When you click on links to various merchants on this site and make a purchase, this can result in this site earning a commission. Affiliate programs and affiliations include, but are not limited to, the eBay Partner Network.
I am actively working away on the engine trying to find out why it's performing so poorly - relative to what I might expect. I am working with Colin to check the cams look ok timing wise and they are set up correctly but there is the possibility that the cams might not suit my engine set up.
I did take a lot of timing measurements for the cams to try and work out if anything looked wrong regarding the set up of timing between the inlet and exhaust cams. Measurements were done on cylinder 1 and 6 with a dial gauge. I definitely have these set up between the inlet and exhaust as per the instructions and I have had 5-8 cam installed with one tooth more advance for the inlet cam which generated a much higher static CR of 220PSI vs 180 PSI I recorded in the previous set up.
I did not manage to measure the LSA to match the stated LSA of 114 but my measurements did match the inlet duration at 0.1mm @230 degrees. I also couldn't match the exhaust duration at 0.1mm, I measured quite a bit longer in both instances.
A believe the stated specs from another post and I also attached a handy picture of other cam durations
There has been a lot of time taken to check the health of the engine both pure mechanical and ancillary items like fuel and ignition. What is clear is that the engine is very healthy which basically only leaves the valve timing as the reason for the supposed lack of power.
I spent a lot of time changing the phasing between the inlet and exhaust cams in case these were out (which they weren't) however what became very clear is that a single tooth out will make the car run so poorly that you would be unlikely to even try running the engine like that.
I then spent a lot of timing changing the timing of the cams but what is completely clear is that this was never going to release 100 hp which I am supposedly down.
That really only leaves the combination of the cams themselves running in an engine of this spec which will now have to be changed. I am having some difficulty finding out what is available but hopefully Colin will confirm sometime soon.
It's been some time since my last update so I wanted to share where I am now.
As the health of the engine and all ancillaries has been eliminated focus has turned to the cams as per my last post.
It would seem that the specification and timing of the Colt cams results in weak scavenging characteristics. This is not maximising cylinder filling for the longer duration and high lift, a factor driven by the longer 114 LSA.
I have partnered with Kent Cams in England to analyse the cams and look at a solution which involves replacing one set of cams (inlet). Sadly there are no blanks available to use so these will be custom made from billet and converted to solid lifters for the inlet cams as some considerable cost. I am firmly putting my money where my mouth is so to speak as I firmly believe there is a good amount of power to be released using a stock 5.0 bottom end.
I did consider trying to get hold of an old set of GT which are like hens teeth (concern about wear issues) or go for a more radical engine build to try which might better use the colt profile and timing.
In the next few weeks I should be starting re-assembly using the new cams, then I need to shark tune all over again for the new set up.
First thing first, get it back up and running with the new cams, it's been apart since last October while I chased for specs and answers and progressed options
It's been some time since my last update so I wanted to share where I am now.
As the health of the engine and all ancillaries has been eliminated focus has turned to the cams as per my last post.
It would seem that the specification and timing of the Colt cams results in weak scavenging characteristics. This is not maximising cylinder filling for the longer duration and high lift, a factor driven by the longer 114 LSA.
I have partnered with Kent Cams in England to analyse the cams and look at a solution which involves replacing one set of cams (inlet). Sadly there are no blanks available to use so these will be custom made from billet and converted to solid lifters for the inlet cams as some considerable cost. I am firmly putting my money where my mouth is so to speak as I firmly believe there is a good amount of power to be released using a stock 5.0 bottom end.
I did consider trying to get hold of an old set of GT which are like hens teeth (concern about wear issues) or go for a more radical engine build to try which might better use the colt profile and timing.
In the next few weeks I should be starting re-assembly using the new cams, then I need to shark tune all over again for the new set up.
First thing first, get it back up and running with the new cams, it's been apart since last October while I chased for specs and answers and progressed options
It's been a while since I updated progress, especially because I needed to get the new cams Big milestone reached today - I am now in receipt of the new cams with all new timings. I am grateful that Kent have the technical capability to complete the job as these are challenging to produce due to the central gear. Looking forward to fitting these which will take a little time as I am converting to solid lifters.
It's been a while since I updated progress, especially because I needed to get the new cams Big milestone reached today - I am now in receipt of the new cams with all new timings. I am grateful that Kent have the technical capability to complete the job as these are challenging to produce due to the central gear. Looking forward to fitting these which will take a little time as I am converting to solid lifters.
