Lotus Elan

QED 420 MOP Setup Recommendations

PostPost by: Pfreen » Wed Apr 29, 2020 4:14 pm

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?

Recommendations?
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PostPost by: mark030358 » Wed Apr 29, 2020 5:34 pm

When I rebuilt a 69 Elan with a Stromberg head, the ex QED engine builder advised against the 420 profile and just use the Sprint Cam. Just my 2p.

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PostPost by: nmauduit » Wed Apr 29, 2020 5:38 pm

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)... ;)
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PostPost by: Esprit2 » Fri May 01, 2020 9:10 pm

The specs I have for the Q420 are as follows:
If I'm incorrect, please let me know.

Mfgr / Seller . . . . . . . QED . . . . . QED Recommends/ Specifies
Cam ID. . . . . . . . . . . . Q420 . . . . Advancing Intake 6° to 100° MOP
In. Opens, BTDC. . . . 36.5°. . . . . 42.5°, BTDC
In. Closes, ABDC. . . . 68.5°. . . . . 62.5°, ABDC
In. MOP, . .ATDC. . . . 106° . . . . . 100°, ADVANCED 6°
Int. Duration . . . . . . . 285° . . . . . 285° _____________________________
Ex Opens, BBDC. . . . 68.5°
Ex. Closes, ATDC. . . . 36.5°
Ex. MOP, BTDC. . . . . 106° . . . . . 106°, exhaust MOP not altered
Ex. Duration . . . . . . . 285° _________________________________________
Overlap . . . . . . . . . . . 73° . . . . . . 79°
Total Lift. . . . . . . . . . . 0.418”
Lobe Separation. . . . 106° . . . . . 103°
Intake C/L Offset. . . . 0° . . . . . . . +3°

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.

Regards,
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PostPost by: rgh0 » Sat May 02, 2020 1:30 am

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 :D

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.

cheers
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Last edited by rgh0 on Sat May 02, 2020 1:40 am, edited 1 time in total.
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PostPost by: rgh0 » Sat May 02, 2020 1:33 am

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

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PostPost by: 2cams70 » Sat May 02, 2020 3:51 am

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.
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PostPost by: rgh0 » Sat May 02, 2020 7:13 am

2cams70 wrote: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

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PostPost by: alan.barker » Sat May 02, 2020 7:50 am

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.
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PostPost by: Pfreen » Sat May 02, 2020 4:01 pm

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.
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PostPost by: 661 » Sat May 02, 2020 5:21 pm

Pfreen wrote: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.

Interesting. Do post how you get on as I feel my S4 SE 1760 on Strombergs and Sprint cams could do with a pick me up.
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PostPost by: dougal9887 » Sat May 02, 2020 9:19 pm

This topic may be of interest.
viewtopic.php?f=39&t=33143&p=224128#p224128
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PostPost by: rgh0 » Sun May 03, 2020 1:23 am

Pfreen wrote: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.

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PostPost by: rgh0 » Sun May 03, 2020 1:25 am

dougal9887 wrote:This topic may be of interest.
viewtopic.php?f=39&t=33143&p=224128#p224128
Dougal.



I had forgotten all about that QED 420 cam analysis I did back then - only 17 years ago :lol:

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PostPost by: 2cams70 » Sun May 03, 2020 1:55 am

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.
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