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Discussion Starter #1
I'm looking to build up a 95 4.6 sohc motor I'm getting from a friend's thunderbird to eventually swap into my 97 bird. I'm looking forward to building up this motor in my spare time between working full time and going to school full time for my degree in automotive technology. I know an explorer motor would cost less and weigh less and so on and so on but I'm looking to build this up over the next few months (no rush) and essentially have a fun reliable rebuilt motor for my daily driver.

I know a P&P PI top end swap is in it's future (P&P PI heads, PI intake, PI cams (or aftermarket cams), as well as new rings, bearings, gaskets, mark VIII pan, poly mounts, etc...

My question is should I swap in some Mark VIII pistons and rods as well or should I just leave it be. A forged stroker would be ideal but thats not in the cards right now. So I'm looking for something that will yield me a bit more power with tried and true relyability because it will be going into a daily driver not a weekend warrior. I know PI heads on a stock NPI short block yield roughly 10.5:1 compression and I hear that PI heads on mark pistons yield almost 12:1. I will also be ordering a chip for it from BOC.

Just looking for some feedback.

Thanks,
Chris_Murder.
 

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Discussion Starter #3
Idealy this would be a mark short block build or a stroker but this engine will be given to me lol.
 

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Discussion Starter #4
Also the PI heads are freebee's as well. They are left over from another project.
 

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Discussion Starter #6
lol alright thank for the heads up.
 

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Discussion Starter #7
are there any cheep take off pistons or rods that would be better in the long run or should I just save some coin and buy a forged rotating assembly (minus the forged crank)
 

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are there any cheep take off pistons or rods that would be better in the long run or should I just save some coin and buy a forged rotating assembly (minus the forged crank)
I think it really depends on what you end up doing with it. If you do plan on running boost and having 450+ HP and beating the hell out of it, I would go forged! But if your looking to just stay N/A i wouldn't worry about spending a bunch on a bottom end.
 

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your best bet are mark VIII rods and pistons....if they can withstand the abuse that the 96-98 cobra guys give them with 7k shifts, you'll be alright.....you can also retard the cams (during degreeing them, of course), to drop the dynamic compression ratio, to make it more prem. fuel friendly, while at the same time, giving you more top end power
 

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Discussion Starter #10
your best bet are mark VIII rods and pistons....if they can withstand the abuse that the 96-98 cobra guys give them with 7k shifts, you'll be alright.....you can also retard the cams (during degreeing them, of course), to drop the dynamic compression ratio, to make it more prem. fuel friendly, while at the same time, giving you more top end power
So it would be worth swapping in mark VIII rods and pistons with the PI heads than? All I would have to do is retard the cams? (and get a tune of course). Couldn't I also retard the timing with a tune? Any idea of HP numbers?
 

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Discussion Starter #11 (Edited)
I think it really depends on what you end up doing with it. If you do plan on running boost and having 450+ HP and beating the hell out of it, I would go forged! But if your looking to just stay N/A i wouldn't worry about spending a bunch on a bottom end.
I have no plans of force feeding this motor, the only reason I've considered it is because of the reliability of forged internals and the option to force feed it should I every have the desire and money to do so, but as I've said this is a N/A build.
 

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So it would be worth swapping in mark VIII rods and pistons with the PI heads than? All I would have to do is retard the cams? (and get a tune of course). Couldn't I also retard the timing with a tune? Any idea of HP numbers?
if your budget is limited at the moment, yes I think they'd be worth it....retarding the cams would cause a slight loss of low-RPM torque, but then again, with ~12:1, it will pretty much get you right back where you started

retarding the cams is one of many things you can do to make your engine live with higher compression without using big cams with late intake valve closing events......anything to keep the combustion chamber nice and cool and the aircharge is a good thing......you will most definitely have to take out some timing...how much I honestly don't know.....you'd have to do more research on it

with everything optimized, i'd say you could get near 250rwhp with a PI intake, heads, mark VIII pistons/rods, and slightly retarded PI cams, and of course a decent exhaust

this list here is courtesy of popularhotrodding.com:

15 COMPRESSION BOOSTING MOVES

1. Feed cold air to the induction
2. Keep water as cool as possible (170 F or less)
3. Keep the air cool in the intake ports
4. Put a heat-reflective shine on the outside of the intake manifold
5. Minimize heat transfer through the common exhaust/intake port wall
6. Keep fuel temperatures down (cool can)
7. Run with plugs a little colder than the minimum required
8. Use an ignition system that is gross overkill
9. Utilize as large a spark plug gap as possible
10. Use no more ignition advance than is necessary
11. Maximize quench action
12. Minimize head chamber volume
13. Use flat-top pistons if possible
14. Minimize under-hood exhaust heat--use coated headers
15. Do not ram in but vent out hot air through hood vents


http://www.popularhotrodding.com/tech/0311_phr_compression_ratio_tech/index.html

while i dont necessarily agree with running coolant less than 170°F, it gives you the general ideal of running lower-than-stock coolant temps.....still a good read right there
 

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your best bet are mark VIII rods and pistons....if they can withstand the abuse that the 96-98 cobra guys give them with 7k shifts, you'll be alright
The Cobra rods and pistons are not really any stronger than what comes in a thunderbird stock. The only thing he would really gain from this would be compression....and I think the Cobra rods are a little lighter.

