I am considering installing qed 420 Cams in my Europa with a big valve stromberg head.
The engine is ported, polished, headers, balanced and has Hitachi 46 mm SU carbs. It currently has DB sprint cams timed at 110 deg intake and exhaust mop. It pulled 116 hp on a chassis dyno recently. Max torque was at 5000 rpm, and max hp at 6700.
My question Is what mop should I set my car up with the qed 420 cams, while maximizing low end torque, because this is a street/ occasional autocross car. Qed seems to recommend 106 exhaust and 100 inlet, which is quite a bit different than other cam manufacturers with similar lift and duration cams. That gives 79 deg of overlap, which seems like a lot.
Any suggestions?
I trust QED for the quality of their work and supply chain, and have taken attentive care to implement Q420 cam timing as per their specs for my road car using vernier sprockets, so that I would only tune spark and carbs on the dyno and not multiply that by on loop of cam testing (longer too)…
The cam lobes are symmetric, and the same cam is used for both intake & exhaust. That’s reflected in the first column of data. The second incomplete column reflects QED’s recommended 100° MOP for the intake.
Given a cam and a dyno, a tuner can play all sorts of games with timing. I have no insider understanding of what QED is thinking, but it appears they have presumed that anyone buying a hotter than stock cam for their Lotus Twin Cam is probably in search of more ‘foot to the floor’ horsepower. And advancing the intake cam would provide more TOP END horsepower at the expense of low end torque and driveability. It makes sense.
However, if you’re not that “All-In, Gung-ho”, then timing the intake cam to the natural 106° MOP that results from the cams ‘as-ground’ timing events would ‘civilize’ the engine a bit for street/ commuter use, at some loss of optimum top end potential. That’s not going from ‘hot’ to calm, just taking the edge off of ‘street-hot’. In that case, driving a 285° cam on the street would be plenty comfortable… in a sportscar sense of the word.
I’ve never owned or tuned a Q420 cam, so if I’m missing a critical point, let me know. But one Q420 part number is used for both intake and exhaust, and the timing events produce the numbers presented above.
The last couple of degrees of cam timing is very engine specific when you get to the details of the actual build but there are general recommendations and the QED timing advice of 100 in and 105 ex for a 285 degree .42 lift cam seems to differ from many other suppliers and builders and experts.
For Twin Cams the general recommendations are as follows from people like Newman cams, Dave Bean,John McCoy and Des Hammil ( writer of the speedpro book - How to choose camshafts and time them) and can be divided into 3 categories for convenience.
1.110 MOP for standard sprint cams of 272 duration and .36 lift or similar which is the standard Lotus timing
2. 108 to 106 MOP range for higher lift longer duration cams in the 280 to 290 duration and .40 to .44 lift range.
3. 104 to 102 MOP range for extremely high lift long duration race cams in 300 degrees plus duration and over .45 lift region
There are also differences in timing recommended for torque versus power settings especially for the second category of cams with the inlet being moved to a lower MOP for power.
e.g. McCoy for his 285 degree .440 lift cam in his extremely well ported 1.625 inlet / 1.4 exhaust valve modified heads recommended to me a number of years ago now 107 In - 110 ex for torque and 102 in - 105 for max top end power. After some experimentation , dyno runs and computer simulations I ended up setting them at 106 in and 109 Ex for a compromise torque rather than top end power setting as that is what gives you typically the best lap times on most tracks
For the QED 420 in a relatively standard head I would start with something around 107 In and 110 Ex degrees MOP. The 100 inlet and 106 exhaust MOP settings recommended seems much to big a step change away from normal for this type of cam and really reflects a race max power setting for a longer duration and higher lift cam than it is in a fully port race twin cam head.
From those who have Dave Vegher built engines I would be interested to know what timing he used on your cams and what cams he used as i have not seen data from his recommendations
I’m no expert on this sort of stuff but perhaps the QED 420 cam has a different ramp profile compared to what is usual. The rate of valve opening may be different compared to what is usual therefore affecting the optimum point at which valve opening should start. I believe that’s a lot of the secret squirrel stuff that makes cams of similar lift from different manufacturers behave differently.
