weslake knew what he was doing, he was a major contributor to race engines as we know them.The mapped ignition would be money very wisely spent..I wouldnt see it as an option, more a necessity
If going to a better flowing head....even more reason to opt for a wider LSA cam.
I think Mini's run such tight LSA's, due to the poor head design.
As for the chambers....I would still keep the shape the head was designed with. Whilst my mini work is many years ago, I did have 2 cylinder heads modified with opened chambers by a head porter already mentioned, and my car would never perform properly with those heads fitted. Its a long story though....and caused me weeks and weeks of headaches, and money thrown away trying to cure the problems, which turned out to be down to those heads.
But I do know it works for many now...
As for other peoples results...some people's "good" might be bad for others. Good doesnt really mean anything. You would need much more info about Stuarts setup with that cam.
But given the nature of a PD blower, It should almost tame a relatively big cam like that, as airflow is always going the right direction through the engine, with less reliance on scavenging etc. But all the more reason to try one with a wider LSA, to remove a little overlap. But I certainly wouldnt reduce it to nothing.
I'll probably go with the MG lump and wait until the BMW funds allow. Probably.
why not run Metro turbo bits? boost sensitive fuel pressure regulator, the apropriate carb and plenum and dizzy. IIRC Alan Allards book on supercharging warns against cams with large overlap, as you'll simply be throwing fresh fuel down the exhaust.Standard cams work very well with boosted engines in my experience(home brew pinto,cologne and roverv8 in the past)
Gassing Station | Engines & Drivetrain | Top of Page | What's New | My Stuff