I have been pondering cams for the 305 in my Monte SS, and got to wondering about how advertised duration affects the performance of otherwise similar cams. The two cams I will compare are the Summit 1103 and Lunati VooDoo 256. I will just quick list the specs for both...

Summit 1103
214/224
288/298
.444/.468
112

Lunati VooDoo 256
213/219
256/2262
.454/.468
112

To get right to the point, how is the advertised duration going to make these cams behave different? Is the Lunati going to build more cylinder pressure due to the decreased duration? I have heard guys say good things about both cams, so how should a guy like me choose?

Help me understand this please.

 

The Summit cam is an old copy of a copied generic copied copy of a generic copy of a generic cam. Which is not to say that it's "no good", "you don't want it", etc.; only, that it doesn't represent anything anywhere near anything resembling "state of the art". It's a late 60s / early 70s design from the days when there basically weren't any valve springs available for a "hot street" type of motor, like there are today.

The Voodoo is a highly aggressive, modern design. Totally different beast.

The "advertised" duration is rated at somewhere around .006" of lift. It is, effectively, the "seat to seat" duration.

The .050" duration is a reasonable estimate of the useful flow duration. Very little flow occurs at lifts below that, and what does, is mostly detrimental... think of it as "leak" as opposed to "flow".

The ONE THING that long seat timing does, is to reduce the importance of valve springs. The Summit / Edelbrock / Melling / A-Motion / yadda yadda yadda cam is within the capabilities of new stock springs; the Voodoo, NO WAY it will work with that little spring. The valves will "float": which means actually, they will land on the seat so hard, that with a spring that has too little control over them, that they will bounce. And that is what breaks parts, makes a motor not turn up to the RPM it's supposed to, etc.

The long seat timing reduces low-end torque, reduces vacuum, reduces gas mileage, and otherwise compromises engine performance. The RPM range that the 2 cams will produce useful power in, is about the same, subject to the above; that being the main effect of the .050" duration, particularly on the intake. But for all-around daily driving type uses, the Lunati is VASTLY superior. Plus, the Lunati will work OK with a stock converter in a 305, whereas the other will have a very soft soggy bottom end snd no "leave" in the same motor with a stock converter.

Get the Voodoo and use the "premium" "upgrade" spring recommendation Lunati gives for it, whatever that is. Too little spring is MUCH MUCH worse than "too much", within reason.

 

Thank you, that is the kind of info I was after. I was/am planning on going the VooDoo, or similar, route. I am also doing some minor porting/polishing on the stock heads, and installing headers. It is going to be a "numbers matching" cruiser, but I thought some "enhancements" would be welcome also. I am not after any certain power numbers or timeslips.

 

check the 262 or 268 cam variations - 256 is really small, prob for towing/marine/RV..

Many other factors make a cam work, you have to factor in the rear gearing etc..

If you are interested in cruising / mileage consider a cam with a rpm range that matches your trans/gearing/tire size..

 

The Lunati is a perfect choice for your 305.

 

Lunati all the way.