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I have an almost TOTALLY original GT5S. Only thing not original is the pain.   I want to build an engine that is bad a**.  I am planning on all new components so I can pull the original numbers matching motor and crate it up for the future the owner  who may be a purist.  My question, is this smart with a car like this, (13,231) original miles on this car.  I have batted this back and forth and have a guy who specialized a few years back building Cleveland engines so I know his abilities.  I would like comments on if I am doing this right or should I not do at all.  I can build the block I have, just think it is smarter to spend a bit more money but to keep the original motor all intact and together..............comments...?

Last edited by George P
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Keeping a “spare engine” would greatly reduce the down time of the car.

If you have your motor built and checked out (already run on a stand, and even dyno’ed), then pulling your original, and installing the new engine  COULD BE done as a long weekend job!

Note I say “could be”….

Nevertheless, building a complete replacement certainly lets you build your motor with a more relaxing timeline!

Thats what I have done, and at this point, I don’t swap as many of the accessories.  I think I keep the flywheel, intake manifold, heads, oil pan, and perhaps the water pump on my spare…


Last edited by rocky

Thanks for your reply Rocky.  I am thinking swaping the complete engine and leave everything on the original one...............I am hoping to find the brackets and pulleys ect available.......if not, that plan obviously wont work.    I assume you replaced your motor with a Cleveland which is what I am doing,  Did you stroke and bore your block or what cubic inch are you running?  My other question is brake booster...........they make an electric instead of vacum so I can run a big cam.........any thoughts?

Yes, my “built” motor is also a Cleveland. I got advice from GeorgeP on a cam, and used it in my build.  I’ve got good vacuum, good idle, and measured 425 HP on the engine dyno with my existing headers/mufflers. My builder thought there were at least 50 hp more with a different exhaust (think 360s).

I’m only bored out .040 (after having sonic tested), not stroked.  I’m running 4V cast iron heads, ported.

I think you can get more, but mine is healthy, powerful, reliable and fun.

I think whatever you decide next, you'd do well to read all of George P's post on the subject; there are savings not to be made as well as limits not to be exceeded even if you can easily find all the parts that allow you to go beyond the reasonable for reliability.


Last edited by rene4406

If you want to make lot of horsepower with a Pantera engine, keep in mind that you are going to produce more heat. If you are using the stock radiator and cooling fans, you might have a problem. If you bore a Cleveland engine, it is a good idea to sonic test the cylinder walls to be sure that there aren't any thin spots. Other than that, a 500 plus horsepower Pantera is a lot of fun to drive!

One of the first things you do to improve a Cleveland is to increase the compression ratio and therefore the thermodynamic efficiency; that is to say that at the same power used, the heat to be dissipated by the exhaust and the radiator is LOWER. It is only when the additional power is used, ie above 270 hp, that there is more heat to dissipate. In other words, in the city where most Panteras or tend to overheat, the increase in engine power will improve the situation.

Last edited by rene4406

I have gotten several opinions on what I am wanting to do............this project is not as clean and simple as I anticipated.  My car #9421 is a VERY orignal GT5S.  Low mileage car with all of the original smog equipment for Amerisport.  With that said, that is what I am wanting to change.  Thought by swithcing complete motors, I would still have the original block and components for a true collector someday.  I am getting so many mixed reviews, some say go for it while others are asking what the hell am I thinking.  Would I be smarter to keep the same block and just re cam it as well as change heads and intake............?  I am not usually this confused (don't ask my wife) but with the condition of this car and what it is, I am on the fence now.  I just want a bit more power out of it?  I could get ride of the converters, and put in a pipe there with flanges to keep the car able to return to stock.  All other ideas could be done with opportunity to reverse as well................If you have done modifications to an Australian 351C and happy with it, I am all ears........


Mike, if your looking for a big power jump I would build a different Cleveland to your liking while still enjoying your car as is. I would ensure your new Cleveland while being built follows George's recommendations and that the proper thermostat, a recommended water pump and the oversized pulley that many run on here are used. Doing this may help completely avoiding changing out a rad and fans later. While disassembling your car for the swap I would photograph and bag and tag everything. This will keep things documented and easier to return to stock If ever desired with your factory motor on a stand.

If a smaller jump in power is sufficient I would remove the smog, try a different intake and tuned carb or fuel injection and check out some exhaust options. Headers maybe from Pat Mical, or mufflers and tips from Dennis Quella. Then get the car tuned on a chassis dyno. That can all be done without opening up the motor. Meeting the smog requirements back then may have killed a lot of hp.

If that doesn't satisfy your power need, then you know you need to do another motor or dig deeper into the factory one. Regardless on a car like that, bag and tag everything.

Lucky guy having a car like that.

If I were you, I would drop off the complete original engine with anti-smog, intake, exhausts, everything and I would store it carefully to preserve the value of the car in the event of resale. And I will buy a complete crate engine from a reputable builder who will guarantee you the performances, power, torque, range of use...

That's just my opinion.

