L14 Cam Install and performance

[Pfreen]

My covid hibernation required that I do something while locked up in a rental house waiting for my new house to be completed.
So, I did a lot of investigating of cams for the twin cam and decided that the QED 420 or the Kent cams L14 cam would be the cam to try.  Theoretically, the Q55 valve springs and retainers allowed the cam to be installed without the machining of the valve spring pockets.
In May, Roger (from this forum) told me he had some reground L14 cams he could sell me.  Sold!

Anyway, then I got serious.  The big decision was what MOP to set the cams at.  It seems there are a lot of opinions on the subject.  Anyway, I downloaded an engine model called Engine Analyzer Pro v3.9B (you get one month for free).  I first modeled the current engine which is a Stromberg head, 10.2:1 CR, and a Sprint cam set at 110/110 deg MOP.  I calibrated the flow coefficients and such so the performance matched my chassis dyno data (Inertia dyno sprint cam 110.png).  I then did a lot of runs at different MOP settings.  I found that the best compromise was to use the Kent cam recommendation 0f 106/106 deg.  The QED 420 cam recommends a 100 int/106exh MOP settings which I found to be unusual, thus the modeling effort.

Anyway, I bought the Q55 valve springs, Q55 valve retainers, new collets, spring seats, vernier cam sprockets and thick pad lifters.  I needed the thick pad lifters to reduce the shim thickness since the cams had been reground and the base circle was quite small.  I did not have to do anything to the head except clean it up.  No machining.  It is ported and polished so I know it flows really well.

The attached an excel spreadsheet which documents the build.

Before I took the head off, I took the car to a new chassis dyno in Orlando (my new home) so I could do a one to one evaluation of the new cam.  The max HP was 105 at the wheels whereas the max hp on the inertia chassis dyno in Fort Lauderdale was 115.  Hmm I thought.

So, I just took the car back to the dyno place in Orlando and I was shocked when I saw 130 HP.  They could not produce curves because they were not at all computer savy.  I will not go back there.

In conclusion, I find it difficult to believe the cam change added 25 BHP, but I guess you never know.  That's the problem with some dyno shops. This shop did not give me much confidence.
I did clean and lap the valves so they were totally bubble tight.  That took a fair amount of work. They were not bubble tight when I removed the head, but none of the valves or seats were worn or burned.  Maybe that added HP.  I don't know.

Anyway, the seat of my pants says the car is a lot quicker.  Another funny thing is the exhaust sounds a lot deeper and it revs forever.  However, my rev limiter is set to 6800, so no rods out the side.

So, in conclusion, I am very happy with the cam.  The idle is slightly less stable, but there is more than enough low end torque.  I suspect the mileage is worse, but that is not my number one concern.  I retorqued the head and checked the valves after 500 miles and all was well.

If some of you are looking for a project, I think this is a good one to add a lot of spice to your Lotus.

[BDA]

Great write up, Pfreen! That certainly seems to have worked out well!

Did they adjust your hp and torque for atmospheric conditions? If not, that might be part of the 25 hp difference.

[Bainford]

Thanks for the detailed account. Very interesting. Agree that 25 hp gain sounds like a lot.  It must be quite a ride.

[EuropaTC]

In conclusion, I find it difficult to believe the cam change added 25 BHP, but I guess you never know. 

It could be right you know, I looked at the QED420 and their data sheet indicated 145-150bhp.  They increased the chokes to 34mm which might account for a few bhp at the top end but even so, it's a very big increase over the standard Lotus Sprint cams.

The L14's were discussed quite a lot on Lotuselan.net and seemed quite a popular choice.

Brian

Edit to add....   when I was looking at cams I found this datasheet on Lotuselan.net and kept it for comparisons. The guy who uploaded it had made some notes on it as well.   I don't know if you've found it in your research but if not it might be of interest where they ended up with fuel settings. There was also comment on increasing the distributor advance but I can't find those notes.

[Pfreen]

I have seen the qed 420 data sheet.  I was going to do the qed 420 regrind but Roger offered he L14 cams.
My car has Hitachi SU carbs and I also have an oxygen sensor to monitor the af ratio.
I needed to enrichen the mixture at idle.  I also had to advance the timing at idle by about 4 degrees to 14 degrees.  I have a crankshaft referenced digital ignition system so timing changes were easy.  The max advance is still 34 degrees at 7000 Rpm.
The funny thing is the oxygen sensor does not work at idle because of the valve overlap.  It measures super lean.

I think the true brake hp at the crankshaft is around 150 hp, which is what I thought would be based on the modeling.

I did the project to determine whether Stromberg heads can be made to produce nearly as much hp as the weber heads, and not limited to 135 shaft hp.  I certainly think this project has validated this objective.  What I did not know was that the drivability of this cam is nearly identical to the sprint cam.  This is probably because the car is so light.  It may also be because of the su/stromberg carb type as well.

The webers may not have as good of drivability because they have a fixed venturi area while the su/strombergs are constant depression carbs.  Put another way, the velocity across the jets in a Stromberg is constant over the speed load range and this atomizes the fuel better.  The velocity through the weber is variable according to the air flow. 
The higher overlap of the cam decreases the manifold vacuum at low speeds so the fuel is not atomized as well with more aggressive cams. This can affect drivability and idle stability.
This limitation is gone at high rpm and hp where the air velocities are high and the fuel atomizes more completely.

The Stromberg head will never be a pretty as the weber head though.

To BDA.  It was hot as always on the three dyno runs I did.  I don't know if they corrects the hp to standard conditions, but the correction would be about the same for all of them.  However, I wish I knew how the data were calculated.

[Roger]

Well, I must say I'm glad that seems to have turned out well, I now wish I had some more to sell!

[jbcollier]

You would get a further improvement switching motorcycle  flatslide carbs.  Round slide carbs like the Strombergs and SUs have disrupted flow due to the raised floor around the jet and the cutaways for the round piston.  Motorcycle flat slides also don't have a throttle shaft or butterfly.  At WOT there is virtually nothing in the bore.  Considering all the junk in the Weber/Dell bores, you might well get a Stromberg head with flat slides to perform better than a side draft equipped Weber head.