Slant Six Forum :: 1981 dodge diplomat performance mods

Hello, ive got a 1981 dodge diplomat with the 3.7L v6 "super six" engine. Ive done a lot of research and can say from personal experience that these engines are kind of lack luster and id like to get some more HP and maybe even a little more mpg here or there. However, im having trouble finding any mods that might help me do that. For instance im unable to find anything like cold air intakes or catback exhaust systems systems that would fit this kind of car.

Long story short is there any kind of relatively cheap mod (cheap meaning under 2000$ all together for anything from turbochargers to air filters) that I can throw into my car to get more bang for my buck?

Mileage improvements

8. More valve lash: .012/.022

10. Cold ram air intake

14. NGK UR4GP 2869 .045 plug gap

Quote:

Mileage improvements

An 81 M body has a cold air intake system stock. It also should have a factory heat shield stock, but this likely disitegrated and fell off long ago.

I have an extra air intake tube and flex hose. Let me know if you want it and I'll shoot you a good price.

I also have a 2.71 ring and pinion as well as a posi carrier for 8.25.

Author:	Trystan_Lake [ Thu Apr 24, 2014 8:31 pm ]
Post subject:	1981 dodge diplomat performance mods
Hello, ive got a 1981 dodge diplomat with the 3.7L v6 "super six" engine. Ive done a lot of research and can say from personal experience that these engines are kind of lack luster and id like to get some more HP and maybe even a little more mpg here or there. However, im having trouble finding any mods that might help me do that. For instance im unable to find anything like cold air intakes or catback exhaust systems systems that would fit this kind of car. Long story short is there any kind of relatively cheap mod (cheap meaning under 2000$ all together for anything from turbochargers to air filters) that I can throw into my car to get more bang for my buck?

Author:	moparmatt441 [ Thu Apr 24, 2014 8:52 pm ]
Post subject:
http://www.slantsix.org/forum/viewtopic.php?t=55118 I have over 5000 miles on it and get between 25 and 28 mpg depending on how much fun I have with the go pedal.

Author:	Trystan_Lake [ Thu Apr 24, 2014 9:01 pm ]
Post subject:
Thanks for the quick response, thats a really cool set up! I'm not really capable of pulling something like that off on my own though. Tomorrow I plan on phoning some garages in town and seeing what they have to say about upgrades and such, maybe if I can find someone whos willing and able ill be able to pull something off thats similar to what youve done.

Author:	Reed [ Fri Apr 25, 2014 9:07 am ]
Post subject:	Re: 1981 dodge diplomat performance mods
Quote: Hello, ive got a 1981 dodge diplomat with the 3.7L v6 "super six" engine. Ive done a lot of research and can say from personal experience that these engines are kind of lack luster and id like to get some more HP and maybe even a little more mpg here or there. However, im having trouble finding any mods that might help me do that. For instance im unable to find anything like cold air intakes or catback exhaust systems systems that would fit this kind of car. Long story short is there any kind of relatively cheap mod (cheap meaning under 2000$ all together for anything from turbochargers to air filters) that I can throw into my car to get more bang for my buck? FYI- the slant six in not a "v-6," it is an inline six cylinder engine. Also, many people on this board will disagree with your personal experience that these engines are "lackluster." Your questions suggest that you don't have much experience with this engine or with older cars in general. However, I do have some polite sugestions for you. You won't find any off-the-shelf or ready-made kits for an 81 Diplomat, or even for a slant six. However, the fact that you have a Super Six mean you are ahead of the game. The Super Six package came from the factory with a cold air intake (the hose from the end of the air cleaner snorkel to the driver's side inner fender wall) and the big factory exhaust (2 1/4 inches). At this late date it is entirley possible that the cold airt intake hose has gone missing and the cats have become clogged. Fortunatley it is simple and cheap to replace the cold air intake hose (get some dryer hose of the right diameter form a hardware store). The cats can be replaced with new high flow three-way catalytic converter, or removed from the exhaust entirely. Free-flowing or removed catalytics will let the engine breathe easier and will help performce and economy. Really, the first thing you should do it give the engine a thorough tune-up. Verify the the vacuum and mechanical advance systems in the distrinbutor are working, verify that all settings on the carb are correct and that it is in good working order, verify that the transmission kickdown linkage is adjusted properly, replace the air filter, change the oil to 5W-30 oil and a new Wix or Napa Gold or Purolator oil filter. Additionally, since your car is an 81 you likely have 2.7 or 2.9 gears in your rear axle. Switching those out for 3.2 or 3.5 or numerically higher gears will greatly improve performance, but possibly hurt economy. For $2000 you can get new gears in your rear axle and do some simple engine modifications like a new cam and some head work and even increasing your dynamic compression ratio. That would be what I suggest, as well as replacing or removing the cats. Good luck. Working on and modifying a slant six powered vehicle is not as simple as buying off-the-shelf parts for a Honda or Toyota. You will need to have a realistic goal of what you want to achieve and do your homework and math on how to achieve it.

