Getting just a little bit more from an 85 Diplomat
#1383481
02/08/13 04:23 AM
02/08/13 04:23 AM
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Joined: Feb 2012
Posts: 21
Mass
Eighty-Five-5th
OP
member
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OP
member
Joined: Feb 2012
Posts: 21
Mass
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Hi I am a previous user of the forum, I had a 85 5th Ave. It had 148k miles and I never got it to run right, ignition swap, 4bbl swap and all. I recently bought a 85 Diplomat with 84k original miles on it, and the ignition is already swapped for $650! I know I scored. The thing about this car is it has much better performance than my 5th had, so now I'm wondering if I can crack some more potential without ruining my gas mileage. I would like to get the heads milled, or buy a set, any reccomendations? I have a D4B intake already, I also have valve covers to dress it up. My question is what can I do to get this car right around the 250hp/325 ft lbs area, without ruing my mpgs. The car has the 727 with the really high gears in the rear (2:26's or something). I wouldn't mind keeping it a 2 bbl, what is a cam recommendation for some low end grunt, and a little highway fun? Any ideas? 
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Re: Getting just a little bit more from an 85 Diplomat
[Re: Eighty-Five-5th]
#1383483
02/08/13 10:32 AM
02/08/13 10:32 AM
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Joined: Oct 2003
Posts: 7,506
Az
Crizila
master
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master
Joined: Oct 2003
Posts: 7,506
Az
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Indy sells sm blk heads for around $499. They are all ready to go with 1.88 / 1.60 valves. Pocket port them and mill them and bolt them on. Dump the 2brl for a TQ. Find a 9 1/4" diff from a 75-9 Cordoba ( or truck as mentioned ). There are still plenty in the bone yards, many with 3.23 gears. Check with Hughes on a cam, but I would go with a HEH1019AL - or the 1523 if you can run a 3.55 gear. Cheap headers and dual 2 1/4" exhaust would be nice. Easy 14 second car with those mods.
Fastest 300
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Re: Getting just a little bit more from an 85 Diplomat
[Re: Eighty-Five-5th]
#1383484
02/08/13 12:35 PM
02/08/13 12:35 PM
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Joined: Jun 2003
Posts: 52,972
Romeo MI
MR_P_BODY
Master
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Master
Joined: Jun 2003
Posts: 52,972
Romeo MI
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I dont know if you drive it mainly in the city or out on the e-way the most.. but a set of 3.23 or 3.55 would actually give you better mileage in the city(you dont have to press the pedal as hard to get it rolling) 
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Re: Getting just a little bit more from an 85 Diplomat
[Re: Crizila]
#1383486
02/08/13 06:00 PM
02/08/13 06:00 PM
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Joined: Dec 2006
Posts: 3,533
Indiana
Fury Fan
master
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master
Joined: Dec 2006
Posts: 3,533
Indiana
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Quote:
Indy sells sm blk heads for around $499. They are all ready to go with 1.88 / 1.60 valves. Pocket port them and mill them and bolt them on. Dump the 2brl for a TQ. Find a 9 1/4" diff from a 75-9 Cordoba ( or truck as mentioned ). There are still plenty in the bone yards, many with 3.23 gears. Check with Hughes on a cam, but I would go with a HEH1019AL - or the 1523 if you can run a 3.55 gear. Cheap headers and dual 2 1/4" exhaust would be nice. Easy 14 second car with those mods.
75-9 Dobas have 8 1/4 axles (at least mine did, and it had a 400.) And don't hte 9 1/4 truck axles have durability issues?
If you're going to swap heads, look for -302s (small chambers for CR and good ports for swirl) which are good for about 250hp or go with Magnum heads for more power and MPG (research teh mods required).
i fyour engine is an 85 IIRC it'll have a rolelr cam. Research posts by Patrick for cam recommendations (and other good M-body knowledge).
Do you truly have a 727 in your '85? If so, consider swapping for an 80-newer 904 as it will have deeper 1st-2nd gears (2.74/1.54 vs 2.45/1.45) and that's the equivalent of deeper rearend gears *plus* it's lighter and absorbs less power than a 727 (you'll need a longer driveshaft but that's a JY part from any 904 Dippy).
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Re: Getting just a little bit more from an 85 Diplomat
[Re: Eighty-Five-5th]
#1383487
02/08/13 06:08 PM
02/08/13 06:08 PM
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Joined: Dec 2006
Posts: 3,533
Indiana
Fury Fan
master
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master
Joined: Dec 2006
Posts: 3,533
Indiana
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Quote:
but I don't have the money to swap to a 4bbl yet. I have the D4B intake, but I'd like to sell it in favor of one that will let me keep my Air Compressor. The reason I mention a cam is because I'd like to do it while the water pump is being done, along with a timing chain/gears.
If you can't afford a carb, have you added up how much a cam is going to cost? That's cam, lifters, springs, timing chian, timing gasket set, intake gasket set. Thats more than a $250 carb.
Although, I've read that the 360 2-V cam is a good upgrade for mild 318s, so you could maybe get a RockAuto regrind of that and your current springs would probably be suitable if you didn't rev it thru the roof.
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Re: Getting just a little bit more from an 85 Diplomat
[Re: Fury Fan]
#1383488
02/09/13 09:00 PM
02/09/13 09:00 PM
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Joined: Mar 2005
Posts: 3,142
Central NC
gch
master
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master
Joined: Mar 2005
Posts: 3,142
Central NC
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First thing I would do is replace the muffler with a less restrictive one and address in crimps or crushed pipe areas.Flowmaster makes a nice 2 into 1 y pipe that will outflow the factory one by a ton.Lose the cat or replace it with a high flow one.Maybe have to jet up the carb one size for max performance. Other than that I would wait until I had the money to do it right. Rear end swap first and then heads/cam/intake/carb and maybe headers. 
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