331 or big bore 347 turbo motor - Ford Mustang Forums : Corral.net Mustang Forum
 
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post #1 of 28 Old 03-21-2007, 01:29 PM Thread Starter
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331 or big bore 347 turbo motor

Which motor would be better for a mostly street driven car, whats the pro's and con's for goin big bore

My setup so far is trickflow box intake, hi-ports(new style), t-56, built 8.8 3.27's, and the turbo system is goin to be the twin b&g setup with 60's or 67's. Yeah its goin in a dart block, thanks for your input.

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post #2 of 28 Old 03-21-2007, 02:47 PM
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big bore would be better. the con is once you go .125 over thats it. there in no tearing down and boring bigger. but the .125 over will make more power

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post #3 of 28 Old 03-21-2007, 02:48 PM
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big bore would be better. the con is once you go .125 over thats it. there in no tearing down and boring bigger. but the .125 over will make more power
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post #4 of 28 Old 03-21-2007, 03:07 PM
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big bore would be better. the con is once you go .125 over thats it. there in no tearing down and boring bigger
Not true... With a Dart block you can go all the way to 4.150. Some have gone 4.160.

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post #5 of 28 Old 03-21-2007, 03:36 PM
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that is possible i guess. i have have never heard of that but im definatley not arguing. thats good to know
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post #6 of 28 Old 03-21-2007, 04:16 PM
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I would most definitely go big bore. You'll gain power from the added volume and also from the unshrouding of the valves, among other things. The only cons I can think of are mentioned above.
What sort of cam are you planning on running? A setup with a short runner box intake, big heads and a pair of big turbos will LOVE RPM. I would probably rev that thing up to 6500-6700RPM with a nice solid roller camshaft. Also, with the T56 and a 3.27 gear it might be lazy off the line. You might want to step up to a 3.55 or 3.73 unless you go with small turbine housings, which will restrict top end power production.
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post #7 of 28 Old 03-21-2007, 05:21 PM
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Trying to run twin T67's run a big bore 363, you gain a lot of torque over the 3.25" stroke and sacrifice nothing.

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post #8 of 28 Old 03-21-2007, 07:39 PM Thread Starter
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What sort of cam are you planning on running? A setup with a short runner box intake, big heads and a pair of big turbos will LOVE RPM. I would probably rev that thing up to 6500-6700RPM with a nice solid roller camshaft. Also, with the T56 and a 3.27 gear it might be lazy off the line. You might want to step up to a 3.55 or 3.73 unless you go with small turbine housings, which will restrict top end power production.
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Dont know yet. Dont want to go solid roller, just a nice streetable cam so the car sounds like a mild cammed 5.0........ untill i hit the gas. I want a super sleeper car
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post #9 of 28 Old 03-21-2007, 07:42 PM Thread Starter
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Trying to run twin T67's run a big bore 363, you gain a lot of torque over the 3.25" stroke and sacrifice nothing.
The car will make more torque than I need at big bore 347 than at 363 on the street but thank you for your input
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post #10 of 28 Old 03-21-2007, 07:49 PM
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I'm not 100% convinced you need better valve shrouding with good heads & turbo?? I would think about reliability and head gasket seal etc...If it was an all out compitition engine then YES !! I kept my bore std.. If you can fit off the shelf pistons its much better too...Nothing worse than damaging a custom piston....


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post #11 of 28 Old 03-21-2007, 07:57 PM
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I believe a lot of the piston manufacturers out there have off the shelf 4.125 available nowadays.
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post #12 of 28 Old 03-22-2007, 03:24 AM
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The car will make more torque than I need at big bore 347 than at 363 on the street but thank you for your input
Says the guy who's asking about building a car with twin 67's. I have experience.

With twin turbos that huge you're going to have lag, and will want as big of a motor as possible. I've run 61mm GT35R's, 64.5mm GT4088R's, and now T72 P-trim's on my car, and when you start pushing into the middle/upper 60mm turbo range ESPECIALLY if you want to keep a hydro roller and you're running a stick you need to go to the 363 or you're going to have a 1500 RPM powerband. Twin .81 A/R PT67's won't be spooling untill close to 5000 RPM's on a 331, and maybe 4500 on a big bore 347. That's not much room to go if you stubbornly want to stick to a hydraulic roller.

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post #13 of 28 Old 03-22-2007, 07:17 AM
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I believe a lot of the piston manufacturers out there have off the shelf 4.125 available nowadays.
I wish...With 27cc dish ?? Not down here .....Down under....

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post #14 of 28 Old 03-22-2007, 11:26 AM
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Dont know yet. Dont want to go solid roller, just a nice streetable cam so the car sounds like a mild cammed 5.0........ untill i hit the gas. I want a super sleeper car
Just because a car has a solid roller cam does not mean it has to sound aggressive. The advantages to going solid roller are not just so you can run some monster cam. Our old twin T66 347 GT had a solid roller cam in it and listening to it idle and putt around town you had NO IDEA it had a non-stock cam or even turbos under the hood.

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post #15 of 28 Old 03-22-2007, 11:43 AM
 
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Says the guy who's asking about building a car with twin 67's. I have experience.

With twin turbos that huge you're going to have lag, and will want as big of a motor as possible. I've run 61mm GT35R's, 64.5mm GT4088R's, and now T72 P-trim's on my car, and when you start pushing into the middle/upper 60mm turbo range ESPECIALLY if you want to keep a hydro roller and you're running a stick you need to go to the 363 or you're going to have a 1500 RPM powerband. Twin .81 A/R PT67's won't be spooling untill close to 5000 RPM's on a 331, and maybe 4500 on a big bore 347. That's not much room to go if you stubbornly want to stick to a hydraulic roller.
I understand the relationship between cubes and spool time......But answer me this cause I still can't figure out why.....Why is it that twin 66's wouldn't be a very wise choice of turbos for a street car with a 306 or 331, but why is it that the 03/04 cobras do just fine with twin 66's on just 281ci?
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post #16 of 28 Old 03-22-2007, 11:50 AM
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Aren't the Cobras using T3/T4 hybrid turbos instead of T4s?

