I am looking to get a CR of about 8.0 - 8.5 I want to build a forged 305 block for a turbo set up, the thing is, i don't have the means to build it in one go. I would like to build the block and put the original 305 heads on and when i get the rest of the parts and time i will install the turbo. Plus in the mean time i can run nitrous Will a set of 350 heads give me the CR i am looking for?

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• 89 Formula 305 WS6
  SFC's, LCA's, Air Foil
  Spohn Panhard Bar
  Flowmaster Cat Back, Tranny Cooler
  A/F Ratio Meter (not a mod but it sure spurs interest)
  Trans Temp Gauge
  Most "Free" Mods
  3:73, Zexel Torsion Posi
• 90 Eagle Talon 2.0
  (Winter Beater)
  Mods? Um, no

 

Omega- Check your email. I just sent you a compression ratio spreadhseet set up already with stock 305 specs.

 

Installing 350 heads WILL lower your compression due to the large volume (64 vs 58).

But, from what I understand, going to a larger volume head is not the best method, especially on a "boost" application. Dished pistons with a smaller head is better than flat-tops with a larger head. The smaller head/dished piston combo gives better "swirl and tumble".

 

And don't try putting larger valves in the 350 heads on a 305 block. The won't clear the cylinder walls.

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87 IROC-Z SuperPro ET Bracket Race Car
461 naturally aspirated Big Block

Best ET on a time slip: 11.242 altitude corrected to 10.89
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Best 60 foot: 1.546

Racing at 3500 feet elevation but most race days it's over 5000 feet density altitude!
Member of the Calgary Drag Racing Association

87 IROC bracket car, 91 454SS daily driver, 95 Homebuilt Harley

 

I am torn here. My little 305 has leakey valve stems. Since i will be taking the heade off (i know i don't have to) the block isn't much more work to rip out. I figure why not just build a forged stock CR 350 and all i have to do is change the ECM, knock sensor and then injectors. Then i would have a 350 that can withstand a few #'s of boost.

 

The only ecm that adequately handles Boost applications is the 749 ecm from a Syclone/Typhoon. Go to www.syty.org to read up on the 749 ecm.

All the rest (SD or MAF) need to either have the prom "cludged" and it is really a "hit or miss" deal or run a FMU type system.

 

I know a little something about this. Run the 350 heads with the low CR. Put the big valves in and tell the machine shop that you're doing this and they'll cut the block so they fit. Run a mech dist with little advance to avoid detonation. Make sure the valve springs can handle some serious RPM. Then you'll have one high flyin' but kickin' 5.0L

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'87 Bird 350 .060 over 700R4 + Lots more

 

Cut the block?.. OK, got it. Will i need some sort of wacky head gasket if they do that? or is there more clearance between the bore and the gasket than i am imagining?