HarleyTechTalk

So, I've read that if you add a turbo charger to an engine, you want to have low compression, or a least not high compression.  I'm guessing the reason for this is that under boost, compression is increased and if you start with high compression you could end up with too much.  But that really is a guess.  Perhaps high compression results from a small combustion chamber and under boost your are packing more air (and fuel) in to the combustion chamber, so you want extra room, which means lower compression?  Again, I am guessing.

Regardless of the reason for wanting low compression when adding a turbo, how low is "low" in this context?  Also, won't the lower compression hurt performance when not under boost?

For the record, I am currently running a 2005 FXDLi punched out to 95" with 10.5:1 compression, head work, and Redshift 577 chain driven cams.

Thanks, and sorry for the blatant display of ignorance.

Personally... I've run from 7.8:1 through 10.5:1 on turbo applications in the automotive realm. Lots of variables and choices on the combination of the vehicle can dictate what it will like for static compression. In the past I used to settle on approx. 8.0:1-8.5:1 static, but with advances in modern 'race' fuels and modern EFI systems I now settle in the 9.0:1-9.5:1 static ratios most usually.

K.

Check out this guys site for Turbos. Harry built my 95".

http://www.atp-hd.com/gallery/5773646_6aEMe

Quote from: Y2KRKNG on September 18, 2014, 07:24:31 AM
Check out this guys site for Turbos. Harry built my 95".

http://www.atp-hd.com/gallery/5773646_6aEMe

I found it odd they suggest using a non syn oil for turbo operation. Kendal GT1 is just a basic motorcyle oil.
Ron

Kendall 1057267 GT-1 High Performance SAE 20W-50 Motor Oil with Liquid Titanium
by Kendall

Exclusive liquid titanium additive technology for extra protection against engine wear
Excellent resistance to viscosity and thermal breakdown at high temperatures
Racetrack proven performance

Here is their Jargon above... What ever Titanium is?

signed....BUBBIE

Quote from: BUBBIE on September 18, 2014, 08:03:35 AM
Kendall 1057267 GT-1 High Performance SAE 20W-50 Motor Oil with Liquid Titanium
by Kendall

Exclusive liquid titanium additive technology for extra protection against engine wear
Excellent resistance to viscosity and thermal breakdown at high temperatures
Racetrack proven performance

Here is their Jargon above... What ever Titanium is?

signed....BUBBIE

It's the new FXR.

Quote from: Y2KRKNG on September 18, 2014, 11:50:29 AM

Quote from: BUBBIE on September 18, 2014, 08:03:35 AM
Kendall 1057267 GT-1 High Performance SAE 20W-50 Motor Oil with Liquid Titanium
by Kendall

Exclusive liquid titanium additive technology for extra protection against engine wear
Excellent resistance to viscosity and thermal breakdown at high temperatures
Racetrack proven performance

Here is their Jargon above... What ever Titanium is?

signed....BUBBIE

It's the new FXR.

It's even a song these days.  lol

Kendal was/is a popular oil in performance circles.  I use to run Kendall in everything,  prior to switched to synthetic 20+ years back.

Sorry for continuing the OT.    Rick

Quote from: Y2KRKNG on September 18, 2014, 07:24:31 AM
Check out this guys site for Turbos. Harry built my 95".

http://www.atp-hd.com/gallery/5773646_6aEMe

Thank you.  If I go with the turbo, as opposed to a 124" from S&S, I will have a (relatively) local indy build one from scratch.  The shop builds them pretty regularly.

I think NCTurbos summed it up nicely but comments below: 

I'm guessing the reason for this is that under boost, compression is increased and if you start with high compression you could end up with too much.  Yes But that really is a guess.  Perhaps high compression results from a small combustion chamber and under boost your are packing more air (and fuel) in to the combustion chamber, so you want extra room, which means lower compression? No, not necessarily.  All that matters is the compression ratio regardless of combustion chamber size and perhaps maybe a chamber that promotes good flame propagation Again, I am guessing.

