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Raising Compression - Head vs Turbo

Austin

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I was readingProvience’s topic on newb boost questions but didn’t want to hijack it.

I switched my Unimog’s M180 motor over to propane and I’d like to get the stock 7:1 compression up to a ‘propane happy’ 10:1. A lot of people swap out to a different Mercedes head that came stock with a 9.3:1 compression. The idea of a turbo is always proposed but gets shot down because the M180 has 5 main bearings vs the donor engine for that 9.3:1 head that has 7 main bearings.

So I’m curious why using a head to get to a higher compression “OK” vs using a turbo to get to the same numbers?
 
abso-fucking-lutely!

that's what spawned todays turbo reading, same/similar question. It all boils down to cylinder pressure as for what the bearings and pistons are going to have to deal with. turbo/heads/compression ratio/cams/valves all of those things can result in bearing crushing amounts of cylinder pressure, or totally happy time power love you long time levels.

so then the question is, how much power are people making with the 5 bearing blocks and getting survival out of them? and also what cam are they using. there is a mention of it in "one of" the articles i linked in the other thread, about intake valve remaining open after BDC on the compression stroke, this is also more extreme on the atkinson cycle engines used in hybrids where the gas engine is more of a generator. running longer power stroke and low cylinder pressure = pretty decent fuel economy for a low power solution to a high torque requirement :rasta:


to directly answer your question: it's easy to overdo it with a turbo and a head swap is safe
 
head swap is safe and easier is why people do that. Just like doing a cam swap in a truck for more power is easier than a turbo. You can turbo a truck with stock cam and everything BUT if you run too much boost or the ring gap isn't enough youre asking for trouble. Some guys have tore apart LS truck motors. One with 30K miles and one with 200K miles. Ring gaps are totally different and within spec but should be opened up more if running a turbo since turbo creates more heat and rings expand more. So turbo would be fine IF you keep the boost and everything low. I'd say find a stock small turbo with built in wastegate and give it a try. One from a small TDI VW Jetta would probably do great on that thing
 
I guess if I ramble too much ya'll just won't read

I just don't know where to begin.. it was a hobby for many many years.. in highschool I had a mustang that ran low 12s.. never took at automotive class

my learning pretty much stopped maybe 10 years ago.. however, im reasonably sure turbos and just changing heads are NOT anywhere near similar

the first mods people I hung out with, in the racing scene usually did.. ???

#1 pull out the silencer

#2 drop in a K&N ... maybe getting one that replaces all your intake

#3 full exhaust (maybe keeping your heads.. depending on what is out there and what you have)

it's all about letting your engine breath..

many different times you do some things at the same time.. like gears and lockers

EDIT what do you have??? is it stock???
 
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I don't know much about propane set ups

I might have more questions than answers

are there other things you can take with you off the mercedes?

how much horsepower does this mercedes have?
 
I don't know much about propane set ups

I might have more questions than answers

are there other things you can take with you off the mercedes?

how much horsepower does this mercedes have?

propane is about a 110 octane but also about 20% lower BTU than gas

E85 is about 105 octane and about 30% lower BTU than gas

diesel is about 13% higher BTU than gas

that's about it as far as it is concerned here. propane with the higher octane than gas let's you run higher cylinder pressure with less risk of detonation.
 
hahaha.. yeah, I use to be about the numbers.. not anymore

you are one of those smart number guys arent ya?

I've seen vehicles runnin propane on trails, and talked a little with owners.. but I dont know basics.. how they run.. what the differences are? the vehicle does still need air right?
 
Both! Have we forgotten our roots already? :flipoff2:

I would honestly suspect it's relatively easy to overdo it with a turbo, and the head swap is "safe", just like Provience said already. You can manage a turbo pretty well with a boost solenoid and controller, but that can get spendy fast. I was able to do my turbo setup on largely junkyard parts, but the Megasquirt 3 Pro engine ECU that I bought planning for exactly that, wasn't cheap (over $1k). The risk on the turbo side for me is, everything working properly, a given condition gets me 2psi of boost. Blow off one vacuum line, and boost is at 6psi in otherwise the same conditions. Depending on where in the RPM/power curve that happens (if it happens), and how gnats-ass-wound your tuning is, that difference could potentially be very damaging.
 
