HOHN

An 80mm bottom charger is going to be around 110-120lb/min in flow. A 62mm charger would work well, imo-- since they can typically manage around 60lb/min. I like to see a 2:1 ratio in mass flow of big to little charger. This is a little on the "big range" of size gap. IMO, the big charger should never flow MORE than double what the top charger is capable of.

On the other hand, the "small end" of the size gap is imo about 2/3rds. In other words, the smallest big charger to use with a 60lb/min top charger is 90lb/min (90# * 2/3rds=60#). So keep your big charger no larger than twice as big as the small one, and no smaller than 1.5 times the small one.

Total cooling and airflow capability is determined by the big charger, and THAT is what you should match your injectors to. For 150hp sticks you could go as small as as a GT4294, but for 220s you'd want something larger-- like that S480.

*this is just my opinion, I have no firsthand experience with this stuff*

Eradan

So at that math ... if i ran the standard 74mm s400 that's floating around ... .i should see 98lb/min flow rates ... at a 2/3 ratio ... i would want to be around 45 - 60lb /min on the top charger ... hx35 w/ 12cm is ~ 55 - 60lb /min (pretty close to the 62mm). So w/ a 14cm should bring it up a little, and pretty close to the 1.5x min between the 2. The hybrid from what i have read flows about 65 - 70lb /min? (hx40 flowing 70lb/min).

74mm = 98lb /min
hx35 (14cm) = 70lb /min
70 x 1.5 = 105lb /min

So w/ the 74mm wheel at 98lb /min drive pressures may be up with an HX35 on bottom, so really i almost need something smaller up top ... I'm really considering a turbonetics or Garrett up top eventually.

I'm afraid of the overfuelling w/ the 220hp sticks, and think i should be able to light just fine with the DDP4's (140hp).

CapnRam

Thanks for all the input!! ? though, couple of you said to use my 62 that i have, i have talked to BD and II, and both said the sps62/14 cannot be used in my application, so i was planning on selling it....so can i use it or not, because i still have my stock one.. ok, i've only been into these diesels for a couple of years, i've been BBC and blowers, so i'm kinda lost when you guys start talking about the housing size? Is it something need to worry about for what i want, and as for my towing, its usually in the summer to the lake and back, but some good hills in it..so i hate having to watch them egts so much! Someone said something about going with the mach1.6's, would that be a good match with twins at my elevation? Thanks again for all the info..keep it coming, i'm taking notes..lol.. 129 here yestereday!! Still waiting for the 140 they keep promising... !! Capn

HOHN

Any turbo CAN be used in almost any application. You can use a 66mm turbo on top if you want. The question is what will come closest to accomplishing what you want?


To help you understand turbos a bit, they are sort of like cams in a gasser application-- they have an optimal rpm range for a given size. A bigger cam goes higher RPM and makes more power-- as does a larger turbo in general.

The reason we do compound (twin) turbos is because one turbo simply cannot effectively multiply air pressure to the high ratios we need to stuff tons of air into a low-revving 5.9L engine. Imagine trying to make 500hp with a small block 350 that can't be revved over 3500 rpm-- pretty tough, eh?

So when you pick a top turbo, you want something that will match well with the bottom turbo, and respond early enough to match your intended usage. Heavier loads, hotter weather, lower rpm, and higher elevations ALL require earlier turbo response to control EGTs.

This is probably why these turbo shops are telling you not to use your SPS62. It's not that it can't be used-- it's simply that it will respond too late to accomplish what you are trying to do.

With any kind of twin turbo setup, you need not go with injectors smaller than 150hp in my opinion. With a box off or on the lowest power level, you'll have no EGT issues with twin turbos at that injector size (assuming decent injectors like DDP or F1). A Mach 4 would work well for a twin turbo truck that still has to tow.

Anyway--back to turbos, I'd recommend the stock turbo in a set of twins because such a set would favor the response that you need for towing in thin air in warm weather.

JMO

HOHN

You have to pick a starting point. Either you are trying to match a small charger to a big one or vice versa. If you have a given big charger, pick a small one between 50% and 66% of its flow. Thus, your 100#/min charger would need a top charger between 50# and 66# above it using this methodology.

FYI-- an HX35 will NOT flow 70#/min! The very far right part of the map is 60#, and that's the ragged edge--- at MUCH lower PRs. At the higher PRs we generally operate the HX35 at, you're looking at more like 45#/min.

Part of tuning twins given a certain pair of turbos (conversely, selecting turbos based on a given tuning approach) is selecting their operating range AS INSTALLED IN THE APPLICATION.

IN other words, the fact that a turbo can do 100#/min doesn't mean anything unless it can do 100#/min at the pressure ratios we're intending to use it.

So how much pressure do we need to operate the bottom turbo at? Well, that depends on the top charger's size, because a larger top charger will swallow more air from the big charger, and lower the pressure in the "cold pipe" that connects the compressors.

Keep in mind that pressure builds up because of difference in flow. If the top and bottom turbos were both flowing 100#/min, you'd never have any pressure building. So if you have a 100# turbo feeding a 66# turbo, you'll have a lower operating pressure for the larger turbo than you would if it was feeding a 50# turbo instead of a 66# turbo.

If you go with a 2:1 flow rate (100# big charger matched to 50# small charger), then that big turbo needs to be operated at a PR of 3:1. So, look for a charger that can make 100#/min AT 3:1 PR (or ~29psi of boost).

If the difference in turbos is smaller (say 100# big charger and 66# smaller), then the operating PR of the big charger might be able to drop to around 2 or even 2.5.

Finally, keep in mind that you want only as much boost as you need for a given condition. This means shooting for low PRs if you can, though it's usually best to be overboosted than underboosted. Overboost is mostly inefficient, while underboosted can cause really high temps.

It's all a delicate balancing act.

PS-- I'm looking at the Garrett and T-netics units myself.

jh

Don Wagner

I would go 64mm over an S480. That being said, people need to realize how large an S480 is and how many people do not need that level of charger.

dodgezilla04

The reason russ cannot not use his existing 62 is it is a Super phat 62, not the regular phat 62. like hohn says, it wont respond fast enough to keep ahead of egt's. that's why we are looking at selling it and going with the hx35 over an s400,k31, or 3b.

CapnRam

Once again thanks for the info... i've looked at BD, there kit is around 3600. II has one for around 4500. Piers has theres around 4000.00 SO what is the difference between these...or is there just to much to even go here? Or is it better to get a kit with a top turbo and use my stock one?