Road cam question for head modified to big valve + status

[au-yt]

The Twink in my 7, has according to engine builder, the head has BRM? size valves 1.625" Inlet x 1.425" Exhaust,
The Head has polished inlet ports are 42mm/ 1.65" Stock? Not sure of the port shape.

83.5 mm pistons and runs 10:9-1 comp. The Cams are stock with .375 lift. but with a course Vernier set up.

Apparently the cam set up at 106 degrees inlet and exhaust, due to the valve size.
I know there is more HP hiding in there and the cams are the culprit compounded by the valve size.

I am thinking Sprint spec as the lift is .360 but more duration but having said that I don't plan to do track work as this is a road car and my question after all this babble is what cams would be suitable?

[TBG]

QED 420

[au-yt]

Great Suggestion thank you, I do like how that reads.
"A high lift cam with fairly short period and fast rise. The Q420 gives excellent torque figures at low RPM, and yet still produces 145-150 BHP at 6500RPM."

[rgh0]

The Twink in my 7, has according to engine builder, the head has BRM? size valves 1.625" Inlet x 1.425" Exhaust,
The Head has polished inlet ports are 42mm/ 1.65" Stock? Not sure of the port shape.

83.5 mm pistons and runs 10:9-1 comp. The Cams are stock with .375 lift. but with a course Vernier set up.

Apparently the cam set up at 106 degrees inlet and exhaust, due to the valve size.
I know there is more HP hiding in there and the cams are the culprit compounded by the valve size.

I am thinking Sprint spec as the lift is .360 but more duration but having said that I don't plan to do track work as this is a road car and my question after all this babble is what cams would be suitable?

No stock cam had 0.375 lift that I am aware of but lots of long duration low lift "hot up" cam used this as its about the most lift you can achieve with the standard valves springs pack. A decently ported head with 1.625 inlet and 1.4 exhaust ( not aware of anyone using 1.425 exhausts even in extreme racing engines) and 10.9 :1 can give well over 150 hp and a great torque curve with a standard bottom end out of 1600 cc and more again out of a bigger capacity or higher revving bottom end. Just need the right high lift short duration cam ( 0.420 and greater lobe lift and less than 290 degrees seat to seat), plus a good exhaust and the right carb and ignition advance settings. If your "engine builder" does not know this then you need to talk to someone who really knows modified twinks.

cheers
Rohan

[au-yt]

The lift is as measured by the builder who specialists in Twin Cam engines.
The Miles Wilkins LOTUS Twin-cam book on page 180 quotes the B type cams with a lift of .375in.

[rgh0]

The lift is as measured by the builder who specialists in Twin Cam engines.
The Miles Wilkins LOTUS Twin-cam book on page 180 quotes the B type cams with a lift of .375in.

Like I said 0.375 is a common lift on old hot up cams designed to use standard valve gear to its limits so I am sure your measurements are correct. Does the cam have any markings ? Most modified or replacement cams will have a number stamped on the front

The Wilkins book is wrong in this aspect with regards the B cam lobe lift Even saints can make typos. The lobe lift on a B cam was .350. Lotus in the FIA homolgation papers listed 0.375 maximum lift which is probably where the error came from. Maybe Lotus listed the higher lift deliberately so they could use it on the race engines or interpreted it as maximum lift allowed by the springs not the actual maximum lift of the cam ?

cheers
Rohan



cheers
Rohan

[au-yt]

Hi Rohan
This is getting interesting thank you for pointing this out about the Wilkins numbers, and that makes a good point.
The Person who rebuilt the engine had to be tamed as he want to build a race engine and I wanted a fast street able engine which it is. Ive set the Jetting close to sprint but one main size down, and the Lambda readings are at 11.-12 so happy there.
The Dizzy that was fitted was a basic Escort one so that went in bin and it now has a 123Ignition unit. Timing for another discussion

If the cams are a high acceleration cam that would explain a few things, Initially I thought it was a D type cam cam as it has no markings.

and if it has been reground there is nothing stamped on it which doesn't surprise me as it was most likely reground here in Australia by either Ivan Tighe in Queensland or Waggots in Sydney.
And as I write this Ill do some inquiries with both these guys to see if its one of there grinds?

I'm actually enjoying discussion thank you,
Cheers
Graeme

[vstibbard]

If they are Waggott regrinds, popular ones in 90's were the D Type and Kawasaki profiles, see specification sheet below.

waggott cams Ford Lotus TwinCam specs.pdf

(16.98 KiB) Downloaded 319 times

[au-yt]

Now that's interesting.

They read a somewhat like the Kawasaki profile, however the lift is not .380 its .375.
I remember these being a thing in the late 70's and Owen Willomun (Spelling?) waxing about them.

Is there anything about there power range?

[au-yt]

Thanks for the link this is the page from the Waggot's catalog, theses have been around since the late 70's

[rgh0]

Given that its a Sydney car the Waggott Kawasaki grind would not surprise me. The lift difference may be measured valve lift versus actual Lobe lift. This was the typical 70's hot up cam with too long a duration (advertised 300 degrees which i presume to means seat to seat) and a lift that works with standard valves.

Interesting that Waggott say standard valve springs will do 0.390 inch lift, again this may mean around .380 to .385 valve lift depending on clearances used. In practice anything over 0.375 valve lift is pushing it unless you check the actual assembly height given the variation in the head spring pocket dimensions and valve seating even when new. Given the amount of machining done on these heads you cant really trust anything these days and need to measure it all.

As I have said these days (and even back in the 70's with Dave Bean cams) the best high performance road cams are 0.410 to 0.440 lobe lift and around 280 to 285 degrees seat to seat. These cams require new valve spring packs and potentially longer valve stems depending on the spring pack design. The produce great midrange torque and strong power up to 6500 rpm. They will work well up to 7500 rpm if you have a suitable bottom end. 160 - 170 hp at 7000 to 7500 rpm if you have a suitable bottom end, in a properly set up 1600cc twink, that is a delight on the road is easily possible depending on the porting and carbs and exhaust setup, the same or more hp at lower revs possible if you build a higher capacity long stoke bottom end.

cheers
Rohan

[au-yt]

It’s hard to know where the engine is from as the car came from Queensland. The rebuild was very extensive and the report by the builder and receipts from work shops is evidence, including unleaded valve seats along with new liners JE pistons balancing and crack testing, so this wasn’t a freshen up.

For the time being I need to work out a decent ignition map with what I have to suit the cam characteristics.
And understanding more about the profile will assist. Just understanding where the cam comes on song will help a lot.

[rgh0]

A cam like that only starts to work well above around 5000 rpm

cheers
Rohan

[au-yt]

Rohan
That's a good start, I get in touch with Waggots today hopefully they can shed more light on which cam it may be. As it could be their "D" type
Graeme

[rgh0]

Rohan
That's a good start, I get in touch with Waggots today hopefully they can shed more light on which cam it may be. As it could be their "D" type
Graeme

if its their D type then the performance and torque curve should be similar to the Sprint cam. You would need to check the seat to seat cam duration I think to positively confirm what you have.

cheers
Rohan