Too much back pressure?
Thread Starter
Staging Lane
Joined: Jan 2016
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I probably could of made more. But the power level was pretty low for 13-15psi
what size motor and compression was your engine
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Thread Starter
Staging Lane
Joined: Jan 2016
Posts: 56
Likes: 14
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No. Manifold boost pressure comes from compressor side compared to turbine side and back pressure as measure by the amount of pressure on the gate to hold it closed. Take gate divided by boost to get your ratio. If it moves past 1.5:1, consider making some changes depending on goals.
Staging Lane
Joined: May 2021
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Very interested in this due to the small a/r size. Looking at the torque curve the responsiveness looks good so that would be a big advantage with the smaller turbine housings, as long as they are not far too small for your power goal. If you decide to go bigger, why not try the next size up with the 0.86 (?) a/r instead of going all the way to the large one?
As far as measuring the pressure upstream of the turbine (in the exhaust) if you have an available exhaust bung somewhere, you can attach a long metallic tube to that. A long piece of tubing, say 2-3 feet will cool off before it gets to the gauge since there is really no flow in the tube. Then you can go to a rubber tube and connect that to a pressure gauge. There is very little flow so the pressure reading will be good even at the end of a long tube. Capture the pressure gauge reading in a cell phone video next to the tach for a poor man's data logger. Hope that makes sense.
Very, very cool engine swap by the way. I have always loved the Clown Shoes, great cars. I had a E36 M3 coupe for a while (supercharged) and it was a great car.
As far as measuring the pressure upstream of the turbine (in the exhaust) if you have an available exhaust bung somewhere, you can attach a long metallic tube to that. A long piece of tubing, say 2-3 feet will cool off before it gets to the gauge since there is really no flow in the tube. Then you can go to a rubber tube and connect that to a pressure gauge. There is very little flow so the pressure reading will be good even at the end of a long tube. Capture the pressure gauge reading in a cell phone video next to the tach for a poor man's data logger. Hope that makes sense.
Very, very cool engine swap by the way. I have always loved the Clown Shoes, great cars. I had a E36 M3 coupe for a while (supercharged) and it was a great car.
Last edited by Deude_Mann; May 10, 2021 at 10:41 PM.
Thread Starter
Staging Lane
Joined: Jan 2016
Posts: 56
Likes: 14
Very interested in this due to the small a/r size. Looking at the torque curve the responsiveness looks good so that would be a big advantage with the smaller turbine housings, as long as they are not far too small for your power goal. If you decide to go bigger, why not try the next size up with the 0.86 (?) a/r instead of going all the way to the large one?
As far as measuring the pressure upstream of the turbine (in the exhaust) if you have an available exhaust bung somewhere, you can attach a long metallic tube to that. A long piece of tubing, say 2-3 feet will cool off before it gets to the gauge since there is really no flow in the tube. Then you can go to a rubber tube and connect that to a pressure gauge. There is very little flow so the pressure reading will be good even at the end of a long tube. Capture the pressure gauge reading in a cell phone video next to the tach for a poor man's data logger. Hope that makes sense.
Very, very cool engine swap by the way. I have always loved the Clown Shoes, great cars. I had a E36 M3 coupe for a while (supercharged) and it was a great car.
As far as measuring the pressure upstream of the turbine (in the exhaust) if you have an available exhaust bung somewhere, you can attach a long metallic tube to that. A long piece of tubing, say 2-3 feet will cool off before it gets to the gauge since there is really no flow in the tube. Then you can go to a rubber tube and connect that to a pressure gauge. There is very little flow so the pressure reading will be good even at the end of a long tube. Capture the pressure gauge reading in a cell phone video next to the tach for a poor man's data logger. Hope that makes sense.
Very, very cool engine swap by the way. I have always loved the Clown Shoes, great cars. I had a E36 M3 coupe for a while (supercharged) and it was a great car.
im not overly worried about being laggy with 62’s and 10:1 compression
Thread Starter
Staging Lane
Joined: Jan 2016
Posts: 56
Likes: 14
ill post the dyno results. Same boost and same timing. See what it does.
took the old ones off.
Last edited by Fallguy; May 11, 2021 at 02:12 AM.
