Lotus Elan and Lotus Elan Plus 2 Forums

A brief history. I bought a '70 S4 (stromberg big valve head) over 13 years ago that smoked and had low compression. Within a year, the engine had been slightly over bored, new pistons, rings...carbs overhauled with new adjustable needles, L2 cams and 23D distributor maintained. It ran well for many years, when a slight head gasket leak developed, I decided to use it as an opportunity to replace the L2 cams with Q360. Also replaced leaking header during this time. When I got the car back, I was disappointed. It just felt dead. The windshield was cracked recently, the exhaust was leaking, I had also bought a new pertronix distributor and adjustable cam gears with the intent of trying to get more from the engine, so now seemed a good time to take it to a local shop for some work. Windshield and exhaust were an easy sort. On the engine, we decided to start easy and replace distributor and run dyno and decide from there if adj cam gears would help. Pertronix fought us a bit, but got it working, so on to the dyno. Results attached. It's making 74 hp at 6400. Expected results for Q360 cams also attached. In a nutshell, should be 135, knock off 20% for at the wheels, say 110. Point with all the background is this engine should be capable of close to cam spec. It is a stromberg, not weber, but I can't imagine that would know off more than a couple pts. I am thinking that when the cams were installed, they set the engine timing off a tooth. It runs smoothly, no smoke, runs a little hot in traffic, sparkplugs looks good, ... Its just not as responsive as before. I am an engine newbie, but I had a brief conversation with the shop owner (as he was heading off to his other job as lead mechanic for a Mercedes GT4 race team), it seems my task will be to take off valve cover, rotate engine to TDC and look for cam markings that indicate lobe position (any pics of what I am looking for would help), then measure how far off they are from TDC, count teeth on cam gear and report back to him. Please let me know what you think. I really appreciate your help. Dan

Dan, You really need to fit a degree wheel to the crankshaft, otherwise you are guessing. If you can slip out the crank pulley then you can bolt the degree wheel on. If removing the crank pulley is difficult there are other ways. My method, arrived at because I had cut the centre out of my old degree wheel is to glue the wheel to the crank pulley, having first removed the water pump pulley and belt for clearance. I use silicone sealant and a couple of pairs of skinny, long nosed vice grips to hold it in place until the silicone sets-it is very rigid once it does. Fit the degree wheel with the TDC marking where it is easy to read and where you can fit a bent wire pointer-from a convenient bolt. Then find top dead centre with a dial gauge and long extension down #1 plug hole and bend the wire pointer to TDC. On my engine the original pointer on the timing cover is spot on but yours may not be.

Once you have done that, with the dial guage you can determine where the cams are set and adjust them.

Have you done a compression test yet?

a picture is worth a thousand words:

Thanks, David, the picture is perfect. I have not done a compression test recently, but certainly can. Honestly it has felt the same since I had the cams changed and now the distributor. IIRC, before the cam change, it was a consistent 170 across all four, but I will recheck this weekend. Since you are so good with pictures, where on the camshaft is the indicator for positioning it relative to the crank at TDC? For these cams, intake should be 105 degrees ATDC and exhaust is 110 degrees BTDC. Thanks, Dan

for what it's worth, last time I checked timing I just bolted the degree wheel in front of the crank bolt (I had purchased a spare one for that purpose, drilled and tapped it, so that I could attached the degree wheel to it with an allen screw). I had to lift the radiator 3 or 4 inches, using the flex of the hoses, but did not flush the coolant. If you don't mind flushing the coolant you'll have more room and easier access to read the disk.

As mentionned above, while at it I would double check the timing completely (including ignition, and verifying if true piston TDC comes at the mark on the crank pulley, or if a correction needs to be recorded for future reference). You may want to use a dial feeler to check the cam timing accurately, which will give you a better diagnosis. Adjustable camshaft sprockets are quite handy when trying to set an engine accurately (otherwise you need offset dowels, but it's not always easy to get right the first time when ordering them).

