347 Header Size and exhaust Diameter

Wellzy55

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Hi everyone. I'm new to the Forums so I'm sure this question has been asked before but if you could help I would greatly appreciate it.

I recently picked up a 91 foxbody with a built 347 stroker. It runs great but I feel I can get more out of it. I took it to the track on street tires and ran 13.6 @ 110mph. I spun 1st and 2nd pretty bad bit it ran strong. I bought some drag radials and put them on it, but with the Covid-19 I haven't been able to get back to the track.

I also had it Dyno'd on a Mustang dyno and i was kind of disappointed with the outcome. 355tq @4500 and 322hp @ 5500. What do you all think about those numbers? Sound about right?

Here's my setup to my best knowledge. The previous owner had paperwork for the parts he put in it...

Cast Eagle Crank (4.030 bore) (3.400 stroke) (piston head volume of + 5cc)

Hypereutectic Flap top piston with 2 valve reliefs

Victor Jr Aluminum Heads 210cc ( not sure about valve train) does have roller rockers.

RPM performer Intake

750 holley Double Pumper ( squared jetting of 76 without a powervalve) and also has about 4 inches of spacer

BBK shorty headers with 2.5 in dual exhaust with x pipe.

MSD distributor running about 18° intial and 36° total.

I feel I should go to 3inch on the exhaust with a wider diameter long tube header. What are you thoughts?

I'm running a T5 manual transmission.

I thought I would have seen more around 400hp at the wheels but I guess it's harder to get those numbers than I thought.

Any tips or advice on how to get this thing running a little stronger would be much appreciated.

Thank you
 
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revhead347

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The mph isn't too bad. That should be around 12.7 @ 108 once you get a sticky tire on it and it hooks. The dyno numbers aren't too good. Every dyno is a little different, but Victor Jr heads are actually really good, and it should be at least 50hp higher. The shorty headers are definitely holding you back. I'd step up to the BBK long tube headers with the 1 and 3/4" primary and a matching intermediary (H-pipe). 2.5" exhaust is fine, don't waste your money on 3" Those cam numbers don't look good either. I think that cam might be hurting you too. Put a better cam in it. Then put it on the dyno and get it tuned. I think you will be a lot happier with the car, and all of that really isn't too much money.

Kurt
 

Wellzy55

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The mph isn't too bad. That should be around 12.7 @ 108 once you get a sticky tire on it and it hooks. The dyno numbers aren't too good. Every dyno is a little different, but Victor Jr heads are actually really good, and it should be at least 50hp higher. The shorty headers are definitely holding you back. I'd step up to the BBK long tube headers with the 1 and 3/4" primary and a matching intermediary (H-pipe). 2.5" exhaust is fine, don't waste your money on 3" Those cam numbers don't look good either. I think that cam might be hurting you too. Put a better cam in it. Then put it on the dyno and get it tuned. I think you will be a lot happier with the car, and all of that really isn't too much money.

Kurt
Thanks for the reply. That's what I was thinking with the headers i wasn't sure if i should go with the 1 3/4 or the 1 7/8 diameter. In the future I'm planning on putting a procharger on it so I was think the bigger pipes.

Why do you suggest H pipe over X pipe? I'm just curious. What are the benefits?

What would you suggest with the cam? Something less aggressive? The motor comes to life around 3500 rpm and pulls like crazy up to about 6500.

I'll attach pictures of the two dyno pulls.

Thank you
 

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96pushrod

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The bbk collector is a piss poor design. Their collector reduces to around 2.2in, regardless of collector diameter.

1 3/4 with a 3in collector is what I’d use, with 3in all the way back and some straight thru style mufflers. X pipe is nice as well. That cam is gonna want to rev, might as well put together an exhaust that’ll let that happen.
 
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revhead347

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Thanks for the reply. That's what I was thinking with the headers i wasn't sure if i should go with the 1 3/4 or the 1 7/8 diameter. In the future I'm planning on putting a procharger on it so I was think the bigger pipes.

Why do you suggest H pipe over X pipe? I'm just curious. What are the benefits?