Have any of the people who make a big deal about the # of main bearings in this engine actually tried to turbo one and had problems? I'd do the head swap and then the turbo if the head wasn't enough gain on its own. Low compression and boost makes for a lazy engine when it's not making boost. High compression and low boost IMO would be a more drivable trail rig than the other way around at the same HP level.
 
Just like people with 2 bolt main SBC day don't bother unless its a 4 bolt main because they fail. Hell my 2 bolt main revd to 7k rpm and was 475hp and never had an issue. I'd turbo it and have fun
 
to directly answer your question: it's easy to overdo it with a turbo and a head swap is safe
head swap is safe and easier is why people do that.

Thats what I was hoping to hear


how much horsepower does this mercedes have?

The Unimog M180 had 85hp, the donor head i believe is 130hp.

Keep in mind these are like tractors, not 4400 rigs


You can manage a turbo pretty well with a boost solenoid and controller, but that can get spendy fast.

Well I've come to find out that the German word Unimog translates to "spendy" in America.

Have any of the people who make a big deal about the # of main bearings in this engine actually tried to turbo one and had problems?

Not really. People just get the other Mercedes motor ... but they have become like Unicorns and are hard to find. That kind of why I jumped on this NOS Unimog motor.

How much boost is overdoing it? I'm not looking to get more than stock performance from it, just don't want to recover the power loss from going propane.
 
How much boost is overdoing it? I'm not looking to get more than stock performance from it, just don't want to recover the power loss from going propane.

There's more to it than just a boost number. 5psi out of a tiny turbo makes a lot less power than 5psi out of a giant turbo. Look at it more in a safe amount of power/torque to be making with the parts you have, if you boost it back to making a stockish power level, you're not very likely to hurt it provided your fuel and timing are right.
 
Not really. People just get the other Mercedes motor ... but they have become like Unicorns and are hard to find. That kind of why I jumped on this NOS Unimog motor.

How much boost is overdoing it? I'm not looking to get more than stock performance from it, just don't want to recover the power loss from going propane.

check out the other thread, help me figure out a way to organize it better so that it is easier to follow, do the math and take in to account the lower BTU of propane and shoot for 10% higher than what the upgraded motor makes.

that's probably safe :laughing: otherwise, you just turn it up until it stops working, then back it off a notch (if you have a dyno handy) :rasta:
 
Adding boost is like adding displacement, you are cramming more air and fuel into the cylinder effectively making it a bigger motor. Raising the compression is just squeezing the same amount of air and fuel tighter for a bigger bang. Cylinder pressure is the limiting factor. At 7-1, it would be kind of hard to over do it LOL. Somebody with engine simulation software could tell you pretty easily how much boost you could run to achieve the same cylinder pressures as the 9.3-1 head would give you. You would probably make more power with better fuel economy with the turbo if sized properly.
 
Somebody with engine simulation software could tell you pretty easily how much boost you could run to achieve the same cylinder pressures as the 9.3-1 head would give you.

6psi will net him 9.9:1 effective compression ratio

8psi will net 10.8:1 from his starting point.

propane will be happy at, what 14:1? lemme look (14 psi would net 13.7 EffCR)

edit: alright, apparently 11-12 to 1 is a reasonable compression ratio for a propane build. sounds low to me, but maybe that is just a safe general number to account for the great many variables and unknowns from engine to engine :shrug:
 
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guess i'll try my hand at playing with the numbers from the other thread in here:

Mercedes-Benz Unimog S404 series - Mercedes Unimog S404.3 - (M180) - Enginerebuilding.eu

