Zenobian_84 Posted September 15, 2012 Share Posted September 15, 2012 I've heard that a 4.0 TB can be mounted to a 2.5 engine with apparently minor modifications, if any. Is this true? My TBI system is running perfect as of right now, but I know that sooner or later (later, hopefully) it will start to show it's age and wear out. I just want to see what the scoop on this is; if it's true or not; and what negatives there are to installing a 4.0 TB over another 2.5 (mainly to get out of the $100+ NEW 2.5 fuel injector cost. You 2.5 guys know what I'm talking about) A link for viewing pleasure; some guy's help thread about having a WOT symptom after he swapped one onto his 2.5 YJ. http://www.jeepforum...p-help-1343376/ Link to comment Share on other sites More sharing options...
cruiser54 Posted September 15, 2012 Share Posted September 15, 2012 Your 2.5 is TB injected. 4.0 is multi-point injected. You have one injector in the throttle body and the 4.0 has no injector in the throttle body. . Link to comment Share on other sites More sharing options...
Jeep Driver Posted September 15, 2012 Share Posted September 15, 2012 Go to ebay and search for TB for comache.........Won't let me post link here. $249 Link to comment Share on other sites More sharing options...
Zenobian_84 Posted September 15, 2012 Author Share Posted September 15, 2012 Your 2.5 is TB injected. 4.0 is multi-point injected. You have one injector in the throttle body and the 4.0 has no injector in the throttle body. Interesting; I knew about the above stated difference though. I wonder how the YJ guys pulled it off then. Unless there's a difference between the design of the AMC 2.5 and the Chrysler/AMC 2.5 allowing the Injector in the TB to be bypassed. Doubt it though, so that would mean they had to rig it up into the system another way, right? :dunno: Link to comment Share on other sites More sharing options...
Pete M Posted September 15, 2012 Share Posted September 15, 2012 As I understandd it, they are using the 4.0 throttle body and putting the 2.5s injector assembly on it. The 4.0 has a larger diameter hole for more airflow. :thumbsup: Link to comment Share on other sites More sharing options...
Zenobian_84 Posted September 15, 2012 Author Share Posted September 15, 2012 As I understandd it, they are using the 4.0 throttle body and putting the 2.5s injector assembly on it. The 4.0 has a larger diameter hole for more airflow. :thumbsup: Hmmm... darn. Well, I guess this setup is here to stay then. :yes: Too much work for me to squeeze out another 5 HP at most from this engine. Link to comment Share on other sites More sharing options...
Geonovast Posted September 15, 2012 Share Posted September 15, 2012 The HO throttle bodies are identical except for the one for the 4.0 reportedly having a slightly bigger opening. I put a 92 4.0 TB on my 91 2.5 and didn't notice a difference. Link to comment Share on other sites More sharing options...
dasbulliwagen Posted September 16, 2012 Share Posted September 16, 2012 The throttle body swap is only for the multi point injected 2.5's starting in 91. There is nothing available for the TBI 2.5 of 86-90. I had thought about looking into a 2 barrel GM throttle body, seeing if the sensors had similar voltage sweeps to be able to be read by the renix computer, and if the stock fuel pump would work with it. This option may have to be combined with an aftermarket intake manifold as well though.... maybe someday Ill need to look into this. Link to comment Share on other sites More sharing options...
Jeep Driver Posted September 16, 2012 Share Posted September 16, 2012 Now I understand what you want to accomplish. I looked into this some time back and I don't remember the details but..... Search around on the Fiero sites, they are building HP 2.5s using specific S10 blocks with HD mains and billet cranks. Custom ground roller cams, ported heads, headers....etc... also they are using flow through heads (intake on passenger side and exhaust on driver side). Yeah I know......GM 2.5 not the AMC 2.5 but the engine mount and trans and fly wheel should all interchange. Cost about $4K to twist 7200rpm. Everyone want's somthing for nothing........ain't the case with the 2.5. Best thing you can do is make up a CAI. If you really want it to breath port the head and go with the Banks Toruque Tube......run you about $900. Link to comment Share on other sites More sharing options...
Zenobian_84 Posted September 16, 2012 Author Share Posted September 16, 2012 Just to those wanting to know, this question was asked for the sake of seeing whether or not I could use a 4.0 TB in place of my own TB, simply because I don't want to pay an outrageous price for either a NEW TB or a NEW fuel injector. Seems I can't get out of either I'm afraid. I'll have to pick up a spare throttle body next time I find a 2.5 at the pick-and-pull. On the other hand, the info Bulliwagon and Murphy posted is very interesting. I think if I wanted a dramatic increase in power, I'd go with a 3.4 or 4.0 swap-a-rooni though. 3.4 would definitely be cool. :brows: Link to comment Share on other sites More sharing options...
Pete M Posted September 16, 2012 Share Posted September 16, 2012 if you own a 2.5, always always always grab 2.5 injectors if you see them at the 'yard :thumbsup: Link to comment Share on other sites More sharing options...
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