ayousef

Hope to hear some recommendations here. I sold my ZR1, and bought another ZR1, this time its a ZR1 truck! Its a brand new Silverado 1500, with a 427 and a TVS2300 running 8PSI (for now) due to the stock transmission.

Didnt dyno the car, but the HPtuners horsepower (derived from torque figures) calculates to 700bhp (regardless of how accurate or inaccurate this is).

The car however has a dual 2.5 inch exhaust that bottles down into a single 3 inch pipe then splits into dual 2.5 inches to the back. To me it seems that the exhaust is too restrictive and would better find its place on a 4.8 or 5.3L engine and not a TVS 7.0

So the question is: Will I gain horsepower by switching to a true dual 3inch exhaust? A fellow tuner says I might gain 10hp max taking into consideration the fact that free-ing up the exhaust would reduce boost and in turn enable me to run say one additional degree of timing.

Sluggish

iTrader: (10)

That sounds very restrictive. I would put money on it gaining much more then 10hp.

ayousef

honestly a tvs on a 7.0 liter bottled to a single 3inch pipe it seems to me i would gain at least 20+ to the wheels.

what do you other fellow members think about this?

ayousef

to the top

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I think measure the backpressure and you will know if you stand to gain anything.

ayousef

Jim, cant argue with that but just thinking of it from a common sense point of view, wouldnt 2.5 bottled down to 3inch y-pipe be way to small for a big motor and big power?

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Only one way to find out.

I've seen 900+rwhp out of a single 3in downpipe. Is it restrictive? Maybe.

98Z28CobraKiller

iTrader: (17)

I would run 2" primaries to true dual 3", if it was me.

ayousef

Im doing just that. Ill start with the exhaust, and in a few months time ill get 2inch primaries!

98Z28CobraKiller

iTrader: (17)

Blower cars love exhaust. Unlike with a turbo setup, a good, free flowing exhaust can scavenge the cylinders far more effectively and allows for more power/response vs cam overlap.

old motorhead

iTrader: (10)

If you care how much power you're making, you need to invest in long tubes and a true dual 3" exhaust. Straight through mufflers would be a plus too. If you can't see through the mufflers, they're too restrictive.

As an example, I measured 4psi of back pressure on a 5.3L motor with MP112 Maggie that had a mild cam and 8psi of boost. The motor had LT headers, true 3" dual exhaust and dual Flowmaster mufflers. Switched to Magnaflow mufflers (you can see through them) which reduced the back pressure big time. Boost went down and power went up. Exhaust flow on that rig is small compared to a 427 like you have.

Your set up needs some serious exhaust improvements. 1 7/8 headers along with true 3" duals and straight thru mufflers will free up lots of power. Less boost equal less heat which will lead to more power.

What size blower drive pulley are you using now?

ayousef

Thanks for the response.

This is a 10.3:1 427 built by SLP, with a TVS and im not yet sure what size pulley is on the car, didnt check, but it makes 8psi the way it is right now. I dont want to increase the boost since the transmission is stock.

The car does need a little work, it needs coolers for starters, oil cooler and transmission cooler. I need to cover up the bed, lower it, say maybe anti-sway bars and a few things here and there.

The car has long-tubes but it looks from the outside like a 1 3/4 I have absolutely no idea why! Plus is has an SLP cat-back 2.5 to a single 3 inch y-pipe and splits into dual 2.5's to the back, also has cats.

I will take the cats off, fabricate a custom 3inch true dual, x pipe, and straight-through magnaflow muffler, and two bullet mufflers at the rear, im hoping sound doesnt go up much. Sounds like a much more efficient set-up