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Q&A > General Tech Advice > cost of stroking 302 to 347? > Community Forums > Mustang Forum Australia - Mustang Tech

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cost of stroking 302 to 347? Reply to topic

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nick069
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just want more power for my 67 coupe,

currently powered a efi 5L 302 windsor from a 96 ford falcon.

firstly what kind of Horsepower gain can i expect?

secondly what will the approx cost be?

and lastly who can recommend me mechanics in sydney that can do this for me

nick


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boofhead
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If your rebuilding then the costs of going to a 347 is not that more than a standard rebuild. Meaning the machining needed to be applied to your crank, rods, block etc is not much more than purchasing a new crank (with the longer stroke) and the associated parts. It is similar to machining up your old heads compared o purchasing new heads. In this case you get a larger engine with its natural greater power potential.

Power could be an easy 350 HP though to 500+ normally aspirated or far higher if your going with forced induction.

You are better coming up with a plan. What do you want (and how do you want the engine to behave) then workout a budget then work through what can be done to reach the goal with your budget.

Costs are far harder as you have not provided your goals and budget. Paying someone to do it will cost far higher than doing it yourself. Might be best to consider a create engine. A good provider would charge around 8k (for good parts and build quality). For around 3k you can get a DIY short block and bolt it together yourself. For around 4.5k you can get a built short block so you build the top end. Obviously you could get the crank, rods, and piston kit and you (or some else) installs it. This would be 1 - 1.5k not including installation.

This generally is not the end s you would likely find worn parts or want to replace parts (such as your heads) to make better use of the extra capacity of the engine and release that extra power. This adds to the budget. For example, any change will affect the EFI computer fuel delivery. So are you running a programmable EFI controller. You would likely need to change your fuel injector size at a minimum.

It is worth doing for sure. You just might just need a head and cam change to reach your goals. Take it step by step.

Pick your mechanic carefully and keep us informed how you go.


I will someday think of something clever to say.

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hybrid
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If you like to rev your engine hard, you might want to consider the 331 instead - it's shorter stroke does not bring the pistons so far down in the bottom of the bore and is considered safer.

I did 347 in mine as I prefer a bit more torque and can't see myself flogging its ass at 6k rpm on a regular basis.

Keep in mine that EFI re-tuning will probably be required, so if you're running the stock computer, this may be tricky for you.


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nick069
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well i want to use it as a daily drive, have the power there at my disposal but i don't want to have to modify or change my gearbox. I currently have a 4spd toploader and 9 inch diff, i'd be happy with 400hp.

Budget would be pretty conservative around 3-4k?

my other option is super charger but them my budget may easily blow out to $10k.


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ozbilt
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nick069 wrote
well i want to use it as a daily drive, have the power there at my disposal but i don't want to have to modify or change my gearbox. I currently have a 4spd toploader and 9 inch diff, i'd be happy with 400hp.

Budget would be pretty conservative around 3-4k?

my other option is super charger but them my budget may easily blow out to $10k.


Why would that blow the budget?

5.0 EFI easily handles a Paxton. That is all that is done to the 5.0 in my avatar & it is still driven daily after 5 years or so.


Kerry

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Pinto-Pete
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3-4k would get you a low boost paxton out of the states + shipping last time I checked and as Oz says a 5.0 will handle it..


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boofhead
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nick069 wrote
well i want to use it as a daily drive, have the power there at my disposal but i don't want to have to modify or change my gearbox. I currently have a 4spd toploader and 9 inch diff, i'd be happy with 400hp.

Budget would be pretty conservative around 3-4k?

my other option is super charger but them my budget may easily blow out to $10k.


Low boost super charger is one approach. As stated above your looking at 4.5k for a new Paxton imported from the US.

I would suggest for your current budget look at a top end kit plus change your rear gearing. Base top end kit will get you around 350 HP and gearing will make it feel you have a lot more. I am not sure you would want more any way. It also leaves some room for more later if desired.

