Just another 26R replica build attempt

[nmauduit]

Hi Roy
I dug out the McCoy 490 lift cam I tried a number of years ago in 2009. it had the similar dyno result curve in my 1600 cc engine as in your engine with great power above 6000 rpm but not much below. its was a too narrow a power band for my racing so I took a step back in lifts and durations and have ended up with the McCoy 460 inlet 440 exhaust combination after many trials

thank you, most interesting...

That springs me some side questions :
- what about non symetrical profiles, with a faster opening and slower closing to keep the spring lower ?
- are you aware of existing intake profiles that would have a lift between .46 and .49 and a total opening duration of or near 300?
- is the mid range torque loss mainly resulting of the overlap, so that a relationship between effective overlap and mid range torque could be drawn (then maxing out the exhaust lift acceleration to minimize overlap)?

ps: ever been tempted to get your own profile ground ?

[rgh0]

answers to your questions below - I am no cam design expert so this is just the outcomes of my investigations and experimentation over the years. I have the ultimate respect for Johns engine design and building capabilities but I differ in a few areas of detail but that is mainly about what works for me like maximum mid range torque spread so I dont have to be swapping diffs for different circuits .

- what about non symetrical profiles, with a faster opening and slower closing to keep the spring lower ?

I dont know anyone who has tried non symetrical profiles with a higher acceleration on inlet side for a twin cam. Most cars that use them seem to have heavy pushrod valve trains where the valve springs struggle to keep the follower on the cam on the downside. With the twink with thin steel followers, light valves, titanium retainers and good springs that is not a problem with any of the profiles I have tried and 9000 rpm. You dont need to run as heavy a spring as John does IMHO

- are you aware of existing intake profiles that would have a lift between .46 and .49 and a total opening duration of or near 300?

The McCoy 460 cam is the highest lift I have found with around 300 degrees seat to seat duration.

- is the mid range torque loss mainly resulting of the overlap, so that a relationship between effective overlap and mid range torque could be drawn (then maxing out the exhaust lift acceleration to minimize overlap)?

Yes the overlap needed for a long duration cam is what gives it the mid range torque loss. You can play with the cams a little to reduce overlap but you quickly run into problems with the exhaust opening to early or the inlet closing to late. The shorter duration exhaust cam gives you more room to play to improve the mid range torque without affecting top end power significantly

ps: ever been tempted to get your own profile ground ?

My local cam grinder has collected over 1000 profiles in his long career and I have talked to him about better profiles but within the limits of what he believes are acceptable cam accelerations there is a few that are similar but nothing around that's any better than the McCoy 460 and 440 cams in short duration high lift cams

cheers
Rohan

[nmauduit]

thank you for your detailed insight Rohan...

I'm (still) contemplating a racy built for my GTS project, and as you guessed still undecided between the lures of overengineering in the never ending quest of the magic trick that every racer is after (or is it just me ?) - most likely reinventing the wheel along the way... and it's not easy to arbitrate between all the little gain/cost options to try. Ideally the first engine would lead to a better second one, first then kept as a spare.

I have identified 2 personal objectives that would depart from all out racing
- reliability to reduce maintenance time and cost (including minimal losses and friction towards lower heat operation - possibly with the help of coatings?) - that entails valve springs not stiffer than required by profile
- accept a small decrease in top power to open up the driving experience to non pro drivers, but attempt to compensate that by the ability to run higher revs occasionnally (up to 8.7-9k?) to give a bit more room to shift in the spur of the action
my diff ratio is 4.4:1 (gearbox still under the bench, with a 2.5 and a 2.25 gearset to decide and sort out)

Practical question: as for preventive maintenance, would measuring the valve springs in situ make any sense in order to check head health status during the season?

[45DCOE]

Hey Rohan…… it is interesting that I collect old vinyl record albums and you collect CAMS! You were spot on in that the 490 profile was the dominant cam used in the old Formula B and Formula Atlantic series as I recall John saying. Thanks for a good quantitative analysis of what’s going on and especially valve spring longevity issues.

