347 Build Ideas

[CobraToad]

Taking a bare '94 5.0 roller block and trying to get the most out of it.

Its about to be sent to the shop for a .030 bore and straight bore to fix any cam bearing housing discrepancies.

I have a complete SCAT forged 347 kit sitting around and am starting from there and working my way up.

I do plan to supercharge this platform and keep it EFI.

My main questions for the veterans:

70cc heads with a 10 pound pulley sound okay or not enough?
should I use a vortech centrifugal or go with a ken bell.

For use equally as a street and track car, which cam should I get.
Several mechanic friends say 410 lift or more, but being as this is only my second build ive done, first being a mild 302, im collecting as much data and research as possible before pulling anymore triggers.

HP Goal:500 minimum.

Thanks all in advance.

[olddog]

First decide if you want a centrifugal or positive displacement blower. The positive displacement will give you much more low end torque. Torque can be pretty much a straight level line over a wide rpm range. The centrifugal will give almost no boost at low RPM and it will steadily climb as RPMs increase, which gives a torque curve that looks like a mountain.

In my opinion, trying to run a centrifugal blower in an auto-cross, would suck. At every turn you would have a different amount of torque available. I depends a lot on what you intend to use if for.

Then choose a cam based on the blower and how you intend to use it. When you can get the power with more boost, you do not need to go so radical on the cam. Since you are going to stay with EFI, keep in mind that a lot of overlap on the cam will let un-burned fuel/air into the exhaust and cause the O2 sensor to falsely see a lean condition.

You may need to keep the compression lower to allow the boost you need to make the power you want. I know higher boosted engines typically keep the compression down around 8:1, with an after cooler.

I did see quite a few blower and turbo cars at the London car show this year. More than I have seen in the past. Maybe some can chime in.

Hope that helps and good luck.

[Wbulk]

To be honest I think this is a mistake. Just for starters that block will not handle that that much HP. Seriously, if you have only built one other engine you are over your head.

[blykins]

A 347 with good heads will tax the strength of a factory block by itself. Add in forced induction and you have the recipe for a block split in half. Literally.

If you're serious in starting a project like this, I would get the advice of an engine builder, not a mechanic. Nobody runs .400" lift cams anymore. Modern camshafts are usually anywhere from .500-.600 lift on milder applications, then go up from there.

Do some research, and ask a ton of questions...

If it were me, I'd ditch the blower, and build a 450-460 hp 347 and call it a day. That's more than enough for a Cobra....one of my customers runs one of my 347's in a 7.50 1/8th mile class Fox Mustang and 500 hp in it will get him into the 6's (10's in the 1/4).

[Rick Parker]

CobraToad

Listen to what has been said, or you end up with a light weight 2 piece block.

[olddog]

I do not know exactly where the limits are on the factory blocks. Not sure if it is RPM and balance or torque that kills them. Perhaps it is how hard you drop the clutch.

There are aftermarket blocks, both cast iron and aluminum. They are advertised to take more power. I do not know exactly what they can take. If I was spending the money on one of these blocks, I would get the 4.125 bore block.