Building a 393 low end torque engine

[68ford]

How are they gonna fight someone they have no hope of catching?

 

[pcf_mark]

I think I have been a member here for 7 or 8 years and I love this forum more than any other. The people are great, quality of responses is educated and we respect each other. This is the first thread I have been on where the OP asked for specific advice. Then has said repeatedly, in essence, we are all stupid and our advice is worthless. If I want that I'll go to the Honda, G8 or other forums populated by net trolls.

Post up your dyno sheet and a video driving on the street. Maybe we will all learn something. None of this is rocket science and testing has proven directionally what works and what does not.

 

[ntsqd]

You haven't seen MISF drive! One of his favorite games is to see how long he can keep the little BB in the inclinometer pinned at the extreme of its travel in a corner. Worst gift I ever gave him....

Actually, his next Scout will have a 383 stroker SBC in it, with an appropriately sized cam in it. He has all of the parts, just needs to put it together.

 

[pcf_mark]

I have looked at cylinder head flow data on 383 SBCs and they can suck a stock head dry at low to mid range rpm! The dwell time at the top makes them more knock sensitive but the downward pull can create a huge pull on the intake stroke without a lot of rpm. They do not rpm well - the stroker benefit reverses.

 

[68ford]

The OP probably came up with the idea for restrictor plates in NASCAR hahaha

 

[Montoya]

The OP probably came up with the idea for restrictor plates in NASCAR hahaha

^^^^THIS^^^^ I love a good laugh first thing in the morning.

Seriously though, he's basically doing the exact same thing.

 

[ntsqd]

I have looked at cylinder head flow data on 383 SBCs and they can suck a stock head dry at low to mid range rpm! The dwell time at the top makes them more knock sensitive but the downward pull can create a huge pull on the intake stroke without a lot of rpm. They do not rpm well - the stroker benefit reverses.

His Scout II weighs about 7600 lbs. (not kidding) due to all of the spares he has onboard. Grunt is what it needs, not high RPM. I'm sure that the heads he has will limit it, but his budget won't stand a better head. Tried to at least get a set of the ZZ4 heads to make it less knock sensitive, but those are apparently NLA.

 

[Joe473]

The idea is maximum torque at about 2200 RPM with max HP at around 4400. That's a broad power band that idles at 500 RPM and pulls hard at 1500. The new cam has more lift and about the same duration as the Lightning cam. The 4 degree advance should help the low RPM torque. It, as I said, is very close in specs to the Lightning, 1969 Mustang, and Explorer cams. All these are mild easy to live with cams.
Today I talked to local engine builders and all agree the roller rockers with this cam won't make any noise, as I suspected. They also agree a 9.2-9.4 to 1 compression ratio with regular gas is about right.
If you want a 10 sec. 1/4 mi. EB, go for it. There are an infinite number of better places to start.

I can appreciate what you are going for here but to avoid tuning issues and not maximizing torque available I agree that you would need parts to match and complement each other. Think about cubic inches. Think about airflow and a 351 built right may match up better with the parts you want to use and give you a reliable torquey Engine at lower cost

I loved my 300 straight 6 from high school as well and my goal was a stock looking stock sounding 347 that has low end TORQUE.

On roller rockers. Scorpions fit under stock power by Ford valve covers with massaging of baffles. Some cam profiles can be noisy.

I love my 4100 but even on the 347 I used the 1.12. Throttle response is great and many who ride in it feel almost as good as EFI. There is a 1.23 version but they are like the holy grail of 4100s. On a stroked 351 the 1.08 may cost you torque and primary cruise metering may be an issue that could cost you economy. Consider the 1.12 at a minimum and spend the time tuning it right.

Headers help with flow. Drawbacks noise and heat. I'm using BC shorty's. I considered high flow cast iron but found they were even restrictive to mild 302s. Based on those cubic inches they may choke power even at 3500 rpm

On your heads make sure springs are upgraded to handle the roller cam profile you choose. Check size of chamber. I'm running 9.6:1 but never run less than 91 octane since it's a carbed engine with non computer controlled timing.

On the cam you will have low end torque but I think you can maintain a great amount of low end torque and gain midrange with a little more lift and duration.