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Fallguy, hope my above post regarding gate pressure measurement made sense. No need to have a port in the turbine drive side to measure back pressure when using gate pressure to manage gate opening. The exhaust back pressure is basically a 1:1 correlation to gate pressure. Always good to have back pressure measurement info before tweaking turbine housing, exhaust system, etc. Side note - Your back pressure could be the 4" exhaust. 4" pipe flow is 1.5sqin less than (2) 3" pipes feeding it. Just some thoughts.
Keep us posted.
Keep us posted.
Staging Lane
Joined: May 2021
Posts: 97
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I am not that familiar with external waste gates (internals so far) so this is a great tip. Thanks.
Last edited by Deude_Mann; May 11, 2021 at 12:57 PM.
Thread Starter
Staging Lane
Joined: Jan 2016
Posts: 56
Likes: 14
Fallguy, hope my above post regarding gate pressure measurement made sense. No need to have a port in the turbine drive side to measure back pressure when using gate pressure to manage gate opening. The exhaust back pressure is basically a 1:1 correlation to gate pressure. Always good to have back pressure measurement info before tweaking turbine housing, exhaust system, etc. Side note - Your back pressure could be the 4" exhaust. 4" pipe flow is 1.5sqin less than (2) 3" pipes feeding it. Just some thoughts.
Keep us posted.
Keep us posted.
ill have to try that technique
4” is smaller than dual 3” but should not start to choke it at such low power levels I would think.
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Swapped to a gen 4 5.3 and changed nothing turbo wise. Ran 10.69 on 15 PSI on pump gas, with a T56 and stock rear suspension in an S10 that weighed 3400 lbs (without driver I believe).
Staging Lane
Joined: May 2021
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Fallguy, very clean installation by the way, looks great. The mirror image turbos, BOVs, and exhaust wrap are all very nice. I would have to take some measurements, but fitting a front-mount dual setup is something I have considered in the Miata (rather than a rear mount). It is a very tight squeeze, maybe even more so than yours. What are you using for exhaust manifolds?
Thread Starter
Staging Lane
Joined: Jan 2016
Posts: 56
Likes: 14
Fallguy, very clean installation by the way, looks great. The mirror image turbos, BOVs, and exhaust wrap are all very nice. I would have to take some measurements, but fitting a front-mount dual setup is something I have considered in the Miata (rather than a rear mount). It is a very tight squeeze, maybe even more so than yours. What are you using for exhaust manifolds?
for manifold i just made some out of sch10 304ss. They are just a flowing log style. Simple and compact.
Thread Starter
Staging Lane
Joined: Jan 2016
Posts: 56
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Staging Lane
Joined: May 2021
Posts: 97
Likes: 11
Right now I am leaning toward a rear-mount single (larger) turbo, something like a 76mm T4, and know I can make that fitment work. There is a lot of volume between the rear subframe and the bumper to work with so it's plenty of space for a turbo, a muffler, external waste gate, scavenge pump, and then some. I'd use a non water cooled CHRA to make the plumbing easier.
Nice work
Thread Starter
Staging Lane
Joined: Jan 2016
Posts: 56
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If you used a pump to get the oil back to the pan you could low mount them under the headlights in the bumper. Then feed into a vertical flow intercooler.
Staging Lane
Joined: May 2021
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Yes I looked there as well. That could also work. There is a lot of space in front of the front tires, behind the bumper, especially with the front air dam and splitter. The only thing is that might force me into a direct exhaust dump (no muffler) because routing the exhaust back to the rear of the car would be tricky; there is not much space between the subframe and the short block, and going underneath the subframe is not an option; the bottom of the subframe is the height of the bottom of the car. I'm hoping to make the exhaust note stealthy so I'd want at least a small muffler.
Maybe I could have a blown front splitter, HA!
The rear mount also shifts most of the additional weight to the rear of the car. The Miata LS1 swap does not throw the weight balance off enough to be a problem; the car is very balanced even by road race standards (I know, hard to believe). But adding the turbo weight to the rear would shift things 1-2% backward which would be a secondary benefit.
Maybe I could have a blown front splitter, HA!
The rear mount also shifts most of the additional weight to the rear of the car. The Miata LS1 swap does not throw the weight balance off enough to be a problem; the car is very balanced even by road race standards (I know, hard to believe). But adding the turbo weight to the rear would shift things 1-2% backward which would be a secondary benefit.