They still had hypereutectic pistons and the rods are just pressed pot metal. Yes, they are put through a lot of abuse, but 9 times out of 10 when a Cobra motor "blows" it is indeed because of a broken rod. The only thing that is really strong about a pre 03' Cobra motor is the steel crank.
 

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Discussion Starter #14 (Edited)
Alright after lots of thinking and talking it over with myself and the Mrs. and those who have been there and done that. I've decided what I'll be doing with this motor.

Due to added reliability I will be adding forged pistons and forged connecting rods, and keeping the stock crank.

All of the bearings and seals will be replaced, the block will be prepped and depending on tollerances may have the crank ground and may have the block bored. It all depends on how the tear down goes. As per every rebuild. I assume the motor wont be in too bad of shape since I've seen it run and know who owns it but you never can be too sure until tolerances get measured.

I will not be using the mark VIII rods and pistons, I will keep to my tried and true ways of the PI top end swap lol. With the forged pistons and connecting rods and 10:1 compression I will have the possibility to run a small amount of boost if I ever choose to do so, as unlikely as that is. Also to minimize reburning of the chip I will also be upgrading the injectors, maf, exhaust, etc...

More will be reveiled. Thanks for the input.

Chris.
 

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The Cobra rods and pistons are not really any stronger than what comes in a thunderbird stock. The only thing he would really gain from this would be compression....and I think the Cobra rods are a little lighter.

They still had hypereutectic pistons and the rods are just pressed pot metal. Yes, they are put through a lot of abuse, but 9 times out of 10 when a Cobra motor "blows" it is indeed because of a broken rod. The only thing that is really strong about a pre 03' Cobra motor is the steel crank.


Contrary to what 94DD is saying,the Mark8 rods are the same as the '96-'98 Cobras,and are a slightly better rosd than the 2V part. Sometime in '99,Ford decided that the 2V rod was good enough for all of the modular 4.6L's(probably saved a few pennies to use it instead of the 4V rod),and swapped over to it on all of them.
The 2.8cc dish of the Mark8/Cobra pistons will yeild approx 10.5:1 CR with a NPI head(depending on deck height,etc)and will make good power/torque with a decent set of heads on top.
I know of one car that's making around 280rwhp with a stock mark shortblock,and a set of ported NPI's. He's using a stock PI intake manifold,and a set of Kooks.
I'd say you'll be around approx 250rwhp with the manifolds if they're cleaned up good,and if you have decent exhaust on the car.
I was making right around 230rwhp with PI cams and ported exhaust manifolds with 2.25" compression bent duals. That was with the old terrible NPI intake too.
JL


Dimensionally they're different.
The 4V rod is stronger-it has a bit more material in the right places.
They use the same bolts as the 2V,but that's never been an issue.
JL


R8D-XXX, I'll trust sources that have been there-done that, thanks


Chris_Murder, good choice on the rods/pistons....forged parts never hurt anyone :)
 

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R8D-XXX, I'll trust sources that have been there-done that, thanks

QUOTE]

Thats a good thing.....cuz my forged bottom end and pi swap majically put itself together, thanks
 

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Discussion Starter #18
Will do.
 

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R8D-XXX, I'll trust sources that have been there-done that, thanks

QUOTE]

Thats a good thing.....cuz my forged bottom end and pi swap majically put itself together, thanks
I didnt mean to say that you haven't done any work yourself....what I meant with my previous post is that given all the things at JL has seen and worked with all these years, I'd trust what he says instead of what someone else says, whom we know very little about, let alone possibly not seen mark VIII rods and inspected them how JL has...that is all.....carry on with the thread
 

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I didnt mean to say that you haven't done any work yourself....what I meant with my previous post is that given all the things at JL has seen and worked with all these years, I'd trust what he says instead of what someone else says, whom we know very little about, let alone possibly not seen mark VIII rods and inspected them how JL has...that is all.....carry on with the thread

Sorry man. It just sounded like your statement was a low blow on me. I know I only have 50+ posts and nobody knows me, but I feel that I have good info to offer. I have always been big on the mustang side of things and have been around many Cobra's. My dad and I are currently building a 4V for his 01 GT.....and using mark 8rods and pistons as a matter of fact. Yes, this setup is just a little stronger than in a thunderbird and as I said before, the rods are a little bit lighter. That is one of the reasons they can be spun at 7G. But they do break from time to time. And I also said that if you plan to stay N/A, this setup should be fine as we are doing in my dad's GT. I would not use it if you planned on boosting to 450+ HP.

Good luck with the build Chris
 
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