Watch the LSA. Higher LSA will increase idle quality but it will cost midrange torque. I am running the 35-349 that timmy has. For a 512 lift cam in a 347 when you hear my truck idle you would think its a Stock 302. Look at the engine it and you would think its stock 302

My advice find some desktop dyno software maybe comp online one and see what your choices yield. Then bring cubic inches down to 351 and you may see the stroker may not add much value using small heads, cam, cast iron manifolds.

It's your truck and your engine. All your choices. I made many compromises on my 347 that brought it from a 425 hp engine to probably a 375hp engine but with great torque, great idle quality, vacuum brakes, and a very stock looking engine bay. I think what many are trying to say is match the parts so the stroker cubic inches are adding value to the equation.

Good luck!

Sent from my SM-G960U using Tapatalk

 

[jckkys]

I've owned several 600 CFM or 1.12" venturi 4100s. They worked well in my '66 428 PI. The solid lifter cam came from the 427 so the 428 ran strong to nearly 5800 with that 4100. I've also used a 450 CFM Holley that ran better over all than 600 Holleys on the 351. I don't think Holleys are nearly as good as 4100s and a stock appearing engine compartment is important to me. If I wanted EFI I'd get a Wrangler. EBs are carbureted. I'm glad to see another 4100 in an EB. I believe Ford would have done well with a 351 Bronco starting in '69 when they put them in Mustangs. They were slow to do upgrades like the C4, power steering, or power brakes, hell they NEVER offered AC or AM/FM. The corporate weenies saw Broncos as farm implements. My build will incorporate features that Ford had, but never included in the Bronco option list. I'm sure by now Ford knows they blew it. My whole valve train is included in the Comp Cam kit. The 1 exception is rocker arms I'll go with Comp Cams roller tip magnums, now that I know noisy rockers is a non issue. I did look into the 347 but decided the 351 is less $ and it's stronger in terms of durability. A lot of work went into building a 351 top end that fits under the stock hood with no body lift, while using the stock air cleaner.

 

[WheelHorse]

Joe, what heads are on your 347?

 

[jckkys]

Carburetor size is something I've experimented with for many years and I found it's difficult to go too small. When a 480 runs as strong as a 600 on my 351 I can see no reason to go to 600. After all the engine is only occasionally pushed at full throttle. There's usually vehicles, red lights and speed limits keeping a light throttle as the only choice. So part throttle is where the engine lives. Smaller throttle bores and venturis are always advantageous at part throttle. So even if at full throttle a larger carb is a little better and for my engine it's not, the smaller carb is better for drive-ability, fuel economy, and resistance to bump stall off road. The Comp Cams 35-349 is designed to work from 1500-5500 RPM. My C4 shifts at 4500 and I see no reason to change that. If I had chosen to work for more HP through deep breathing heads etc. a higher shift point would be indicated. I don't need the HP I have. Why would I want or need more? As I stated in my first post the 133 HP of the stock 302 was plenty to do what I need. My "restrictive" 302 heads and exhaust manifolds worked well then and kept working well with a far more powerful 351. I'm going to try GT40 heads that don't change the original look of the engine compartment. I'll see if that does anything. The same with the roller cam and valve train. Headers can never look original that rules headers out by itself even without the noise and heat. The question of going to a 3.85 crank is contingent on things that haven't happened yet and likely won't. The point is to explore ways of gaining low RPM torque that won't break the bank. At less than 2000 RPM all the big cam, big carb, big heads, and exhaust are useless if not harmful. They certainly are not going to improve drive-ability or MPGs.

 

[68ford]

I'm still confused, if part throttle torque is everything to you, why spend money on any aftermarket parts at all? Save money, skip gt40s, rollor rockers and roller cam. Spend part of that on a 4in stroke crank kit. The only additional cost is rods. They are much cheaper than you above mentioned parts. If all you want is torque at part throttle where flow is least relevant, make the most by using the longest cost effective stroke crank.

 

[ntsqd]

I too experimented with carb size, on a 302. You can go too small and it's not that hard. Just put a Holley 390 on the engine. Throttle response right off idle was great. That's all it had. Even in city traffic it was clearly too small of a carb. I was hoping to see a part throttle cruise MPG increase. Drove it long enough to tell, didn't happen. Was not a fun carb to drive. As a poor college student at the time I'd have lived with it if there had been an MPG gain and there was not.

