1984 Mustang - Just want to see some opinions on my build.

MikeROD16

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Feb 4, 2008
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Miami, FL
Hey guys. Just seing what the thoughts are out there. All these parts I have are used and on a budget. Some things I got free. So I'm just working with what I've been able to get.

I have a stock 302 mated to a Weiand 174 right now. Very easy going on the road and decent power. Not enough though, but not bad considering i have the stock flat tap cam and big 69cc chambered heads. I have ready, a set of windsor sr heads for the motor (prepped and cleaned with a valve job), some Probe SRS pistons used in a 347 (I wont be stroking it) on boost and a custom ground cam. Im just going to swap out the pistons on a stock crank and balance the rotating assembly.d As for the cam, its a custom ground turbo cam from comp if im not mistaken.

Its a .598/.600 lift, 254/248 dur @ .050 with a 114 lsa and 112 intake cl. (based off 1.6 rockers). Just curious, what will the idle be like? anyone have anything similar?

The car also has 4.10 gears, stock t5, and exhaust. Not much, i know, but with some decent drag raidals, what would be a reasonable 1/4mi time?

The blower will be boosting about 10-12 psi and will be topped by a 930cfm Predator carb.

let me know if you guys need anymore info.

any feedback is appreciated. Thanks guys and gals.

PS. I know my t5 wont last, but let's just say its bulletproof for the sake of conversation.
 
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Don't think the 347 pistons will give you the right compression height to work, unless your looking for like 7:1 compression ratio or lower. Might want to rethink that.

Scott
 
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Don't think the 347 pistons will give you the right compression height to work, unless your looking for like 7:1 compression ratio or lower. Might want to rethink that.

Scott
Well, with the stroker crank (347), its at 8.5:1 and 331 is at 8:1. But I compared the pin height and rod length and piston height, and it looks the same as the stock trw pistons i have from a seperate motor. It just has the bigger and deeper valve reliefs. That allows me to boost more. I was thinking of compound boosting in the future, but thats a whole different story. I was planning on boosting around 10 psi depending on my CR after the pistons.
 

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I think you are wasting your time swapping the pistons and balancing the crank, I would just roll with what you have in there now. The money and time you are spending is not worth the minimal result gained.
 
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Like already said, I wouldn't use the pistons. You're going to have a half inch of deck clearance which is senseless. I can't remember if stock '84 pistons are forged or not, but if they are, I would just continue using the short block as-is. If not, just buy a used 87-92 5.0 off Craigslist, you'll have less money in that than what you would trying to swap pistons and rebalance.

The cam sounds to be pretty rowdy...
 
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Like already said, I wouldn't use the pistons. You're going to have a half inch of deck clearance which is senseless. I can't remember if stock '84 pistons are forged or not, but if they are, I would just continue using the short block as-is. If not, just buy a used 87-92 5.0 off Craigslist, you'll have less money in that than what you would trying to swap pistons and rebalance.

The cam sounds to be pretty rowdy...

The internals are cast. But I need the pistons to clear the valves on the heads. i could always put a smaller pulley to boost more lol.
 
cam is too much for a small motor IMO. Sell it, and put the money towards something more useful. As already stated, the pistons arent going to work either. Put a stock shortblock together, and turn the boost up. You can make enough power with a stock cam to put you into block cracking territory.

I am also a believer that boring a stock block .030 over is going to contribute to its weakness. You want to keep as much material with a stock block as possible. That is worth more than 4 ci
 
That cam was in a real low 10 sec mustang turbo. Cant be too big with high boost and those big heads. I know i can get 400hp out of a bottom end, but why push things to the limit? Could it be that I have stock sized crower rods with .40 over pistons?

I know the boring makes the block weaker, but I want to push around 475hp which should be safe. I want to be able to have a very good power band while running all my components at 80% of their full potential. This is my Daily driver, so it has to be reliable as can be. I'm going to get the parts inspected by a shop and see what they say (regarding the pistons and rods) and if I can use my stock crank, ill use it, if not, ill have to suck it up and get a $200 cast crank from scat or eagle.
 
475 hp, is 100% of the blocks potential, if you ever run into detonation, you run the risk of breaking parts. With todays pump fuel quality, i'd be worried about DDing a 475hp stock block motor. If i were in your position, i wouldnt waste money going to a machine shop with stock stuff. Id just throw a stock shortblock in, and let it eat.
 
But I want to use my heads. I was thinking a balance (abnout $200 here) to get things to last longer under that power. I understand stock parts will work, but to use my heads, I neeed to notch the pistons and thats a big no for me. Im gonna measure the stock components I have in a box and compare it to the forged stuff I have and see how it matches up. If it happens to be the same as the stock pistons and rods, and I got sold something other than what was advertised, then I'll use those pistons i bought on a stock crank and balance it. If its a different height than stock, I'll slap on a stroker crank and not bother balancing it. Either way, its the same cost for me.

As for the hp, I know thats awful close to the 500hp threshold, but Ive seen people push 600 on a stock lower block. Yes its on borrowed time, but Im hoping 475 should be fine. I guess it also depends on the individual blocks integrity. I guess time will tell. Regardless, I have a whole other block I'll be assembling in case that one decides to go out on me. Im thinking of going draw thru turbo on a fully stock 302 compounding the boost into the blower. But thats future plans.
 
How do you know you need to notch your pistons? Have you checked PTV clearance?

There is also no magic number for block strength, some break at 300(ask MFE), some 400, then you hear about the 600 hp ones. Im guessing the 600 hp ones are run on good gas, and never detonate, and when they do, its game over.
 
You should really check it before anything. I have a .580(.600 at the lifter) lift cam and the valves are nowhere near the pistons. Lift doesnt have as much to do with PTV clearance as when and where the valves open.
 
Also consider that stock parts are heavy and will have a direct effect on the block strength, ie cap walk. When mine was built at the time SRP had a super light set of .030 pistons, my balancer stated that is the lightest SBF rotating assembly he has seen for non custom. I have been on the dyno and have made 510 to the wheels, do I believe the numbers well no it is a number. But I do believe it is making a honest high 400s. I do and have spun it up to 7800 rpms countless times and have not had the block fail yet.

Where did you measure from center of pin to top of piston for compression height? I find it hard to believe they are the same or even close. Last I knew all the 347's had a oil rail support rail in the pin boss.

Scott
 
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Ok, so I got the spec sheet from Probe. They are custom ordered pistons. The rods are 5.4".

Piston Specs:

bore: 4.030
comp height: 1.300
comp ratio (with 64cc heads): 8.5
pin dia: .927

Let me know if these adds up to a long rod 302. Thats what I'm thinking because of the comp height.