elle88

On my L88 Replica I have the following heads
1965 3873858
1966 3904391

I was just thinking to replace them with these 3919842, to have a more correct L88 replica engine

http://cgi.ebay.com/ebaymotors/Chevr...spagenameZWDVW

how do they look? may I use on those Alu heads the valve springs, retainers and the other missing stuff taking them out from my iron heads?

help...I have to decide quickly

after the swap , I'll resell the iron heads.from a quick search on Ebay, they seems to be quite valuable

63mako

If the seats are not pounded out of them, no crack repairs, no stripped bolt holes they are good cores. Think there was a NOS set on the forum. Your parts should interchange but you will have to do a valve job, seals. set installed spring height, check spring pressures, may need guides. Lots of work and $$ to set these up properly.

63mako

http://forums.corvetteforum.com/c3-p...s-ls6-l88.html $$$$
These are open chamber heads the 842's are closed chamber. Both used on L88's

elle88

I need closed chamber heads...so a good amount of job is needed

I already bought these heads bolts because one of my iron head needs servicing

http://store.summitracing.com/partde...1&autoview=sku

are they OK just for iron heads and not for Alu heads? is so, where's the difference? the washers?

I'm there to open the engine due to a oil leak at cylinder 5 ( a valve guide or piston ring...I have to check tomorrow ).Since I'm opening the engine , I would take the chance for a head swap too ( Alu heads were already on my mind)

GDaina

do a search on aluminum heads there are a few listed...

elle88

I searched ebay for 3919842 or 3904392 Alu heads but nothing good or very-very expensive.
Should I give up or any forum member can help me?

p.s.

here is a video in my car in (not hard) acceleration...

http://www.youtube.com/watch?v=uqg7BpGyjBk

p.s.2 Gdaina, I'm sending you a PM

Solid LT1

We used to run a L-89 Nova (396 with aluminum heads VERY RARE!) and I remeber the time it was sputtering and backfiring after a pass and we found the valve guide had fallen out of the casting. There are MANY problems with the old Chevy castings and better heads are in the aftermarket like Dart, RHS, Brodix, Canfield, and even Edelbrock. If you have to have closed chamers, Edlebrock and Brodix are some of the only sources.

elle88

I know that with new heads I have less troubles, more hp...
but you know, I'm more on the vintage side
I quite lucky in this time because I have a really clever friend-pro mechanic. He can fix , tune everything and for cheap. I'm taking the risk of troubles with vintage stuff just because I have him on my side and he is happy to work on these things

gkull

If you want better fuel mileage you need to get away from old chamber designs. Modern heads have fast burn technology.

It appears that those old 842's on e-bay even have exhaust cross over ports. That is a very poor design.

63mako

A new set of Brodix Race Rite Rectangular port heads setup with proper springs for your cam and milled to 110 CC's will set you back about $2400. You can't buy the 842 cores for that and these will flow way better, increase fuel mileage and have better power numbers across the board. They are a much superior chamber design and much more durable option. These also have the exhaust ports and intake ports in the stock location so they are a bolt on upgrade. Your car is not a numbers matching car so why worry about "correct" heads. You drop a seat or guide on those 40 year old castings you will be building a new motor. Not only that they are very suseptable to cracking, thinner decks, inferior material and design. Leave those 842 heads for the NCRS guys.

elle88

Hmmmm.... you guys let me think...

yes , non numbers matching car , but i like the idea to make a good replica with vintage stuff.
But the reliability of vintage heads seems to be a serious matter.

does it make any difference if I put really few miles on the car ?and I carefully check-restore the heads before fitting them?
Or should I stay with my iron heads? ( stronger than ALU ? )and just fix the problem at cyl number 5 ( still don't know where's the problem : piston rings, valve guide...I have to open the engine)

I usually take the car out 1-2 days a week for short 30miles rides. But always "spirited driving". Impossible to go slow with that engine under the hood. Gas mileage is not a matter anymore

63mako

I am all about vintage parts myself but when I built my motor, Roller cam, AFR heads, Forged lightweight rotating assembly. 500 + HP small block. Would be lucky to get 400 HP out of vintage parts and it would be much less streetable. I do know where your coming from though. You said the key word (replica). Does it look "vintage".

elle88

I think I'll follow your advises and give up with the old Alu heads...

I have read some old posts in the forum about the old GM Alu castings, and I've heard bad words only! valve seats that come off , loose valve guides, cracks between the 2 valve seats, holes that cracks all of a sudden , spark plugs threads that goes... Terrific ! what else?
I had found a good pair of those heads at one of the forums members ( GDaina) and I really apologize for not going ahead with him in the thing...

