Here's the scoop.
A friend is putting together a 350 from a pile of spare parts. The plan for the car, which is a 1st gen Firebird with a manual trans, is to be a cruiser. No drag racing intentions. No autocross. Maximum engine speed will be less than 6000 rpm. Probably want to keep it around 5500-5700.
The heads are from GM's original ZZZ crate engine (aluminum L98) from about 20 years ago. They've been worked over porting wise (by professionals) with bowl work, 2.02/1.60 valves and gasket matched to a FelPro 1205 (very few miles on the heads despite their age). Stock springs and retainers with 1.5 ratio rockers.
Compression will be about 10:1 with the (now) 57 cc head and what we estimate to be a 12cc dished piston. Guessing (for now) at the OEM piston below deck at .025" and a .026" head gasket. The short block is not the ZZZ short. (This engine is still assembled as it was delivered from the machine with the (junk) heads still on it. We haven't gotten into yet to confirm our calculations).
A 625 cfm Carter carb on top of a dual plane intake (possibly a Performer but I'm not certain) is on the top side and 1 5/8 headers with dual exhaust at the other end.
Those are the details, now for the cam.
There seems to be a lot written about maximum valve lift. .480" is thrown around quite a bit. Springs are GM P/N 1013458. 110 on the seat, 356 spring rate, 1.273 diameter. Coil bind is 1.16. They ran a .510 cam on the ZZ3 with these springs.
I've searched the forums here (lots of postings when I search L98 heads and cam) and I have an idea of what to spec for a cam however I'm interested in hearing other peoples experiences in building a engine of a more pedestrian nature.
Any input is appreciated.

 

Sure they arent 2.00 valves?
Anyway-
Without knowing how the heads are moving air its real hard to suggest what may be "right"; Spending on a good spring from there is everything.

 

You are correct. 2.00” intake valves.
The heads were ported at one of the leading shops around here at a time when the aftermarket wasn't quite as bountiful as it is today. They were worked over and to quote the owner of the heads, " The heads are heavily ported: a 1205 gasket, pockets worked over, 2.00 intake and 1.60 exhaust with 1 piece stainless valves. I had them work the heads to the most that could be done with them so I would estimate at least a 10% improvement in flow unless you happen to find some real results on the web that can corroborate actual numbers. "
I dug up an old story from one of the magazines (don't shoot the messenger please) and have included flow values as determined by them at various stages of porting. I'll use these numbers in some simulation software to see what trends might develop.
As for the springs, depending on the cam (which we would like to be kept on the smaller side because of the vehicle's intended use) the springs may or may not be adequate. I agree with you on the spring thing. I've taken deliberate steps with my own personal builds to ensure that the spring (and accompanying hardware) is never an issue.

 

Tpis zz9 cam sounds like it would work well. Your rpm range is going to have a cam with lower duration, 212-218 range. Those heads like alot of timing too.

 

Gonna guess hes in the 240-250cfm/180-190 cfm @600range somewhere with those heads and valves assuming a decent job was done.

 

I meant to add this in my previous post. I would suspect that the published flow numbers are similar to the heads being used in the build in question.
Having said that, even in ported form, they lag behind a stock Vortec head in terms of intake flow. The exhaust looks a little better though.
Considering the nature of this build, which isn't directed towards outright power numbers but rather low engine speed torque production, it may not matter too much if the flow numbers are off a little. I like the smaller runner volume as I feel it'll help in the low speed department.
I'll look into the TPiS ZZ9 cam. 221/226, .483"/.520", 112 LSA. Interesting. I'll certainly have to check clearences on the exhaust side.

 

The motor I have in my Camaro is a 1990 L98 with ported heads, stock cc carb, and a Lingenfelter 219/219 roller cam - makes about 400 engine hp at 5600 based on the trap speeds. The heads were flowed at 255cfm at both .550 and .600 lift. Car idles so close to stock most people can't hear the cam and it is extremely streetable and gets low 20's on the highway.

Cam wise, I would say a split pattern 215/225 or something like that would work well. With street cars, I think split patterns are a good compromise for power and efficiency as you don't necessarily need as much intake duration with the larger exhaust duration. This is the route I would go if I were to attempt the same thing again.

 

From what i have seen and heard, 260 cfm out of a 2" valve is about all you can get but thats enough for 11 sec slips if all else matches up well.