What would you suggest with the cam? Something less aggressive? The motor comes to life around 3500 rpm and pulls like crazy up to about 6500.

I'll attach pictures of the two dyno pulls.

Thank you
I haven't seen too many 1 7/8" headers that are bolt in replacement (meaning they fit properly). 1 3/4" should be more than enough. It's hard to recommend a part that someone will struggle to get to fit, when I know the BBKs bolt up right almost every time. The BBKs are reduced to a 2.5" flange, even though they advertise a 3" collector. So there really isn't a whole lot of power gained by putting in a 3" exhaust past that. The H-pipe or X-pipe is a matter of taste. It comes down more to sound than actual power. Pick what you want, the difference either way will be negligible in performance. I might get cursed out later because something I recommended didn't absolutely optimize the engine, but I don't want to recommend something that frustrates someone to no end and get cursed out for that.

I never make specific cam recommendations. That's way over my head, and should be left to the professionals. I can only say that your particular cam doesn't look right number wise. 107 degree lobe seperation sounds like something you would put in a 9000 rpm engine, that falls flat on it's face below 7000rpms. Most cams are in the 110-114 lobe seperation range. There are 2 different camps on stangnet regarding cams; the guys that pick stuff off the shelf, and the guys that insist you get a custom ground cam. I have a custom ground cam, but it could go either way for me. A custom ground cam is a little more money, and you have to know every single detail about your car when you order it. At this point I would recommend calling Comp Cams and getting something off the shelf. They have more cam grinds than anybody on the shelf to zero in on what your setup needs. That's opposed to calling Steeda who has like, 3 cams, and they sure are going to push one hard to get a sale. Be prepared to provide information like carb, intake, heads, compression ratio, transmission, final drive ratio, and most importantly, what you want to get out of the car.

Kurt
 
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96pushrod

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Lobe separation is kind of a funny thing. All things being the same, the tighter lsa will tend to make more lower rpm torque than an identical cam with a wider lsa. A wider lsa can actually be more peaky than a narrow one, due to cylinder pressure actually decreasing. Sometimes it’s not a huge difference, sometimes it is.

Tight lsa will also lead to lower vacuum readings at idle, which can be an Issue for power brakes and other vacuum actuated options. This for many is usually the deal breaker.

As much as the company sucks, MAC makes a pretty solid 1 3/4 X 3in header. They’re just terrible to deal with, only buy if you can find a company that physically has a set sitting on their shelf ready to go. Coupled with their x pipe of pro chamber you will make more than the bbk design. The trick is finding those suckers

Did you ever pull up to 6500 on a dyno pull? That cam has like 245 ish degrees @.050 and a bit more than that on the exhaust. It should be peaking a good bit higher than your graphs show.
 

revhead347

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I never had any luck getting Mac headers to fit right, and I've owned 2 sets in the past. I do have a Mac Pro-chamber, and I love it. I actually reworked the inlet tubes on it to work with my BBK Fox headers. Very smooth sound, and always wins in the dyno comparisons. Given the fitment issues with Mac stuff though, I can't recommend them.

Kurt
 

revhead347

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I have a 347 with 170 cc aluminum heads, a custom cam, restrictive GT40 FI intake and BBK shorties, and made 330 hp and 350 tq at the tires. I would think you could do better with the bigger heads and a carb intake.
His heads are bigger than yours. That's a good comparison though. I think it's the cam. Obviously the tune will cause it fall flat on it's face too.

Kurt
 

2000xp8

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Headers and exhaust may be a problem, but they aren't your only problem.
It's not like you are 15rwhp away from the potential of the heads (more like 75rwhp+). I could have sworn one of the guys I know ran those heads with a victor EFI intake on an R302 to 7000rpm and made 477rwhp.
If yours is a stock block (with a t5, i'll assume it is), i'd forget about running it too much past 6500rpm, unless you don't want it to last long.

The build sounds a little questionable, like they spent all their money on the heads and nothing else.
Higher end heads with shorty headers, a t5, high rpm cam (according to you guys, I have someone who chooses cam specs for me) and worst of all, a carb swap, why?
If it's a stock block, it's even less sensible since they don't like high rpm.