Now , I'll probably stay with my iron heads. open the engine, check everything... should I pay great attention to iron head too?

is the Brodix Race Rite the only way to go if I want an aftermarket Alu head? i need closed chamber heads. Nothing good from GM ?

63mako

https://store.gmperformanceparts.com/store/SelectProd.do?prodId=7576&redir=true&man ufacturer=GM&category=Cylinder%20Heads&n ame=Bowtie%20Aluminum%20Cylinder%20Head% 20Assembly%20&model=<!--12363400-->
The only rectangular port aluminum head they list. Have to check and see if they are compatable with your pistons and the springs are compatable with your cam.
Spring specs here. http://www.karlperformanceparts.com/...?idproduct=737

elle88

63mako,

the GM solution seems pretty fine too me ( and prices fair).

but how to behave about combustion chambers ( closed-open)?
now I have ( specs given by the man who made my car ) : pistons that give 12.5:1 CR with 107cc heads, L88 cam

-to mill the GM heads to reduce the chamber size to 110cc or so? but what about valve to piston clearance?critical?
-to switch for new pistons suitable for open chamber operation?

to mill the heads looks to be the easiest way for me...

63mako

The big advantage to the GM heads is you can probably buy them at you GM dealer there. Closed chamber heads don't work with open chamber pistons but I believe open chamber heads will work with closed chamber pistons. Milling would be the best option, maybe mill less and go with a thinner gasket or just leave the additional CC, go with as thin of gasket as possible to drop compression slightly and be able to tune it to get maximum power and run on pump gas. What little power you lose with a slight compression drop will more than be made up with the more efficiant fast burn chamber design, better flow numbers and ability to run full timing advance on pump gas. Here is a spring spec comparison. The GM heads use the 12462970 springs The L88 used the 3916164 springs. The new springs have more seat pressure and a heavier rate (hydraulic roller springs). Might want to respring the heads. Might also be able to just reshim the spring to #116 seat pressure and it would also reduce the spring rate by unloading the coils some. Piston to valve clearance is critical and should be checked but is probably not an issue with your low lift cam. A lot of the built big blocks are running close to .800 lift with more compression than you have. Modeling clay works to check piston to head clearance and valve to piston clearance. .100 minimum


Chevrolet Big Block V8 Quick Valves Quick Reference Chart

Part Number Description Outside Diameter Pressure at Installed Hgt. Solid Hgt Pounds per inch Retainer Part Number Notes
3970627 Dual 1.487" 105" @ 1.88" 1.28" 450 3964264 Used with high-performance 396/427/454 production engines; LS-6
3916164 Dual w/damper 1.487" 116# @ 1.88" 1.10" 317 3879613 Used with heavy-duty 427/454 engines; L-88, ZL-1, LS-7.
3989354 Dual w/damper 1.538" 128# @ 1.90" 1.26" 330 3989353 Used with camshaft P/N 3994094.
14097002 1.487" 110# @ 1.88" - - 14096274 Used with 454 and 502 HO Engines.
12462970 Dual spring 1.514" 140# @ 1.940" 1.20" 368 12366990 Used with 502/502 engines.

elle88

Thanks!!!!

here another idea. let me know if it works in your opinion

https://store.gmperformanceparts.com/store/SelectProd.do?prodId=7574&redir=true&man ufacturer=GM&category=Cylinder%20Heads&n ame=Bowtie%20Oval%20Port%20Aluminum%20Cy linder%20Head%20Assembly%20&model=<!--12363392-->

the combustion chamber is already 110cc. so no milling needed
the intake ports are large oval . Could I machine them to match my vintage intake manifold?

if you compare the pics of the 2 heads ( "oval" and rectangular) really little difference. And I suppose the intake runners are pretty similar too ( 290cc versus 300cc)

63mako

Smaller valves, mismatched ports and same springs. Easier and cheaper to mill than reconfigure intake ports. The port design really extends all the way to the valve pocket. They probably have the same exact chamber design. The smaller valves would be a lot of work to increase to the 2.25. The bowl has to be opened up to unshroud the bigger valve. Your only talking 8CC bigger chamber. A thinner gasket drops that difference and would really help with tuning for pump gas. The true L88 runs on US 100 octane. All we have here is US 93 octane so you have a race fuel motor unless it is detuned. Detuning to run on 93 will cost way more power than dropping a few .0's on compression. My opinion is the 118 CC chamber is a win win with your motor. Don't know how thick your head gaskets are but if you reduce thickness .020 you lose 5 CC

TheSkunkWorks

FYI, you are aware this is an OT query in a 7+ year old thread, no?

TheSkunkWorks

There's a "New Thread" button at the top left of each forum thread list.