BOSS 357

iTrader: (1)

While I wait for my replacement fuel injector to arrive, I've begun to research an upgrade for my measly 165 cylinder heads. I've spent hours upon hours looking over the info on the boards, but I still need some clarification.

The car is a weekend warrior, TPI 355cid sbc. It may or may not ever see a strip, but will definately see a dyno. My goal is stop light to stop light low end/mid range torque. The intake is an open element, 52mm TB, ported plenum, AS&M runners, and ported Accel manifold w/ 30lb injectors.

The current heads are Dart Iron Eagle SS 165's: http://store.summitracing.com/partde...5&autoview=sku
72cc combustion chamber, 165cc intake, 1.94 & 1.50 valves
intake flow is rated at 210cfm @ .500 lift
not sure which springs are in it (.520 max lift is minumum on 1.25 spring)
stock length pushrods
1.5 rocker ratio

The current (and future) cam is a Comp Cams 08-302-2: http://store.summitracing.com/partde...8&autoview=sku
210/210 @ .050
264/74 duration
max lift .480 in/out
112 LSA
I want to stay with the cam I have.

Using the (bore x bore x stroke x peak RPM x .00353)/614 calculation, I get 1.80 as the "minimum crosssection of head to maintain optimum power w/o hurting velocity. But I don't really know how to apply the end result...

My questions are more about specs than "My AFR is better than your TFS". I'll decide on which brand after I have all the data I need to make the decision. My questions are these:
1) will lower comb chamb cc or intake cc yield more torque in my power band?
2) will my 1.5 rockers affect the max lift of my cam? (the .480 listed in the cam spec is noted with "factory rocker arm ratio")
3) shouldn't I be able to use these rockers in my new heads?
4) I read that I may well need new pushrods, where would I look to determine the new size? head spec sheet?
5) which will yield the better result: a 195 & 64ish or 175 (or 180) & 54ish combo? which spec is more important to my goal?
6) as far as the valve spring set up, with TFS I have a choice of springs, do I need to match that to my cam exactly or should i get a bigger spring just to be safe?
7) when looking at head flow data, my max lift is .480, do I want the best flow there or somewhere else in the lift?
8) also for flow..is it better to have the peak flow number of the head be the same as, more or less than my intake flow? (which I also read to be around 240-260 cfm)

Thank to all who read and reply. This is also posted in the General Engine section.

Eric

formula_novice

iTrader: (1)

Eric,
Most lift specs are measured using 1.5 ratio rockers. So if you increase the rocker ratio, you will get more valve lift which makes the cam "act" bigger than it is. For example if you currently have 1.5 ratio rockers and your cam lift is .480, you would do some quick math to see what your lift would be with 1.52 rockers...

.480 / 1.5 = 0.32

0.32 * 1.52 = 0.4864

So your valve lift would go from .480 to .487 with 1.52 ratio rockers. The same formula applies if you go with 1.6 ratio rockers, etc.

Hope this helps!

formula_novice

iTrader: (1)

On most SBC heads, 1.5 ratio rockers are standard so you should be able to use them on different heads. However, I would recommend upgrading to some form of roller rockers. I went with Comp Cams 1.52 Magnum roller-tip rockers in my setup. In general, roller rockers are better cause they reduce friction which frees up a little HP and helps extend the lift of your valve-train.

Hope this helps.