Engine type: M180.928
Construction Year: 1960-1975
Number of cylinders: 6
Bore ø: 80 mm
Engine content: 2195 CC
Compression ratio: 7 : 1
HP: 80

psi boost for horsepower target calculator - racingcalcs

134 cubic inch, guessing 3500 RPM peak 80 HP for 80% VE, and then dropping off from there (if we pretend the curve is flat at 80 hp up to 5k rpm, we'd be at a dismal 56% VE, i'm confident peak is somewhere between 3500 and 5k :laughing: ) let's compromise and say max 4k rpm for a 70% VE

134 * 0.5 * 4,000 / 1,728 = 155 CFM of air that it "could" pump

155*0.70=108 CFM of air that we are actually pumping, with our 70% VE

8 psi will net us 10.8:1 compression ratio, so let's shoot for that

(8+14.7)/14.7 = 1.54 pressure ratio

108 * 1.54 = 166 CFM that we will want to pump

[(0.5 * 134 * 4,000) / 1,728 ] * 0.70 * 1.54 * 0.069 = 11.5 pounds of air (mass air flow)

with apparently a 1:10 ratio between pounds and HP, should result in about 115 hp :rasta: slightly better than a 22re :flipoff2:



with a 1.5 pressure ratio and 11.5 lbs of air, the below GARRETT® GT2554R at the link

PT Turbo | PT Turbo

seems to have a map that has the most potential to be functional across the range you might see. Somebody, anybody, else please please double check me on this and let me know why i'm out to lunch :beer:

they claim:

Horsepower: 170 - 270

Displacement: 1.4L - 2.2L


but i think they are working with better base engines :laughing:



ORIGINAL GT SERIES AERODYNAMICS
INTERNALLY WASTEGATED TURBINE HOUSING
SOLD AS A COMPLETE TURBO (INCLUDES TURBINE KIT & ACTUATOR)
SMALLEST BALL BEARING CONFIGURATION AVAILABLE
WATER COOLED CHRA


internal wastegate makes this $800 turbo pretty nicely priced for a brand new unit, that you could probably call and get setup closer to what you want from them and have support


and then the next question would be: can you flow enough fuel to support 115 hp? should be pretty easy with the propane, i'd imagine any setup that could support 80 hp could support 115 :rasta: set the base timing back, i dunno, 5? 10? degrees, start and WOT a full pull on a flat spot, check for knock. no ping? add some timing, try again. do a good loaded pull until it starts to have a problem, back it off, i dunno, 2 or 3* for safety and call it a day


double edit: that final 115 HP would be with the 80 HP gas as a base reference, max tuned, probably 100-105 ish HP on the 'pane?
 
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hahaha.. yeah, I use to be about the numbers.. not anymore

you are one of those smart number guys arent ya?

I've seen vehicles runnin propane on trails, and talked a little with owners.. but I dont know basics.. how they run.. what the differences are? the vehicle does still need air right?

i might not be smart anymore, but i'm certainly still a numbers guy :laughing: :D

yes indeed, still need air to get mixed in there. biggest difference is the octane and BTU ratings. i.e. propane is more stable and less energy dense than gasoline.

less important, propane goes from a liquid to a gas at a low temperature, so it is pretty easy to mix with air and droplets are less of a concern, hence gas with fancy direct injectors and such to increase atomization.

added bonus of the low flash point, no fuel pump needed for propane either. storing it under pressure helps keep it dense and a liquid, so simply venting that pressure flows enough that a pump isn't required.

also less important for most people, propane is shelf stable for years without all the additive crap that our tax dollars go to pay for in the name of junk science and theft (ethanol subsidies are widly accepted as junk science these days, instead of when that was a fringe view during considerations for subsidy programs; just another real life example why we should all fear "trust the science" from anybody, on anything)

semi-important, propane burns significantly more clean and takes much longer to kill you :) nice for crawlers and trail rigs
 
Factory solution to save the day.

