What lobe separation for quad webers?

[347]

I am doing my homework on solid roller cams to put into my 11.1 comp 347.

It has 48 ida's etc. 4.1 diff, tremec 3550,Its rarely street driven see's mainly track days.

Would 106 or 108 or 110 or 112 lobes be the best choice for webers? Or doesnt it matter?

Cheers Dave

[Jac Mac]

Is your 347 a 4" bore x 3.4" stroke with 5.4" rod or a 4.125 x 3.25 with 5.4 rod ? Also what rpm do you want to rev it to? cheers Jack.

[347]

4" bore x 3.4" stroke with 5.4" rod.......7000rpms

Cheers Dave

[Jac Mac]

Hi 347, I hope your Tremec has the .82 fifth gear. This will give an O/A top ratio of 3.36 to 1. With the 7000 limit you should be able to run around the 160 mph mark(with suitable tyre dia) without suffering in the acceleration dept. I would suggest around 108 deg lobecentres with up to 290 deg adv duration. Consider anti- reversion cones in your headers to help with low rpm response with the IDA's. Longer duration will require wider lobe centres. cheers Jack.

[347]

What do you think would be a suitable duration @050 and lift?

[Jac Mac]

Hi Dave, I have one client that runs a 347 on the street with a CC288R.(110deg L/C). This has 246deg@0.050 &.586" valve lift on 1.6 rockers. It is a 'baby' cam but is very stable long term lash&valvetrain wise. I would like to know a more complete spec of your engine & car weight before suggesting a specific grind. Some of the more radical profile's will require frequent maintainance &high quality valve train components to match etc. None of these are likely to pass a "smog" test!
cheers Jack.

[347]

Sorry to say its not a GT40. Its a 68 mustang , 99% of mustangs run 4 barrels and its hard to find people who run webers.


My old engine (347, 10.2comp, 238/248@.050 .540lift 108lobes solid flat tappet.Alloy windsor snr's, 650dp and rpm air gap.)it put down 252rwkw's @5800rpms.

Ok smog test is not an issue.

The heads have been ported (212 cc intake runners)

Intake cfm Exhaust cfm
67.2@0.100 57.8@0.100
139.4@0.200 117.2@0.200
197.9@0.300 151.9@0.300
243.4@0.400 185.6@0.400
275.1@0.500 193.7@0.500
298.1@0.600 203.2@0.600
309.2@0.700 209.2@0.700

Yella Terra platinum shaft mounted roller rockers (1.65's)

Valves yet to be decided(currently have manley's 2.02 &1.64)

Forged scat crank and h beams,srp forged pistons, one piece chromoly push rods ............

Did I leave anything important out?

I have been told my heads wouldnt be suitable for any more cam than I allready have?

Do I need to change them?

[Jac Mac]

Hi Dave, sorry should have got back to you but the hacker thing spooked me for awhile. Your heads have fairly big runners@212cc. What you have to watch out for with IDA's etc is that you dont over scavenge with overlap and that you maintain good intake flow velocity .As large as the 48IDA may seem you have to remember that it is smaller than the valve throat and cant borrow a bit more flow from the barrel next to it. With this in mind I suggest you keep the 0.050" duration around 260deg or less. Since 48mm dia= 2.84 sq" an easy way to check would be to measure the inlet port area of your cyl head. The ideal head/ intake runner will have a slightly decreasing area from carb to valve throat. There has been much discussion about this in the past if you want to search back on this Tech forum. I have some flow figures here but have mislaid them ,will compare and get back to you. Cheers Jack.