So while you may need to worry about the headers, there is a lot more to it.

Me personally, i'd keep the heads and 347 and replace everything else.

As for the procharger, you get the engine right NA and it won't be needed, especially if the block is indeed stock there won't be any real room for gains.
You have the most important (and expensive) parts of the recipe, there is no reason with the right supporting parts that shouldn't be 400rwhp+.
 
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revhead347

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Headers and exhaust may be a problem, but they aren't your only problem.
It's not like you are 15rwhp away from the potential of the heads (more like 75rwhp+). I could have sworn one of the guys I know ran those heads with a victor EFI intake on an R302 to 7000rpm and made 477rwhp.
If yours is a stock block (with a t5, i'll assume it is), i'd forget about running it too much past 6500rpm, unless you don't want it to last long.

The build sounds a little questionable, like they spent all their money on the heads and nothing else.
Higher end heads with shorty headers, a t5, high rpm cam (according to you guys, I have someone who chooses cam specs for me) and worst of all, a carb swap, why?
If it's a stock block, it's even less sensible since they don't like high rpm.

So while you may need to worry about the headers, there is a lot more to it.

Me personally, i'd keep the heads and 347 and replace everything else.

As for the procharger, you get the engine right NA and it won't be needed, especially if the block is indeed stock there won't be any real room for gains.
All good points. I question that cam. Supercharging a carb is a little bit of a hassle anyway. The fact that someone did a carb swap in the first place is an indication of a rookie mistake. That cam though.....it doesn't make any sense. The heads make sense. I've been there. Those heads were on Craigslist at a good price that week. Or they had a friend that used those heads, so the owner had to have them too.

The RPM kills the stock block more than the power. I put almost 400hp to the tire NA, and spray 150 on top of that. Been doing it for 18 years now on a stock block.

Kurt
 
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2000xp8

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The fact that someone did a carb swap in the first place is an indication of a rookie mistake.
I feel the same way, the carb swap makes me question the entire build. Questions arise, like can you prove it's really a 347? A purpose built 347 with Hyper pistons?
Nobody that knows what they are doing puts a carb on an 86+ foxbody (at least not in the last 25 years).
If it were my car, i'd do a standalone EFI system, rpmII intake, 30lb injectors and me personally, I wouldn't be afraid of a good set of equals to keep the headers simple.
I bet going back to EFI would add more in value to the car than it costs to do.
 

revhead347

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I feel the same way, the carb swap makes me question the entire build. Questions arise, like can you prove it's really a 347? A purpose built 347 with Hyper pistons?
Nobody that knows what they are doing puts a carb on an 86+ foxbody (at least not in the last 25 years).
If it were my car, i'd do a standalone EFI system, rpmII intake, 30lb injectors and me personally, I wouldn't be afraid of a good set of equals to keep the headers simple.
I bet going back to EFI would add more in value to the car than it costs to do.
Hyper pistons on an NA car is perfectly fine. Dare I say a forged piston would actually be money poorly spent. I would not want to be the one who has to put fuel injection back on it. That's a nightmare. Carb swaps are still somewhat popular. There is no reallly good reason in this case to go back to fuel injection. The carb will make the power, it just has to be tuned right. A big help would be a programmable ignition box. That's another thing that came up in my mind. Is the person who decided to put a carb on it the type of person that would put the effort into a good distributor, and tune that correctly? Doubt it. A programmable ignition box would go a long way.

Kurt
 

Monkeybutt2000

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People carb their build because they think it will be cheaper and simpler. Usually doesen't work out that way. I'm wondering why the rpm intake and not the Victor jr. A 4" spacer? What?? And FWIW, my buddies Fairlane made over 420 crank hp with a 331, out of the box AFR 185's, and an Edelbrock carb. Can't remember what intake is on it,but the cam is a flat tappet as well.
 

Wellzy55

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Thanks for all the replies!! I'm not sure what the guys were thinking when then built the motor. I think they were not to concerned on maximum horsepower. Maybe just something that was decent. They completely re did all the interior and did a paint job. So they were leaning more towards a nice daily driver with some extra pep.