One possible example;
www.summitracing.com/p.../make/ford

Though a Paxton is here as well...

www.summitracing.com/p.../overview/

Maybe try both... In either case, expect a few extra parts will be needed and tuning the EFI.


I will someday think of something clever to say.

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gbx78
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boofhead wrote
nick069 wrote
well i want to use it as a daily drive, have the power there at my disposal but i don't want to have to modify or change my gearbox. I currently have a 4spd toploader and 9 inch diff, i'd be happy with 400hp.

Budget would be pretty conservative around 3-4k?

my other option is super charger but them my budget may easily blow out to $10k.


Low boost super charger is one approach. As stated above your looking at 4.5k for a new Paxton imported from the US.

I would suggest for your current budget look at a top end kit plus change your rear gearing. Base top end kit will get you around 350 HP and gearing will make it feel you have a lot more. I am not sure you would want more any way. It also leaves some room for more later if desired.

One possible example;
www.summitracing.com/p.../make/ford

Though a Paxton is here as well...

www.summitracing.com/p.../overview/

Maybe try both... In either case, expect a few extra parts will be needed and tuning the EFI.


yes or both!! . Ive read a common combo for guys in the US with foxbody 5.0s, street driven with the TFS kit + stroker + Paxton using a stock5.0 block ran this on the Dyno... it was noted that running this hard constantly would surely split the block .. .paxton tell me that the 5.0 block is good for 500hp before it will show signs of weakness if run hard ALL the time. But whether you would be able to use all of that HP on the street i guess is debatable.

(block your ears/eyes Bas, you are not going to like what you read Very Happy )

Max power - 585 HP at 6200 rpm
Max torque - 518 ft-lbs at 4500 rpm

Equipment
331 Stroker
TFS twisted wedge heads- stage 1 porting
8.65:1 compression, forged pistons
Cam - XE274hr
Intake - weiand stealth
Carb - 650 Mighty Demon
Paxton Supercharger Novi 1200 - w/ 7.5 lbs boost
Full carb enclosure.

I believe (according to the web and the workshop manual Kerry lent me for later model mustangs) the HO motors have forged internals from the factory).

Ive been researching these avenues for a while now. Ive settled on my choice for my path .. but ive read ( and each to their own) .. that adding a supercharger to a stock motor definately changes the feel of the engine and obviously gives you a torquey and more powerfull feel at the foot (with rear end gear change too) and some are content with this change alone .. but i dont speak from experience at all .. just the research ive done over the last 6months or so on the topic . .

of course the gurus here can give more real world advice.

Good luck with your choice .. i always enjoy reading engine threads as you always learn something new and alot of the time the same advice is given which has to tell you something..


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boofhead
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Good input gbx - so Go for it George...... you have the main component - any way you need to kick Steves backside -- he he.

A few comments though;

I don't like 331 - I would always go for the 347 - in my view there is just no point to a 331 - you just leave HP on the table with the 331 and spend the same money.

One of my Favourite OTS Cams is the XE274HR.
Weiand stealth - great manifold but why on a carbed super charged application? In my view a better choice is to use the Weiand X-celorator manifold. I would also consider using an EFI set up (but this adds to the cost though it can be tuned more accurately).

Early blocks are stronger though Windsor are tough and can take a pounding.

So go George go....


I will someday think of something clever to say.

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gbx78
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boofhead wrote
Good input gbx - so Go for it George...... you have the main component - any way you need to kick Steves backside -- he he.

A few comments though;

I don't like 331 - I would always go for the 347 - in my view there is just no point to a 331 - you just leave HP on the table with the 331 and spend the same money.

One of my Favourite OTS Cams is the XE274HR.
Weiand stealth - great manifold but why on a carbed super charged application? In my view a better choice is to use the Weiand X-celorator manifold. I would also consider using an EFI set up (but this adds to the cost though it can be tuned more accurately).

Early blocks are stronger though Windsor are tough and can take a pounding.

So go George go....


hahah i agree on those points .. i remember reading with a s/c application a 331 is better than a 347?? compression? i dont know im still learning internals. I guess its much the muchness.. run lower boost and still benefit from more torquey 347 .. well either way .. thats what guys seem to do in the US with that combo .