Regardless of the reason for wanting low compression when adding a turbo, how low is "low" in this context?  Also, won't the lower compression hurt performance when not under boost? I think NCturbos is correct and 8.5 used to be about the limit of compression on a turbo motor, so if you were running a camshaft designed for high RPM, when not on boost the low end torque could really suffer.  I have a Mazda Speed 3 sports car that runs 9.5 and has a turbo but it has direct injection, variable valve timing and a very sophisticated engine control module.  Harley's don't have that, so I think you will be limited to about 9-1 max and the higher your static compression the less boost you can run.  Then there is the possibility of "turbo-lag" throttle response but that has been eliminated with modern technology on most turbo designs.  Reliability-wise the S&S T124 sounds more reliable IMHO and comes with a warranty. Just my humble opinion.  Maybe your local shop will offer you some informal warranty for the engine they build for you.  That being said, you get extra points for originality and a "coolness factor" with your turbo that very few have!  Regards, -Tutt 

Quote from: CowboyTutt on September 18, 2014, 05:59:23 PM
Reliability-wise the S&S T124 sounds more reliable IMHO and comes with a warranty.[/color]

Andy,  I'm still thinking you would be contemplating the same for yourself,  given all you've been through.   Rick

Quote from: CowboyTutt on September 18, 2014, 05:59:23 PM
I think NCTurbos summed it up nicely but comments below: 

I'm guessing the reason for this is that under boost, compression is increased and if you start with high compression you could end up with too much.  Yes But that really is a guess.  Perhaps high compression results from a small combustion chamber and under boost your are packing more air (and fuel) in to the combustion chamber, so you want extra room, which means lower compression? No, not necessarily.  All that matters is the compression ratio regardless of combustion chamber size and perhaps maybe a chamber that promotes good flame propagation Again, I am guessing.

Regardless of the reason for wanting low compression when adding a turbo, how low is "low" in this context?  Also, won't the lower compression hurt performance when not under boost? I think NCturbos is correct and 8.5 used to be about the limit of compression on a turbo motor, so if you were running a camshaft designed for high RPM, when not on boost the low end torque could really suffer.  I have a Mazda Speed 3 sports car that runs 9.5 and has a turbo but it has direct injection, variable valve timing and a very sophisticated engine control module.  Harley's don't have that, so I think you will be limited to about 9-1 max and the higher your static compression the less boost you can run.  Then there is the possibility of "turbo-lag" throttle response but that has been eliminated with modern technology on most turbo designs.  Reliability-wise the S&S T124 sounds more reliable IMHO and comes with a warranty. Just my humble opinion.  Maybe your local shop will offer you some informal warranty for the engine they build for you.  That being said, you get extra points for originality and a "coolness factor" with your turbo that very few have!  Regards, -Tutt 

Thanks, CowboyTutt.  That's the kind of information I was looking for.

Depends on durability, too. More fun = more work= more $. Red is 120 @ 11.3 w/Tman 662-1 cams. Blue is 113 @ 10.5 with Woods 8 and a Procharger.

You want to keep the static compression as low as possible. You make up for it with boost, the boosted air contains your
fuel charge, so more boost = additional fuel.

I ran 8:1 on my blown boats (dished pistons).

If you are going to put a turbo on a Harley, you really want to talk in terms of dynamic compression, not static.   Focusing on static compression is a sure way to screw up an expensive turbo installation.

The turbo motors we build .we try to keep  below 9.1 we are able to run more boost and timing .we like to run cams 114 to 112 lsa no more than 240 duration. On motors running more than 20 .we run the on e85.or methanol  injection.we don go crazy with porting and we focus on the exhaust side for as much velocity as possible to keep the turbos spooling .then again i dont know how much this would apply to the harley motors but a 4 cycle motor is a 4cyle motor in any application with forced induction this should apply .if you start to building to much compression your going to smash the ring lands together and seize the piston in the bore .then the pinbore in the piston will break and the connecting rod will destroy the  cylinder and case.so tred light with compression  and forced induction.

Bagger Paul, that reinforces what I also have read about supercharged motors: that the exhaust port flow in the heads is much more important than the intake port flow and that a greater camshaft lobe separation angle is beneficial.  Not too much cam overlap either.     -Tutt   

Off topic but I remember the V6 Buicks at Indy hauling the mail. Keep the cubes small and pack em full of charge. As was said before, low comp.dish pistons and after 15 pounds a great intercooler with good blow numbers.

