t88 and 408 suggestions
t88 and 408 suggestions I am limited to a t4 size turbo on my car and got a good deal on a 408. I know that as I turn up the wick backpressure will rise. Should I stay with a semi stock cam and heads to keep the comsumption on the motor low? Or should I stay with a decent set of heads and cam and just find my stopping point with backpressure? TIA
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Why don't you just put a restriction orifice behind the throttle body? That would have the same effect as restricting the cam and heads. . .
The poor backpressure/boost ratios offered by T-4 turbo's on large displacement engines is the nature of the size of the cylinder. Good heads and cam will only increase power at the lower boost levels and break even when you max out the turbo at 25+ psi.
The poor backpressure/boost ratios offered by T-4 turbo's on large displacement engines is the nature of the size of the cylinder. Good heads and cam will only increase power at the lower boost levels and break even when you max out the turbo at 25+ psi.
It will have a very free flowing exhaust only a foot or so of open 4 inch downpipe. As far as my comment about good heads and cam, I was reading over a post where people said making the motor more efficient would cause higher backpressure. Where as if you had a 408 that didnt move as much air it would help some, and just run more boost to get the power where you need it.
This is the post I was refering to by JOSE:
Addressing bacpressure starts on the exhaust side. Making the engine breathe even better will make it worse actually. The further the PR gets away from 1:1 the worse it will get and the more hp you will lose.
Addressing bacpressure starts on the exhaust side. Making the engine breathe even better will make it worse actually. The further the PR gets away from 1:1 the worse it will get and the more hp you will lose.
That is true, the futher the pressure ratio gets from it efficient state the hotter the discharge air from the turbo will get. Now of course I'm sure he is talking a max effort setup here. If you ask him about pump gas he will change the answer. For pump gas setups he will tell you larger cubes, cause you can get to 700rwhp easier with a 408 @ 12psi, then a 346 at 16psi with 93.
Originally Posted by DrTurbo
That is true, the futher the pressure ratio gets from it efficient state the hotter the discharge air from the turbo will get. Now of course I'm sure he is talking a max effort setup here. If you ask him about pump gas he will change the answer. For pump gas setups he will tell you larger cubes, cause you can get to 700rwhp easier with a 408 @ 12psi, then a 346 at 16psi with 93.
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i have a t4 flanged t88 with a 3 1/2 dp to a 3" exhaust...havent had any problems even when 820rwhp on pump. Its a 408 as well with victor intake setup/afr heads/ very small cam
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Originally Posted by PurEvl
i have a t4 flanged t88 with a 3 1/2 dp to a 3" exhaust...havent had any problems even when 820rwhp on pump. Its a 408 as well with victor intake setup/afr heads/ very small cam
Originally Posted by black98ws6ta
Has the boost ever been over 15 lbs? Do you have a backpressure reading at 15 psi? What afr heads?
Havent had any signs of heat or back pressure related issues so never tested it. (yet)
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Originally Posted by black98ws6ta
This is the post I was refering to by JOSE:
Addressing bacpressure starts on the exhaust side. Making the engine breathe even better will make it worse actually. The further the PR gets away from 1:1 the worse it will get and the more hp you will lose.
Addressing bacpressure starts on the exhaust side. Making the engine breathe even better will make it worse actually. The further the PR gets away from 1:1 the worse it will get and the more hp you will lose.
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Originally Posted by black98ws6ta
It will have a very free flowing exhaust only a foot or so of open 4 inch downpipe.
Originally Posted by engineermike
I hate to disagree with Jose because he's helped me out a bunch and is very knowledgable. However. . . the backpressure/boost ratio is little decieving here. Boost pressure is measured in the intake manifold plenum. When you make the cam, heads, and intake flow better, you are doing a better job of transporting the air from the plenum into the cylinder. Since more air is exiting the plenum and entering the cylinder, the pressure in the plenum is lower. This makes the backpressure/boost ratio look worse (on paper at least), when you're actually getting more intake pressure in the cylinder and that's where it counts.
The more power you make with your engine, and the more air it flows, the lower the boost you will see at a given hp level. So a built 408ci could hit 800rwhp at a much lower boost level than a 348ci with the same heads and cam... maybe 15psi vs 21, who knows.
I've been told repeatedly to keep the backpressure at 1.25:1 and lower.
I've been told repeatedly to keep the backpressure at 1.25:1 and lower.
Originally Posted by Pro Stock John
The more power you make with your engine, and the more air it flows, the lower the boost you will see at a given hp level. So a built 408ci could hit 800rwhp at a much lower boost level than a 348ci with the same heads and cam... maybe 15psi vs 21, who knows.
I've been told repeatedly to keep the backpressure at 1.25:1 and lower.
I've been told repeatedly to keep the backpressure at 1.25:1 and lower.
Jose
So my 408.....should I stick to a smaller cam and unported heads to keep the motor flow down, that way it seems as if it is a smaller motor. I will have very free flowing exhaust about 2 ft of 4 inch downpipe, I would love to make 1000rwhp without backpressure issues.
Originally Posted by Pro Stock John
Almost seems like the opposite would be true right? If you run a bigger cam you will make less boost, and thus run into less backpressure issues.
the better you make an intake flow= more exhaust gas getting backed up at the manifold before the turbo
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Originally Posted by Bill @ Hi-Flo Turbo
less pressure on the intake side.
the better you make an intake flow= more exhaust gas getting backed up at the manifold before the turbo
the better you make an intake flow= more exhaust gas getting backed up at the manifold before the turbo
If you build an NA 572 and an NA 350, then force them both to exhaust through a single 2.5" orifice, then which one will make more power? My bet is that the 572 will, albeit with more exhaust pressure. That would hold true up until you reach sonic gas velocity through the orifice, or "choke", at which point both would make the same power. "Choke" is also known in the turbo world as the absolute limit in flow of a particular turbocharger.