Weber and cam question

[Dean Lampe]

I know a lot of you run the webers on your car. Maybe you can help. I have a Weber cam question. How big of a cam can I run? I understand that my overlap needs to be kept to a minimum and the duration can't get to big but can someone fill in a little more detail?

I am thinking about 114 lobe center angle, 108 intake center line, dur @ .050 242, lift 636.

I am running a 380 ci aluminum 302 w/ an 8.7 deck hieght, custom weber setup and Yates heads with titanium valve train to mention just the basics.

The desktop dyno seems like that cam but who knows!

 

[Jac Mac]

Need more info Dean,
Rod length,Bore or stroke,Type of Cam(FT,Hyd or Solid,Roller?), Intended use,Rev Range you intend to operate in.
Jac Mac

 

[Dean Lampe]

Sure, here is some more info.

Rod length 5.7in
Bore 4.125
Stroke 3.55
Cam solid Roller
Compression 11 to 1
I have enough gear to shift before 6500rpm. I think on the track I should be happy in the 4000 to 6500 range.

I have the stock 37mm chokes and the 42mm chokes. We plan on testing them on the dyno when the engine is done. I just don't want to give up all my bottom end.

 

[David Briggs]

Too much cam for the RPM range and available choke size, valve spings won't live too long with that lift. Is this primarily a street car?
IMHO

 

[Dean Lampe]

It will spend 90% of the time on the track but I want to be legal (barely)! What advice would you have for me?

 

[David Briggs]

I am running a Crower Hydraulic roller #15514 on my 347, it is primarily a street car but this cam is perfect in the RPM range you are talking about.
Specs; @.50 234 intake, lift .533; 240 exhaust lift .544. 110 lobe separation, using 1.6 Comp Cams steel roller rockers.
I am not sure that I needed a split duration cam w/AFR heads but old habits die hard.
Your engine is bigger and can take more cam and your heads probably flow quite a bit more so I would think you could get away with more duration but I would keep the lift down so that the valve springs will live.
I don't think that 42mm chokes will allow you max your combo out.
But I will defer to Jacmac who I think has more actual track experience.
Dave

 

[Dean Lampe]

Thanks for the input. I would love to hear from Jac Mac.

 

[Jac Mac]

Deane, you have had me scratching on this one a bit due to your parts combo. Most of the cams I have used in combos like this have around 0.700 valve lift( largely due to the rocker ratio) . At your 6500 rev limit you could use a similar hydraulic roller to David, but that would be about as high as you could spin it with regard to floating the lifters( most roller hydraulics have a top rpm limit of 6500 recomendation when you check thru the vendors catalogs).
If you go with a solid roller one cam that I have used for road cars is a Comp Cams 288R. It is an older profile but will suit your combo which if you will pardon the expression is a bit old school with the 1.606/1 rod ratio & hi-tech with regard to cylinder heads etc.

The 288R specs out as follows;Duration 288adv/[email protected]", Valve lift is 0.586"@ 1.6rr or 0.633"@ 1.73rr. It is a single pattern cam on 110deg lobe centers. This gives 68deg overlap.If anything this cam may be a bit on the small side for your purpose, but I know its fairly trouble free as the owner keeps telling me that he has not had the rocker covers off since I built it and thats a few years ago! A couple of 9" diffs & twin plate clutch's have hit the trash bin though.

One more thought , Bernard/Nanard was running a similar setup on 48IDF in his Daytona, he was using up to 8000rpm @ 347 ci which is a larger air requirement than you will have at 380ci/6500rpm. If he cares to divulge his cam profile it may be of help to you.

Jac Mac

 

[Dean Lampe]

Thanks, Jac Mac. That does help a lot. I have 2 more questions. What if I went to 114 on the lobe seperation? I thought that might lower the overlap. And second, How much lift would you recomend? The only reason I was stopping at 6500 rpms was the lack of airflow through the carbs. Thanks again for your help.

Dean

 

[David Briggs]

I agree with Jacmac, you have the heads for higher RPM horsepower but you choice of carbs and RPM range don't max out that combination. The joy of webers is excellent torque and throttle response off the corners I don't think that you will be getting that with the wrong cam.
Dave

 

[Jac Mac]

Thanks, Jac Mac. That does help a lot. I have 2 more questions. What if I went to 114 on the lobe seperation? I thought that might lower the overlap. And second, How much lift would you recomend? The only reason I was stopping at 6500 rpms was the lack of airflow through the carbs. Thanks again for your help.

Dean

Dean, If you have crossover exhausts on this car remember you will have more efficient scavenging which is a good reason to try and keep the overlap down, however if you keep the duration at 295deg or less you should be able to run 110 deg lobe centers and install the cam with inlet at 108deg.( On your 380ci combo straight up @110deg should be possible,might kill off a bit of low end torque to help your transaxle reliability wise).

Valve Lift; Comes down to to the components in your valve train & how often you want to check lash and inspect(very closely)every,coil,retainer,lock,rocker,pushrod etc for any sign of failure or wear.Bear in mind that when your cruising around on the street at low rpm that all those valve train components will still have huge spring pressures imposed on them but with marginal lubrication etc. Look into a flooded or spray bar setup if you dont have one already. I dont think you will find many cams for this setup that have less than 0.650"/675" lift @ the valve.

Jac Mac

Sorry meant to add that you will need every bit of the 42mm in the IDA with your 380ci.