cumminsdriver635

Im making 40psi with a 16cm housing. No problems yet.

Eric

HOHN

Hard to say without the maps.

I'd expect it to flow more at lower boost levels, but at the upper limit, you'll be limited by the turbine housing--not the compressor.

jh

Shortshift

When i had bigger inj's I was going on the overpass from the 405 s to the 605 n in Long Beach Ca, and had a guy in a corvette pushing on me so I decided to turn the **** up on the APB and give him a run from about 45-50 on. There werent hardly any cars around so i just decided to "go for it" and see how long I could stay ahead of him. I was moving over lanes and looking in the mirror at the same time checking on his progress.. He was trying but he wasnt gaining and I was holding him off much to my surprise. In all the excitement I started noticing this "screaming" noise (hehe) was the HX35 sounding like it was gonna spin-off into orbit so I checked boost and it was at 45! I shut off and he blew by me (which tells me he WAS trying). Took a bit with the exhaust brake and standards to get back down to 65. Later I realized the GPS was recording max speeds and i checked it. It said 112.. Gulp! Was still pullin' pretty good at that speed too. Thats the hardest my truck has ever run but its amazing what that little HX will take. Since then Ive set it back to 38 max but it hardly ever sees more than 25 nowadays.. It is good to know it'll take it though as long as you dont keep hammering on it. Probably frusterated the guy in the corvette a bit. : ) Especially when he was eating my smoke and trying to get around it (but didnt do a very good job). : ))

kas83

I've run mine to about 39, that's all I have fuel for anyways. After about 32, it goes from a nice whistle to a whail that just doesn't sound right. I've watched one at 45 psi, 1600 degree pyro pegged. As fas as I know, that turbo was still functional after being replaced by a large HTB.

Jetpilot

Dyno results have shown 32# to be the max for efficient HP. Above the point no more gain just egt rise. At 35# and above HP was a loss. Almost everybody tries and push turbos way too hard. I made 610 RWHP on a moderate size single @ 42# boost.

Doug

Shortshift

Sounds like its time to set the boost elbow for 35#. Thanks for the good info..

(And the APB - It works great)

HOHN

This somethine we should all be paying more attention to. Not just the 32psi for the stocker-- but more the 610hp from only 42psi of boost.

Of course, this 42psi figure itself might be a little misleading- 42psi on a dynojet will be a lot less than what 610hp will need on the street.

But the point is that we often end up overboosting because we install a hot-side to the turbo that's very small so that we can get better spoolup. But we usually take it too far.

For example, take the factory 12CM housing at the factory 245 rating. This housing is super small to help with emissions. Spoolup is maximized even at this low HP. Yes, the wg pops at ~21psi or so but even with the WG blocked, a stock truck will barely kiss 26psi running empty.

Truth be told, for power a 14 or 16 housing is a much better choice AT THE STOCK power level. The decrease in spoolup is not excessive, and the peak EGT will be lower, and the turbine will be more efficient.

My 6-speed truck illustrates a good point. My factory turbo will make boost in 2nd gear running empty. This isn't a very high gas flow level, but the turbo's already in the game. I can pass 20psi in 3rd gear. In 4th, I can hit over 30psi. In 5th and 6th, I'm pushing it to 38psi and nearing the choke point of the turbine housing.

So, we start out with a turbo that's already on the "tight side" for spoolup, then dump all this fuel at it and get used to having instant boost response. We then expect any other turbo to have the same instantaneous boost.

Instead we should shoot for "acceptable" spoolup. With a little more lag, the turbo will respond more to load, and the the peak boost (wg blocked) will be different in each of the 6 gears instead of peaking in 4th or 5th.

Higher boost is a self-defeating phenomenon, because the more boost you make, the hotter it is, and the more boost it takes to offset that heating, etc etc etc. Fortunately, the intercooler helps, but once you've reached its saturation point and intake temps start climbing, the power output falls off and EGTs will soar.

I'm starting to "embrace the lag" and that represent a certain amount of efficiency.

JMO

Jetpilot

HOHN,

I have to disagree with you here..... This truck made good HP on a load dyno as well, in fact once we got wheelslip cured the numbers were almost identical. Boost was up to around 45# where it was wastegated. Boost isn't a direct function of HP but more the work of the engine given the installed components. The boost number is not as important as guys think, more doesn't always mean better.

HOHN

Good news!

It's good to know that 42psi valid-- and it further proves the point that boost numbers are all but meaningless, and the less boost it takes to make a certain amount of power, the better.

