I knew talking about a 5.8 would get someone's attention on the inline part of the forum, but I was wondering if I could pick up any performance by swapping in the Throttle Body off my 351 onto my 4.9. I know it's bigger, and I've always wondered why, but If it would help me at all in making power I'm going to do it.

I'm changing my bronco (5.8) to carb anyways, so I really don't need the parts off of it. I'm thinking about taking my intake off the 300, cleaning it up really good, and taking the air filter box, the tubes, and the throttle body off the 351.

If anyone has any suggestions on how it will work please let me know, I might take the drill and port match the TB with the intake, but I'm going to see how much bigger it is before I start screwing with my daily driver...

Matt.

 

Anyone??? As soon as I'm out of school I'm going to start pulling the TB off. I think it would help in the upper RPM's...if it fits that is, but I don't wanna hurt the lower torque any. I will let you guys know how it does.... lol, but doesn't anyone have any predictions???

Matt.

 

It won't do anything for the peak power but will help the throttle response significantly.

 

Why wouldn't you think it would help any in the performance? I thought the restrictive 4.9 throttle body would really be holding it back. I'm going to definatly take the Throttle Body off both trucks and see what all I'm going to have to do to get the thing to bolt on there.

The 5.8's Throttle body is held on by much smaller bolts, so the first thing is to drill out the holes so that it will fit over the studs of the 300's intake.

I need to invest in one of those dyno's you put on your dash cuz there's no where around here I can get my truck dynoed at. I'd like to see if there's any power difference, even if there's like 15 or so It would be a start on what I'm planning on doing with it.

Matt.

 

A bigger TB is of no use on an engine that can't use the extra flow. Do a search. We've covered this material many, many times before.

A 15 hp gain is a pipe dream for a bolt on mod. You have to do something significant to pull 15 hp out of a 300.

I think the threads of the 5.8 and 4.9 throttle body fasteners are the same, the 5.8 just uses smaller heads because the stud nuts on the 4.9 are too big to clear the outside of the TB bores.

 

Ok, thanks for the reply, I just thougth that if I used the bigger TB, the tubes and the air cleaner that it would be much less restrictive than the stock 4.9's. I was thinking about like a K&N air filter, they give a big jump in horsepower from stock, and most of the time they are just adding a different filter to the stock box. I might still do it, but first of all I'm going to have to get the 5.8's cleaned up.

Matt.

 

I just finished installing a 5.8 throttlebody on my pickup this morning. The throttle reponse is much better. I barely have to put my foot on the gas to get it to move. The engine gets to 4k alot quicker and it pulls harder in all gears. I haven't hooked it to a trailer yet to see if it pulls any better, and I have no idea what it's done to my fuel economy.

Here are some things I learned while installing the 5.8 TB.

1. The 5.8 TB has one vacumm port on the bottom, instead of the two on top like the 300 has. You will need to just remove the T from the 300's vacumm line and run a single vacuum hose to the underside of the new TB. No big deal.

2. The bracket that supports the upper intake plenum is in the way. You will need to remove the two water outlets from the new TB. You will also need to cut off the two small freeze plug looking things from the bottom of the 5.8TB and will have to continue grinding about another half inch into the TB to clear the bracket. You could also just pull of the bracket and cut it... but this was an experiment and I refused to alter my truck in anyway. I'd rather cut and hack on the 5.8TB.

3. The linkage issue. The 5.8 and the 4.9 linkage hooks up in different locations. Some folks cut the little pivot ball off the 5.8 linkage and weld it to approximately where the 4.9's pivot ball was. I did something different. You'll notice that there's two seperate linkages on the side of both TB's connected by a little bar with plastic clips on the end. Remove the 5.8 linkage that has the pivot ball and replace it with the 4.9's. Yes... it's easy as that. There is a catch though. The 4.9's idle plate that the little screw adjusts your idle... is kinda backwards using this method. Luckily for me the TB is large enough to naturally keep my idle at 700RPM. Hopefully you'll be lucky like me and won't need the idle adjustment screw. If you do... then you're stuck cutting the pivot ball and welding it in place on the 5.8TB. Try my method first. It easier.

4. The throttle position sensor has a different connector on the 5.8 then it does on the 4.9. The sensor mounts slightly differently. This will make more sense when you're actually looking at the stuff but i'll give a description a try. Again, I did it this way because I refused to cut the wires on my truck and didn't want to use the 5.8 TPS... When you pull off the 5.8TPS and try to install the 4.9TPS, you'll notice that the 4.9TPS won't push down in the hole. There is a small phenolic (plastic) bushing in the 5.8TB that you need to remove. I was able to EASILY break the brittle bushing with a flathead screwdriver and one swift kick of a ball peen hammer without damaging the TB. The 4.9TPS will now slide into the 5.8TPS hole. At this point you WILL need to use the 5.8TPS screws to hold in the 4.9TPS. They are a different size.

