220cc head with a turbo

[a6t8vw]

Hi i wondering about useing a high flow sbc head on a less than ideal displacement block. i know if you want to run a 220cc head you really want to use a 383 or 400ci motor, for velocity reasons. but if you had a 305 or 350 and a turbocharger wouldnt the power gains be substantial? and doesnt the whole "port velocity" thing go out the window when useing a turbo?

 

I ask this question because i was going to buy a set of heads and plan on running a pair of turbos. For about the same price as 180cc i can get the more flow more power 220cc heads

 

what do you all think, thanks

 

http://www.cardomain.com/ride/2314369

[grumpyvette]

youll be almost correct in thinking that

"the whole "port velocity" thing go out the window when useing a turbo?"

as it becomes far less critical to the low rpm throttle responce and the larger ports help the upper rpm power curve, but youll need to match the cam timing, compression and turbo size/type to the application to take full advantage of the larger ports,higher flow rates and potentially higher lift cam youll use

 

but Id also point out that with the cost youll be looking at in a well built turbo engine build, your fooling yourself if you think the 305 with its smaller bore that shrouds those valves,and the weaker block will be a good investment, and the stock 305 block may not even allow you to have the necessary clearance for the 2.02 inch valves in the bore at full lift) or will save you money

 

youll be FAR better off useing a well designed aftermarket block with 4 bolt main caps and a thicker web on those main caps and thicker decks and cylinder walls....a stock 305 block is designed to handle about 350-400 hp MAXIMUM and with those heads and a correctly tunned turbo your obviously looking for more than that!

 

Id strongly suggest a minimum of a 383 displacement and ALL FORGED COMPONENTS in an AFTERMARKET 4" or 4.125" block with 4 bolt main caps, since youll need a NEW FORGED 4340 crank, ID suggest a 3.75-3.875" stroke, as the costs will be similar to the same basic crank in the 3.5" stroke version the 350 has (look closely at the MAX rated hp of even the 350 production block)

 

http://www.sallee-chevrolet.com/frame.html?/Engine_Blocks/gm.html

 

now look at a good block,(cylinder walls and decks are easily twice as thick)

 

http://www.dartheads.com/sbclittlem.aspx

 

http://www.dartheads.com/manager/uploads/tech%20-%20Little%20M%20Iron%20Small%20Block.pdf

[dr_hunt]

Good question, I asked the same before and I still can't find an answer, I'm fixing to find out though. I built a 355 inch sbc with full CNC AFR 227 heads complemented with a custom comp solid roller for my TT project. I think from what I've read the converter has alot to do with making big heads work in a turbo application. So, I opted for a 4000 stall custom converter from art carr.

 

We'll see how it works.

 

Interestingly enough, more power is extracted by bore size from a turbo engine rather than stroke since F=PxA. The larger the area of the piston, the more torque and HP you'll get out of a turbo engine. Grumpy's right, the 400 cubic inch or larger would be the biggest bang for the buck. I have thought of the 4.125 bore and a 3.25 stroke combination as being probably a good fit for the z.

 

Let us know how your plan comes together.