I spoke to a rep at Powered By Ford in Orlando and he said the same thing about the cam and Intake. He said to do those before doing anything to the exhaust. He suggested going to a solid roller vs the current hydralic roller as well. We didnt get into what size cam though.

What would you all think about lift/duration and LSA? I looked at the flow charts of the heads and they peak right around .500 - .550 lift with a maximum of .650 lift. I am struggling to wrap my head around what would be best because so many people have so many different opinions.

I was at the track last night and realized I have to stop worrying about more horsepower for now. I'm having a real hard time putting down the power its currently making. I guess it's time to figure out how to put more rubber in the back. I currently have some toyo r888r 245 50r 15 the biggest I could put on the stock 10 hole rim's. It didnt matter how much I throttled it I just couldnt get it to catch in 1st or 2nd. My best run was a 13.243 @ 111mph. I'll be working more on the chassis tuning then Power gains for now.

Any one know how big I can go on rear rims and tires with out having to roll the fenders? And what size slick would you go with?

Thanks guys!
 

revhead347

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You're not going to get anywhere on 10 hole rims. They are too narrow to get a decent tire on. Get a set of dedicated track wheels and put drag radials on them. You should be fine with a 26"x10" tire in the back. You are really going to need more tire if you are racing at Orlando Spin World.

Not many people do solid roller cams these days. There isn't much gain there. That's more of a high rpm race car thing. It's hard on the valvetrain, it's hard on the block, and you have re adjust them all the time.

Kurt
 
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nickyb

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Thanks for all the replies!! I'm not sure what the guys were thinking when then built the motor. I think they were not to concerned on maximum horsepower. Maybe just something that was decent. They completely re did all the interior and did a paint job. So they were leaning more towards a nice daily driver with some extra pep.

I spoke to a rep at Powered By Ford in Orlando and he said the same thing about the cam and Intake. He said to do those before doing anything to the exhaust. He suggested going to a solid roller vs the current hydralic roller as well. We didnt get into what size cam though.

What would you all think about lift/duration and LSA? I looked at the flow charts of the heads and they peak right around .500 - .550 lift with a maximum of .650 lift. I am struggling to wrap my head around what would be best because so many people have so many different opinions.

I was at the track last night and realized I have to stop worrying about more horsepower for now. I'm having a real hard time putting down the power its currently making. I guess it's time to figure out how to put more rubber in the back. I currently have some toyo r888r 245 50r 15 the biggest I could put on the stock 10 hole rim's. It didnt matter how much I throttled it I just couldnt get it to catch in 1st or 2nd. My best run was a 13.243 @ 111mph. I'll be working more on the chassis tuning then Power gains for now.

Any one know how big I can go on rear rims and tires with out having to roll the fenders? And what size slick would you go with?

Thanks guys!
You should get in touch with team z motorsports, they have what you need to get that power to the pavement,they race what they sell.
 

2000xp8

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The paint job is probably your biggest asset, these days prices and time frames for paint work are horrific.

I dunno about a solid cam lifter setup, did you let them know it was a stock block (if it is?)?
I can't possibly see it lasting. If it's a dart, i'd consider it, but stocker, no way.

Me personally, i'd just get in touch with a cam specialist and let them spec one out for you, Yes it will likely cost $150 more, but IMO it's worth it.

Another thing to consider is that the more traction and power you make, the more likely you are to break the t5. Sounds like you are willing to drive it hard, just be prepared.
 

Wellzy55

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I am going to contact QA1 and Team Z today and see what they think. I've been looking at all the components and man on man to do it right the first time your talking some big money lol.

What would you guys recommend doing first? Kinda the best bang for my buck scenario.. I am thinking coilovers with double adjustable valving would give me the best starting point and then upgrading the 4 link to get it properly positioned under the car.

What do you think I should do first the front or rear coilovers? I can't afford both sets at once.

And if I do rear coilovers can I ditch the quad shock? That would free up some extra room for bigger tires.

Thanks!
 
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