DOHC camshaft design?

[Juho_]

I've been working on my six cylinder Volvo B6304 N/A engine for quite a while now.
Still running stock cams (about 208*@0.050" and ~9mm lift) - they are for hydraulic lifters, but I've converted them solid because I rev my engine up to 7500rpm.
The valve clearances take away some lift and duration.

I'm looking for peak hp around 8000rpm on new custom grind cams.
The engine can live at near 9000rpm or even higher, but not when cornering hard (wet sump pump causes issues = bye conrod bearings).

Spec list (2922cc six cylinder, 24 valve all aluminium engine, 83 x 90mm bore/stroke):
- 33 / 29.6mm valves, 6mm stem.. a lot of porting to head (no flow data, I don't have a flow bench)
- about 14:1 uncorrected compression ratio (cranking pressure is ridiculous: 19,5-20,5bar all cylinders)
- Kawasaki ZX12R pistons
- Nissan RB30 152.4mm conrods, h-profile
- Stock B6284T (RN) crankshaft, pulley and damper (bigger in diameter compared to older version..the crank is only slightly lighter than original)
- 110 intake centerline, 103 LSA
- Triumph Daytona 675 invidual throttle bodies, 44mm plate
- DIY exhaust headers 6-2-1, 3->2,5" exhaust (for sound reduction, restricts a bit power)
- E85 only
- standalone ecu, alpha-n mode (Maxxecu street)

Power curve raises till 6000rpm and then flattens and keeps the power 'till about 7300rpm before drops - at this point (7500rpm limiter).
Still a lot of work finding the best cam timing and ignition timing (seems to like a lot less timing.. no knock issues so far).. also intake lenght might need a bit testing.

I've used Pipemax 3.98 to figure out what the engine might need.
The question is, should I care about intake/exhaust lobes operating range and intake/exhaust systems operating range??

Here's the current cam info I get with 7000rpm peak hp and stock cams:

Recommended Intake Valve Lift to prevent Choke = ,346 Lift @ 7000 RPM
Recommended Exhaust Valve Lift to prevent Choke = ,294 Lift @ 7000 RPM
Recommended Minimum Normal Maximum Time-Area-Duration Lifts
Intake Valve Lift = 0,3208 0,3455 0,4257 0,4440 0,4680 0,4920
Exhaust Valve Lift = 0,2732 0,2943 0,3449 0,3798 0,3984 0,4170
IntOpen= -5,60 IntClose= 34,40 ExhOpen= 19,95 ExhClose= 7,95
Intake Duration @ .050 = 208,80 Exhaust Duration @ .050 = 207,90
Intake CenterLine = 110,00 Exhaust CenterLine = 96,00
Compression Duration= 145,60 Power Duration = 160,05
OverLap Duration = 2,35 Lobe Separation Angle (LSA)= 103,00
Camshaft Retarded = 7,00 degrees Cylinder Ignition Interval= 120 deg.

-- Operating RPM Ranges of various Components --
Best estimate RPM operating range from all Components = 5239 to 7239
Intake Flow CFM @28inches RPM Range from Flow CFM only = 5160 to 7160
Intake and Exhaust Systems operating RPM Range = 5165 to 7165
Intake and Exhaust Time-Area operating RPM Range = 4049 to 6049
Camshaft's Intake and Exhaust Lobes operating RPM range = 5844 to 7844
Intake Valve Curtain Time-Area at 0,355 Lift RPM Range = 5192 to 7192
Exhaust Valve Curtain Time-Area at 0,353 Lift RPM Range = 6390 to 8390

Intake Valve Close RPM = 8452 Exhaust Valve Open RPM = 6021
Intake System RPM = 7320 Exhaust System RPM = 7011
Intake Time-Area RPM = 5597 Exhaust Time-Area RPM = 6501
Intake Mach Z-Factor = 0,472424 Exhaust Mach Z-Factor = 0,530198
Intake Z-Factor Lift = 0,349397 Exhaust Z-Factor Lift = 0,283334

Clearly the cams are way too small, if I understand correctly what I've bolded.

I've been advised to aim for 250*@0.050" duration, both cams.
Lift should be around 12mm.

But, Pipemax seems to disagree?
8000rpm peak, 250*@0.050" duration and 12mm lift, intake/exhaust.

Recommended Intake Valve Lift to prevent Choke = ,395 Lift @ 8000 RPM
Recommended Exhaust Valve Lift to prevent Choke = ,335 Lift @ 8000 RPM
Recommended Minimum Normal Maximum Time-Area-Duration Lifts
Intake Valve Lift = 0,3667 0,3949 0,4865 0,4256 0,4486 0,4716
Exhaust Valve Lift = 0,3109 0,3348 0,3924 0,3623 0,3801 0,3978
IntOpen= 15,00 IntClose= 55,00 ExhOpen= 41,00 ExhClose= 29,00
Intake Duration @ .050 = 250,00 Exhaust Duration @ .050 = 250,00
Intake CenterLine = 110,00 Exhaust CenterLine = 96,00
Compression Duration= 125,00 Power Duration = 139,00
OverLap Duration = 44,00 Lobe Separation Angle (LSA)= 103,00
Camshaft Retarded = 7,00 degrees Cylinder Ignition Interval= 120 deg.

