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HT4100 4.1, 4.5, 4.9 Discussion, 4.1 to 4.5 in Cadillac Engine Technical Discussion; NEW PROBLEM --- Went to the junkyard today to see when im getting the engine and the guy was pulling ...
  1. #16
    nickh is offline Cadillac Owners Member
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    Re: 4.1 to 4.5

    NEW PROBLEM --- Went to the junkyard today to see when im getting the engine and the guy was pulling the 4.5 out of a 90. Sequential fuel injection. Now this engine does have less miles and all that crap but i am not sure if it will work. He said he would drop give me the TBI and that shnaz (spelling ). Also he docked off $100 for the new gaskets i will need. Will i be fine or is there more that i will need. I am on a pretty tight budjet and wanted to get this car running for less than 700.

  2. #17
    Edahall's Avatar
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    Re: 4.1 to 4.5

    The 1990 MPFI 4.5 was kind of unique and very similar to the 4.9. Just about everything was the same as the 4.9 except it had a smaller stroke due to a different crank and it's own unique rods. The compression ratio was quite a bit higher on this engine than the 4.1 or 88 & 89 4.5.

    Yes, it'll be more of a challenge to get it to work correctly than a 88/89 4.5. The compression ratio is higher on this engine, displacement is bigger and heads have larger intake ports and larger valves. You will almost certainly need an adjustable FPR to richen it up so it doesn't run too lean and ping. You'll also need an 88/89 4.5 intake manifold. You should also use the exhaust manifolds from this 4.5L. They were larger and breathed better. Also, you'll most likely need to run premium gas with this higher compression engine.

    Have you thought about just sticking in a 4.9L? With this 1990 4.5, you're almost there.

  3. #18
    ehall's Avatar
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    Re: 4.1 to 4.5

    It'd be easier and better to get the full 4.5 but it's feasible to keep your 4.1 intake manifold and slide in the engine with some minor tweaking (I'm looking to do this with a 4.9 engine which is about the same but a little harder). I was looking at the gaskets today and everything is identical except the 4.1 has larger water ports but you can put some JB Weld filler in your 4.1 intake if you want to match the smaller 4.5 ports, and you might be able to just use the 4.1 gasket (eliminates overlapping gasket) and ignore it. The 4.5 has a bigger throttle body and bigger injectors but that shouldn't matter with the adjustable FPR compensating for the displacement. You should also be able to reuse your 4.1 distributor too. So yeah, it's not as straightforward but it should work fine with some workarounds. Let me know if it doesn't

  4. #19
    nickh is offline Cadillac Owners Member
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    Re: 4.1 to 4.5

    that adjustible fpr says it goes from 30-40 my haynes manual says my fuel pressure is 9-13 on TBI.

  5. #20
    Edahall's Avatar
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    Re: 4.1 to 4.5

    Quote Originally Posted by nickh View Post
    that adjustible fpr says it goes from 30-40 my haynes manual says my fuel pressure is 9-13 on TBI.
    It should still work. Someone else did the research on this adjustable FPR for the purpose of doing exactly what you're doing. Yes, it'll go from 30-40 psi if your in the tank pump puts out this much. However, the TBI pump puts out much less.

  6. #21
    DedWrng is offline Cadillac Owners Member
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    Re: 4.1 to 4.5

    I had a rebuilt 4.5 dropped in to replace a blown HT4100. Used the '85 TBI system intact, and it does compensate for the slightly larger engine with no worries about FPR or fuel pump. Only quirk that I can see is that rather than show '70' mpg instantaneous when I lift my foot, it maxes out at 54. WOT acceleration has been no problem at all. I have nearly twice the HP of the clapped out engine and BETTER MILAGE. Aside from the aformentioned plumbing and vacuum issues, my problem has been the engine needing more torque to start. I'm on my second used starter in two weeks, and I suppose I should get a NEW one. Does anybody make a heavy duty starter?