Roy

[rgh0]

thank you for your detailed insight Rohan...

I'm (still) contemplating a racy built for my GTS project, and as you guessed still undecided between the lures of overengineering in the never ending quest of the magic trick that every racer is after (or is it just me ?) - most likely reinventing the wheel along the way... and it's not easy to arbitrate between all the little gain/cost options to try. Ideally the first engine would lead to a better second one, first then kept as a spare.

I have identified 2 personal objectives that would depart from all out racing
- reliability to reduce maintenance time and cost (including minimal losses and friction towards lower heat operation - possibly with the help of coatings?) - that entails valve springs not stiffer than required by profile
- accept a small decrease in top power to open up the driving experience to non pro drivers, but attempt to compensate that by the ability to run higher revs occasionally (up to 8.7-9k?) to give a bit more room to shift in the spur of the action
my diff ratio is 4.4:1 (gearbox still under the bench, with a 2.5 and a 2.25 gearset to decide and sort out)

Practical question: as for preventive maintenance, would measuring the valve springs in situ make any sense in order to check head health status during the season?

I guess I have been on the same journey for the last 40 years. Build one engine race it. Build a second with a few changes to hopefully make it better. Swap out the engine and then rebuild the first with a few more changes. it a never ending challenge both intellectually and to my bank account

It really depends on how many hours you run and how much you push the limits on the particular valve springs as to how often they need checking / replacing. I also collect Valve springs in addition to Cams. The attached spreadsheet which I have put on the site before is the measurements of the collection including the John McCoy springs. This list covers all the high lift springs I have found over the years for twincams. There is supposed to be a Porsche 911 spring that also suits but I have never tracked down which spring.

On the chart green is the acceptable operating range from 60 to 210 lbs spring load and red is coil bind. I have been using the Tony Ingram springs in recent years due to their wide operating range that means they can be set up properly for a wide range of heads and cams. I apologise for the mixed units of lbs and mm in the chart but its just the way I think about valve springs

spring load ranges.pdf

(38.42 KiB) Downloaded 149 times

cheers
Rohan

[holywood3645]

Just a short reply in these loooog responses in regards to gearboxes.
Look at the ZF S5-18/3
There are several different gearing options from 5speed close ratio 1:1 5th to a couple of overdrive options for 5th.
The close ratio box is used in historic racing, However the OD boxes were supplied in several 70:/80’s cars.
The gear leaver is about 1/2” different in one of the options.
They are dogleg 1st.
I’m a little surprised that not a lot of people go this route. I bought my last one for $700 USD as a spare for my CR version in a MK1 escort race car.

[2mAn]

Hey Roy

Will you be bringing this down to the Petersen on Sunday? Its a little bit of a drive from Santa Clarita, but should be totally worth it as its the British Day so lots of Lotus, Jags and Astons.

Would love to pick your brain and maybe go for a ride

-Simon

[45DCOE]

Hello Simon….. It would be really fun to participate in this rare event at the Peterson celebrating British cars focusing on the cars of James Bond. It seems seems they are giving priority to all Lotus cars especially the iconic Esprit. Actually the build project is still about 1 1/2 years away as I am constructing it deliberately and I work and move slow. It should be a unique event given the theme so have a blast, Simon.
Speaking of car events, I met James (holywood 3645) about one month ago at the South Cost Orange County (San Clemente) car show billed as the world’s largest weekly gathering. There are so many Lambos, Ferraris, McLarens, GT40’s, all manner of Porsche’s, AMG’s, BMW’s, Corvettes, Mopars, and classics that your head will spin. James brought down his Mk 1 Escort with a BDA making 180HP, the best and cleanest Escort I have seen. The sponsors seem to be from Australia or Kiwis. Here’s a link:

https://youtu.be/dJNwIESToRc


To James…. Thanks for the heads up on the ZF S5-18/3 and will do some research on it. Another one that came up on a thread about a year ago is the Tremec. It seems TomR has been running a T5 for years now and I wonder if anyone else has fitted a Tremec successfully, especially a TKX.

Thanks

Roy