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Here's one of two turbo test stands that our old sister company had. They also had one that Mahle owned. This one was set up right next to our chassis dyno bay. A must to get the real world #'s, as even though they were an authorized Holset, Garrett, Mahle, BorgWarner/Switzer dealer & repair shop, the turbo companies are very secretive about a lot of their info. They had over 10 cnc machines & made many of their own turbo parts.
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Lots of interesting info here.

I thought charr and dougal have been preaching for years that the boost ratios should be about at about the 2:1 ratio for the high pressure to low pressure turbo.....i.e. if the 35 is making 20psi the manifold pressure should be 40psi. But now Nascar guy is saying something a little different. Not that I'm throwing anybody under the bus here, please noone take offense; just trying to piece this together. I also thought I've heard that in a hx30/35 compound it's best to have the 6cm hx30(w/ 40mm comp) and best to have a 12cm hx35. Now it sounds like maybe a 14cm hx35 is better?

This thread has been a good read with differing opinions. I currently have my 4bt out of my expedition and trying to decide if I want to upgrade the 35's exhaust housing. Not a full out power build, just looking for good engine response. This thread has me thinking!

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58mm compressor wheel with 12cm is fine....lots of guys even go with a aftermarket 60mm comp wheel with 12cm but that's where the choke just starts.
This hybrid is the 57mm comp wheel,
65/52 turbine, and 16 cm housing.
I wouldn’t even consider myself an amateur when it comes to turbos but I’m reading and learning a lot off this site. I figured guys were running the 35 or the 40 and this feel in between. Any real world experience to back that up or prove me wrong? Ha
 

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Lots of interesting info here.

I thought charr and dougal have been preaching for years that the boost ratios should be about at about the 2:1 ratio for the high pressure to low pressure turbo.....i.e. if the 35 is making 20psi the manifold pressure should be 40psi. But now Nascar guy is saying something a little different. Not that I'm throwing anybody under the bus here, please noone take offense; just trying to piece this together. I also thought I've heard that in a hx30/35 compound it's best to have the 6cm hx30(w/ 40mm comp) and best to have a 12cm hx35. Now it sounds like maybe a 14cm hx35 is better?

This thread has been a good read with differing opinions. I currently have my 4bt out of my expedition and trying to decide if I want to upgrade the 35's exhaust housing. Not a full out power build, just looking for good engine response. This thread has me thinking!

Sent from my SM-G970U using Tapatalk
Here's my post from earlier in this thread about boost split. The considerations are turbo strength, thermal failure and power: hx30/hx35 build
 

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Selling 4bt & 6bt parts to all of N.America
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This hybrid is the 57mm comp wheel,
65/52 turbine, and 16 cm housing.
I wouldn’t even consider myself an amateur when it comes to turbos but I’m reading and learning a lot off this site. I figured guys were running the 35 or the 40 and this feel in between. Any real world experience to back that up or prove me wrong? Ha
Got ya. Yes, that particular hybrid combo is one I came up with for a guy that tows heavy in the 1st gen crowd. Not the fastest spooling turbo because of the larger 16cm exh housing but not bad considering the smallest stock one that came on the 1st gens was a 18.5cm. The 16cm was once considered the best all around turbine housing due to faster spool up while maintaining good fuel mileage still. I've sold a hand full to the 1st gen crowd & feed back has been good.
 

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Discussion Starter #67
20210324_212415.jpg
down pipe tacked together. No way 4 inch was fitting right from the turbo unless I leaned the turbo back and that had other issues. I can't see this down pipe robbing power. Any thoughts? Isn't 3 inch exhaust good for 300 hp?
 

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3" is good for much more than 300hp, so your good.
 
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I've had the same 3" vs 4" question as well. Thinking I might rebuild my downpipe while everything is apart. I had to take a hammer to it as it was being 4" to clear the firewall before.

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On a 4bt, a 4" exhaust from the primary wouldn't be required. Now if it was a 6bt then you'd probably want that since the primary would be much larger. Also, the down pipe connecting the 2 turbos shouldn't be much larger than the exhaust outlet of the secondary. Usually around 2.5" on a HX30W. This will keep the exhaust velocity higher to help boosting the primary.
 

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Discussion Starter #72
Well I got my truck all together and have done a few test drives and some tuning. So far I'm quite pleased but it does need a bit more tweeking. Egt's are pretty low. Around the block it's hard to get it over 900(can t get it going much faster than 80 km/hr). Boost is around 35 psi. High pressure turbo is gated around 28 psi, i started at 22psi and it ran bètter as i added more. I did lower the fuel twice, might play with it a bit more. Spool is almost instant, so that is good. What sort of max boost should I be shooting for with these compounds?
 

