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Ford V8 Discussion Discussion relating to getting the most out of your Ford-based V8 Miata's engine

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Old 07-31-2017, 09:23 AM   #1
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Default 302 vs 347 Input Requested

The basic question is what is better in a v8 Miata and why?

Is a 302 enough or not enough, AND

Is a 347 (or other stroker) too much or not.

I'm interested in hearing all opinions and explanations, and especially interested in hearing from any who have had both and which is preferred and why...
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Old 07-31-2017, 04:51 PM   #2
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There's no replacement for displacement. You can't beat cubes.

IMO, if you're going through all the trouble of swapping in a V8, why not put in all the V8 you can get? I can't think of any reason not to use a 347.
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Old 08-01-2017, 08:06 AM   #3
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Plus, if you are going to drop a V8 into a Miata and are a Ford guy you want to be able to be in the same league as the GM guys. The LS engines put out impressive horsepower in a lightweight package.
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Old 08-01-2017, 09:40 AM   #4
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What tires (brand, model and size) do you stroker or LS guys use to harness the power/tq of these larger motors into use-able power?
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Old 08-02-2017, 11:45 PM   #5
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Haven't changed tires/wheels yet because that is the last item on my list but Flyin Miata has some nice packages sold thru Tirerack that fit with no or minimal modifications and the information page mentions which they prefer for various usage styles.
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Old 08-10-2017, 04:39 AM   #6
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Default 302 or 347

Hi,

I just thought I would share my experiences with you.

The 302 is OK. Has decent torque but runs very smooth (from a rod ratio perspective), and can be made to make decent power in a budget minded street car (350HP is doable and reliable TFS 170-190 heads and a decent cam 224-230 deg @ 50 duration with 0.55-0.6 lift. Cheaper to build too as you will reuse the crank if rebuilding. If its a fresh build up and you give it frequent and quality oil changes it will see over 150,000 miles successfully.

The 331 (my favourite) is a great package. So much more torque than a 302 and the power is much lazier. No need to rev it. An easy 400HP with a decent set of heads TW190, TFS R Intake Manifold and a 75-80mm Throttle body. My last build made 425HP with a tiny cam 216 @ 50 (daily driver) and 0.6 lift.

The great part about the 331 is that the rod ratio is still favourable and runs smooth-ish. The oil ring does NOT intersect the piston pin (no oil consumption) and it will have a long life like the 302 above. The piston size is smaller and as such the skirt has less area which makes it less stable in the bore. A little bit of piston rock will occur as the piston is pushed slightly sideways into the bore. No big deal but its not as nice as the std 302 setup with the nice big piston skirt which make sit very stable (long life).

The 347 is a good stroker too, the torque is higher than a 331 and it makes a little more power. However it is less stable in the bottom end at higher RPMs, some engine builders use girdles to try and help this . The oil ring on some stroker kits hits the piston pin, thereby increasing oil consumption. Overall the engines run OK, not as smooth as the 331 or 302 from a vibration perspective. Some people don't care for this and just want max cubes and power. But if you sit in traffic with it all day and it shakes and shimmies where a 302 would be smooth, you start to notice it. Also the engines have even smaller piston skirts than the 331, thereby reducing piston stability. Block needs to be notched a little for clearance but its no big deal.

My advice is if you want a daily street driven stroker and want to go 400HP+ go with the 331, it makes the almost the same power as the 347 without some of the headaches. Many will argue this point but having built both I like the 331 better..

But be prepared to pay more for your engine, as strokers need different, pistons, cranks, heads, intakes to perform at their best. But for 400+ HP the stroker works better than any 302 could. But they typically will not last quite as long as the 302.

But if < 350HP is your goal then I would stick with the 302 it will be cheaper to build, run smoother and use less fuel

But all of them built properly will work great.

Just for the record my Miata has a 331

Hope that helps...

Cheers
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Old 08-10-2017, 05:32 PM   #7
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Quote:
Originally Posted by Five-o-joe View Post
What tires (brand, model and size) do you stroker or LS guys use to harness the power/tq of these larger motors into use-able power?
They make some wheels for Miatas that come in 15x10. 6UL wheels. People regularly fit 245s under them with no rubbing on NBs. NAs will need to have the fenders rolled, ad possibly slightly pulled.
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Old 08-11-2017, 03:53 PM   #8
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Engineer....are the power numbers you quoted crank HP?

Thanks
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Old 08-20-2017, 09:21 PM   #9
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Default Crank or Wheel HP

Hi 5.0 Joe,

The numbers were based on crank HP :P
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Old 08-21-2017, 10:15 AM   #10
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Engineer, a couple of questions since you appear to know your stuff on small block Ford engines.

What is your experience as to the cost to build a 425 HP stroker engine from scratch?
What is the cost of the T5z transmission to be reliable at that torque level?

Do you have any experience using (or building) the LS based GM engines? If so, what do you consider the pluses and minuses of each when comparing the same displacement?