Well im half way there with the s/c when i save up cash down the track i shall change the heads, cam and any other internals. I read an article on flow comparisons between TFS, Holley and Edlebrock and they are all pretty much similar give or take.. really only important to those chasing better drag times.. but im not really chasing specific numbers or "the best" i grabbed the deal as it was and im happy to work with what i have.

sorry hijack to the original poster ..

many ways to skin a cat as they say (i think thats steves quote).. ive learnt there is no wrong or right way to get more power but each path has its purpose and price .. planning is the key!!!!


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boofhead
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Agreed - planning which leads to good parts selection and the combination that is important.

For example - real budget combination see this ported heads #3 combo

www.hunterstyle.com/th...combos.php

Always wanted to see if this does result in the claims being made. I have never do all that well with stock ported heads hence I am interested to see this work.

Worth it for the money though import costs would be high due to the weight.. still well below Nicks budget.


I will someday think of something clever to say.

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gbx78
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boofhead wrote
Agreed - planning which leads to good parts selection and the combination that is important.

For example - real budget combination see this ported heads #3 combo

www.hunterstyle.com/th...combos.php

Always wanted to see if this does result in the claims being made. I have never do all that well with stock ported heads hence I am interested to see this work.

Worth it for the money though import costs would be high due to the weight.. still well below Nicks budget.


thats interesting .. what sort of $$ do people charge for head porting here in AUS? as that maybe an option. If they are E7 heads might be worth playing with them but i understand that E6 and below its not worth the cost and just go aftermarket. Saying that GT40 heads might be a middle ground they seem cheap on ebay... but i digress from the original question.


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hybrid
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The only issue with 347 is that the piston comes a long way down in the bore, and the angle of the connecting rod is greater when the crank is at 90/270 degrees. The block actually has to be machined to clear the rod cap bolts for a 347 because it adds so much extra stroke.

So there's a couple of things:
- big angle can be hard on the pistons
- the piston can come down a long way in the bore and the skirt can hang out the bottom of the bore, causing it to be able to rock at the bottom of the stroke. Also not healthy for the pistons.

That's why I said if you want to rev it hard all the time, a 331 may last longer. Having said that, I built a 347, but I'll be relatively gentle with it really. I don't think the 331 needs the block machined for clearance.


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boofhead
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gbx78 wrote
boofhead wrote
Agreed - planning which leads to good parts selection and the combination that is important.

For example - real budget combination see this ported heads #3 combo

www.hunterstyle.com/th...combos.php

Always wanted to see if this does result in the claims being made. I have never do all that well with stock ported heads hence I am interested to see this work.

Worth it for the money though import costs would be high due to the weight.. still well below Nicks budget.


thats interesting .. what sort of $$ do people charge for head porting here in AUS? as that maybe an option. If they are E7 heads might be worth playing with them but i understand that E6 and below its not worth the cost and just go aftermarket. Saying that GT40 heads might be a middle ground they seem cheap on ebay... but i digress from the original question.


The best flowing factory heads are the GT40P heads then GT40s then the rest are worse. He has the touch/skill for porting those heads to get them to flow so well. They do not flow as well as most after market heads though for the price it is excellent value and is impressive. In any case, flow alone is not important it is the combination so his work plus his selected cam performs well together - that is the key e.g., head/cam combination.


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boofhead
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hybrid wrote
The only issue with 347 is that the piston comes a long way down in the bore, and the angle of the connecting rod is greater when the crank is at 90/270 degrees. The block actually has to be machined to clear the rod cap bolts for a 347 because it adds so much extra stroke.

So there's a couple of things:
- big angle can be hard on the pistons
- the piston can come down a long way in the bore and the skirt can hang out the bottom of the bore, causing it to be able to rock at the bottom of the stroke. Also not healthy for the pistons.

That's why I said if you want to rev it hard all the time, a 331 may last longer. Having said that, I built a 347, but I'll be relatively gentle with it really. I don't think the 331 needs the block machined for clearance.