5. Connect your sensors and fire it up.

My truck started and idled just like it did before. The idle kicked up when I put my A/C on and it kicked up when I first started it for the cold start cycle. Just like it should.

The biggest PITA is i've got a K&N FIPK on the truck... that uses the STOCK FREAKIN tubes. The new TB is so much larger the old tubes won't slide over and you're stuck with designing your own intake tubes. You could try going to the part store for a length of exhaust pipe... but you'll have to bend the pipe in the shape of the stock intake tubes to make it all seal correctly. For the time being i've got my stock intake tubes duct taped to the TB. So embarassing.... I'm going to go the exhaust shop this week to have them bend up some intake tubes and i'll just connect them with some of those ricer intake couplings. Hopefully they have them in black and not some stupid neon color.

Good luck and let me know if you have any questions.


FORGOT TO MENTION... The 5.8TB slides over the 4.9's studs on the intake manifold. Just use the 4.9's nuts to hold it on. No mods necessary here.

 

Thanks alot for the info! I am really glad someone did this before me, lol...I don't like being a guinnea pig. So do you feel any difference in power? I notice on my 300 that it when you step on it, it really doesn't like to start running until about 2000 RPM, then it picks up power. Does it start picking up power lower now?

Give us a heads up on the fuel economy, I don't think it would make much of a difference, but I guess a little drop is worth it in the hopes for power, lol.

Oh, and one more thing, So are you using the stock 4.9 air hoses? I'm going to try to fab up the 5.8's to where they will fit in the stock location, since they are much larger than the 4.9's. Once I get it mounted up I'll let ya know how mine does.

Matt

 

CJSTEAK....what year model truck did you do this to, and what year model tb did you use?

 

Ok, so I took my throttle body off, and the only difference than what you've described is the vacuum lines. there's two on mine. I don't know if it will make a difference, but I'm about to cut the little freeze plug things off at the bottom. Keep us posted on how it does!!! I'm pretty excited that someone had the same Idea I did, lol.

Matt

 

alright, so I guess I waited too long to edit...but I ground down the little freeze plugs and cut off the tubes. I bolted it on and eveything fit up fine, except for the throttle cable. The closest thing that it's to is the kick down **** for the cabe on an auto tranny. For the time being I'm going to zip tie it to that little ****, but tomorrow I'm going to take a file and file that down so that the throttle cable will fit over it.

I didn't have any troubles with the tubes, either. I just cut them to length and put them back on the throttle body and air filter. It isn't really hard when you have all the stuff of the old truck, lol.

I'll let you guys know what it does in a little bit.

Matt

 

Great Question!
Mtthwvn73 if you could answer this as well, Thanks

 

My throttle body was off a 1988 bronco. I do have an update also, There's alot better way to mount the throttle cable. What you do is take the little braket that the thottle connects to on the original TB and put it on the 351TB. It mounts exactly the same, and you don't have to use fishing line like I was trying it out with, lol.

I wish I had a camera, this thing looks like it came from the factory this way.

Matt

 

Sorry for not responding sooner... been a while since I was at my computer. My pickup is a 1995 F150 2WD short bed regular cab 300 x M50D 5 speed. Mods to the engine were just K&N FIPK, 5.8TB, 8.5mm Taylor wires (I think) and 201,350 original miles.

You better not be taking credit for my linkage swap on step3! (Just kidding)

Power wise... it pulls harder off the line a bit mid range is better and top end just slightly better. Mileage seems to be roughly the same... maybe a slight decrease like 1/2 mpg. I paid 10 bucks for my TB and you got yours free from your Bronco. In that case it's worth it. On a dyno there might be a 5-8HP pick up at best. Just enough to feel and make me feel my 10 bucks was well spent. The issue i'm running into is I want to tune my engine for the mod. I'm going to try stopping by an exhaust shop this weekend to have some intake tubes made up for my truck. The stock stuff doesn't allow intake velocity to build up and i'm sure i've probably lost a small amount of torque somewhere. My truck also needs long tube headers. Velocity in and out respective to one another is very important with inlines! At this point i've installed a good mod... but my pick up lacks the tuning to really take advantage of it. If these stinkin' EFI trucks were tuneable like EVERY OTHER FREAKIN' EFI vehicle is... you'd see more dramatic improvements instead of the mediocre stuff we have to live with. I can't stand how putting a TB on a 302 gains real power... headers do too.. cam and injectors do... and on a 300... it's aaaaallll mediocre gains in comparison. Ok enough ranting and moaning about crap I can't really change.

I wish I was smarter... i'd program my truck myself. lol

Oh yeah... the TB I used was off a '91 Bronco.

Let me know if you have any questions.

 

Lol, Yeah, it was as simple as that. The truck I installed mine on was also a 95 with a M5OD tranny, and 223K original miles.