The carb that had way more driveability than any of the Holley's was an AFB. It didn't quite have the off idle response of any of the various Holleys that I tried, but it had far better driveability and a slight increase in MPG. I was gearing up to test a Q-Jet when a turbo-diesel Ribbit Pick-up landed in my lap and I sold that car.

 

[jckkys]

Never tried a 390 CFM, but the list 4548 450 CFM gave me no better acceleration than a list 1850 600 CFM. The 4548 drove better with better MPGs too. Ford used these as replacements on 390s so they have Ford a part number. If the 600 accelerated slightly better, but was unable to give me drive-ability or MPGs, I would choose the 4548. Winning a race isn't what my EB is to me. I like AFBs too and my 500 CFM has great off idle response and is the easiest to tune of any carb. This build must retain a stock appearing engine compartment.

 

[pcf_mark]

Carburetor size is something I've experimented with for many years and I found it's difficult to go too small. When a 480 runs as strong as a 600 on my 351 I can see no reason to go to 600. After all the engine is only occasionally pushed at full throttle. There's usually vehicles, red lights and speed limits keeping a light throttle as the only choice. So part throttle is where the engine lives. Smaller throttle bores and venturis are always advantageous at part throttle. So even if at full throttle a larger carb is a little better and for my engine it's not, the smaller carb is better for drive-ability, fuel economy, and resistance to bump stall off road. The Comp Cams 35-349 is designed to work from 1500-5500 RPM. My C4 shifts at 4500 and I see no reason to change that. If I had chosen to work for more HP through deep breathing heads etc. a higher shift point would be indicated. I don't need the HP I have. Why would I want or need more? As I stated in my first post the 133 HP of the stock 302 was plenty to do what I need. My "restrictive" 302 heads and exhaust manifolds worked well then and kept working well with a far more powerful 351. I'm going to try GT40 heads that don't change the original look of the engine compartment. I'll see if that does anything. The same with the roller cam and valve train. Headers can never look original that rules headers out by itself even without the noise and heat. The question of going to a 3.85 crank is contingent on things that haven't happened yet and likely won't. The point is to explore ways of gaining low RPM torque that won't break the bank. At less than 2000 RPM all the big cam, big carb, big heads, and exhaust are useless if not harmful. They certainly are not going to improve drive-ability or MPGs.

Show us the dyno sheet of any engine that has been put together like this. At 2000 rpm filling 393" with a 302 port / valve / cam / 450 cfm carb is not going to make any more power (torque) than a 351 or 302. Period. It is just math. Your power output is result of the air and fuel and you can take in because that is the energy source. You get some variation in output from crank angle and stroke but that realyl just moves the power around the rpm band.

I have seen Big Block Chevys make motorhome moving torque with 800 cfm Quadrajet vac secondary carb, small comp cam, ported OEM oval port cylinder head. It makes almost no power until you actually open the throttle. Trying to make torque (power) by choking off the intake is not good science.

 

[jckkys]

I hate to break it to you, There may be at most one engine dyno in Tucson. They're may be one in everybody's garage in Penn., not here. Even if my running 351 was out of the Bronco I'd have to haul it to the builder and pay $1000+ to hook it up, for what reason? So I can get you dyno sheet. Don't hold your breath. In other words that's a ridiculous thing to say. Do you really think that's a persuasive argument? I can see that my personal experience is worthless to you and your opinion is worthless to me if you ask for a dyno sheet to make a point. You forfeit any credibility you may have had.

 

[68ford]

I have a couple Cummins ISB 6.7s at work. Make you a deal on one. Make a deck plate to lower the compression and put spark plugs in the injector bores like the CNG engines. Gobs of torque from a really long stroke. I'm sure the cam is absolutely perfect since we know all it has to do is slightly open the the valves

 

[Bickster]

So it’s ridiculous for someone to ask for data vs. seat of the pants personal experience? Credibility?


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[ntsqd]

There's no arguing with a closed mind that is made up. I'm done here.

 

[68ford]

There's no arguing with a closed mind that is made up. I'm done here.

He's closed minded just like his valves and throttle plate hahaha