boosting a 305

[SMSC27]

i'm boosting my 305 and just want to hear some opinions. let me start with what i have:

- 305 bored .030 (jasper crate motor with hyp pistons and .010 under cut stock crank)
- mild crane cam
- stock heads
- edelbrock air gap
- 600 cfm edelbrock carb
- flowtech shortys

fully understanding that hyp pistons are no comparison to forged, i know i can't go crazy on boost/running lean. i know my fair share about turbos and what's what, as it won't be my first turbo smallblock build (first sbc in a while, though). my question is, being .030 over, how likely am i to run into overheating issues? i know .030 with a 305 is pretty much the max bore, in most people's minds, because of overheating tendencies with larger bores. i plan on replacing the thermostat with a 160*, running an electric fan and an oil cooler (my turbo is oil cooled). i plan to keep it on the rich side of things, to prevent detonation. i plan on starting with 5psi, before working my way up to 8, 10 or 12 (depends on my intake air temps and coolant temps)

as far as overall longevity, it doesn't have to last me years upon years. i'm in the middle of gathering everything to build a forged bottom end, 4 bolt 355 with aluminum heads.. possibly even injection, but i doubt it (i like blowthrough carb setups, gives me something to tinker with that doesn't involve a keyboard)

 

[tetomas]

I would be more concerned with the .010 cast crank than I would with the overbore. I have seen and assembled lots of overbored 305s for daily driver duty, most ran 195 theromostats, and had no overheat troubles. Mind you NONE of these were boosted. With reasonable boost levels i dont think there would be a problem with the cylinder overbore causing an overheat condition.

 

[SMSC27]

the rods are a weak point, as well, but i've seen some stock cast rods/cranks kick up over 15psi. would i ever go that high with cast parts, NO WAY.. even 12psi is looking for trouble, in my mind lol.. but that may be the number i reach, when it's time to put the 355 in, to kill the 305.. when the 355 goes in, i'll be starting at 10 after break-in and working my way up to 18-20. the reason i brought up overheating is, i've seen many posts on various sbc forums about 305's being bored more than .030 having cooling troubles, due to cylinder wall thickness. boost raises the cylinder temps (it's basically raising the compression ratio, with every psi). that's why it lead me to asking the question

 

[565bbchevy]

What if you added Methanol injection to help cooling that you could carry over to the 355.

 

[SMSC27]

i actually run a 70/30 mix of premium/methanol in my boosted toys. my only turbo coupe with the turbo 4 still under the hood absolutely LOVES an even 50/50 mix. i guess i should have mentioned that in my first post. the first time i mixed, i only did it as a way to clear out the injectors on my 2.3 and ran 70/30 meth to gas. ran like sh*t, until i added 5 gallons of premium. my compressor housing temps actually dropped about 30-40*, which i never really would have ever expected. head/block temp was down about 20*, which is great for an iron headed 2.3T with 20lbs being shoved down it's throat. i should see a slightly larger drop in head and compressor housing temps, when i finally put a B234F volvo head on it (aluminum DOHC head, designed by cosworth for volvo's 2.3 in the late 80's)

i ramble too much..