Valve Maximum Opening Point (MOP) varies a little between manufacturers but for the type of cam the QED 420 is, the timing has been varied a lot. I dont think the QED 420 is anything special in the way of a grind that would warrant such a radical departure from the normal range. In a light open wheeler with a Race Weber head if seeking absolute maximum top end power and where midrange torque was not critical maybe it would make sense, but on those circumstances there are much better cams than a QED 420 so you would not do it anyhow. For a Road / Trackday car the weight of the Europa and a Stromberg head it has way to low MOP’s being specified by QED IMHO.
I guess the Stromberg head may respond differently to a Weber head due to its siamesed ports and potentially the recommendation from QED works with this but it appears the timing is not Stromberg specific and also applies to Weber heads
For the QED 420 what would be the Operating/Rev range.
Would it start at about 1500rpm or would it be a little higher say 1800rpm.
Also the weight difference between an Elan and an Elan +2 of 200kgs would make a difference on how it pulls at low Revs.
Sorry for side tracking a little but when choosing a Cam many just look for Max power. This makes a big difference for driveability on the road.
Alan
I have actually not got a specific recommendation from QED for my car. I certainly will ask before purchasing. They are not responding to emails. I did call them and the gentleman who answered said he was the only one working, and had not got to the emails.
I am not in a hurry. I just wanted opinions since the cam timing is significantly different than other manufacturers. I am actually trying to disprove the notion that stromberg heads significantly limit power compared to weber heads. I am an engine engineer by trade and am in the process of modeling the different cams and cam timing for the Lotus twincam. I have done this for many paying customers in my consulting past, but never for my own car.
I agree that with the right tuning a Stromberg head could come close to a Weber head in most road going states of tune. The charge robbing effect of the siamesing will always make its performance a little less. But then you can always develop some “Scatter” cam timing like the racing Minis and MGs use to minimise the charge robbing effect. There was a guy who posted here many years back who was working on developing his Stromberg headed Elan, if I recall correctly he got it up to around 150Hp.
I reckon you can’t assume anything unless you know the actual plot of valve lift per degree of cam or engine rotation. Knowing just the start and end points of valve opening is not enough to accurately predict how the cam will behave. Dyno tuning of course would sort it out in the end. Note also that the QED timing recommendations are given using sprint sized valves. QED420 specs.pdf (192 KB)
Specifications on my Dave Vegher 1700 twincam. This engine was built for the street, not like most of Dave’s race motors.
Cams:
Kent brand. I don’t know the part number. (I believe these were recommended by Tony Ingram as a good high performance street cam)
0.44" lift
Duration: 250 deg @ .050" lift MOP: 105 on the intake, 107 on the exhaust
Valves:
Intake: 1.625"
Exhaust: 1.375"
Carbs:
Weber 40’s
32 mm chokes
Airbox: Oversize custom Weber box with cold air trunking (Standard airbox robbed 7 hp)
Exhaust: TTR Extra Large Bore Race System
Head: SAS new Weber casting. Street ports, although Dave increased these, as well as other head “tweaks”, from as delivered.
CR: 10.3 : 1
Pump gas (91 octane, (R+M)/2
Result: 181 hp @6900 / 143 lb-ft @ 5100
Torque relatively flat, shown on dyno.
Thanks for that data. That Kent cam is very similar to the McCoy .44 lift cam i have used with similar MOP timing. While seat to seat duration and total lift are not the total determinants of a cams performance they tell you 70% of what it will be like. Duration for lift at .050 inch and 0.200 inch lift checking points tell you a bit more and area under the lift curve ( inch degrees) at these points tells you a bit more.
it makes sense to set the cams for more lower end torque for a road application. When I built my twincam for my S3 Elan I played around changing offset dowels until I found a cam position that gave me a nice amount of low end torque and still lots of high end power, but as it was a road engine I definitely wanted the driveability of the low end torque. My point is it is easy (and fun ) to try different cam settings after the engine is built, and “trust your bum”… if it feels right then it is right.
My experience back in the 80’s with my S4SE DHC (MJY740J) which was delivered from factory with the Stromberg head with big valves and D types (Sprint) cams, I had Ed Winter rebuild and port the head and Ken Snailham (WED) built up the bottom end and ran engine in dyno, then did final set up, it had 10.3:1 comp, with some tweaking of timing and bob weight springs, richer needles, it had twin muffler exhaust, this engine produced 128bhp with similar torque to a Sprint.
Only element missing was the carb sound!!
On balance I had performance and when touring in France to LE Mans’s and Med I’d get 40miles/gallon and on motorways mid to high 30’s!!