Author:	Reed [ Fri Apr 25, 2014 2:43 pm ]
Post subject:
Quote: Mileage improvements 8. More valve lash: .012/.022 81 should be a hydraulic motor, so no valve lash to set. Quote: 10. Cold ram air intake An 81 M body has a cold air intake system stock. It also should have a factory heat shield stock, but this likely disitegrated and fell off long ago. Quote: 14. NGK UR4GP 2869 .045 plug gap I don't believe those are the right plugs for the 81 peanut plug head. I could be wrong though. Quote: 17. Electric fans An 81 Diplomat may already have a factory clutch fan. I don't think the cost and difficulty of swapping to electric fans from a clutch fan is worth it. By 81 Chrysler was already doing many of the easy things to improve economy and power. Like I said, short term a good and thorough tune-up, oversize exhaust with free flowing muflers and no cats, and a rear axle gear change will likely get this guy closer to what he wants. Long term he can start learning about things like disributor re-curving, cams, dynamic compression, etc...

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Author:	Aggressive Ted [ Fri Apr 25, 2014 2:21 pm ]
Post subject:

Author:	DusterIdiot [ Fri Apr 25, 2014 5:25 pm ]
Post subject:	It's...
UR4 (GP) is hotter than the stocker UR5 that would be used in that head...I would advise against going hotter since the car is heavier than loaded A-bodies, and the BBD might need going through (it might be lean if it has a throttle shaft leak and causing it to be a little "lack luster), going to the UR4 would cause some misses and possible other issues. x2 on checking axle ratio (if the previous owner tanked the original 8 1/4", and used a junkyard replacement a 2.45/2.56 might be under there making things realllly bad). -D.Idiot

Author:	1930 [ Fri Apr 25, 2014 5:42 pm ]
Post subject:
Quote: Quote: Mileage improvements An 81 M body has a cold air intake system stock. It also should have a factory heat shield stock, but this likely disitegrated and fell off long ago. Do you or anyone have pictures of this heat shield, I have seen Teds, plan to do the same but would like to see an original and compare what they look like. I like the original look and will always try to get as close to that as possible. Thanks

Author:	Mr Zeal [ Fri Apr 25, 2014 6:55 pm ]
Post subject:
I have an extra air intake tube and flex hose. Let me know if you want it and I'll shoot you a good price. I also have a 2.71 ring and pinion as well as a posi carrier for 8.25.

Author:	Aggressive Ted [ Fri Apr 25, 2014 8:49 pm ]
Post subject:
Reed, This question is asked so many times.....over the weeks, months, years.....I just put every-bodies answers into a list...and did a cut and paste from my SL6 folder. It's food for thought......thanks guys! You never know with some of these cars if they still have the stock motor in them at this age......so I covered all the bases..... IT should be a sticky in the Engine FAQ.

Author:	Reed [ Fri Apr 25, 2014 9:53 pm ]
Post subject:
I figured that was what you did Ted. I just wanted to make sure this guy knew what he had.

Author:	Trystan_Lake [ Sat Apr 26, 2014 12:06 am ]
Post subject:
Reed, Tons of useful information in your posts, thanks a lot. I am indeed new to older vehicles and this kind of engine but im eager to learn anything I can. I apologize if ive insulted you or anyone else by calling the engine lackluster I really shouldn't be so hasty to put down the engine because it is a great engine and I do like it. I do still have the cold air intake hose but the hose running from directly below the air cleaner housing and towards the side of the block is super dry rotted so im going to replace that hose asap. Also, im actually booked to go down to the muffler place next week and talk to them about possibly throwing a new high flow catalytic converter in there and changing my exhaust around a bit.

Author:	Trystan_Lake [ Sat Apr 26, 2014 12:19 am ]
Post subject:
Ted, First I want to say I like your 74' swinger and I like being able to look at the pictures of your engine next to mine. I've got to say mine could use a really good cleaning of pretty much everything in the engine bay and maybe some fresh tubes/wires after the 33 years its been on the road. Thanks for that list of mileage related bullets and thanks again Reed for clarifying a few points from it.

Author:	1930 [ Sat Apr 26, 2014 2:53 am ]
Post subject:
Quote: I have an extra air intake tube and flex hose. Let me know if you want it and I'll shoot you a good price. I also have a 2.71 ring and pinion as well as a posi carrier for 8.25. Hell Mr Zeal, I am in need of the mentioned part and have sent you a P.M Seems like Trystan has the part already so I guess its ok for me to show an interest. Thanks

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Author:	wjajr [ Sat Apr 26, 2014 4:40 am ]
Post subject:
Trystan_Lake: I apologize if ive insulted you or anyone else by calling the engine lackluster When these engines are out of tune, smogged up due to ancient technology they are lackluster. In fact most of the cars produced between 1974 and 1986 or so were pigs in the performance department, great wallowing hogs sporting dinky detuned engines in the quest for more mpgs, and cleaner air. The government even lowered the national speed limit to 55 just to keep up with these heaps. LOL We can show you how to breathe some perkiness into your ride. Mr. Zeal: I also have a 2.71 ring and pinion as well as a posi carrier for 8.25. I think 2.71:1 is still in the too tall range for much increase in performance. I would figure out what rear gear your car has, and go from there.