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Javelin v8 swap

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sweatlock View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote sweatlock Quote  Post ReplyReply Direct Link To This Post Posted: Nov/16/2016 at 7:24pm
Originally posted by oldironneverdies oldironneverdies wrote:

My jav definitely has the t14, Looked under it today. The rear is a 15.
  It seems like this is not a good idea.
The jav averages 23 mpg as is and cruises 70 75 mph getting 21 mpg.
 I think Ill leave it alone and enjoy it as it is.
 Thanks for the great responses !


I think that's an excellent idea - there aren't many 6 cylinder Javelins left anymore and I think it would make a practical and interesting daily driver for commuting to work or what-have-you.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote mitchito Quote  Post ReplyReply Direct Link To This Post Posted: Nov/16/2016 at 11:29pm
I agree, there are plenty of V8 Cars out there and so few 6s. Even if you wen't with a V8, the car would still be slow compared to today's cars, so why not keep it original?
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Post Options Post Options   Thanks (0) Thanks(0)   Quote farna Quote  Post ReplyReply Direct Link To This Post Posted: Nov/17/2016 at 6:02am
IF you feel a need for a bit more power you can easily upgrade the six you have. An Isky 256 Supercam will give a bit more power (10-15 hp by itself) without hurting gas mileage. A good 2" exhaust system with turbo muffler will help, probably already have that. Larger exhaust or true duals won't help at all. Too big an exhaust reduces low speed back pressure too much, and you need a little for best cylinder scavenging. Big exhaust only helps high rpm engines, like drag racing -- those expected to run 4000+ rpm a lot and make power there. The average street engine spends most of it's life in the 2000-3000 rpm range and should run well there. You can add an Offy DP 4V intake with a 390 cfm carb and get another 10-15 hp (maybe 20 if you have a 1V now). That can cost you gas mileage, but not if you leave your foot out of the other two barrels. The primaries on the 390 cfm carb are actually a bit smaller than those on the stock 2V carb. 

Those hp gains are just rough estimates based on other's results. Yours may vary depending on overall engine condition.

If you want a header.... I'd do the 4.0L head swap. That will get you better breathing and a better exhaust with the factory header. A new header alone can cost as much as the swap. 
Frank Swygert
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Post Options Post Options   Thanks (0) Thanks(0)   Quote maximus7001 Quote  Post ReplyReply Direct Link To This Post Posted: Nov/17/2016 at 6:11am
That 15 rear is not as weak as most people claim it is. I have had 2 of them over the decades doing burnouts in a Concord and some severe off roading with an Eagle as well as many 2wd burnouts, 500000km between the two. No issues. I have broken my fair share of gm 10 bolts over the years.

Edited by maximus7001 - Nov/17/2016 at 6:14am
1968 Javelin SST

1997 GMC Safari AWD

2001 Daewoo Nubira SX (Winnipeg only model)

1997 Honda Accord EX (Canadian Model)

Winnipeg, home of the Jets.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote amcfool1 Quote  Post ReplyReply Direct Link To This Post Posted: Nov/19/2016 at 12:10am
hi, absolutely agree with the above. Keep the six! A six can be a lot of fun, and they are SO easy to work on and around. (Except late Eagles :) whoo, that's another story!). If you want to upgrade it, a 4.0 head is a good idea, or if you don't want to go that far, get an intake/exhaust manifold set from any 81+ AMC/Jeep 4.2. Bolt right up, cheap, (ahem, inexpensive!), gets rid of that old cast iron intake/exhaust, save some weight, presto chango, you now have an ALUMINUM! 2bbl intake that can take a stock non feedback Carter BBD, or with an adapter, a MC2150, or even a Holley 350 2bbl if you want. Better cam of course!
Point being, you can leave that six as is, or take it as far as your wallet allows. Harlan Sharp roller rockers bolt right up, (unless this is a shaft style, dunno about that).
Anyway, with a little research, a couple of bucks, and some time, your six could be putting out 175-200 hp, more than the stock 290/304 of that era. And, you won't have to re-engineer the whole drive train.
good luck, gz
george z
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