Poor man thunderjet mods?

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Poor man thunderjet mods?

Post  bigblackbronco on September 2nd 2013, 9:41 pm

I have a stock 429 thunderjet with a 4bbl of an unknown cfm carb (edelbrock) in this 79 bronco hooked up to a C6 and a NP205 transfer case. My block is a D0VE-A, the heads are both D0VE-C and the intake manifold is D0VE 9425-B. Crank and cams have not been verified. I want this truck to roast the tires but it wont. Boo. Does anybody have any ideas on pumping up the horses without doing any machine work. Small budget, big dreams. Any help would be much appreciated.
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Re: Poor man thunderjet mods?

Post  bigblok2000ranger on September 2nd 2013, 9:55 pm

Change crank and pistons to 460, verify what cam you have, 2500rpm stall(assuming stock or smallish cam), proper tuning of carb and timing, straight up timing set, proper gearing... just a few ideas.
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Re: Poor man thunderjet mods?

Post  rmcomprandy on September 2nd 2013, 10:14 pm

bigblackbronco wrote:I have a stock 429 thunderjet with a 4bbl of an unknown cfm carb (edelbrock) in  this 79 bronco hooked up to a C6 and a NP205 transfer case.   My block is a D0VE-A, the heads are both D0VE-C and the intake manifold is D0VE 9425-B.  Crank and cams have not been verified.  I want this truck to roast the tires but it wont.  Boo.  Does anybody have any ideas on pumping up the horses without doing any machine work.  Small budget, big dreams.  Any help would be much appreciated.
Leave the engine alone and change the torque converter to around a 2,800 RPM stall speed; (or even a bit more).
Until you know what cam is in it and exactly where, EVERYTHING you do to it will be just a "shot in the dark" guess.

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Re: Poor man thunderjet mods?

Post  jasonf on September 3rd 2013, 8:46 am

What size tires and gearing do you have?
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Re: Poor man thunderjet mods?

Post  bigblackbronco on September 3rd 2013, 10:14 am

jasonf wrote:What size tires and gearing do you have?
I have 35 mudders and a 9" rear end. Not sure what the gears are. When I got this truck I had the carb tuned on a 1960's Dyno. The old man doin it said my motor was putting out around 260hp at the wheels.
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Re: Poor man thunderjet mods?

Post  bigblackbronco on September 3rd 2013, 10:28 am

rmcomprandy wrote:
bigblackbronco wrote:I have a stock 429 thunderjet with a 4bbl of an unknown cfm carb (edelbrock) in  this 79 bronco hooked up to a C6 and a NP205 transfer case.   My block is a D0VE-A, the heads are both D0VE-C and the intake manifold is D0VE 9425-B.  Crank and cams have not been verified.  I want this truck to roast the tires but it wont.  Boo.  Does anybody have any ideas on pumping up the horses without doing any machine work.  Small budget, big dreams.  Any help would be much appreciated.
Leave the engine alone and change the torque converter to around a 2,800 RPM stall speed; (or even a bit more).
Until you know what cam is in it and exactly where, EVERYTHING you do to it will be just a "shot in the dark" guess.
If I upgrade the torque converter. Do I need to upgrade the flywheel also?
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Re: Poor man thunderjet mods?

Post  IDT-572 on September 3rd 2013, 11:48 am

No need to upgrade the flex plate unless there are damaged teeth on it, and then just go back with a stock one.
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Re: Poor man thunderjet mods?

Post  bigblackbronco on September 3rd 2013, 1:10 pm

thanks for the info IDT-572 and everyone else. Good lookin stang IDT-572
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Re: Poor man thunderjet mods?

Post  5pointslow on September 3rd 2013, 2:00 pm

i would find out what the gears are .

i mean if someone left stock gearing in there and threw some 35s on there id assume it be sluggish trying to rotate those tires .

Put some bigger gears if needed and a new convertor ......
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Re: Poor man thunderjet mods?

Post  supervel45 on September 4th 2013, 6:18 am

5pointslow wrote:i would find out what the gears are .

i mean if someone left stock gearing in there and threw some 35s on there id assume it be sluggish trying to rotate those tires .