2005-2009 Subaru outback/legacy turbo is "factory set" to 8 psi.

hit up a junkyard and take the intercooler, turbo, oil fittings, and whatnot. easy button and probably the cheapest option out there. should work plenty well enough.



turbo pressure | Subaru Outback Forums

Just to clarify the 16.x pounds was an instantaneous peak reading and I wasn't in road conditions that allowed for sustained full throttle acceleration, so I wasn't showing a sustained 16 psi and I wasn't doing logging.

Realistically if the 2.5 liter NA does 180 HP, the 2.4 should be approximately 175 hp with zero boost.

260 divided by 175 gives approximately 1.5, and ignoring things like heating of the intake charge, intercooler efficiency, a theoretical 8 psi boost in the 2.4 would give 260 horsepower, so I'm pretty sure that the boost at the rated 260 horsepower is not 16psi, at least not above 5000 RPM. To flatten the torque curve the boost at mid-RPM on a small turbo (to reduce lag) is higher and it tapers off at higher RPM.

My guess is that the boost on our 2.4 is closer to 12psi average in most conditions under full throttle instead of the 16 which is overly optimistic.https://www.subaruoutback.org/threads/turbo-pressure.525600/
https://www.subaruoutback.org/threads/turbo-pressure.525600/

Rev9Power: T25 Internal Wastegate Turbocharger - Turbocharger - Force Induction

Turbos, Nitrous & Superchargers for 2008 Subaru Outback for sale | eBay
 
Factory solution to save the day.

2005-2009 Subaru outback/legacy turbo is "factory set" to 8 psi.

hit up a junkyard and take the intercooler, turbo, oil fittings, and whatnot. easy button and probably the cheapest option out there. should work plenty well enough.



turbo pressure | Subaru Outback Forums



Rev9Power: T25 Internal Wastegate Turbocharger - Turbocharger - Force Induction

Turbos, Nitrous & Superchargers for 2008 Subaru Outback for sale | eBay

I have a Forester intercooler of that vintage I don't need on a shelf if anyone needs it.

Also, all the Bajas came with a turbo so if you're hitting up junkyards looking at those is a better use of your time than the wagons.
 
that final 115 HP would be with the 80 HP gas as a base reference, max tuned, probably 100-105 ish HP on the 'pane?

So for giggles and shit's, how much power from the 10-1 head? I'm not buying the claims on power gains.
 
A lot of people swap out to a different Mercedes head that came stock with a 9.3:1 compression.

Sorry, 9.3-1. So roughly 4% gain per compression point would have you at 92.82HP. Totally worth it :lmao:

Turbo that bitch!
 
So for giggles and shit's, how much power from the 10-1 head? I'm not buying the claims on power gains.

going from 7:1 to 9.5:1 should result in a pretty decent gain, relatively. you'd be looking at a much better VE for the airflow you are moving. from 80 to 90 is pretty respectable, but it is no 105! :laughing:
 
Why does every engine thread never talk about what's really important?:flipoff2:

TORQUE

You'll get larger torque gains from boosting the engine as opposed to bumping the CR a couple points. Since i assume the Mog engine isn't a screamer, a smaller turbo can be used to spin up the boost quick. The propane can also be used to cool the charge.
 
Have any of the people who make a big deal about the # of main bearings in this engine actually tried to turbo one and had problems? I'd do the head swap and then the turbo if the head wasn't enough gain on its own. Low compression and boost makes for a lazy engine when it's not making boost. High compression and low boost IMO would be a more drivable trail rig than the other way around at the same HP level.

This is good advise.
 
Well all this planning has gone out the window.

It never fails, but after giving up on finding one, I scored that unicorn of a motor, the M130 from a late '60s mercedes 250s. It has 140HP stock at 9:1 compression. So with the potential loss from going propane and all that extra HP .... I think I'll be happy lol

Anybody want to buy a crated NOS M180? :lmao:
 
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