6.9 vs. 7.3 boost?
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Postmaster
Joined: Jan 2010
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From: Elk City, OK
6.9 vs. 7.3 boost?
just wondering if there would be any boost difference between the 6.9 and 7.3l. like, if i am getting 7lbs of boost on my 7.3, throw my exact turbo setup on a 6.9 will there be any boost gain? i would thing tops 1lb of boost if any. heres the deal.... im debating if the engine i build up for my beast should be a 7.3 or a 6.9. im planning on keeping my intercooler and turbo. doin the ats turbo manifold, downpipe, moose pump and injectors. also upgrade the cam. any suggestions would be helpful. what are the base specs of the 6.9 vs 7.3? like, hp and tq at the crank.
Lead Driver
Joined: Dec 2002
Posts: 5,493
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From: Kuna ID
I think most people prefer to build the 6.9 as it has thicker cylinder walls than the 7.3 and you dont have to worry about sleeving it to rebuild it. IIRC, the only real differences between the 6.9 and 7.3 is the cylinder bore(larger displacement) and the rocker arms.
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Postmaster
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From: Elk City, OK
well, im not sure the condition of my spare block yet. i know it ran, guy said there was under100k miles on it. but dont they all say that? if the walls arent scared at all, then i wouldnt have to sleeve it. just a quick hone and ready to go. just wondering performance wise...
Elder User
Joined: Apr 2002
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From: West Bend
Of course that was *after* payment/signing
Fleet Owner
Joined: Jul 2006
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From: Mi'kma'ki
Peak Horsepower: 170 HP @ 3,300 RPM
Peak Torque: 338 lb-ft. @ 1,400 RPM
Horsepower & torque ratings peaked in 1986, producing 170 horsepower @ 3,300 RPM & 315 lb-ft. @ 1,400 RPM.
7.3l:
Peak Horsepower: 185 HP @ 3,000 RPM (190 w/ turbo)
Peak Torque: 360 lb-ft. @ 1,400 RPM (388 w/ turbo)
the 7.3l will out perform the older 6.9l.
there's no replacement for displacement.
source:
http://www.forgottendiesels.com/ford_diesel.html
cavitation is not so much of a concern today with modern coolants.
look around the diesels sites,and see how many threads you can find where the last 7.3l was taken due to cavitation.you'll likely find it's not a primary concern with the quest for the most power from an IDI.(many warning threads/posts,but not many examples of failure.)
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Postmaster
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From: Elk City, OK
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Fleet Owner
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From: Mi'kma'ki
actually,the 7.3l has less issues stock.however all can be upgraded to the 7.3l style/parts.
for example,you need to be mindful of 6.9l blocks that where weak around the block heater.
the GP system on the 7.3l is better.
the fuel filter w/built in water separator is better.
the rockers on the 7.3l are better.
overall the 7.3l is the better engine stock to stock imho.
well,it was to IH and Ford too of course as they replaced the 6.9 w/ the 7.3l of course.
there are a many 7.3l where the engines of course outlast the trucks.
dont underestimate 15 ponies and 22 lbs extra grunt to start with.your talking about a major mod to reach the same hp/tq as a stock 7.3l
when talking IDI performance,those numbers are quite impressive.
if you need a rebuild,boring out a 6.9l to a 7.3l is a good start.if it wasn't safe,IH wouldn't have done it,and we wouldn't have stories of 7.3l's going for several hundred thousand miles.
for example,you need to be mindful of 6.9l blocks that where weak around the block heater.
the GP system on the 7.3l is better.
the fuel filter w/built in water separator is better.
the rockers on the 7.3l are better.
overall the 7.3l is the better engine stock to stock imho.
well,it was to IH and Ford too of course as they replaced the 6.9 w/ the 7.3l of course.
there are a many 7.3l where the engines of course outlast the trucks.
dont underestimate 15 ponies and 22 lbs extra grunt to start with.your talking about a major mod to reach the same hp/tq as a stock 7.3l
when talking IDI performance,those numbers are quite impressive.
if you need a rebuild,boring out a 6.9l to a 7.3l is a good start.if it wasn't safe,IH wouldn't have done it,and we wouldn't have stories of 7.3l's going for several hundred thousand miles.
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Post Fiend
Joined: Nov 2003
Posts: 21,285
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From: Nutter Fort, WV
Cavitation is not so much of a concern with modern coolants, as long as you use the right coolant.
Regular green Prestone does nothing to protect from having cavitation issues today that it did not do in 1988.
However in 1988 you had very few choices for SCA protection, and they required adding a seperate addative.
Today there are many pre mixed SCA coolants on the market.
As for not hearing of as many cavitation reports today, the number of high miles driven every year IDI diesels has decreased today from what it was 20 years ago.
As for boost, the top boost numbers will not change because of engine displacement.
So if a turbo can make 20 PSI on a 7.3, it will also be able to make 20 PSI on a 6.9.
Boost is more related to the amount of fuel and RPM than engine size.
In stock form a 7.3 can stand more boost than a 6.9 because of lower base compression ratio and bigger head bolts.
Regular green Prestone does nothing to protect from having cavitation issues today that it did not do in 1988.
However in 1988 you had very few choices for SCA protection, and they required adding a seperate addative.
Today there are many pre mixed SCA coolants on the market.
As for not hearing of as many cavitation reports today, the number of high miles driven every year IDI diesels has decreased today from what it was 20 years ago.
As for boost, the top boost numbers will not change because of engine displacement.
So if a turbo can make 20 PSI on a 7.3, it will also be able to make 20 PSI on a 6.9.
Boost is more related to the amount of fuel and RPM than engine size.
In stock form a 7.3 can stand more boost than a 6.9 because of lower base compression ratio and bigger head bolts.
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