The reason I ask is that here in the USA the aluminum LS based engines have become so inexpensive on the used market that the stroker Ford option prices itself out of the market if you compare similar performance levels. I originally considered a T5 for my LS build but it does not seem to be up to the task of being reliable at 400 ft. lbs. of torque without spending more money than a used T56 costs.
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Old 08-23-2017, 01:47 PM   #11
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Quote:
Originally Posted by BGordon View Post
The reason I ask is that here in the USA the aluminum LS based engines have become so inexpensive on the used market that the stroker Ford option prices itself out of the market if you compare similar performance levels. I originally considered a T5 for my LS build but it does not seem to be up to the task of being reliable at 400 ft. lbs. of torque without spending more money than a used T56 costs.
You are correct on all counts.

For a Miata swap, the LS engine is the better choice. It's lighter, smaller, and makes excellent power. Unless you're building a Ford based car (like a Cobra replica) the LS package just makes perfect sense.

The LS motors are extremely durable, and inexpensive to buy and run. That's why I put one in my race car. Why wouldn't you?

The Windsor engines haven't been in factory production for a very long time, although there is plenty of aftermarket support to keep them going for decades to come. It's a great motor, that's why they're still around 15 years after Ford stopped making them. But modern technology certainly has passed them by.

As for the transmission, you are correct. The standard T5 will not hold up to the power levels that a stock LS3 will make. A stock T5 is only good to about 325-350 ft/lbs in a light weight car. The T56 will easily hold the power of an LS engine. For durability, the best thing to do is buy the engine and transmission as a package. You save money, and get all the parts, brackets, fasteners, etc that you need in one package.

BUT.... the T5 is a much smaller package, and weighs about 50 pounds less than the T56. When I have time (and money) I'm going to have Gordon Levy build me a T5 with a .90 5th gear, along with a 5" dual disc clutch, for my Exocet. That will save me 50-60 pounds, and give me an OD gear I can use, in a much smaller package. Not cheap, but it will add lightness and utility. I never use 6th gear, and only use 5th on the cool down lap.
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Old 08-23-2017, 03:52 PM   #12
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boB,
I am glad to hear that (our) great minds think alike.
On the T5, I gave strong consideration to getting one built for the weight and size savings.
Mostly I was wondering if things are different in Australia.
For all I know their T5 transmissions might be much heavier duty than ours or that LS engines are rare over there.
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Old 08-23-2017, 11:54 PM   #13
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Default 302 or 347

Hi,

BGordon: A 425HP ford stroker form scratch with all new parts will be $6-9K depending on your preferences (forged or cast cranks, pistons, head spec etc.) But around $8K is a good price to shoot for a ready to start engine.

T5z capability: Ok the T5z is a very good unit when treated with respect. I have used T5's behind 400Hp applications with great success. But they wont take "abuse" for too long with high HP/torque engines. In the miata you have more room to accommodate abuse as the weight of the car is very low. Gearboxes let go when the tires are sticky and the car is heavy, all the torque is then absorbed by the box itself. With the miata the car will likely break traction thereby reducing some of the load on the box itself.

My call on this is if someone needs a reasonably strong unit for daily duties and does not abuse the box by flat shifting, regular high rpm take offs or heavy racing...then it will work really well. It is a very light weight gearbox and it shifts very smoothly. In Australia the T5 was used behind 6 and 8 cylinder applications with good success by Ford and GM in the local products. There were some minor differences in the T5 configurations used (input shaft lengths, ratios, shifter position etc.) but they are essentially the same unit.

But if you are running an LS motor then I would use a T56, they are quite bulletproof and although they are double the cost of the T5z, it would be a good investment if you are going to push it hard all the time.

Regrettably, I have no experience with building LS motors.

But as the previous poster correctly stated, the LS engines are miles ahead of the old ford Windsor for technology and efficiency. They are lighter, make great power and do it reliably and they run nice and smooth. In addition (as already noted), they are very cheap, super reliable and readily available. An LS Crate engine is a steal for what you get; a 450+ HP bullet proof engine..brand new..it is hard to beat that.

The ford engine is a great engine but it was designed in the 60's, with a decent alloy head and induction setup it can still deliver 450-500HP without too much effort. But there are much better options now from GM and Ford that one can use...

But if you have a choice between ford Windsor or the LS engine, I would run the LS motor almost every time...and I am a Ford guy!!
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Old 08-28-2017, 07:14 AM   #14
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The LS motor is a great motor and a great option; however, it seems we are comparing the cost of a used, pull out LS against building a similar sized stroker ford from scratch. We really should be comparing used prices against used prices for the purposes of this discussion imho. If I was considering a drivetrain for a fresh build, no question, I would be considering an LS based engine. For the owner who already has a ford powered car, like myself, the ford stroker option becomes a lot more attractive than reconfiguring the car to fit the LS and T56. Regarding the T5, my last Miata was ford powered with a Vortech supercharger and made over 470 whp and 440rwtq. I drove the car hard nearly all the time and the T5 held up just fine. That said, if I had kept the car I would have swapped out the T5 for a used tremec 3550 TKO which is lighter, stronger, and cheaper than the average used T56.....just for peace of mind. I'm a ford guy if you can't tell, but i do feel the the LS is the pinnacle of pushrod motors. For a fresh build, it's nearly impossible to replicate the hp per dollar of a used LS setup.
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