New here. Was left a 67' Mustang 347. Ready to go down the rabbit hole but don't know where to start.


New Member
Jun 27, 2023
Just read the big bold if you don't care about introduction/fluff.
Been obsessed with mustangs since I could remember. Grandmother had a 70' Mach 1 and I still remember her plopping me in the front seat before I could see above the dash and standing on the clutch/brake pedals just to get around town. Grandfather had a 67' auto hardtop with a 347 that he loved to beat the snot out of and drag race. Luckily he only had a habit of totaling Saabs. He left it to me after passing a few years back but my parents were worried I'd kill myself as I was still in high-school so I had to wait. Definitely the right call even though it drove me nuts at the time.

Now that it's all mine I plan on restoring/modifying some things that annoy me, but I'm a little torn what direction to go and was hoping someone could give me their two-cents.
Here's some specs for context:

347 stroker
AFR 185 heads
750 CFM Holley w/ electric choke
RPM performer intake
definitely cammed (all I know)
Eagle forged internals
c4 transmission

When I first got my hands on it I wanted to go big and stuff a stroked to hell z351 Windsor inside, just absolutely goon it right out and modernize it. Thankfully the initial excitement passed and common sense returned. (still dream about it though)

The first thing that bugs me about the car is the torque curve. It's got good low end torque but dips hard in the midrange, then comes back and slaps you in the face once the engine starts to sing. I'd like to take some of that low end torque and use it to fill in the midrange, but not sure what I can do outside of acknowledging it's a NA engine or grind another cam but that obviously a pain. I know it'll be a tad less "street-able" but that's alright, i'm not really a Sunday cruise for ice-cream kinda guy.
This brings me to the second thing, the C4 auto. Unless I bury the pedal from a dig i'm chilling in third whether I like it or not above 15 mph. When I do gun it, the clutch packs take their sweet ass time locking up like they got gravy on them. I know I could tweak the valves and add more aggressive clutches but don't wanna gamble turning it into a lurch-mobile but maybe that wont happen. I've thought about swapping in a manual so I could have my cake and eat it, but don't think it's worth the hassle.

I'm pretty good with a wrench but new to a lot of this, if anyone has some wisdom to drop and suggest a smart direction I would really appreciate it.
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No paper work or any stuff your Grandfather may have left behind? It might have the 'cam card' which has the specs on the camshaft. Did you Grandfather build or have the engine built or did he pay someone else to build it? That might be another way to find out what cam specs you have.

Other than that - how is it running? Lean? Fat? I do NOT miss tuning carbs. Despite what many internet 'mechanics' believe, throwing a carb on it isn't simple if you want it to run correctly, - especially with a modified engine.

When you say 'dips' - does it hesitate? Is there a miss?

Beyond there being a mechanical issue (air/fuel, carb tuning, fuel pressure, spark, ignition etc) it's really hard to diagnose what's going on without knowing more about the components / specs of what's installed.

What rear end gears? Steep gears can greatly effect how you perceive the bottom end power curve. What stall speed torque converter in the transmission?

Look, I've been wrenching for 35+ years. I'm no guru - there are plenty of people out there who know more than I do...that being said, I honestly don't know a situation where I'd choose carbureted over EFI when possible. Aftermarket TBI EFI setups are plentiful on the used market now, and most times people get rid of them because they don't understand them or didn't order what suited their actual engine etc.

I spent YEARS messing with QJets (mainly GM A and F bodies back in the day) to get them to where they ran and performed as they should. Carb tuning isn't "difficult" per se - but it is tedious and it does take time and you have to tune it for the engine/trans/chassis/weather/location combo you are running.

If your Grandfather worked on his own stuff at all, try to dig around and see what info you can find. You might be surprised.

Hope this helps.
If' your thinking 4 speed there are more than likely plenty of parts cars around, nobody buys standards anymore, except me of course. All my cars are stick except my Falcon, and there hasn't been anyone at an inspection station in years that can drive any of them. I have a complete setup for a '68 GT, but I wouldn't part with it, it'll swap into any of my cars if need arises. As for Carbs, all of mine are NA carburetors.
You could always buy some different size jets and take it to a dyno shop to test...spend an hour or two adjusting the carb to chech A/Fs and play with timing...that alone should help with drivability and get some good TQ and HP would be a place to start... once you get some dyno charts you can select a good tq converter to match the combo.... car would be night and day better with just that.... eventually over time you will get more of the performance bug so start with some tuning and fine tune current setup .... you wont be disappointed...

So let me preface this by saying whether or not you need a 650 or 750 and whether or not mechanical secondaries or a vacuum secondaries would hinge on the cam specs, what rear gears the car has, and what the shift point will be. My T-Bird has a Carb Shop 830 cfm Holley 4150 on it (was a 750 and they massaged it and set it up for road racing). Car has 4.10 gears, 0.598/0.598 lift cam, ported AFR 185's, Vic Jr intake, and 11:1 compression. There is no hesitation with my combo but I shift at 6,800 and I deal with the exhaust smell when putting around as a vacuum secondary carb will not perform like I want it to in this case.

You really need to know the specs on the cam and what rear gear the car has as these will help in knowing where the cam will make power. My immediate guess is you should sell the 750 and move down to a 650 with vacuum secondaries which will perform better and you will not experience the hesitation you describe. Read Post #10 as this guys explains it really well:

If you do determine that the came and gears will support the 750 then pull the carb off the intake put a kit in it as it probably needs to be gone through. It sounds like its having an issue when the secondaries are coming on which can be improper jetting and/or the carb needing a kit. If it has two metering blocks its a 4150 and if it has one metering block its a 4160.

4150 Kit

4160 Kit

This is all based on if the carb is a Holley 750 with mechanical secondaries. You can play with the jetting and get it pretty dialed in just by reading the plugs so do some googling there.

If you are just going to driver around town and hit the track with the car then the C4 is fine but I would go through it and at a minimum put a shift kit in it and most likely change torque converters. If you plan on some highway driving and have any kind of gear in the car (3.55's or steeper ) then I would pull the C4 out and sell it. Get a 4R70W and a USShift transmission controller. You want a 4R70W from 98 to 2002 as they have the diode pack and still have a mechanical speedo provision. This is not cheap but if you want an automatic I would go this route as the 4R70W will hold alot of hp in stock form. If you want to go manual then that can get even more expensive as you will need a transmission (go all in and get a T56), bell housing, flywheel, clutch, either cable or hydraulic clutch actuation, and you will need to find a manual transmission brake and clutch pedal assembly.