3 bolt turbo or 4 bolt turbo?
- Thread starter JOHNZAZA
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An a/r ratio is a percentage. Basically the turbine housing is snail shaped. The snail shape is basically a funnel thats wraped around to a circle shape. An the a/r ratio is how big the the funnel is at the end( gets smaller as it wraps around) compared to how big it was at the begining. Now this has nothing to do with how big the funnel is. Its just basially how big it is at the end divided by how big it started out as. If you had a huge funnel that the end was half the size of the opening its a/r would be .50. Now a small funnel where the end was half the size as the beginning then it also would have a .50 a/r ratio. Now you have two funnels with the exact same a/r but totally different sizes.
This is where 3 and 4 bolt turbos get screwy. They are two different size funnels to start with and then you have the different a/r's to choose from. 4 bolt housings are usually bigger funnels and so they have less back pressure and pull harder on the top. In fact a freind of mines buddy measured the internal volume of a PTE 3 bolt .82 and a garrett 4 bolt .82 and the 4 bolt .82 had about 1.5 times the volume.
If you go with too big of a housing and too big of an a/r you wont get your boost. Infact you can go with out any waste gate at all and get the boost you want by switching housings. If your boost is too high then go to a higher a/r. If you cant hit the desired boost level then go to a smaller a/r. This is called a "free floating" system. I would imagine that a "free floating" system would build the most power per pound of boost and by far have the most lag.
The other huge factor you have to thro in here is the turbine wheel. Bigger wheels equal more lag and also more top end pull. I think what it comes down to is how much power the turbine section of the turbo has to produce to drive the compressor side of the turbo. The bigger turbine wheels are just that, they are bigger turbines and therefore create the power needed to drive the compressor section with less exhaust pressure. a.ka less back pressure on the motor, and more power for the same amount of boost.
Now in the "old days" people used to say that going from a garrett 3 bolt .63 a/r to a garrett .82 a/r 3 bolt was worth 2 tenths and 2 to 3 mph at the track. If you went to a four bolt you would get even more. The mph's could probably be found by just going to the different housings, but the ET drops probably could only be found if you had enough motor and converter to spool them good enough to still 60' good.
That last part brings up even more into the piture. "How much motor do you got". heres an example:
I run a stock long block with a T63E, P-trim turbine wheel, and .63 a/r PTE 3 bolt housing.
my buddy Rodger ran a built motor with a LT70, P-trim turbine wheel(same as me), and a garrett .75 a/r 4 bolt housing.
Both cars ran the exact same converter. The car that had every aspect of the "more lag and more top end pull" stuff was the one that actually had the quicker spool up AND murder me on the top end both! I know this for a fact because I ran both cars down the track.
There is some thing I never hear about but have been thinking of lately. Wouldn't the cam your running have an effect here also. I mean if a guy has a big cam with more valve over lap wouldnt he be the one to find the BIGGER gains in the bigger housings and a/r ratios. Its supposedly the back pressure of a turbo motor that makes bigger cams with there longer valve over laps not run properly.
Sorry for the long post but there is just way more to this than can be stated in a sentence or two.
HTH: Jason
This is where 3 and 4 bolt turbos get screwy. They are two different size funnels to start with and then you have the different a/r's to choose from. 4 bolt housings are usually bigger funnels and so they have less back pressure and pull harder on the top. In fact a freind of mines buddy measured the internal volume of a PTE 3 bolt .82 and a garrett 4 bolt .82 and the 4 bolt .82 had about 1.5 times the volume.
If you go with too big of a housing and too big of an a/r you wont get your boost. Infact you can go with out any waste gate at all and get the boost you want by switching housings. If your boost is too high then go to a higher a/r. If you cant hit the desired boost level then go to a smaller a/r. This is called a "free floating" system. I would imagine that a "free floating" system would build the most power per pound of boost and by far have the most lag.
The other huge factor you have to thro in here is the turbine wheel. Bigger wheels equal more lag and also more top end pull. I think what it comes down to is how much power the turbine section of the turbo has to produce to drive the compressor side of the turbo. The bigger turbine wheels are just that, they are bigger turbines and therefore create the power needed to drive the compressor section with less exhaust pressure. a.ka less back pressure on the motor, and more power for the same amount of boost.
Now in the "old days" people used to say that going from a garrett 3 bolt .63 a/r to a garrett .82 a/r 3 bolt was worth 2 tenths and 2 to 3 mph at the track. If you went to a four bolt you would get even more. The mph's could probably be found by just going to the different housings, but the ET drops probably could only be found if you had enough motor and converter to spool them good enough to still 60' good.
That last part brings up even more into the piture. "How much motor do you got". heres an example:
I run a stock long block with a T63E, P-trim turbine wheel, and .63 a/r PTE 3 bolt housing.
my buddy Rodger ran a built motor with a LT70, P-trim turbine wheel(same as me), and a garrett .75 a/r 4 bolt housing.
Both cars ran the exact same converter. The car that had every aspect of the "more lag and more top end pull" stuff was the one that actually had the quicker spool up AND murder me on the top end both! I know this for a fact because I ran both cars down the track.
There is some thing I never hear about but have been thinking of lately. Wouldn't the cam your running have an effect here also. I mean if a guy has a big cam with more valve over lap wouldnt he be the one to find the BIGGER gains in the bigger housings and a/r ratios. Its supposedly the back pressure of a turbo motor that makes bigger cams with there longer valve over laps not run properly.
Sorry for the long post but there is just way more to this than can be stated in a sentence or two.
HTH: Jason
My motor is stock 104,000 mile "bolt ons only" motor. I did take the valve covers off to install new valve springs with the heads still on the motor. BTW if your valve springs are weak this is a good investment.
Now Rodger's motor was a typical higher end stock block build up. he had GN1 heads, 210 roller, j&e's, billet center main caps, stock rods and crank, atr headers, FAST fuel managment system, PTE front mount, ect..
The point I was trying to make is that even though Rodger's set up had all the things associated with "more lag" he still spooled better than me do to having a motor that was able to flow enough air to spool a turbo of that size properly.
Hope this helps and good luck with your set up: Jason
Now Rodger's motor was a typical higher end stock block build up. he had GN1 heads, 210 roller, j&e's, billet center main caps, stock rods and crank, atr headers, FAST fuel managment system, PTE front mount, ect..
The point I was trying to make is that even though Rodger's set up had all the things associated with "more lag" he still spooled better than me do to having a motor that was able to flow enough air to spool a turbo of that size properly.
Hope this helps and good luck with your set up: Jason
I have run both, and I would have to say that my4-bolt .82 garrett is by far the best for MPH........
My long block is what some may call a "high end" block, but Im not that hard on it... 22-23PSI at the track, and at the same boost levels I see 1-2mph over my 3bolt percision....
My best advise is to try both, and stick with what works
(for you)..........
Matt
My long block is what some may call a "high end" block, but Im not that hard on it... 22-23PSI at the track, and at the same boost levels I see 1-2mph over my 3bolt percision....
My best advise is to try both, and stick with what works
(for you)..........
Matt
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