-- Operating RPM Ranges of various Components --
Best estimate RPM operating range from all Components = 6516 to 8516
Intake Flow CFM @28inches RPM Range from Flow CFM only = 6183 to 8183
Intake and Exhaust Systems operating RPM Range = 7804 to 9804
Intake and Exhaust Time-Area operating RPM Range = 7647 to 9647
Camshaft's Intake and Exhaust Lobes operating RPM range = 9884 to 11884
Intake Valve Curtain Time-Area at 0,472 Lift RPM Range = 7562 to 9562
Exhaust Valve Curtain Time-Area at 0,472 Lift RPM Range = 9277 to 11277

Intake Valve Close RPM = 12500 Exhaust Valve Open RPM = 10037
Intake System RPM = 9847 Exhaust System RPM = 9761
Intake Time-Area RPM = 8872 Exhaust Time-Area RPM = 10422
Intake Mach Z-Factor = 0,406078 Exhaust Mach Z-Factor = 0,452786
Intake Z-Factor Lift = 0,399311 Exhaust Z-Factor Lift = 0,323811

What kind of advice would you have for cams?
Cam profile makes a huge difference tho. Small cam followers don't allow very aggressive camshafts, but I don't think this engine really requires crazy duration and lift to actually make power at more than 8000rpm.

The engine is only for testing purposes.
So it is actually supposed to blow up at some point. Not enough rpm or power if it holds.

[CamKing]

If your follower diameter is 31mm or larger, here's what I recommend.
254/252 @ .050"
.480"/.455" Lobe Lift

[Juho_]

Yes, the cam followers are 32mm at diameter.
I'll go with the specs you recommended, and see how it'll work.
Thank you very much!

[digger]

notwithstanding CK post the new version of pipemax is recommended if you also wnat to look at cam specs. the older versions are much cruder

[ptuomov]

Very interesting engine. Any photos?

I have no useful input beyond a question: Are the intake and exhaust cams independently adjustable? If not, can you create a system that allows for those adjustments?

[Juho_]

Yes, they are adjustable independently and I've tried some slightly different timings.

Pictures I found from my imgur account (minor changes done to engine, engine bay..mostly just 'cleaning' and added restrictive filters)


Intake port (vinamold) with 7mm stem valve, didn't make new mold from latest form with 6mm stem valves (don't know why).

Latest GSF Dyno testruns the "245hp" peak is just some random error.





Intake port is quite straight. When valve is open at full lift, it is possible to see a bit of exhaust valve through the throttle body (with a light of course).

[crazypj]

It looks like there's room to fit at least 35mm valves? It shouldn't be difficult to plot out the largest lift you can get without binding on the bucket bores, they can be relived (slot milled) for clearance if you get a bit crazy with lift/duration. I'm way more familiar with motorcycles but older Kawasaki KZ1000 and Suzuki GS1000 or 1100 maybe GSX1100 have had a lot of development, maybe looking up spec for them will give a better idea? (modern bikes rev much much higher so doubtful cam spec would be any use) If you intend to drive on street you will probably need some lower end torque to deal with traffic, motorcycle spec will be too radical for car engine

[Juho_]

36mm is the biggest intake valve, that is possible to fit (with larger seats).
But I think 33mm is enough for quite high hp potential (and rpm).

Bore is another restriction (valve shrouding), making larger intake valve worth less hp in my opinion.
If the bore was something like 86-87mm, I would have considered 34.5-35mm intake valves.

This car is not being used much on the streets. Only driving it for fun on the streets, and when going for testing.. when possible, track days.
Interior is fully stripped, and it is very noisy. Fuel consumption is ridiculous with short gear ratios, expect when keeping speed at 80km/h or below and no heavy accelerations.

[ptuomov]

Looks very nice. What hp/l and bmep targets do you have in mind for this project?

[Juho_]

My very optimistic target is to try achieve near 400hp (@ crank) naturally aspirated at some point, but also try how high the engine actually can be revved.
Current target is to reach 300hp @ ~7000rpm (stock cams).. which shouldn't be a problem with more work, since the current results are already quite promising.

Engine capacity stays the same, since the cylinder liners are not very strong.
Next engine (when the current one blows up) is probably going to be with darton sleeves and dry sump oil pump to gain reliability.

One of the reasons for such as goals/targets was people who say it is not possible to achieve such as numbers in naturally aspirated form.
Second is just because I want to learn about developing 4-stroke engines (like I have done with 2-stroke engines earlier).