Marti, now things are getting interesting. Did Kent Cams manufacture the camshafts complete with chain gear from steel blanks? Could you please give us the technical data of the camshafts. What kind of solid lifters, also from Kent, will you be using? DLC coated? How do you plan to adjust the valve clearance? In my opinion, the best way with the lowest weight is lash caps. The downside is that you have to lift the camshafts to change the lash caps. In my experience, the valve clearance is usually quite stable after the first break-in and adjustment is not often necessary. Can't tell from the photo if the gear is fixed or if it is adjustable. Adjustable gears are one big advantage. I have made my own design. You will probably have to cut the edge of the lifter bores for cam lobe clearance.
Åke
Good to see you posting again was wondering where you were just a few days ago! Let's hope the cams work as good as they look.
What is the rationale behind solid lifters? Presumably that means you are to have to install shims on each valve. Presumably DLC lifters do not tickle your fancy.
Marti, now things are getting interesting. Did Kent Cams manufacture the camshafts complete with chain gear from steel blanks? Could you please give us the technical data of the camshafts. What kind of solid lifters, also from Kent, will you be using? DLC coated? How do you plan to adjust the valve clearance? In my opinion, the best way with the lowest weight is lash caps. The downside is that you have to lift the camshafts to change the lash caps. In my experience, the valve clearance is usually quite stable after the first break-in and adjustment is not often necessary. Can't tell from the photo if the gear is fixed or if it is adjustable. Adjustable gears are one big advantage. I have made my own design. You will probably have to cut the edge of the lifter bores for cam lobe clearance.
Åke
Hi Ake
Kent manufactured the cams from solid billet, I forget the particular type of steel but needless to say they have a well proven process to produce high quality cams. The only down side is they do not recommend running them with hydraulic lifter for wear purposes so you need to convert to solid lifters. There is another advantage that you can run a more aggressive profile with solid lifters.
The new buckets have an internal 'stilt' to make up for the hydraulic dimensions and you use a lash cap to make the clearance adjustments. It will be a little fiddly to set up compared to just chucking in the hydraulic lifters and forgetting about them (unless you have one not pump up) but TBH I have had the colt cams in and out so ofter chasing an imaginary fault that this will seem like a piece of cake in comparison.
The gear is fixed and set to work with the exhaust cams to create a 108° LCA, inlet fully open at 106° ATDC and exhaust fully open at 110° BTDC. Maximum lift is 12.1mm and duration is 289°. So they are a bit longer duration than the colt cams and more area in total, but the big change is the amount of overlap and the LCA. There is so little energy in the exhaust side for scavenging with the colt cams, they are much closer to a turbo timing that N/A.
So I guess we will see when I get these fitted up what sort of a difference these make.
That adjustable gear would have been ideal to change the LCA for Colt cams, have you tested the adjustable gear?
Very interested to here how it worked out and any testing results
Good to see you posting again was wondering where you were just a few days ago! Let's hope the cams work as good as they look.
What is the rationale behind solid lifters? Presumably that means you are to have to install shims on each valve. Presumably DLC lifters do not tickle your fancy.
Hi Fred, I am hoping also that these make a step change. It would certainly be a just reward for all the effort and energy put into the whole process and it would validate where I reached in terms of conclusion.
The biggest single issue facing this engine is the lack of aftermarket camshaft, an inability to get away from the OEM 'brain' conceived by porsche. They moved in the right direction for the GT for a mild road car but should have gone further. That is what I am doing, picking up where Porsche left off
Hi Fred, I am hoping also that these make a step change. It would certainly be a just reward for all the effort and energy put into the whole process and it would validate where I reached in terms of conclusion.
The biggest single issue facing this engine is the lack of aftermarket camshaft, an inability to get away from the OEM 'brain' conceived by porsche. They moved in the right direction for the GT for a mild road car but should have gone further. That is what I am doing, picking up where Porsche left off
Marti,
Your efforts are admirable and if anyone is capable of assisting you in your quest then Kent Cams are probably as good as anyone on the planet.
I have only "lusted" after two cars- the 928 and the BMW E39 M5. I view the latter as what the 928 might have been had Porsche gone after it. That motor has individual throttle bodies and VVT. I cannot help but feel that ideal cams alone are always going to have limited potential but I would be absolutely delighted if you can get a result. Of course you doubtless understand this given your efforts with the inlet manifold. Indeed I think it is Alex in London that grafted BMW ITB's into the 928 motor and John Gill in Australia something similar not to mention GB's amazing motors. Louie also used ITB's in his amazing 928 as have other 928 friends.
