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I wanted to see what everyone thinks is good/bad in terms of backpressure. What kind of numbers and ratios are you seeing on your cars? What have you done to help or hurt these?

Thanks!
 

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I have always wondered this myself. I knew a guy that had 65 lbs pre turbin. lol he was trying to run a single t4 pt88 on a 408 ci motor. lol
 

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You need to shoot for as close to 1 to 1 as you can get.On our car at 30 lbs of boost we have 33 lbs of backpressure and are working to get it even closer.

The way I look at it is if you can get to 1 to 1 the engine thinks it is a NA engine and it is alot easyier to tune and pick camshafts for.
 

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Different AR raito on the turbo is the first thing we are going to try.Right now it is kind of small to try to get the fastest spoolup time we can get(clutch car) but it is spooling pretty fast so now we can go to a bigger AR and see what happens.

We are useing Turbonetics Y2K 88mm turbos.

And no,I won't tell you what AR we use now..haha.
 

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Can 1 to 1 be accomplished with a single turbo system? I just can not see it happening. I do believe that it can be accomplished with twins depending on engine size.
 

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I think a 1:1 could work on a 400 - 480 small block with a huge T6 maybe a GT47 big AR or a GT55 or what not. I think you'll always struggle with pressure before the turbine though
 

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I put a s480 on a old wore out stock camshaft, 355 one time. at idle the wheel just sit still. so i bet i had a 1.1 ratio!! lol but u are right, on a single setup i wouldnt think it would be that good.
 

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Back pressure to Boost
1 to 1 or .97 to 1 is ideal and can be gotten.
At 1.5 to 1 on street motor is ok.
2 to 1 for logs or manifolds... ok ish.
And adding a wastegate doesn't fix high back pressure it just bandaids it.
 

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I would encourage everyone here to look at old Indy turbo motor setups. Really small turbines with monster gates. Gotta do something to build boost on those tiny motors.

A wastegate if properly setup can add as much AR to the turbine housing as a larger turbine housing but with the improved spool up behaviors. Just gotta pay attetion to gate geometery

Back pressure to Boost
1 to 1 or .97 to 1 is ideal and can be gotten.
At 1.5 to 1 on street motor is ok.
2 to 1 for logs or manifolds... ok ish.
And adding a wastegate doesn't fix high back pressure it just bandaids it.
 

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I would encourage everyone here to look at old Indy turbo motor setups. Really small turbines with monster gates. Gotta do something to build boost on those tiny motors.

A wastegate if properly setup can add as much AR to the turbine housing as a larger turbine housing but with the improved spool up behaviors. Just gotta pay attetion to gate geometery
Yep - it just depends on whether you're looking at using the turbocharger to help make a very powerful large motor stronger, or if you're looking at taking a smaller motor and relying on the turbocharger to supply significant amounts of the power. You also have to determine what the primary purpose of the car is. A T4 .81 on my engine is a nice sized street/strip turbo, but would probably spool real fast on a 350 - 427 and limit power. So - if the car is a street car a medium AR is probably ideal. If an all out drag car, you probably want to restrict the exhaust as little as possible as you're probably running a good size motor to begin with. I would definitely prefer a large single over twins though personally - just my opinion.
 

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A turbo setup that needs huge wastegates to maintain boost is also wasting alot of energy that could be better used spinning a turbine. Indy turbo application is very different than a drag car application. Indy motors are not trying to achieve high power over a narrow rpm window.
 

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...look at old Indy turbo motor setups. Really small turbines with monster gates.
Big wastegates yes...HUGE. But the turbines were actually big too (compared to compressor side). Ford Cosworth XB used a Holsett with a big 1.00 trim turbine wheel. And the old Drake-Offys had a big turbine side too.
Can 1 to 1 be accomplished with a single turbo system?
Depending on where the pressure sensors are placed, you might see 1:1. There is a very dynamic pressure gradient in each pipe...all the way to the valve.

Keep in mind, backpressure is a necessity. It is the "working fluid" driving the turbine. How much you need depends on what the overall combo likes...less isn't always better. Same with boost.
 

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I put a s480 on a old wore out stock camshaft, 355 one time. at idle the wheel just sit still. so i bet i had a 1.1 ratio!! lol but u are right, on a single setup i wouldnt think it would be that good.

LOL you floor it and it sound liek a helicopter blade starting to spin haha. :)
 

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Big wastegates yes...HUGE. But the turbines were actually big too (compared to compressor side). Ford Cosworth XB used a Holsett with a big 1.00 trim turbine wheel. And the old Drake-Offys had a big turbine side too.

Depending on where the pressure sensors are placed, you might see 1:1. There is a very dynamic pressure gradient in each pipe...all the way to the valve.

Keep in mind, backpressure is a necessity. It is the "working fluid" driving the turbine. How much you need depends on what the overall combo likes...less isn't always better. Same with boost.

Didnt they change from track to track depending on the characteristics they were after powerwise? I could have swore i've seen pics of them with obvious differences in size of the turbine housing itself. I wish I would have been old enough to witness these cars, as well as some of the gp turbo machines, seems like motorsports has taken a step backwards to limit costs. Yet they could afford it in the 80's...
 

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You need to shoot for as close to 1 to 1 as you can get.On our car at 30 lbs of boost we have 33 lbs of backpressure and are working to get it even closer.

The way I look at it is if you can get to 1 to 1 the engine thinks it is a NA engine and it is alot easyier to tune and pick camshafts for.
With a N/A engine at WOT there is normally zero pressure in the intake manifold, but I would think there would be positive pressure in the exhaust manifold(s)???? So that wouldn't be 1:1 would it????
 

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All I know is when you start to get to 1 to 1 a engine that is turboed will like the same stuff a NA engine does.As you get more backpressure you have to use different cams with less overlap to account for the backpressure.And I see that as a crutch to fix something that should be fixed by making the engine 1 to 1.

If you have alot of backpressure it will blow the charge back into the intake.If the engine is 1 to 1 the pressure equals out and you don't get as much blowback in the intake

As we have got rid of backpressure our engine acts more like a NA engine and has been easyier on parts and easyier to tune.

I am very new to the turbo stuff,just posting what I have found with my car.I have ALOT to learn still.
 

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hmmmmmmm....
 
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