Lotus Elan

Cam Timing Help Needed!

PostPost by: lotusanglia1965 » Sat Dec 04, 2004 9:51 pm

:ph34r: Does anyone know cam timing figures for brm phase 1v and L1 cams? Also need to know best tappet clearances for these, brm on inlet and L1 on exhaust. Engine is 82mm stroke x 83.5mm bore and i'll be running approx 11:1 compression with 1.688 inlet valves and 1.4 exhaust. any help/advice(apart from don't do it!) much appreciated.
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PostPost by: types26/36 » Sat Dec 04, 2004 10:40 pm

LA1965,
L1 as follows:
46/78/70/50. Duration 304 degrees. Lift .410"
Valve clearence (cold) inlet .008" exh .009"
Inlet full open @ 106 degrees ATDC

Only specs I have on BRM is for a "PHASE 4"
57/87/87/57 Lift .440"
and I doubt this will help.
Specs as per Burtons book.
Sounds like you are going racing! good luck.
Brian
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PostPost by: lotusanglia1965 » Sat Dec 04, 2004 11:16 pm

:) Brian,thanks for your reply,i did mean phase 4, so info is very helpful. From these figures am i right in thinking phase 4 would be inlet fully open @105 deg atdc and L1 would be exhaust fully open @100 deg btdc? Also,is 4degree difference in inlet/exhaust duration down to larger clearance on ex? All i need now is inlet tappet clearance for phase 4 and i can go building! This engine is going in my 105e anglia,with 45mm throttle body injection,sprints and track days only. Bit too wild for my roadgoing +2! cheers,
Martin
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PostPost by: rgh0 » Sat Dec 04, 2004 11:40 pm

Hi Martin

The quoted BRM phase 4 cam timing is a little late for a 324 degree cam I would advance it to give about 102 degrees MOP not the 105 degrees in the quoted timing based timing for other cams of similar specs and match the exhaust at the same MOP

You will need to watch clearance between the valve on overlap with this cam combination and may have to sink the valves into the head to get a working clearance between them.

Why the 82 mm stroke ?, what crank,rods,pistons and block are you using to achieve this.

The cams you are using will really only work effectively in a 9 to 10,000 rpm engine in a light weight open wheeler. With these cams and 11:1 comp ratio you will have a big hole in the torque curve a higher compression ratio would help a little but you still will not have any torque below about 6000 rpm. So I hope the bottom end you are building can produce the revs needed (and this may be a little hard to do with a 82mm stroke). You will also need to swap gears and diffs for each circuit to keep the engine in its very narrow power band. In an Anglia I would personally be using a much shorter duraton cam while keeping the high lift you have gone for.

just my 2 cents worth

Rohan
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PostPost by: lotusanglia1965 » Sun Dec 05, 2004 12:30 am

Rohan,thanks for advice,maybe i'm being too hopeful! i thought longer stroke would cope better with long duration cams,i know that there are better profiles for short stroke. i'm using 1600 crossflow block, 1.8diesel crank and accralite forged pistons to give a lower revving true 1800cc.will be able to get round lack of mid-range torque with masses of advance due to mappable ecu and injection. have achieved very good results on e-type like this.also will try to fit longest con-rods i can. needs more consideration,but want to try something different! p.s. 1.8d crank successfully allowed 149bhp at wheels on mexico with 1861cc,this crossflow had full race cam,normally in 4500-9000 rev range,dropped peak to about 7500.it's fully counter-weighted and cheap! cheers,
Martin
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PostPost by: lotuselanman » Sun Dec 05, 2004 2:36 am

:P ;) :D
Oh joy, all this going into an Anglia. You are my hero !!
A word or two of warning. Do the exhaust timing first.
As for the timing of the L1's, you need that info from the grinder as every man and his dog has tampered with the timing of L1's over the years.
As for the P4 BRM the same applies, I had dealings with genuine BRM ground P4'smany years ago, if you give me some time I can dig out the information ex BRM. Also with BRM cams it is very easy to have the valves kissing.
You maybe able to advance the timings and flatten out the rev range.
In an Anglia, go for it and keep in touch with the results,
Les.
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PostPost by: rgh0 » Sun Dec 05, 2004 6:05 am

Hi Martin

Out of interest I ran your engine design through the simulation program I use for my engines. The program is called DynoSim and gives pretty good correlation between its output and the dyno tests I have done. Investing in a simulation program is money well spent if your going to spend a lot of money and time developing a fairly special twin cam like you are doing to ensure you get it as close to right the first time. Its a lot easier and cheaper playing with different setups in the simulation than in a real engine.

