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  • December 12, 2018, 06:54:03 PM

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Author Topic: Improving General Performance  (Read 450 times)

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Offline schimke12

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Improving General Performance
« on: July 20, 2018, 11:51:21 AM »
I have an 1981 SX4 with the 151 iron duke and I'm wondering if there are a few things I can do to improve it's general performance. The engine and the carb were completely rebuilt, but I still feel like it's too sluggish and isn't reaching it's full potential (especially on acceleration). It just seems like it's working harder than it needs to be while under normal driving conditions. I swore I saw something about converting the carb to direct injection years ago on this forum, but I haven't been able to find it since. Is that a common or even possible swap? If not, do you have any other ideas on how to improve it's performance?

Thanks in advance!
« Last Edit: July 20, 2018, 12:18:10 PM by schimke12 »

Online vangremlin

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Re: Improving General Performance
« Reply #1 on: July 20, 2018, 12:04:51 PM »
I did a quick search online and found someone that did the upgrade in their jeep.  Kind of an older thread but you may be able to get some info from it. Good luck!!

http://www.binderplanet.com/forums/index.php?threads/pontiac-iron-duke-151cid-2-5l-4-cyl-fuel-injection.48817/
1981 Kammback 258 - "Pepe"
1980 Coupe 258 - "Ginger
1972 Gremlin X 304
1978 Gremlin 4 cyl 121 - sold
1964 TBird 390 - sold

Offline jebidia24

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Re: Improving General Performance
« Reply #2 on: November 29, 2018, 01:17:22 PM »
GM did make throttle body injection for this engine and renamed it the tech 4.  This didn't improve performance much.  The iron duke was made for economy and GM took out weight everywhere they could in the name of economy.  Because of that, the iron duke crank is very weak, the block is thin, and the rods snap easily at high RPM. Offenhauser made an after market intake manifold and possibly some headers but they are not worth the time or money on this engine.  The best two ways to increase performance is to increase air flow and/or increase RPMs.  This engine isn't suited well to either.  The head flow is very poor and the RPMs can't be increased because of the crank, block, and rod weakness.  All is not lost though, as stated many time before, the Mercruiser Marine 180 is a maritime counterpart to the iron duke but is much stronger and more powerful.  It does use different components which can be swapped into a duke with machining work.  It is easier to swap in a complete mercruiser 180 into your car.  There are people on this forum who have done this.  Another route is to go to a SD-4 (Pontiac Super Duty 4).  The SD-4 is the racing version of the iron duke originally developed for the ARCA racing series.  They make a lot of power but parts and/or complete engines are hard to come by and very expensive (I have a 2.5L SD-4 with the 801 head and dual webers and I am probably $10,000 in).  Being race engines, they aren't well suited for everyday street use.  Guys have been building them and all variations of the iron dukes for performance in the fiero and S10 world for years.  FYI, Cosworth Engineering in the UK developed a DOHC head for the SD-4 (which is super rare, the only time I saw one for sale, the kit was $12,000) that can make over 500 hp NA but is peaky.

 

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