My stock 624 boat anchors are due for a valve job, but rather than sinking good money into bad heads, I am considering a swap to 062 or 906 Vortec castings--the hope being that I can net some small economy/performance improvements "while I'm at it." In my ideal world, each time I dive in for some significant wrenching, the car will wind up a little faster/more efficient than before.


Vortec heads can be drilled & tapped for the conventional 12-bolt intake, thereby allowing retention of the stock Crossfire TBI. The castings are reportedly thin in the necessary areas, but it's been done and documented, and I'm willing to assume the risks. The "Renegade" aftermarket intake manifold I'm using should have plenty of material to match up with the taller Vortec ports, so fitment is a non-issue.


My big concern for this project is the jump in compression ratio when changing from a 76cc to a 64cc chamber (9.0 to ~10.4:1), while still running iron heads. I'll need to use a .015-.024 head gasket to keep quench below .050, and I don't currently plan to replace my stock pistons/bottom end...so I would essentially be stuck with a high static CR.


However, I'm wondering whether I can add an improved cam that will retain a low enough dynamic compression ratio to use 87 octane pump gas, and still cooperate with the stock ECM. I figured a dynamic CR of ~6.27:1 with just the head swap, using stock 6* timing & cam specs. From what I've read, some consider 8.0:1 to be a "safe" DCR limit for pump gas, though I think that'd be w/93 octane. I'm fully aware this limit will vary considerably between engines, but I'm probing for any gains (primarily MPG & TQ) hiding in the wiggle room.


So, my question to performance gurus, cam experts (I also submitted this info to Comp Cams), and any with Vortec/Crossfire experience...are my goals at all reasonable? If I can't achieve this swap with 87 octane I'm not totally opposed to running 89/93...but I'd much rather cheap out The Vortec heads look to be a prime budget upgrade for a mild Gen 1 daily driver, and I'd really love to put their low-lift flow & chamber design to work...but, if it forces me to change out the pistons and/or ECM, or run 93 octane full-time, a basic stock/ported aluminum L98 head swap will probably bring better bang for my buck.


As a final note, I am definitely planning on a later upgrade to EBL, Megasquirt or the like, which would of course greatly expand cam options...but trying to teach myself to tune before addressing those leaky valves would be an exercise in futility

 

I don't have a crossfire but when I had my vortec heads I had no problems with 10:1 with 87 octane, a hotcam and .036 quench. The vortecs didn't want or need near as much timing. No problem with detonation but too much timing at low speed and light throttle would cause severe bucking. Took a lot of tuning to figure that out.

 

While not quite specific to my application (as you noted), I'll still consider that favorable testimony--cheers!

 

Why not swap over to a complete vortec 350? You'll can get a roller cam.

 

Would that I could, and just throw the xfire on top...but while my long block remains in good condition, a replacement just won't make it into the budget.

 

I used a Sealed Power CS179R which has the same specs as the old GM 151 350 horse 327 camshaft. It has a great idle with plenty of vacumn for my very ported stock crossfire manifold. Did this in 2013 and still running great! Good luck with your rebuild.

I had no problems with 87 octane fuel.

 

I bet you could have some material welded to the top of the intake flange and then port match it to the heads.

 

Thanks for the recommendation; noted!

Intake fitment is already covered in my first post, folks Pretty much just looking for input/testimony about dealing with the smaller Vortec chamber, and whether or not I can improve the cam, retain stock pistons/ECU, and maintain ping-free drivability on 87 octane.

 

Talk to Tom400cfi, He has hands on experience with using the CFI and vortec heads.

The late CFI-EFI (RIP), did this a few years back and I do remember Tom doing this with him.

 

I was going to post, but Jim's projects was slightly different; I had a wrecked truck at work (it "ghost rode" down the ski resort and crashed at the base!). "Vortec 350 engine was still good...Jim's engine was worn out. In our case, we pulled the engine from the truck, transplanted the ported CFI intake onto it, then installed that into Jim's car. Box-stock Vortec 350 (lame cam included), with a ported CFI intake. It made 220 RWHP, which isn't bad, considering the cam.

Still I can't answer the OP's question about compression with the '84 pistons and Vortec heads. I think one could make it work, but I haven't done it.

 

I went with edlebrock 70cc heads with my CFI, however it's still in the build stages...

 

Not too shabby for CFI on a truck cam Yeah, stubbornly clinging to my pistons puts me ~1pt higher static CR than a stock Vortec long block. While I'm still awaiting a response from Comp, I'm fairly confident the right cam grind will help offset that difference.

The big unknown is how the ECM will deal with these changes. VE improvements can be futzed in with fuel pressure. Really hope any spark advance mismatch will be minor enough to correct in base timing...or it'll be an exciting leap of faith to EBL!

 

I hear you.

It all depends on how much duration you end up going with to "kill compression" some...and also, what you're willing to accept, as acceptable.

Sounds like fun, no matter what.

 

What is a renegade aftermarket intake? Is it off a jeep? Will it work on a 1985 corvette to produce more horsepower for my engine?

 

http://garage.grumpysperformance.com...ss-fires.2796/

 

I worked out alot of the details in the above thread, including choosing 64cc heads or not...

 

No idea what you mean...if you have the answers I'm looking for, please elaborate?

 

Click on the link above for grumpys forum and enjoy the read!

 

Ah, thanks, will do!

 

My 85 runs TPI/Vortec noticeably better with 93.

I swear, I can tell what gas is in it my the sound it makes. If you do it, I would plan on running 93. YMMV.