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post #17 of 28 Old 03-22-2007, 12:02 PM
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I understand the relationship between cubes and spool time......But answer me this cause I still can't figure out why.....Why is it that twin 66's wouldn't be a very wise choice of turbos for a street car with a 306 or 331, but why is it that the 03/04 cobras do just fine with twin 66's on just 281ci?
You can't directly compare the needs of a dohc 281 to a pushrod 302. The volumetric efficiency of the engines are different…and the stock 03/04 cobra heads flow extremely well.

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post #18 of 28 Old 03-22-2007, 03:01 PM
 
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You can't directly compare the needs of a dohc 281 to a pushrod 302. The volumetric efficiency of the engines are different…and the stock 03/04 cobra heads flow extremely well.
So do that mean that if I put a set of trick flow heads on my pushrod 5.0 that flow 290cfm, does that mean that my motor is now ready to efficiently utilize twin 66's???
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post #19 of 28 Old 03-22-2007, 03:02 PM
 
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Aren't the Cobras using T3/T4 hybrid turbos instead of T4s?
I think that your probably right there....I don't know anything about the turbos they use for the mod cars.....I know having that big of a compressor on a small engine, you'd have to have quite a bit of backpressure in order to make decent boost and power down low.....
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post #20 of 28 Old 03-22-2007, 03:08 PM
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So do that mean that if I put a set of trick flow heads on my pushrod 5.0 that flow 290cfm, does that mean that my motor is now ready to efficiently utilize twin 66's???
What the heads flow is just one piece of the puzzle in what makes a motor efficient as well in just how it performs.

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post #21 of 28 Old 03-22-2007, 03:55 PM
 
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What the heads flow is just one piece of the puzzle in what makes a motor efficient as well in just how it performs.
I know....I was just making a statement in response to what Millhouse said to show that there's not much relevance to cylinder head flow and proper turbo sizing for a particular engine...There's some but not that much....

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post #22 of 28 Old 03-22-2007, 03:59 PM
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I read his post differently then because really I felt like I was just restating what he said. I thought he was just making a note on top of the efficiency of the engine when he made the head comment.

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post #23 of 28 Old 03-22-2007, 04:44 PM
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I read his post differently then because really I felt like I was just restating what he said. I thought he was just making a note on top of the efficiency of the engine when he made the head comment.
You are correct sir...and I thought twice about the cylinder head comment in fear of being misinterpereted.
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post #24 of 28 Old 03-22-2007, 09:13 PM
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I understand the relationship between cubes and spool time......But answer me this cause I still can't figure out why.....Why is it that twin 66's wouldn't be a very wise choice of turbos for a street car with a 306 or 331, but why is it that the 03/04 cobras do just fine with twin 66's on just 281ci?
Because the 03 Cobra kits are running those turbos not only with T3 turbine housings, but much smaller turbine wheels as well. Stage III or Stage V wheels in .63 A/R T3 housings will spool much quicker than a .68 A/R P-trim setup. And who says they're doing fine? I've seen dyno charts, and they spool very slowly for a street car with a 6-speed. If you want to keep the revs down, you have no reason not to run more cubes. Pull some timing out of the mid range if you want to make a bit less torque, atleast you'll have it spool up at a reasonable time.

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post #25 of 28 Old 03-22-2007, 10:19 PM
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with boost I don't think you have to go wild with cubes, hell the cobras are only 281ci and lots of them are putting down 1000 with t3/t4's.
All I run is a 306 and mine spools crazy early with a T56 & 327's(T3 turbos). actually I don't even know an rpm where it won't spool, If I'm in 6th at 1000rpm and matt the gas it will start boosting. (almost deisel like)

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post #26 of 28 Old 03-22-2007, 10:42 PM
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with boost I don't think you have to go wild with cubes, hell the cobras are only 281ci and lots of them are putting down 1000 with t3/t4's.
All I run is a 306 and mine spools crazy early with a T56 & 327's(T3 turbos). actually I don't even know an rpm where it won't spool, If I'm in 6th at 1000rpm and matt the gas it will start boosting. (almost deisel like)
Cubes does matter with boost, if you want look at an extreme example and that being a lot of the single turbo supras out there.

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post #27 of 28 Old 03-22-2007, 11:25 PM
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Of course cubes matter, more cubes equal more torque production and a quicker powerband (comparative setups).
And TFSCoupe, there is a world of difference between a 281 DOHC and OHV 302. The heads are a small portion of that difference, never mind the flow numbers but velocity plays a huge part too. Aside from the difference being that the 302 is oversquare (bigger bore than stroke) and the 4.6 is square (similar bore and stroke), there are many factors that tell you which turbos will work best. As with everything, it comes down to combination combination combination. You cant expect the same turbo from a 302 to work the same way on a 281.
Getting back to the thread starters concerns, a large bore 347 will work great and I would personally rather run a large bore 347 than a smaller bore/larger stroke 347. It helps to keep piston speed down among other things. There are many benefits to going this route, and it will make awesome power with the right parts.
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post #28 of 28 Old 03-24-2007, 09:45 AM
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I know more cubes should always create more power but like stang seller says "with the right parts". I just can't see a 347 making any huge gains over a 331, 10hp on a 700hp motor?? more??

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