Dan, don't try to set the cams at TDC. Don't trust any marks would be my suggestion. Once you have established TDC and have bent the pointer to position, turn the crank over in the normal direction until you reach the numbers you have given: ie 105 degrees after TDC for the intake. Ideally have the dial gauge already set up on #1 intake cam follower so that you can see it reach maximum travel-that should occur as the pointer reaches 105 degrees after TDC on the degree wheel on the crank. Or, you can turn the crank to 105 degrees atdc and then fit the dial guage and swing the cam back and forth to get max lift. Remember the engine must be turning in the normal direction when you check these two readings together-if you are turning the engine backwards there will be a delay in the camshaft due to the timing chain tensioner etc. Now you get to set the sprockets-you may need an offset dowel in at least one sprocket-I would order two or three offset dowels of different size to give yourself some room to play.
I am sure others will have suggestions also. Rohan, where are you?

Edit, nmaudit must have been typing at the same time as me. I have the radiator fitted down in the nose so I don't have to even think about it!

Looks very similar to mine, juat a little down on power across the board. Is the dyno accurate? Do you know its conversion factor? Im assuming yours are at wheel?

That was my reaction as well. Everything looked fine, except that it was expecting them to be 30 pts higher across the board. Yes, mine are at the wheel numbers. He mentioned that his dyno is no more than 8% off compared to others. Is yours at the wheel? If so, that's the numbers I was expecting. Thanks for posting. Dan

Dan,

Yes these are at the wheels figures.
Also a point to note is its a weber head runing jenvey/emerald fuel injection.

I dont believe that changes much tho if at all anything, i personally was expecting a bit more torque if im honest, but i was put straight on the subject.

I think it was a conversation with Rohan via PM that said 6bhp loss per 1000 rpm.

So add say 40bhp to your 75, 115bhp ish at the fly. Does sound reasonable when put against the expected numbers.

Hope it helps

Yes around 6 hp per 1000 rpm loss in top gear over the 4000 to 7000 rpm range in top gear with 3.7 diff and strapped down hard between two rollers and is about the maximum loss possible with our sort of cars

Loss less with higher numerical diff ratio ( slow slower wheel speed in top)
Loss less with car set on a single roller or not strapped down so hard

Typically a good 126hp sprint spec car will get in the 90 to 100 wheel hp range with losses ranging from 4 to 6 hp per 1000 rpm depending on the set up.

A useful reference to read is the articles on the page below around rolling road dyno testing
http://www.pumaracing.co.uk/index.htm


Getting 135 hp with Q360 cams requires a ported Weber head. You will be in the 125 to 130 hp range with a well set up Stromberg head I suspect

cheers
Rohan

Hi Dan,

I thought I might chip in here, as I also have a Stromberg engine with compression figures of 160-170psi. I have CPL2 cams, not your cams, and a standard manifold.

I think that to get up to 130bhp you need to get the compression up to a higher figure - 160-170bhp are the figures for a low compression head with a bit of skimming. I am ready to be corrected on this though....

I do not have any dyno figures for my engine, but my 50-70 time in 4th is 4.5 to 5 seconds, if that is any help.

Cheers,

Dave Chapman.

After 13 years you know your engine well enough, I reckon your gut feeling will prove to be right re the cam timing, when you blip the throttle do the revs pick up as fast as they ever did if not faster? If not then its a very good indication of the cam timing being out.

I am assuming that during the rolling road set up the ignition timing was correctly set and the advance curve looks like it should, the dizzy alone could give you the same poor results but I would not expect a RR operator to get it wrong or not see that it was responsable for the power loss.

david.g.chapman wrote:I think that to get up to 130bhp you need to get the compression up to a higher figure - 160-170bhp are the figures for a low compression head with a bit of skimming. I am ready to be corrected on this though....

I'm not sure compression ratio alone would alter drastically the power output : going from 9 to 11 may bring about 4-5%, pushing to 12 an other point or two, then you're in for avgas if not topfuel...


from http://www.dukeengines.com/advantages/a ... ion-ratio/

According to Mr David Vizards performance with economy book, an increse from 9 to 11:1 c/r will yeild just 3.2% performance increas, based on short duration camshafts. A longer duration will give more.
Incidently it states millage gains will be double the percentage gain.

Slightly off perhaps but maybe usefull

Thanks for all the advice. Yes, blipping the throttle has lagged since getting the cams installed. The new distributor has done nothing to affect that. I do not know the advance curve, but fellow lotuselan.net member, Don Butler, and I are going to go over ignition and cam timing in the next couple of weeks. Will report back on results. All the best, Dan

Sounds definitely like at least one cam is at least one tooth out.