I've got a 1988 350 iroc-z that needs valve stem seals and possibl valve guide work (Smokey on start up)
I've got a good deal available for a set aluminum heads off a 198i 350 corvette whats the difference in valve size, combustion chamber size and ports. Is it a simple straight swap and what advantage is there as opposed to rebuilding the origial cast heads

 

Not sure what year 198i is.

If it's 1981, they're 70s smogger heads, and are total crap. "Vette" doesn't somehow turn turds into gold. There IS NO advantage to those.

 

not the best typist in thde world that should have read 1988 corvette 350, so they're the same year as mine.

 

88 is a different matter.

They are roughly equivalent in terms of power output to what you have. However their intake bolts are at a different angle, and they don't have EGR passages, if that's an issue where you live. There's no particular advantage to them. If you still have the actual original castings your L98 came with, which are casting # 083, you'd do better to just have them freshened up... freshening costs the same in either case, but you don't have to buy the castings you already have. Have THOSE heads refreshed; DO NOT turn them in as cores for a set of off-the-shelf rebuilts.

 

and with the small 58cc combustion chamber volume on the L98s you have to really ensure you end up with the right compression ratio before bolting them on...

 

113s are aluminum, and as such, REQUIRE higher compression than otherwise equivalent iron heads to achieve the same results, by something in the range of ½ to a full point. Which in this case, they are interchangeable with 083 (64cc) in this particular regard: the compression will change from around 9.6 to around 10.3, right in line with the requirements of the situation. But the other incompatibilities remain.

 

I have used these heads since the late 80s early 90s on every L98 I had. The difference for me was I had the heads worked on such as 2.00 1.56 valves being installed, better valve springs, new head bolts from ARP and some had received port work along with an aftermarket cam. The 58cc chamber size helps increase compression and the aluminum helps dissipate heat better.
The only drawback is you will need to modify the angle of the bolt holes on the F body intake base or get the Y body base and the egr issue is easy to address...

 

the geometry of the combustion chamber also impacts the propensity for knocking at high CRs.

but also available octane is important here. in SoCal with 91 octane you will not get away with 10.3:1 compression on a Gen 1 small block even with aluminum heads (if you want decently aggressive spark timing). I was running 10.1:1 and attempting to run the LT4 Corvette spark map, but could not get rid of knocking (even tried a 160F thermostat). it wasn't until I lowered the compression to about 9.9 that I could get knock-free performance with that spark map. this was with AFR heads too which are light years better than L98s.

 

You are missing a key ingredient that allows the LR4 to run the timing it does on pump gas. Reverse cooling in itself allows the LT1 based engines to run at almost 1 point higher compression.

My 2011 M56S is direct injected and has a 12:1 compression ratio.

 

yeah when I say Gen 1, I'm not referring to the LT1/LT4.