You make an argument that is sound to a point but it is the context that is important here. So what is the primary context?

It is that 99% of people here are using their cars for the street hence cubic inches matters the most.

Most people use cams that are limited to under 6000 RPM for maximum performance. I would argue that 6000 RPM is perfectly safe for both engines. For example, a XE274HR would peek at 6500 in a 302, peek at 6200 in a 331 and peek at 6000 for a 347. In all cases, valve bounce will limit high RPM and also be the area of failure not rod length related stress or piston slap. Most people would spend an occasional 10 Secs in that range then back to the 4-5000 and cruise at 2500.

Hence for dollars spent to get performance then a 347 is the best choice (be it super charged or not). I will though look at the points you raise a little closer as it is a interesting topic.

Point 1: Ease of build (e.g., no notching for clearance).

Both the 347 and 331 in general needs to notching. There is a little more room in the 331 but most of the time the rods included in kits or purchased separately are of a H beam design. These also usually have the larger rod bolts. A smart move to use these rods as this is one of the week points of the small block Windsor engine. If your using the H Beam rods in both cases you will need to add the clearance. It is not hard and will not weaken the block. On a 331 if you use the standard rod I bean design with standard (factory skinny) rod bolts then yes it will clear the block though you would agree it is not as strong hence would not (in theory) live as long as a 347 with far sturdier H bean rods and larger rod bolts at the same upper RPM limit.

In summary; same strong H bean rods need clearance in both cases. No difference.

Point 2: Rod length and ratio.

This is the main point raised and hence we need to look at the details.
I agree there is the general idea of under, over and square engine bore to stroke sizes. I also agree there is the angle of the rod to the bore and hence this has an influence on piston slap and side load. Bore size is a non issue as all these engines are a 4 inch bore hence the rod length verses the stroke is the key to the argument. So the theory is that a long rod to a shorter stroke provides the smallest rod angle. Indeed it does but the theory is this makes an engine survive high RPM better. Again context - Ford went from the smallest e.g. 289 to a 302 (shorter rod same piston) which is against this theory. Why? Because the RPM limit of these engine were (approximately) 5000 hence well within an load parameters hence a non issue. Interestingly the 351W had a higher deck (1 inch) hence the rod ratio was not so affected when the extra 1/2 inch stroke was introduced. Having said that the extra deck high allows a full skirt piston to be used which is more important to control piston slap especially considering the state of material science not being so advanced in the late 50s early 60s when this engine was designed. Modern materials makes shorter piston skirt less of an issue.

So looking at the 331 - it has a 1/4 Inch (0.25") stroke added to the 302 standard 3 inch stroke. In most kits the piston pin position is similar to factory pistons being located below the oil rings though they do have shorter piston skirts to clear the crank.

So looking at the 347 - it has a (0.40") stroke added to the 302 standard factory 3 inch stroke. This is just over 1/8th extra stroke (which is the 289 to 302 difference). In this case, the pistons used have the piston pin located higher toward the top of the piston. In fact the pin goes into the oil control ring grove. This was one of the early arguments to use a 331 verses a 347 but this point has disappeared as this fear of oil control problems in 347s has been dismissed with repeated success of 347s being build correctly. With the rod pin so high this allows a longer Rod to be used in 347 builds while short rods are used in 331 builds. Hence the rod/stroke ratio is better (or at least no worse) in the 347s.

The extra side loads would not vary greatly between the 331 and 347 at least in no meaning full way that would worry any street situation. If racing and your needing 8000+ RPM then sure a 289 might be the preferred choice.

In summary, no difference between 331 and 347.

So why a 347 ? The engine not only has more cubes it is has a longer stroke hence better leverage to transfer the power to the drive line - hence more torque which is king on the street. Lastly, you get this for the same price as the 331 and (I have argued) the same longevity.

This is my view and my reasons for my position. I would not bother building a 331 though I would happily help someone build a 331 if that is what they selected. Just wanted to clarify for those that are reading.


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