You know, surfing the Garrett catalog has been a real education for me. It's remarkable how much more efficient a larger compressor can be at higher pressure ratios, and how much more versatile.

For example, a GT4088 map stretches from 36-65 lb/min at a 3:1 PR-- a range of about 30lb-min.

But a ginormously huge GT4718 stretches from 63-138 lb/min at 3:1 PR -- a range of over 70lb-min! The larger charger is also very efficient, with the bulk of the map over 70%.


Doug, which turbo was making the 42psi on the 610 truck? Did the truck have a cam or other items to help the engine breathe?

Every psi less boost is a step in the right direction, imo..

Justin

A97dodge4x4

I had a frined that had bullydog 8's and a drag comp on his and if i remember right he blew his up running it at around no more than 38lbs on a consistant basis. but my brother runs 42 + on his and it's been going good for over a year now.

HOHN

Well, bullydog 8s might be the sloppiest injectors ever sold on mass market, so the fact that a turbo failed with them doesn't surprise me much.

AlpineRAM

I have been wondering for quite some time about the boost discussions. In reality we are interested in mass air flow.
Assuming a crappy efficiency of 0.5 lbs/hp/hr and a relation of 25lbs of air to 1 lb of fuel to get a clean burn every hp needs 0.208 lbs of air per minute in the turbo diesel. (naturally if you assume a better efficiency like 0.4lbs/hp/hr you can knock off 20% of my estimate of air needed)
So a 600 hp engine would need 125 lbs of air per minute, not regarding scavenging losses that occur when boost is much higher than exhaust backpressure, but which is very good to keep the piston crowns cool.

Now very much depends on the pressure needed to cram the said amount of air into the cylinders at a given set of values like air temperature, valve size and opening, cam curve etc. Since all this isn't easy to calculate I suggest using a MAF sensor to determine the flow through the engine while testing turbos or even wastegate settings. If you block the WG on an HX35 you will raise mass air flow only to a certain point. (that does depend on a lot of factors in the engine)- I tested mine and for my configuration I got maximum mass air flow for a wastegate setting of 31 psi. To avoid boost creep I drilled the divider and opened up the wastegate a bit, used a backplate extender to allow the WG to open a bit wider (the megamouth wasn't available then, I think it's a truly cool idea)- and since the idea behind a wastegate is to reduce backpressure, adding more exhaust gas will make it necessary to rethink the dimensions of the WG.

So for a given engine load you should try to optimize airflow (boost) to avoid unnecessary work of compressing air to achieve nothing. Naturally there is a tradeoff because you'll want a bit of reserve air available to be able to get on it and not have to wait for the turbo to spool, but for the long stretches of running with the engine at partial load the higher cruising boost costs fuel economy.
Personally I think that it would be worth while to research mass air flow characteristics of twins that use an HY35 with a modified internal wastegate (as big as possible, but internal to avoid heat losses), a megamouth like setup and some primary that will flow approx. 100-130 lbs/min at a PR of 3:1 - This should IMO give you a system that has the "lightning spoolup of the HY for part load driving and with the secondaries WG set at 18-22 psi you should get a nice transition to the lower flow part of the efficient land for a rather big primary. (like a GT4202). It might be necessary to close the WG of the secondary a bit when the primary has spooled to get enough dp across the turbine of the secondary to stay within compound compressing, but IMO the pressure difference the secondary will make with the primary at full flow will be quite small, because there is a very big mass of air to be compressed and the energy needed won't be easily delivered by the secondaries turbine.
But for tuning this as an entire system with an engine I think that mass air flow data from a MAF sensor would be very valuable.

Just wanted to throw some ideas around..

AlpineRAM

Jetpilot

Justin,

The truck was an 2002 an it did have a ported head and Helix 2 cam. The turbo was an old school B-1 steroid..... Your beliefs are in line with mine, airflow is what is important not boost #.

Doug

A97dodge4x4

hahaha they were pretty nasty injectors but I figured the HX35 didn't have much of a chance anyways. He made it las for about a year and a half with them though. i was suprised it even lasted that long. Now rockjeep73 runs runs them in his truck but i don't know if he hashad the nozzles cleaned or replaced ever or not cuz hey have been through at least 3 trucks since 03. It's seems to do ok for him when he runs the nitrous through the truck. it's one heck or a show when he pulls that for sure.

XLR8R

Alpine, where did you sample for the MAF sensor?