cam shaft choice

[bengalcharlie]

Hi,

my 69 plus two is a converted federal car to euro specs.
it has a tubular manifold, ignitor ignition with curve adjusted to euro spec, balance pipe etc..
Car runs well but would like to see some improvement.
It runs fine but engine moves around a lot when taking off and I have checked everything including valve timing, carb and dizzy settings etc..
It could be the fuel here in NZ because I know it is crapp!

I noticed that the cams are one grooved cams with 0.35 lift.
Have not checked duration but I think they are standard.
Would a super sprint ( D-type cam) make a big difference?
Or any other suggestions.
I also have to add that I have a stromberg big valve head but with the normal compression S embossed in the head.
I ahve not rebuild this engine so I do not know the compression ratio.
Is there any way to measure the compression ratio without taking the engine apart?
cheers
Robin

[steveww]

My S4 is European specification and is using the Sprint cams which I feel provide the best compromise. The cams are 272 duration with 0.36" lift.

If you are unsure about the engine's condition I would perform a compression and leak down test to give you an idea of it's health. If you are after more performance a large bore manifold (headers) and exhaust system really help the twinc.

My web site has a lot of information on what I have done to my S4 and the results achieved; see http://steveww.org/

[bengalcharlie]

Hi Steve,

Many thanks for your reply and I did have a look at your website which looks great and plenty info there!
My engine is very healthy, compression is very good and it runs fine apart from a run on problem that is most likely due to the bad fue l quality here in NZ.
I talked about it to a well known carb specialist and explained to him the problem and he agreed that I could solve this by installing a solenoid that closes and opens the butterfly shaft.
I just installed it last week and it seems to work but I was not 100% happy with the pick up of the engine but most likely I have to balance the carbs again.
I noticed that you have an fuel analyser as well. I should invest in one of those as well, I know that my elite friend in california uses the same one and he highly recommends it .
Steve, just to be sure, your cams are the ones with the two groves?
cheers
Robin

[steveww]

The cams in my S4 are specially ground by Piper to the Sprint profile, so no grooves. As I could not find any Sprint cams at the time I had them made. The engine came to me with L2 cams fitted which really did not suit the rest of the engine.

The Wilkins Twin Cam book states 2 grooves for the D type Sprint cam.

[bengalcharlie]

Steve,

what do you mean by L2 cams?
Do you think switching for my one grove cam to your cam ( same profile as a 2 grove cam or sprint cam ) would make a big difference?
Secondly how expensive are these sprint cams?
Or better to have my ones reshaped to sprint specs?
sorry for all the questions but you have been there.
cheers
Robin

[steveww]

L2 is a cam profile, Cosworth I think? They are long duration and similar lift to the Sprint Cams, a bit old school now. For the twinc you want more lift not duration. However fitting in more lift is tricky as there is a shortage of space. Piper do a camshaft which is essentially a copy of the Sprint profile LOTBP270 see www.pipercams.co.uk A wild cam needs high rpm to work, the bottom end needs to be built to match or it gets messy with it goes bang!

As for cast I do not know the market in NZ. I had Piper do my cams as I know the Sales Director there so I got a good rate

There is no magic bullet for engine tuning, it must be treated as a whole. Everything really comes down to flow. So wilder cams will increase flow but this needs to work with better induction, exhaust and cylinder head. The standard Lotus airbox is rather restrictive I have seen claims that 8bhp can be lost here. The twinc responds very well to a better exhaust system including headers.

Remeber to keep in mind what the engine is going to be used for. A 9,000 rpm racer is a real pain to drive in traffic.

[Old English White]

... Cams are a never ending story ...
I'm thinking about and after many discussions with meccanics , something arround 300? duration(both exh & inl) seems to be THE compromise : still usable on road with a standard clutch , a long power band making track days a pleasure , and a noticable difference from stock making your efforts worth ... if all with a strong short engine .
Is it right , your opinion , for those who experienced such combination !?!
Christian.

[steveww]

IMHO 300 is too long for road use, I would go for 280 maximum. More lift is good but tricky to fit in.