I assumed a good quality race porting job on your twin cam head, 5.2 inch BDD rods, 11:1 compresson , throttle body fuel injection and exhaust headers and open exhaust.

Results as follows for 3 different cam combinations, while absolute numbers are probably plus or minus 5% the relativity between the 3 different cam setups will be pretty good.

BRM phase IV inlet and L1 cam exhaust:

peak power 190 hp at 8000 rpm ( this would be around 150hp at the wheels)
peak torque 140 ft lbs at 7000 rpm

2 x L1 cams ( actually the local variation on the L1's that I currently use with shorter 300 degree timing and a more aggressive lobe acceleration, this is a more tractable cam with same or better top end HP):

peak power 200 hp at 8000 rpm
peak torque 145 ftlbs at 7000 rpm

McCoy 450 cams ( 290 degrees .440 lift):

peak power 200 hp at 7500 rpm
peak torque 150 ftlbs at 6500 rpm

The McCoy 450 cam had about 20 to 30 ftlbs more torque across its curve from 3000 rpm up to 6500 rpm than the BRM&L1 combination and the 2 x L1 cam torque curve ran midway between the other two.

eg at 4000rpm

McCoy 450 - 125 ftlbs
2 X L1 - 110 ftlbs
BRM & L1 - 95 ftlbs


John McCoy from Omnitech engineering in the USA developed the cams for his racing twin cam Escort and Cortina's hence the focus on torque. He has a .520 lift inlet cam of the same 290 degree duration if your really serious and dont do a lot of racing hours or dont mind frequent valve train rebuilds. I am currently building an engine with the McCoy 450 cams and I will be interested to see the outcome on the dyno compared to my current L1 cam engine.

The real cause of the hole in the torque curve for the BRM & L1 cammed engine is that the bigger overlap reduces effective compression ratio at lower revs, big ignition advance on a mappable ECU cannot over come the basic problem of lower effective compression and cylinder charge.

190 to 200hp seems to be about the breathing limit of a developed twin cam head no matter what size block you put under it unless you go into very exotic valve and porting modifications with around .50 lift cams as Brian Hart did with his big valve engines. At least on your 1800cc engine you get it coming in at a sensible rev limit


regards
Rohan
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PostPost by: lotusanglia1965 » Sun Dec 05, 2004 3:04 pm

:ph34r: Hi folks! Thanks for your replies. It seems i may have to modify my modifications! How about regrinding the phase4 inlet (steel) to something like burton's blf42,which has 304 duration and 440 thou lift,keep exhaust as L1 and raise comp to 11.5 or so. mapped ign will help avoid det.I'll keep you posted with anymore developments, cheers
Martin
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PostPost by: type26owner » Sun Dec 05, 2004 3:33 pm

Have had recent first-hand experience with mangled valves on a BRM III racing engine. <span style='color:red'>Imperative</span> you check the valve to piston pocket clearances upon assembly and set the minimum gap to at least 1/8". Both my younger brother and I went entirely over the car looking for loose fasteners but we both missed the fact the chain tensioner was left just finger-tight. When the tensioner fell off out on the racetrack, the chain did not jump a tooth on either cam and the engine ran fine until he came back into the paddock and shut it off. That's when the slack was enough to close the gap between all the pistons and valves and the damage was done. :( It was a very expensive and time consuming mistake to make and kinda ruined the track event.

BRM kicks butt! :D
-Keith
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PostPost by: rgh0 » Mon Dec 06, 2004 10:36 am

Hi Martin

I think the direction you are going in to shorten duration while maintaining lift is the way to go. The end result will be similar power with a fatter torque curve. You also have less problems maintaining clearance between valves on overlap !

Rohan
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PostPost by: lotusanglia1965 » Tue Dec 07, 2004 7:09 am

:) Hi Rohan,
am taking some of your advice! I bought cams second-hand as this whole project is a low budget one. I'll lessen duration of inlet and possibly exhaust. Good thing about long stroke is that valve to piston isn't such a problem, as piston spends less time in the vicinity of the valves,but I will still have to do proper checks.Wondered if you could run my spec on your program to see if any better torque than before. Many thanks for everyones' replies and advice,
regards,
Martin
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PostPost by: rgh0 » Tue Dec 07, 2004 10:02 am

Martin

Iwill have a go in the next couple of days and post the outcomes.

Rohan
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