Ya tutt there is really no reason than too just clean up the intake ports with a stone and a sand roll nice valve job and call the intakes done .it is forced induction.good quality intakes and exhaust valves are a good idea to spend money on for high end builds delwest is a no brainer for good quality valves .

I saw a recipe recently with the same speak as baggerpaul is taking. He had cam made along those lsa numbers. Super numbers on the exhaust and a custom made compressor wheel and intercooler. He made over 200 hp easily. I will give him a call today and see if can get some better specifics.

-- ALL my automotive turbo cams, which I designed and have Comp Cams grind for me, run 112* LSA and 110* ICL, and NO overlap. I did have Andrews grind me a set as well... 

-- I disagree mostly with what is being said about the importance of the exhaust to intake flow ratio...

--jam65, you ever see the cylinder heads from the Buick Motorsports programs? I have had a few sets here, both Indy & NASCAR style heads. Man they move some air!! Especially the intake side...

--Static compression, dynamic compression, cylinder pressure... It's amazing what you can do with the right fuel, some datalogging, and the ability to make program changes. The oem EFI systems on our Harleys is light years ahead of the oem ECM systems on the cars I build, unless I'm working with XFI, BigStuff3, etc...

--Most turbos these days incorporate MFB compressor wheels & high flow exhaust wheels. Choose the correct A/R exhaust housing, and keep the back pressure down...

K.

Quote from: gordonr on September 20, 2014, 05:21:00 AM
I saw a recipe recently with the same speak as baggerpaul is taking. He had cam made along those lsa numbers. Super numbers on the exhaust and a custom made compressor wheel and intercooler. He made over 200 hp easily. I will give him a call today and see if can get some better specifics.

The engine is a 105" @ 9:1 cr. Has a Garret 25 on it set at 13 psi. Using a Trask kit hardware. With a custom made intercooler that mounts directly on to the intake manifold. He wouldn't allow me to mention particulars about the heads but they are stock castings.

Quote from: jmb79 on September 18, 2014, 06:15:00 AM
So, I've read that if you add a turbo charger to an engine, you want to have low compression, or a least not high compression.  I'm guessing the reason for this is that under boost, compression is increased and if you start with high compression you could end up with too much.

Sounds like you have a good grasp on the fundamentals but just to clarify, compression does not increase with added boost. The compression ratio remains constant but "cylinder pressure" will increases dramatically with forced induction.

I think a turbo charged Harley would be a lot of fun but the biggest issue I would be concerned about is heat. Harley engines are air cooled and turbo chargers tend to generate a lot of heat which is difficult to manage without the aid of liquid cooling. On top of that, the intake charge also heats up as a result of the air being compressed by the turbo which is why many automotive applications also run an intercooler. As the intake charge heats up, it can quickly become a case of diminishing returns...

I would personally be inclined to lean toward a big-inch naturally aspirated V-twin for long term performance and reliability on the street.

Just my two cents...

Quote from: NCTURBOS on September 20, 2014, 06:38:15 AM
-- ALL my automotive turbo cams, which I designed and have Comp Cams grind for me, run 112* LSA and 110* ICL, and NO overlap. I did have Andrews grind me a set as well... 

-- I disagree mostly with what is being said about the importance of the exhaust to intake flow ratio...

--jam65, you ever see the cylinder heads from the Buick Motorsports programs? I have had a few sets here, both Indy & NASCAR style heads. Man they move some air!! Especially the intake side...

--Static compression, dynamic compression, cylinder pressure... It's amazing what you can do with the right fuel, some datalogging, and the ability to make program changes. The oem EFI systems on our Harleys is light years ahead of the oem ECM systems on the cars I build, unless I'm working with XFI, BigStuff3, etc...

--Most turbos these days incorporate MFB compressor wheels & high flow exhaust wheels. Choose the correct A/R exhaust housing, and keep the back pressure down...

K.

MAYBE I SHOULD HAVE SPECIFIED lol we have very good flowing heads to begin with so we don't start to hog the intake side just a nice clean up and a good valve job we do spend time to keep velocity high on the exhaust side .  always depends on the stick you use on what flow want for them to compliment each other but with forced induction its very forgiving . when you start with a 225 cc runner what digging are you really going to need on a nice head  running a 2.07 intake with forced induction