Any of those cams in the mid 2-teens duration to 220 deg should be awesome for a mild driver. Alot of guys like the zz4 cam. Its a cam designed to pull to 5500, but its a hyd roller, but fits stock l98 heads well. With port job you likely dont need the huge exhaust split, typical 6-8 deg dual pattern would work.

 

Seems a tad optimistic however seeing as these heads came out of one of the premier shops (here in Ontario) those numbers may not be far off the mark. My concern is that the porting may have adversly affected the intake velocity however with the L98s stock port volume of around 163cc (from what I've read) then even a full porting job would leave behind a runner volume that's small by todays standards.
What intrigues me though is the relationship between intake and exhaust which looks pretty good percentage-wise.
As has been suggested maybe a single pattern cam would work well.
I'm also considering the idea of a wider than ususal LSA to help broaden the torque curve. Whereas in my performance build (another 350), I had flirted with 108 LSA but was scared off by the increased overlap (all else being equal) and the resulting dent in mpg that it usually brings, I settled on the typical 110. Maybe a 112 for this one would yield the kind of results we're looking for. Low speed torque and some fuel economy.

 

Those published #s....so hard to say thats what yours are or arent doing as porting isnt universal depending on how they come out

So what youre guys heads did who really knows.

Anyway going conservative on your cam as you said is probably the right thing to do.

70-75% imo is plenty personally prefer a little more on exh but its really not a big deal imo till you get into higher power ranges.

 

I know my neighbor and his 85 monte carlo ss with zz4 engine has no complaints. He loves that motor and it drives well. Carbed zz4 cam setup, thats a 112 lsa and only 208 deg duration. He drives it to shows all over on sunny days. No hiccups past few years. Stock L98 heads, about a 330-340 hp deal. Most crate zz4's are in that 340 hp range, slightly below advertised.

Better head flow numbers and another 10 deg duration and i can see an easy 375 hp and maybe closer to 400.

 

I have the flow sheet from the TPIS hand ported heads that are sitting on my shelf:

Stock intake 199cfm at .600"; Stock exhaust 173cfm at .600" - average 84.3%

Ported intake 249cfm at .600"; ported exhaust 196cfm at .600" - average 76.5%

The Lingenfelter ported CNC heads were the ones that flowed 255cfm - but I dont have the sheet handy.

But since you lose about 8% intake to exhaust flow with the ported heads, ending up about 76.5%, nothing wrong with some more exhaust duration. You don't need it for unported heads honestly.

 

I've put some numbers together and I'm somewhat surprised at what I'm finding from a computer simulation point of view.
I've used the ported L98 flow values from an on-line source. They're not as good as the Lingenfelter or TPiS heads that Paul has mentioned but having the full flow chart makes my data entry simpler.
In the absence of any real measurements of the short block being used, I'm assuming that a 10:1 scr will be achieved with the 57cc heads, 12 cc dished piston, 025" piston below deck and a .026" gasket.
I've attached three documents that include a dyno graph as well as the DCR calculation for each.
In each case the baseline was a Comp Cam (I'd like to get advertised values for the TPiS ZZ9 though). XR270HR w/ 110 and 112 lsa as well as a XR276HR w/ 112 LSA. The latter I've included as it's in my pile of parts I'm trying to use up for this build.

 

If for whatever reason somebody wants to check out the files and can't open them, I may be able to repost them in a different format.

 

Any reasons for the surprise? Bigger cam does what i expected, made abit more power abit higher up in the curve

 

I suppose the surprise comes in that I believe the smaller cams would basically be unusable. Maybe with 110 octane fuel be definitely not with pump gas. At least not in my experience.
The early intake closing of the 270 especially with the 110 LSA pushes the DCR beyond what I consider to be truly streetable let alone something that's going to be dropped in a pleasure cruiser (read that as in put in gas and go).
My experience with high cranking pressures (as in what results with high dcr) is that beyond about 10.25:1 scr and 8.25:1 dcr (which are the specs for my current engine albeit with iron heads) leave me with few options other than to run 94 octane. It'll run on 91 with no evidence of detonation but it tends to diesel ever so slightly when the ignition is turned off. This thing runs cools as a cucumber too. I'm at the edge in that regard.
This is my thinking anyway. I'd be curious to hear what other experiences are with short cams and high compression.