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 TPI section.

Eric

 

Lower chamber volume will increase static compression, and increase power across the board somewhat. Smaller intake ports will have peak torque at lower RPM than larger ones.

1.5 is "factory rocker arm ratio"

Which rockers are thos?

To determine pushrod length, you have to assemble the engine and measure.

Either of those could meet your goals. I'd probably go with the smaller heads with your small cam.

As long as it's in the ballpark you're fine. Sticking with the recommended spring is probably the safest bet.

The valve will be spending very little time at peak lift, so the mid-lift flow is more important.

They don't correspond exactly.

 

It sounds like you've done your homework pretty good. I can't add much to what Apeiron posted, but I'll add this....

Watch your compression ratio! Many people have less compression than they think. A few have more than they think. Not sure what pistons you used in the motor, what their deck height is or what head gasket you're using but your current combo with 72cc heads is likely around or slightly less than 9:1, even if you used flattop pistons.

Example: 355 with flattops (6cc of valve reliefs), .025" piston deck height and a typical Fel Pro .039" rebuilder head gasket and those 72cc chambers gets you only up to 8.9:1 compression. If you're using stock dished pistons (12cc dish) you're down at a dismal 8.4:1 (all else held equal).

On a little 350 with flattops you're going to build compression a lot easier with ~64cc heads than with those "bathtub" 72s. If you're using stock dished pistons they're just about mandatory if you want to build any reasonable compression ratio.

Compression isn't all about peak horsepower, either. It's about low end and midrange torque. And that's going to count for a lot with a low-RPM combo like your current TPI setup. You've got a well matched combo- make sure you don't overlook this part of the package!

As for heads and how big you want your intake runners..... that's debatable. Certainly my experience is that runners in the 200cc range are OK (but just barely so) on a low-RPM 350. On a larger 383+ci motor they won't cost you a thing down low. On a 400+ cube motor they're the bare minimum, short of a tow-truck motor.

Don't be afraid of larger intake runners (at least up to ~200cc). They're not going to kill low end torque like changing to a bigger cam will. It's a lot more subtle than that. For instance, a set of AFR 180cc heads will kick your current SS head's rear end clear into next week everywhere in the RPM range, despite having 15cc larger intake ports.

 

Personally I would keep the heads you have and change over to a set of 2.02 /1.60 valves and have who ever does the valve job blend the bowls in with a radius cutter. Youll gain a little runner cc, and also gain some cfm. But you should not hurt the velocity in the port so you will keep your good low end torque.
By increasing you head flow over .500 lift you will need to go bigger in the ports but that is a waste of money since your cam is not over .500 lift. Also by running a bigger port you will hurt bottom end torque. This is just my opion but 30Lb injectors is to much

 

Aperion & Damon, thank you both for the constructive replies. Let me clarify a couple of points raised by you both.

Damon, my compression right now as estimated by Jasper is 9:1. I do think I want to go higher so I am looking at the 65cc chamber in the AFR Street Eliminator 180's. Pricey or not, after reading what they offer over most every other brand, I am definately going to reach for the brass ring here! (I will say, the TFS 175/56 look pretty good too, but questions raised by board members about their spring failures, lack of any CNCing or port work done during manufacture gives me pause.) I like the price but, from what I have read, I will get the best for my money with the AFRs. If someone wants to tell me otherwise, I'd be open to hear it. My pistons are flat top hyper-neurotic or whatever they're called. I feel this will give my combo the power down low I am looking for.

Aperion, the questions I raised about measuring pushrods was partly due to AFR's website has listed a bunch of parts that are suggested with their heads. They specifically list 5/16 & 5/16 +.100 pushrods that should go with these heads. I was thinking that somewhere out in space, there was a number I would have to find for the length. With only 2 choices, I feel a bit better about what I will be seeing and looking for. Also, the rockers I was mentioning were the ones I currently have on my Darts. They are 1.5 and I was asking if I could transfer those over to the new heads instead of buying something new; it seems most of the companies suggest you buy x-brand or whatever of rocker arm. These do not even have 10k miles on them yet so I was thinking I would reuse them.

Seems like the more I read, the more I have to replace. I will be ordering assembled heads, so other than gaskets, what else might I need to replace? Can I reuse the head bolts?

Thanks again to everyone who reads and replies.
Eric

 

The exact pushrod length will vary depending on your cam, rockers, heads, deck height, head gasket thickness, etc. The "nominal" length may work for you, but it's better to measure before ordering to be sure.

You should be able to reuse your rockers if you'd like. Head bolts can be reused as well.