Put some bigger gears if needed and a new convertor ......
3.50 gears where pretty common in that year Bronco. Check and see what you have and go from there. 4.10's are pretty good for 35's, 4.30's might be pretty good too, if you don't like going down the highway to fast. Don't get carried with the stall, if you have low numerical gear ratio's, you might not like all the slippage.

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Re: Poor man thunderjet mods?

Post  rmcomprandy on September 4th 2013, 9:42 am

supervel45 wrote:
5pointslow wrote:i would find out what the gears are .

i mean if someone left stock gearing in there and threw some 35s on there id assume it be sluggish trying to rotate those tires .

Put some bigger gears if needed and a new convertor ......
3.50 gears where pretty common in that year Bronco. Check and see what you have and go from there. 4.10's are pretty good for 35's, 4.30's might be pretty good too, if you don't like going down the highway to fast. Don't get carried with the stall, if you have low numerical gear ratio's, you might not like all the slippage.
He is not gonna be anywhere near to much slippage with anything under 3,000 stall RPM in that kind of vehicle. It is not like this will be going steadily down the highway for miles upon miles. Wink 

Having the gears changed will cost him at least  $1,500.00 minimum before it is all finished and he is a "Poor Man" by his own definition.

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Re: Poor man thunderjet mods?

Post  supervel45 on September 4th 2013, 12:10 pm

Gear swaps are pretty common in big tired 4x4's and alot of guys do it themself for less. Just saying, it is something to consider. And alot of people take their 4x4's hunting and do drive a few miles to get there, esp. in states like Texas. Different strokes for different folks, I guess. He should at least check his gear ratio, so that he can base his other choices better.

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Re: Poor man thunderjet mods?

Post  bigblackbronco on September 4th 2013, 1:10 pm

Checked my door panel and the axel code is H9A.  According to fordification the gearing is 4.11(stock tires).  Haven't done the math to see what the adjusted ratio is now that the tires are bigger.  Right now I'm not to worried about the gearing.   I take this truck out wheeling alot and it has no problem torqueing over anything, especially in 4 low.  Very impressive and definitely not tired.  Changing them out is pricey to a degree because unlike a car you have to change both the front and rear gears.  But as for the budget I have right now is little due to lack of work.  So its little things.  But all these ideas everyone is giving are good for future mods.

I was tinkering around the top side of the motor yesterday and noticed that the vacuum advance on the carb was hooked up to the part time vac port.  I switched it over to the full time and capped the part time.  Definitely a lot more response in the initial take off all the way up to highway speed.  I beat one of those crappy rice tunners off the line during the test drive.  But alas, no burnt rubber.  I've attached a pic of my carb and intake manifold (D0VE 9425-B) and carb (Edelbrock 1407 750cfm manual choke).   I've seen vacuum diagrams online and they show a ported vacuum switch at the thermostat housing.  Mine has been capped.  Anyone using a ported vacuum switch?  Also does anyone use the intake manifold vacuum port that my finger is pointing at?  My distributor is a single diaphragm from the the original 351 that was in the bronco.  Is there an advantage to switching to a double diaphragm distributor?


Last edited by bigblackbronco on September 4th 2013, 1:14 pm; edited 1 time in total (Reason for editing : no pic came in)
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Re: Poor man thunderjet mods?

Post  bigblok2000ranger on September 4th 2013, 9:03 pm

The iron heads love timing so bump your timing up two degrees at a time until it pings or hard to start then back it down just below that. Some will disagree with this but I have gained .200 and 4mph in the quarter mile by getting after the timing on the iron heads, we don't race dynos!
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Has the engine...

Post  XEngr on September 4th 2013, 10:23 pm

Has the engine been rebuilt or refreshed? The original timing chain was link belt with nylon teeth on the cam gear, the valves had rubber oil seals and the original head gaskets were mediocre by todays standards. The cam gear teeth get old and will strip out. The valve seals get hard, break apart and fall down into the oil pan where they seize the oil pump. The heads gaskets will eventually leak water if original, not that the stock head gaskets were really that bad for mild use but now they are 40+ years old.

