4.1 question

[6SENSE]

Deck the block, yes or no? What head gaskets are you guys going with?
The deck height is same as 84/85 3.8 and not shorter from the factory like the later 109 blocks right?

Those of you using the 4.1 how did you set yours up as far as this and compression ratio goes?

Thanks

 

[Lee Thompson]

block

Leave block as is and use Felpro 1000 gaskets

 

[6SENSE]

Leave block as is and use Felpro 1000 gaskets

Thanks Lee. Any idea what range compression ratio would be? Should I be shooting for a particular #?

 

[Lee Thompson]

block

Gm steel shim gasket------.018 compressed
Gm 87 composite gasket---.060 compressed
Felpro 1000---------------.040 compressed
If block has not been decked and you use a 1000, some where just above 8-1
Don't try to over think it. That will work just fine. I ran that for some years.

 

[cool 84]

I run the Felpro 1000s also and they seem to be detonation proof. None of the water seepage problems some people warn about either.

I went .035 over making it a 4.00" bore and making pistons much cheaper.

I run 8.5-1 compression and it works for me. I'm only able to run ~13psi on pump gas even with an 18 degree chip not sure it it's the super crappy CA gas or extra compression. I'm sure there are a lot of factors but with the extra displacement and a little extra compression, I use a tight 3,000 stall with the 66 turbo and it spools very fast for it's size, about like the 49 did on my old 3.8. I will never run a 3.8 again in a street car.

 

[6SENSE]

Thanks all. I lucked up on a set of good used .020 over forged pistons awhile back so Ill be using those. The '84 Riv block I found [and have been sitting on for some time now] was in great shape. Just needed a good cleaning. Dont even need to turn the crank, so it will stay std/std
Compression ratio around 8.5:1 ~ sounds good. 8:1 like Lee said is probably the lowest Id want to go and 9:1 which is what a couple of the 86/87 guys recommended would be the highest. I have been dealing with a stock '84 3.8 (undecked) and '87 Gm gaskets for too long now. Car is wicked with lots of boost and WOT but just isnt as fun the rest of the time. Tough to tune. Im starting to believe the VERY low compression ratio is not helping too much. Gas mileage sucks and I wouldnt be surprised if its limiting my mph.
Just need to decide on what to do about heads and cam, [and if I really need to worry about center main caps or not]. Either port a set of 8445s or if I can luck up on a set of Champions used?? I should probably go with a nice big cam with this motor [bigger than the 204/214]. Lee, I remember you said something about a 224/224? I think that was right but not sure. Schraeder I think?

P.S. Not saying that Ive decided [yet] that Im going to add an IC but Ive got to admit that those pics of Hotsix's setup with the JS kit look pretty good. Pipes look a hundred times better than the old turbomotion or spearco.

 

[Lee Thompson]

cam

Schneider 208-224, with a set of good heads and a 3200 stall convertor.

 

[getchasum]

question for Cool84......

I went .035 over making it a 4.00" bore and making pistons much cheaper.

Got any specs or a little more detail on these? Were they an over the counter chevy piston?

 

[cool 84]

Got any specs or a little more detail on these? Were they an over the counter chevy piston?

They are an off the shelf Chevy/Ford blower slug machined for the Buick specs. I think I paid ~$550 for the new set of JEs with tool steel pins. They are 8.5 to 1 compression with a 3/16,3/16,1/16 ring pack for Total Seals.

To answer the question, they aren't off the shelf but I don't think it costs extra to make them as long as they start with an off the shelf forging.

 

[WH1]

Lee or anybody who can answer this: I've got an '84 3.8 block with single steel shim gaskets. What would the compression be on this with the taller deck but single gaskets? It runs great, I'm just curious if I did the right thing by running single steel shims. I know John Bruce told me he used to run them like this on his car.

 

[Lee Thompson]

Wh1

Your ? is a little confusing. An 84 block with a single steel shim gasket (.018) is as it would have come from the factory. The 86-87 blocks had a lower deck to make up for the thicker gasket (060).