Engine Power

[TomC]

All this talk about going up and down hills made me reflect back on the changes I've done to my 8V-71 with V730.  When I first bought the bus, the N55 injectors (253hp and 680lb/ft torque) were changed for brown tag N65's (304hp and 800lb/ft torque).  While it performed better, it did smoke a bit at sea level and alot at higher altitudes.  So much so, I went through the expense (about $12,000) to have the engine turbo'ed and air to air intercooled (don't know of another 2 stroke with air to air intercooling).  Now with 9G75 injectors, am getting 375hp and 1125lb/ft torque.  Compared to the original setting, is a substantial increase in both hp and especially torque.  On my recent Mammoth trip, cruising most of the time at 1850rpm and 58mph, got 5.8mpg-which I can live with.  I can tell you the performance difference is almost unbelievable, the turbo really wakes up the 8V-71. I personally like the 71 series better than the 92 series mainly because the 71 has dry cylinder liners that can't leak and it is more tolerant to overrevving than the 92 (92 series should be maxed at 2350, while I know truck drivers that regularly revved their 71's to 2800rpm).  My point- if you have 55 or 60 (280hp and 745lb/ft torque) injectors in your engine, keep them.  Going to the 65 injectors will give you a bit more power, but a big hit on fuel mileage.  If you want to do anything for getting more power, either a complete engine change to a much bigger engine, or like I did the turbo for a substantial power gain is the only real way to go for any noticeable change in performance.  Good Luck, TomC

[luvrbus]

Tom, make that 2 with air to air just now finishing up on mine

[bobofthenorth]

So Tom, short of putting it on a dyno, how would I tell what HP my 8-92 is supposed to be making?  It doesn't really matter - its enough for me the way it is but I get asked fairly regularly & it would be nice to give an intelligent sounding answer. 

[Ncbob]

Tom, you make me very proud.  I've been a 71 series fan since the 60's and don't have much respect for a wet liner engine.  If it weren't for the old 185 HP Graymarine 6-71 conversions in the landing craft...we might not have won WWII.

Detroit Diesel had a tremendous record of reliability for many years, having cornered the market in the Marine field...perhaps the toughest, most stressful condition an engine could be placed in...uphill all day long. It wasn't until Penske decided to change things that the record got messed up.

My 8V71, in my MC5A, is the cleanest burning, smoothest running engine I've had under me since I got off Motor Yachts in the mid '80's..and I always ran with pairs.

Give 'em clean fuel, clean air, clean oil and clean coolant and don't lug 'em and they'll run forever. They're "Inefficient, hot running, Mother Breezers" but they've always brought me home!

Bob

[lostagain]

As mentionned earlyer, I turboed my 4-71 last winter and it was well worth it. I don't know the numbers, but there is a very noticeable difference. With the 5 speed Spicer, I now go up hills one gear higher than last year, and don't notice the little rises on the highway as much anymore. I stayed with the same injectors (N65) so I'm not making more heat than before. I'm doing 6 to 7 psi of boost. I'm thinking about a intercooler Tom! That turbo really did wake up the 4-71 and it is well worth the trouble and I recommend it to anyone with a 71 series, which is indeed the greatest engine ever built!...

[TomC]

Bob- if you pull one of your valve covers, look at the round tag on the injectors and post what it is.  Usually something like 9G90, etc.  If it is electronic, you'd have to hook up to a lap top to see what it is set to.  Give me the injector size and year of the engine, and I'll be able to come very close to your power setting.  Good Luck, TomC

[bobofthenorth]

Thanks Tom.  Like I said, its not a real high priority and, since it involves pulling the valve cover, not likely to happen in the near future.  If for no other reason, I seem to have a non-leaking Detroit & pulling a valve cover for no good reason is just asking for trouble in my opinion.  But if I ever do have occasion to have the valve covers off I will get the information.  In the meantime I'll just enjoy the power I've got and continue answering the questions with the line of BS I have been using. 

[TomC]

You shouldn't be afraid of pulling the valve cover. The modern gaskets are silicone and won't stick and are reusable.  I pulled the valve covers several times on my first truck and never had a leak.  In fact I had to tip the cab many times to show other truckers that it didn't leak.  My bus engine is leaking from the alternator gasket, or the gasket under that with the adaptor plate.  When the weather cools, I will pull the alternator (not looking forward to that 100lb beastie) and the power steering pump to replace what is called the figure 8 gasket on the adapter plate, then the gaskets on the power steering pump and the alternator, then reinstalling the 100lb beastie.  Probably around November, in the meantime, just have to wash the rear of the bus after a few hundred miles of driving.  Good Luck, TomC