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What sort of max boost should I be shooting for with these compounds?
That depends on your max expected power and max expected altitude.
Basically add fuel until you're happy with the power and then drop boost until you're happy with the EGT.

My 300hp calculation set was showing 43psi boost by 2200rpm (about 900Nm ~660ft/lb) and about 235kw (~315hp) at 2900rpm. Fuelling ~190cc/1000 shots which is a hair more than a maxed out VE pump. A/F at 18:1 (clean and safe).
Big turbo gated at PR 1.8 (12psi) in that calculation to keep intake temps down on the smaller turbo. It will give you more power for less boost using more pressure on the bigger turbo.
 

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Discussion Starter #74
That depends on your max expected power and max expected altitude.
Basically add fuel until you're happy with the power and then drop boost until you're happy with the EGT.

My 300hp calculation set was showing 43psi boost by 2200rpm (about 900Nm ~660ft/lb) and about 235kw (~315hp) at 2900rpm. Fuelling ~190cc/1000 shots which is a hair more than a maxed out VE pump. A/F at 18:1 (clean and safe).
Big turbo gated at PR 1.8 (12psi) in that calculation to keep intake temps down on the smaller turbo. It will give you more power for less boost using more pressure on the bigger turbo.
Fair enough.
It does seem like my hx30 gate might be opening too far and there's not much compounding in the top end. But I've got to do more driving. So far so Good tho!!
 

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Yeah, there is a bit of trial and error to get it just right. To be on the safe side, most try to keep the total boost around 40 PSI or a tad lower to protect the head gasket. In theory, lowering the small turbo wastegate setting should spool the primary turbo faster. Starting point used to be 18 PSI for the HX30W. There are just a lot of variables that play into the equation. Low EGT numbers are one of the great things with twins. More heat is being converted to power.
 

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Discussion Starter #76
Yeah, there is a bit of trial and error to get it just right. To be on the safe side, most try to keep the total boost around 40 PSI or a tad lower to protect the head gasket. In theory, lowering the small turbo wastegate setting should spool the primary turbo faster. Starting point used to be 18 PSI for the HX30W. There are just a lot of variables that play into the equation. Low EGT numbers are one of the great things with twins. More heat is being converted to power.
You bet trial and error for sure. I had the gate at 18 to start with and it is much happier around 30, closer to the way eggman has his set up. It builds faster and makes more overall boost. My old setup was the same principle. Not sure why but I'm gonna do what works. I'm suspecting my hx35 gate is tripping because around 30 psi of manifold pressure I suddenly get a bit of smoke. I might disable it and see how that goes
 

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Discussion Starter #77
Seems to me I'm compounding in bitten to mid and sequential-ing up top. My hx30 gate might be opened all the way
 

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I wouldn't see how the HX35W gate could be opening unless it's defective. The factory setting on those is around 18-20 PSI and it's not likely you're getting more than that out of it. Now if the actuator is defective or set to a low setting that could cause issues. Might connect a regulated air source to it an see when it opens. If it opens early that would also be a reason for running the HX30W to a higher level. Years ago guys were running at 300 HP and the HX30W was set at 18 PSI. Do you a 2 boost gauges to see how much the HX35W is producing?
 

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Seems to me I'm compounding in bitten to mid and sequential-ing up top. My hx30 gate might be opened all the way
I'm thinking the gate on the 30 is open too much to keep it powered properly as well, might try limiting it's total travel.
 

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Discussion Starter #80
I wouldn't see how the HX35W gate could be opening unless it's defective. The factory setting on those is around 18-20 PSI and it's not likely you're getting more than that out of it. Now if the actuator is defective or set to a low setting that could cause issues. Might connect a regulated air source to it an see when it opens. If it opens early that would also be a reason for running the HX30W to a higher level. Years ago guys were running at 300 HP and the HX30W was set at 18 PSI. Do you a 2 boost gauges to see how much the HX35W is producing?
I've got two gauges. Both turbos I manually checked and set boost actuators. 18 psi on high pressure turbo was too low, bumper to 30. My hx35 is set to 30 and intermediate pipe boost was 30 and it was tripping the gate. If that makes more sense.
I know that the text book way of doing things is where I start but compounds seem to rarely conform. You usually have to play with things to be happy with your set up
 
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