Low compression question

[Magoo]

Just so I understand correctly. Lower compression with the turbo, allows more boost, hence, more air and more power? Also. Does the IP need to be calibrated for different comp, boost ratios?

 

[argve]

No - it will still run just fine.

Yes - if you want to reap the bennies from having more air to play with... hence meaning more air which can handle the added fuel from recalibrating the Injection Pump.

It's the fuel that makes the power or more so the more fuel you can burn in the cylinder.

By just adding more air without adding more fuel will equal out the same amount of power - but add more air then add in more fuel will yield more power.

 

[chris88]

Can these pumps be turned up enough to benifit from lowering compression? With lowered compression and maxed out pump and possibly intercooler what sort of boost numbers could you be looking at?

Chris

 

[Magoo]

Can these pumps be turned up enough to benifit from lowering compression? With lowered compression and maxed out pump and possibly intercooler what sort of boost numbers could you be looking at?

Chris

I was leaning that way myself.

 

[argve]

I don't know first hand but from talking with Ken at DPS over the 2004 IDI Rally he says that he built a pump that really poured out the fuel - he built it because he was running a lowered compression engine. I know from talking with him he mentioned that he had to remove the vane supply pump and regulator inside the injection pump because it could not flow enough volume to keep the pump supplied. Both of these items are located in the nose cone of the injection pump.

But I have no first hand experience with lowering the compression in these engines - but from talking with Ken his is a real pain to get started even at 50 degrees. so that is something to consider...

 

[Magoo]

I thought the 94 factory turbo was lower in comp than the non turbo units. What im looking at is more reliability and longevity of the block, along with some increased power "without" sacrificing much in mileage. Tall order I know.

 

[tuckerd1]

I thought the 94 factory turbo was lower in comp than the non turbo units. What im looking at is more reliability and longevity of the block, along with some increased power "without" sacrificing much in mileage. Tall order I know.

Aren't the MAIN differences between the NA and turbl IDI's the rods are larger and have larger wrist pins.

Do the turbo IDI's have different piston tops for lower compression??

 

[NapaBavarian]

I was considering lower compression, but decided I wouldn't do it on a daily driver, perhaps on a toy truck. It seems the chebbie guys need it, but their engines are lighter duty than ours, not sure if that has anything to do with it.

 

[Magoo]

This is what I remember hearing. NA motors were 20 or 22 to 1 comp. Aftermarket turbo boost is around 7lbs. Factory turbo 7.3 was somewhere around 17 to 1 and was boosting around 14 or 15. I dont remember when or where I got this but its been in my head for a few a while.

 

[94f450sd]

This is what I remember hearing. NA motors were 20 or 22 to 1 comp. Aftermarket turbo boost is around 7lbs. Factory turbo 7.3 was somewhere around 17 to 1 and was boosting around 14 or 15. I dont remember when or where I got this but its been in my head for a few a while.

youre thinking psd

max boost on a factory turboIDI is around 6PSI.max safe boost level on any IDI i believe is around 12PSI before popping head gaskets.94-earlier 7.3 idi is 21.5:1

 

[argve]

Yep all the IDI had about the same comp ratio... the only difference was the first year of the 6.9 which was slightly lower (not by much)... All the engines were 21.5:1 Didn't matter if it had a turbo or not. The PSD is where they lowered the compression so that they could stuff more air in the mix...

 

[Magoo]

Thank you guys. So the lower comp on an idi is gonna create hard cold start issues? Wouldnt be a problem normaly for me anyway except when i am elk hunting and its 10 degrees and none of the trees have an outlet. Well I guess this is a gain in the apples lose in the bannanas issue. Too bad. I feel pretty confident that lower comp and more air fuel mix would to a point improve milage and reliability. My thinking is that if you had more power available you would not have to push so hard to get the momentum. Its the old 4 barrel- 2 barrel argument. If you dont stick your foot into it all the time the 4 barrel will get you better milage.

 

[Freight_Train]

well,you can drop the compression a tick or two and it won't hurt hold starting.But if you drop it to like 18-1 or 18.5-1 then your gonna need really really good batteries,starter,and Glow plugs(and maybe thrown rod in a can).They sell "Low compression' pistons on Ebay.They are actually Mahle Turbo pistons that have the crown lowered for blocks that have had the deck ground down a little.I think they have a compression ratio of like 20.5-1 give or take.

 

[dieseldummy]

On my GM 6.5 and current 6.2 I've ended up lowering the compression. I know they're not exactly the same as a 6.9/7.3, but the idea is there. The 6.5 was 18:1 and the 6.2 is around 19:1 and they both always start. My 6.2 only has one battery and I started it this winter when it was around -10 unplugged. I had to run the glowplugs alot longer and keep running them after it started, but it did start. If your planning on doing it to your daily driver I would probably discourage it for the starting reasons. If you plan on running a big turbo and lots of fuel then I consider it a must. At least you guys get to worry about the headgaskets in stead of the rods/block...