A simple distributor recurve will help a bunch, if it is not already a Duraspark that may be a good upgrade.

You probably already have headers?


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Re: Poor man thunderjet mods?

Post  supervel45 on September 5th 2013, 3:13 am

Sounds like you have a nice gear ratio with the 4.10's. You can put a mark on the tire and the drive shaft and count them, just to be sure. A 2,500-2,800 stall with 4.10's and 35's would pep it up, like the others have said, and not slip much at highway sppeds. I am running my 351 distritor in my 429 and it works good, with the proper curve. The suggestion to turn the timing up until you get some valve clatter, then back it down a little does work. Then recheck it with a timing light, with the vacuum advance disconnected. The dist. vac. should be hooked to the ported vac. line on the carb. You should not get much or any vac. at idle, and none at full throttle. The vac. switch on the thermostat housing, if set up correctly, will switch the dist. from manifold vac. to ported vac., to help the engine warm up. Alot of the old switch's are bad as mine was, so be sure it still work's before you use it. I think most people just delete it. You may want to get an adjustable vac. diaphram on your dist. so you can fine tune it for your high compression engine, as the old 351 was only 8/1 comp, and you may be too high on timing with the 429. 35" mud tires are pretty hard to roast, as you put it with a good posi, and you will need alot of HP to due it. Tire spin only make's a vechicle slower, so if the engine is tuned to it's full potenital, be happy that you don,t have traction problems, as people spend alot of money to fix that as well. If you want a bolt on no machine work big gain on Hp, put a 125HP nitrous plate on it. Be shure and run 93 oct. fuel and back the timing down a few degree's, and the traction problems should start then.

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Re: Poor man thunderjet mods?

Post  jasonf on September 5th 2013, 8:04 am

You know 429/460's were alright for their time but they are gutless in stock form especially by today's standards. Everybody assumes that when they put a 429/460 in a Bronco that it is just going to be some kind of rocket. I have had several 460 powered 70's 2 wd trucks and until you change the timing chain and adjust the timing they were pretty gutless. When you swap them into a 4wd they are really gutless. My brother had a 78 Bronco that the previous owner had swapped a 429 in and it was a gas sucking hog. We've also had a few 460 powered jet boats. My whole point is these engines have more potential than almost any other engine out there but unless you change somethings it will never be the fire breathing, tire smoking dragon that you think or want it to be.

The best bang for the buck when you have no money is to re-curve the distributor. If it doesn't already have a duraspark dist. in it get one. Ford Racing used to sell a re-curve kit for around $10 bucks. All it is different springs so you can adjust how fast the timing advances and it comes with instructions. It is easy to do.

Here is a little info. http://www.reincarnation-automotive.com/Duraspark_distributor_recurve_instructions_index.html

As mentioned I would advance the base timing as much as you can stand. Stock is probably super low around 6*. Bump it way up to around 10* and keep increasing 2* at a time till it starts pinging. You can mess with this and the distributor springs to get a setup that will work well. Once you get up around 15-16* timing it will get hard to start when hot but it will pull a lot better.

Someone like Randy or Lem could hook you up with the parts necessary.

It will respond to all the usual other changes as well. Headers, intake, cam etc.
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Re: Poor man thunderjet mods?

Post  bigblackbronco on September 8th 2013, 3:54 pm

Just advanced the timing. Part time vac. 20-22 deg full time at 35. Keeping the carb vac hooked up at full time. What a difference. I can roast the tires, with my brakes barely engaged. And the tires don't break loose flooring it off the line. Very Happy Perfect Very Happy . Haven't recurved the distributor yet, but that's another day. Fun times with a stock thunderjet cant wait to take this off road or smoke a bow tie
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Re: Poor man thunderjet mods?

Post  Dave C. on September 8th 2013, 4:40 pm

Jason's right about tweeking the distributor. My old cleveland picked up .5 seconds with no other changes. Cool 

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