Here is a suggestion that might not be as expensive as someone might think. Original Cleveland blocks are getting hard to find and finding a good rebuildable one might even be harder. Why not purchase one of the new aluminum reproduction Cleveland blocks? That block eliminates the original Cleveland block thin cylinder wall problems and they use the Windsor style oiling system. If you want it to look original, just paint the block Ford blue. Of course it would make sense to bolt on some nice aluminum cylinder heads and a matching intake manifold.


    I found a good cleveland block that is a 4 bolt main.  The guy that owns it use to build engines for a Cobra continuation guy and has a great reputation.  He actually knows the tricks that Bill Elliot did to his cleveland engines back in his glory days in Nascar.   We are discussing building that engine and doing all the cool trick stuff.  The biggest issue in my head is, it wont just be an unbolt and bold in thing.  Lots of brackets and pulleys to switch over..............hince my delima.  Might just switch cams, intake and bold on aluminum heads on my block and eliminate the swap as well as changing things over........

I have switched back and forth so much even I'm tired of dealing with myself........LOL  I will figure it out.........I don't drive this car, but would probably if it performed like I am use too.  I am a Ford dealer in the Kansas City market and have enjoyed HP my whole life.  This car is my 5th pantera but my first GT5S  which is what I always wanted.  The smog stuff is probably part of why it seems so sluggish.............looks awesome, just seems doggy.........

Is the engine in your GT5S a Windsor? If so, there are a lot of good high performance parts available for the 9.5 deck 351 Windsor engine. New blocks are available in either cast iron or aluminum and the selection of heads and intake manifolds is quite large. Since you are a Ford dealer you most likely have had the chance to play with the new Shelby GT500 or perhaps even the new Ford GT. To even come close to the performance of those cars with a Pantera you are going to have to spend a huge amount of money and produce a lot of horsepower. If you just want more horsepower and still be able to enjoy the Pantera on the street, then getting into the 500 plus horsepower range isn't that hard to do.

Mike if you plan appropriately there isn't a lot of brackets and pulleys to switch. Personally I would leave the ones on your current motor and source from the vendors. I think with planning this can be pretty much a drop in.

IPSCO has crank and water pump pulleys, and new A/C bracket.

Alternator brackets are minimal and needs to be changed if you decide to change the style of alternator. Kirk Evan's  from Amerisport would be an excellent source for you to contact and talk too, knowing your car. He will know exactly what your motor can do with the smog and without. He may even suggest his bulkhead reduction kit that includes an ac and alternator braket, plus increases room in your cab.


I pulled my 351C and put in a 427 Windsor Stroker. Dyno’d 608hp @ 5,800, 585 torque @ 5,500.  Bought the engine and ancillaries complete and Dyno’d from PI Motorsports in California talk to Jerry.  They have built over 100 of these engines. This car is almost frighteningly fast.  I recommend a  total engine swap.  It’s a beast with this level of power.  You’ll never go back.  

Jake,   Thanks for the information.  The  motor nor the cost of the motor is not an issue with me.  My hesitation is the value of this GT5S after I do this.  Do you think it kills the car or makes it worth more or has no bearing on it at all?  I know that answer is different for many, just curious as to your opinion or anyone else who owns these cars.  The Pantera market is so small, most people dont wake up and decide to buy thier first pantera today.  Most Pantera sales are to other owners, especially the 5S cars.  I have owned other Pantera's before this 5S so I finally found a 5S that for some reason I could never get out of my head to own one.  So here I am..............LOL

If your GT5S is bone stock, numbers matching then if it was my car I’d keep the original motor for sure. But the original motor by todays standards in a supercar is grossly underpowered.
I’d take out the original engine and keep it on an engine stand for future consideration. This is done in the collector corvette, mustang and mopar communities. If you plan on driving the car regularly and the odd track time then putting in a 351W stroker is a great option.  Now the GT5S can keep up with the big dogs. When I did my engine swap I only got $1,500 for the 351 Cleveland that was in it (non numbers matching). I had Jerry at PMI Motorsports do a bunch of upgrades to the tune of almost $50,000. My car still looks very stock outside of the 17” billet Campanola’s.  I wanted the 335’s on the back that just completes one of the meanest rear ends of any car ever made, besides the engine the rear half shafts,  bearings and universals need to be upgraded to handle 600+ HP. Jerry offers a set guaranteed for life to 700HP. The ZF transaxle is fine as long as the pinion gear is wired. Your car is very rare and pulls much higher sell prices so that will factor in. Personal choice.  As long as you keep all the stock parts a future owner can always put the car back to stock, I wouldn’t know why though once you experience the upgraded performance.  I’ll attach a couple of pictures of my car. If you look on Bring a Trailer some of the highest prices were for highly modified Pantera’s.  On Pantera’s tasteful functional upgrades do not diminish the value. Opposite to Ferrari or almost any other supercar made today any major modifications like an engine swap would surely tank the value and be frowned on.  My 2 cents  8E89A910-3DE7-4497-86B8-A40370840281753C82B0-BD5E-46E5-950B-40A7B58EA3F8261299E4-807D-460A-946D-0C7D261D8C91D938B8A1-F33E-4EE3-B928-076D0F5989E6716685CB-820E-4ACF-AACB-A56FFAE4F9E4


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