[paros]

I would agree that 280 degrees is about right for road use with more lift.
One very popular cam in the UK is the QED 420 with .42 lift and 280 degrees. Minimal work needed on the head but care in setting the springs to ensure they don't go coil bound [ unlikely with later heads ].
I used this on the road and on track - completely tractable at road speeds and peak power about 6500.
Also had CPL2 for a while which whilst being old fashioned was a good cam but nowehere near as good as the 420. Burton do a fersion of this cam also, BLF14.
QED and Burton can supply springs, retainers etc for the cams so they can be installed as a 'kit'.
Richard

[rgh0]

My 2 cents worth on cam timing for what its worth>


280 degrees seat to seat timing is plenty to get good power to 8000 rpm and 170hp in a 1600 twin cam so you dont really need more unless your racing a light open wheeler and are after ultimate horsepower (and ultimate is around 180 to 190 hp) at the expense of torque and power band and engine life as you need to rev it to 9000 rpm to get these few extra hp.

The secret is getting the maximum lift into this 280 degree seat to seat timing. QED and Dave Bean and others seem to be able to get .41 to .42 gross cam lift in this timing. John McCoy of Omnitech gets .44 lift into this timing which is the most I have found and his cams work great. John also does a .52 lift cam in a short duration cam but valve gear life is low due to the high valve accelerations at around 15 hours and is really only for the very keen racers who dont mind frequent rebuilds.

Lots of other cams with 280 timing or longer duration but lower lift but they are really a waste of money and have been developed for the market that does not want to spend money on valve gear mods and believes the longer timing the better and more power.

Also lots of cams with longer durations and .41 or higher lift but most have too long a duration and not quicker in a race car in most circumstances due to lack of torque at lower revs

Also be careful of the durations quoted as some quoted as timing above base circle, some seat to seat timing allowing for valve clearances and some quoted at small nominal valve lifts such as 0.50 in.

Going above 280 degrees seat to seat starts to generate a noticeable hole in the torque curve around 3000 to 4500 rpm. This hole gets worse and wider the longer the timing. Its also worse with road compression ratios at 10:1 compared to race compression rations at 12.5:1.

290 and 300 degree seat to seat timing is usable in a road car just if everything else is right but does not provide any real benefit.

In an Elan race car the desirable seat to seat timing seems to be in the 280 to 300 degree range with the biggest lift possible. I suspect the best for an Elan on the tracks I race on would be around 290 to 300 degrees with a .45 to .46 lift. No one make this cam that I have found yet but I keep looking

cheers
Rohan

[steveww]

I suspect the best for an Elan on the tracks I race on would be around 290 to 300 degrees with a .45 to .46 lift. No one make this cam that I have found yet but I keep looking

Piper Cams will grind cams to any profile you want. So you could certainly get your ideal profile made if you really wanted to.

[bengalcharlie]

Many thanks for all your experience in this matter.
I certainly will print all this for future reference.
After almost 18 years of ownership I just discovered that the cams in my car have one groove!
For all those years I must have had a mans look! if you know what I mean.
A lotus friend overhere has offered me some D cams (sprint) so I will fit these although I do not know if the difference will be noticable.
I hope it does!
Robin

[rgh0]

Steve

Most cam grinders stick to a limited range of acceleration profiles they have developed. The sorts of lift and duration I am looking for are outside what grinders in Australia have developed in their standard range . John McCoy found the same and the profiles he developed he worked on to create with Elgin Cams.

I am sure with enough time and money I could come up with something to match my ideal race cam working with Piper or a similar cam development company but its a bit hard to do from Australia and a bit expensive for my modest engine building ambitions currently.

You could similary develop a special scatter cam for your stromberg car using something like the McCoy profile but using offset timing for each cylinder to compensate for the siamesed ports. This approach works great on A and B series race engines in MGB's and Midgets and could be adapted to Stromberg Twinks .

cheers
Rohan

[steveww]

Rohan,

The thought had crossed my mind However I don't think the cost is worth it, it would be cheaper just to buy a new Weber head from QED. I now have the Stromberg twinc where I want it and no flat spots. The large bore exhaust certainly released a bit more power/torque, just trying to find some time to get to the dyno to see what we are getting now. As the car is primarily a road car I am not after maximum power, good torque across the rev range is more important.

I am looking at installing some sort of ECU for ignition only, possibly