I never made the M5 acquisition but came close at the time I purchased my Cayenne 955 Turbo S some 10 years ago - with 520 BHP and a shed load of torque that is an awesome motor- pity it cannot be shoe horned into a 928!
Your efforts are admirable and if anyone is capable of assisting you in your quest then Kent Cams are probably as good as anyone on the planet.
I have only "lusted" after two cars- the 928 and the BMW E39 M5. I view the latter as what the 928 might have been had Porsche gone after it. That motor has individual throttle bodies and VVT. I cannot help but feel that ideal cams alone are always going to have limited potential but I would be absolutely delighted if you can get a result. Of course you doubtless understand this given your efforts with the inlet manifold. Indeed I think it is Alex in London that grafted BMW ITB's into the 928 motor and John Gill in Australia something similar not to mention GB's amazing motors. Louie also used ITB's in his amazing 928 as have other 928 friends.
I never made the M5 acquisition but came close at the time I purchased my Cayenne 955 Turbo S some 10 years ago - with 520 BHP and a shed load of torque that is an awesome motor- pity it cannot be shoe horned into a 928!
Alex also runs different higher compression pistons and I think cams if I recall correctly. Seems to make good power as a result.
VVT is really like having to 2 different sets of cams, so you retain good torque but also get that high end power. Then there is variable intake length to help torque also. All tricky stuff which is ultimately effective.
Cams alone would make a difference but ultimately you would get more out of a package which includes a manifold, pistons and exhaust.
I have a second version of my manifold ready to pull the trigger once I am satisfied that I have an engine which would benefit from it.
My engine modifications simply dont suit cams with limited scavenging properties. What I concluded was there was too little exhaust flow to generate useful scavenging and scavenging is exactly the property you need for a NA cam. I realised this when I adding the larger bore exhaust system, what little scavenging there was became diluted further. I would have gotten more performance fitting a smaller exhaust!
The profile amd timing of the colt cams (which is fixed as in cannot be altered) explained why I got great MPG, simply because there is so little overlap and hence very little scavenging.
So now that this has been addressed I am expecting a step change. It should be like taking your foot off a hose pipe or opening the taps fully. Whats more the performance exhaust system will finally come into its own. Then depending on how things are going I might decide to throw my revised intake manifold at it.
Might be interesting to ditch the hydraulic lifters altogether and aim for a higher rev limit like 7500. I bet that's going to sound pretty amazing
Good work on this , stock hydraulic lifters as in my race engine , will happily rev to 8500 rpm , so they are not limiting in our engines , some say more , I do not know why they would recommend solid , as you indicated the maximum lift of 12 mm , I would love to build 14mm lift units as per GT3 spec , so your arrangement i interesting .
With the solid cam route I believe this will drive you insane with the continual adjustment , that will be required due to the , way the top end of these engines are designed .
Is there a difference in the grind of the cams from the original flat tappet arrangement ,( Note not my field of expertise) ?
My engine sees 7000 rpm regularly due to my lack concentration on the track , but reaches it easily and without complaint , I am hoping that you will be addressing the oil surge issues , with the stock arrangement , as the wet sump system will fail if you are going to try and reach upwards of 7500 rpm , you will face some expensive lessons as I did with my learning curve .
Kent manufactured the cams from solid billet, I forget the particular type of steel but needless to say they have a well proven process to produce high quality cams. The only down side is they do not recommend running them with hydraulic lifter for wear purposes so you need to convert to solid lifters. There is another advantage that you can run a more aggressive profile with solid lifters.
The new buckets have an internal 'stilt' to make up for the hydraulic dimensions and you use a lash cap to make the clearance adjustments. It will be a little fiddly to set up compared to just chucking in the hydraulic lifters and forgetting about them (unless you have one not pump up) but TBH I have had the colt cams in and out so ofter chasing an imaginary fault that this will seem like a piece of cake in comparison.
The gear is fixed and set to work with the exhaust cams to create a 108° LCA, inlet fully open at 106° ATDC and exhaust fully open at 110° BTDC. Maximum lift is 12.1mm and duration is 289°. So they are a bit longer duration than the colt cams and more area in total, but the big change is the amount of overlap and the LCA. There is so little energy in the exhaust side for scavenging with the colt cams, they are much closer to a turbo timing that N/A.
So I guess we will see when I get these fitted up what sort of a difference these make.
That adjustable gear would have been ideal to change the LCA for Colt cams, have you tested the adjustable gear?
Very interested to here how it worked out and any testing results
Is the 289 degrees of duration at 1mm of lift (traditionally used by Germans) or at .050" (traditionally used by American cam grinders?)
09-25-2021, 02:00 PM
