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Old 03-26-2013, 08:38 AM
dually502 dually502 is offline
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Opinions needed on BBC swap vs upgrades for 350

I had been busy building a roller block .030 454.. Everything has been machined for the bigblock. After much testing the flow of my Bowtie heads, the pressure drop from the intake manifold runner to the head runner kills power production from 2400 to 3900 rpm. Its almost equal at 80hp and tq drop and then it starts to climb right back up once above 3800rpm.. Needless to say heads are just too big..

How we got the numbers was, having the heads flowed on a bench and using 3 desktop dyno simulators with head flow data and engine specs.. Each simulator shows pretty much the same thing except the Dyno 2000 inflates the tq number by 5 to 10% over the other two programs. So i need a smaller runner intake on the heads. My plans are aluminum heads , also means I need another set of pistons with a dome to compensate for 118cc chamber of most other aftermarket bbc heads.

This motor was going to go into My ext cab 1994 Chevy truck. I have everything for the BBC swap as far as accessory brackets and what not. Currently truck is Stock TBI 350 engine(roller block) and healthy built 4l60e trans, 14 bolt semi floater 3.73 gears.Truck has some issues with fuel pump and the throttle body. I think the TBI unit is worn out and I gotta upgrade the fuel pump either way. Was going to go mild BBC to have that TQ to get this thing moving. Its my daily commuter. About 10 to 15 miles a day is all its driven.

After a few discussions with my friend while doing a head and cam swap on his race car, he was asking me why not just head and cam swap my stock TBI 350 engine with 167k miles? I am not sure its even got that many miles on it. Block is nice and clean black paint but the heads have no paint on them. Looks like the heads have been atleast gone through already and the driver side head has leaking valve seals on #3 cylinder. Not much if any smoke comes out and compression test shows me the rings are still good.

I looked into the idea of good set of Aluminum heads and a computer friendly roller cam with new intake for the 350. All the dyno numbers completely surprised me on the parts upgrades . 416 HP at 5500rpm and 444 tq at 3800rpm with a nice almost flat tq curve from 2500 up. That took me a while trying all different types of hydraulic roller cams before I found one that has about what I am looking for. Its the XFI252 comp cam.. No stall needed and computer friendly.. I really wanted a cam to make some noise, but my main goal is good strong tq production. Most other roller cams kill the power figures under 3500 rpm..

I have a megasquirtII controler and harness, plus most of the stuff needed to go mpfi. This was my plan for the big block, seeing as how its way more cash to make the TBI system capable of supporting this kinda power for either engine... I can use the MSII on either engine.

Now let me ask u guys, would anyone here be comfortable with putting aluminum heads, roller cam and intake on a motor that might have 167K miles? I have done it on motors with less then 100k miles. I Wont know mileage for sure till I pull the heads. For less then $1400 I can do the upgrades on the 350. Where as I am still looking at another $2500 to finish the big block.

Sorry its long post, just wanted to lay it all out there..
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