  7. #22
    ehall's Avatar
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    Re: 4.1 to 4.5

    According to rockauto the starter motor used on the 4.1 is 1.5kw but the 4.5 uses either a 1.5 or 1.6kw. You might try the latter--ACDELCO Part # 3361907 {#19136216} STARTER,(REMAN) DELCO SD (1.6 KW) $67.79 w/ $8 core

  8. #23
    DedWrng is offline Cadillac Owners Member
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    Re: 4.1 to 4.5

    Thanks! That's why I love this forum...

    Why the discussion point about keeping the intake manifold on the 4.1 when doing the swap? That was the weak point of the whole engine. The plumbing was BAD, and caused the coolant leaks that plagued the HT4100. By the time we got to the 4.5 and it's manifold redesign, we had a good engine, if a bit underpowered. Still, compared to what I had, it's a wonder!

  9. #24
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    Re: 4.1 to 4.5

    Yes, you can use the 4.1 intake manifold, exhaust manifold and skip putting in a FPR. However, it'll run better with the fuel dialed in correctly with an adjustable FPR. As DedWrng points out, his swap is working fine but there are other members who have done this swap (especially with a 1990 4.5) and it doesn't work out well. Several weeks ago, a member wrote how his conversion to a 1990 4.5 was pinging and smashing the spark plug electrodes. Well, what most likely was happening was the engine was running too lean because no adjustable FPR had been installed to compensate for the higher performance engine.

    Yes, the 4.5 will run OK with a 4.1 intake manifold but the 4.5 manifold was designed to run on a 4.5 engine so why not install the correct manifold. One thing I can tell you is that with the dual plane 4.5 intake manifold vs. the single plane 4.1 manifold, you'll get a lot more low rpm torque and better fuel economy. With todays high gas prices, it would not take long to get back the cost of the 4.5 intake manifold from fuel savings.

  10. #25
    nickh is offline Cadillac Owners Member
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    Re: 4.1 to 4.5

    Well i am unable to use the garage i was going to use. I am now doing this in my driveway in nebraska so its not very fun. Also i had a mechanic willing to give me pointers next to the garage and now its just me and a friend who doesnt know much either. Now to take out that intake and put on my TBI do we need to remove the heads and all that or is it just that round thing under the air cleaner? Please i am so screwed the ******* at the junkyard told me tough shit about the 90 engine when i was told it would be an 89. So if worse comes to worse i will just junkyard the car. I do not plan on putting in another $400 for another engine. So please what all do i need to remove to swap from the sequential fuel injection to my tbi. I will hopefully get the motor out first thing saturday and i guess just wait until i figure out what to do.

  11. #26
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    Re: 4.1 to 4.5

    intake bolts are under the valve covers

    you really need to get the books if you are going to try and do this solo

  12. #27
    nickh is offline Cadillac Owners Member
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    Re: 4.1 to 4.5

    i have the haynes and chilton books. Neither of them are that specific about getting the intake off. If all i need is to take off the intake covers i think i can hopefully figure it out. If any of you have pictures or anything of the sort it would be greatly taken. Thanks

  13. #28
    fj12 is offline Cadillac Owners Member
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    Re: 4.1 to 4.5

    The alternator has to come off to move the power steering pump over. The distributor has to come out, so take off the cap and remember where the rotor is pointing. The fuel lines have to be empty so run the engine and pull out the fuel pump fuse. Disconnect the fuel lines and pull them up a bit, take off the valve covers, disconnect the hoses, keep track of the bolts, and pull the intake straight up without prying it. It is definitely worth it to put in a new intake manifold gasket as they rust out at the water jacket ports after 150,000 miles max. Good luck.

  14. #29
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    Re: 4.1 to 4.5

    Yeah, you seriously need a factory service manual. One like this would be a huge help.
    http://cgi.ebay.com/ebaymotors/1989-...spagenameZWDVW

    I also remember looking at a free online service manual in the past but can't find it at this moment.

  15. #30
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    Re: 4.1 to 4.5

    Alright, I found the online service manuals. I found the section that describes how to remove the intake manifold.

    http://arrc.epnet.com/autoasp/index....ain.autorefctr

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