Completed Project Superchargered 347 Stroker Build

This isn't for a truck but for my 1994 Cobra. What started this build is when I broke another rocker arm and bent another pushrod. It was the second time that it happened. The first time was about 20,000 miles prior. With 90,000 hard miles I figured the cause was weak valve springs. So I pulled the heads and and while I had them off ported them. I then took them to Pacific Engine and had them machined and a valve job done. While doing so they discovered that AFR had way too much spring pressure and that some of the springs only had .500 lift before going into coil bind. My cam with 1.7 rockers has .530 lift so it's surprising they lasted 90,000 miles.

Here's the broken rocker.

Here are some of the porting work I did on the heads and lower intake manifold.

After.

Intake manifold.

While the heads were being machined I started cleaning the carbon off the tops of the pistons and noticed a nick in one of the cylinder walls. With that discovery I really didn't want to just slap the heads back on so I started looking into the cost difference of rebuilding the 302 compared to buidling a 347. The cost diference was going to be very little so I'm building a 347.

When I pulled the shortblock from the Cobra and disassembled it I discovered what caused the nick. I found that two studs that hold a splash shield on the intake manifold had come out and fell into the pan. They must have been in there for a long time. There were nicks on the bottom of the pistons, cylinder walls, crank, rods and one lobe on the cam. Here are some pictures of the worst piston.

I ordered a short rod stroker kit from Coast High Performance a couple of weeks ago and picked it up on Friday. Over the weekend I clearanced the cylinders and today I dropped the block off at Pacific Engine. Of course I forgot the pistons so I'll be making another trip out there so they can machine the block for .004 piston to wall clearance.

 

[Runnin'OnEmpty]

Good work.

Just reading this thread and seeing the
pictures is making me tired....

Anxiously awaiting the fire-up, and hoping
it runs smooth as silk.

 

[wood1]

Looking forward to a full throttle pull dude!

 

[rjcooperss396]

Thanks guys. I only worked on it for about 4 hours today but I got the engine and trans back in. I have about another 2-3 hours worth of stuff to do before I'll be able to start it.

 

[rjcooperss396]

It's done and no more vibration! I actually finished it last Monday but when I started it up it had a lifter tap and was missing. It was dark by then and I was pissed so I called it a night and went inside. With the rain I and other things I wasn't able to take a look at it until today.

So this morning I pulled the TB and elbow off so I could pull the valve cover. I found that the exhaust rocker on cylinder one had backed off so I torqued it back down and put it back together. I started it back up and the lifter tap was gone but it was idling a little rough. I took it for a test drive and it was misfiring.

I then pulled the plugs to see how they looked which they all looked fine and did a compression test. All cylinders were about the same and had good compression. So I put it all back together and took a look at the MSD box. I've had issue with the box before so I bypassed it and went for a test drive. Still had the misfire!

Out of frustration I decided I would try the old plugs. I just bought new ones when I put it back together this time because the old ones which only have 800 or so miles looked a little fouled. So I put the old ones back in and would do you know, it was the new plugs. I don't know which one is bad because they all look good but at least one is.

So the car is running great, well rich but other than that great. Now I just need to come up with the money to get the final tune and see what she puts down.

 

[CDW6212R]

Well done, that's a lot of perseverance, and that got it done. Good catch on the new plug, I have had that happen one time myself, on a new engine build as well.

I had a bad Accel coil pack about a year ago(a three year old part with under 10k miles on it), and the old coil pack fixed it. Now I have another rare hesitation, and swapping the other coil didn't solve it. The ignition system is very critical, buy the best parts and expect some bad new parts too.

 

[Dono]

I was wondering how you were making out. Sometimes you just need a break from the pain when things are not going well.

Congratulations on a strong build. You have a great toy there. Im sure there are more than one of us here a tad jealous.

 

[Runnin'OnEmpty]

Super job finding that vibration!
That engine should be good for many miles now.

You can test the resistance of the new plugs to
find the bad one. A good plug will have about
5-8K ohms of internal resistance. Bad ones will
show an open or very high resistance.

What caused the exhaust rocker nut to back off?
Can you put a jam nut on it, or secure it some
way...?

 

[rjcooperss396]

These are pedestal mount rockers and I think what happened is I didn't torque it down. When I built the engine the first time I set the preload to what AFR recommends in their manual for my AFR 165 heads which is 1/4 to 1/2 turn after 0 lash. I had 3 that were at 1/4 and the rest were at 1/2 to 3/4. I had a little bit of a tap that you could hear on decel so when I put the engine back together I made sure that I had at least 1/2 turn on all of them. When I did number one, the intake was one of the 3 that was only 1/4 but the exhaust was fine. I loosened the exhaust though as I was adjusting the intake because with it torqued down it put friction on the exhaust bolt so I couldn't tighten it by hand. I backed it off just enough so that I could tighten the exhaust by hand and then forgot to torque it back down when I was done with the intake. I usually go through after I'm done with all the rockers and double check them but I only did the drivers side. It was all my fault.

I go check all the plugs and see what they read but none of the porcelain was cracked which is usually what I find to be the issue.

 

[Runnin'OnEmpty]

Good to know it was human error instead of
a mechanical problem with the exhaust rocker.

After a fun day in the garage, I tend to start
making mistakes, and even though I don't
feel that tired I know it's time to take a break...

 

[rjcooperss396]

I emailed Steve at Powertrain Dynamics this morning and just heard back. I have an appointment to have the Cobra tuned tomorrow at 1pm. I'll post up the results tomorrow.

 

[rjcooperss396]

So I have good news and bad news. First the bad, we were not able to complete the tune due to maxing out the MAF at about 5200 rpms. I have an 80mm Lightning MAF and need to go up to a 90mm. Luckily my buddy had an extra 90mm housing so I already have that. I just need to get the elbow and filter adapter for it.

Now for the good news. With Steve stopping the pull at about 5400 rpms the car still made 455rwhp. It made peak torque at 4300 rpms which was 474rwtq and at 5200 it was making just over 460rwtq. Steve said there is still some more in it because he's pulling a lot of timing out above 4000. He thinks peak will fall right between 470-480 on the pump gas tune and thinks that it will make 520rwhp and 500rwtq on race fuel.

 

[wood1]

You must feel pretty good about those numbers. Can't wait to hear some track times!

 

[Dono]

wow, that's huge power. Congratulations! Its a fire breather for sure.

I have to wonder why we are not seeing anywhere close to these kinds of numbers on the 347's that guys have dropped in to their Explorers? I know you went first class here, and paid great attention to detail, but still.......

Maybe you need to build another for an explorer and we can see what numbers you get.

 

[CDW6212R]

So I have good news and bad news. First the bad, we were not able to complete the tune due to maxing out the MAF at about 5200 rpms. I have an 80mm Lightning MAF and need to go up to a 90mm. Luckily my buddy had an extra 90mm housing so I already have that. I just need to get the elbow and filter adapter for it.

Now for the good news. With Steve stopping the pull at about 5400 rpms the car still made 455rwhp. It made peak torque at 4300 rpms which was 474rwtq and at 5200 it was making just over 460rwtq. Steve said there is still some more in it because he's pulling a lot of timing out above 4000. He thinks peak will fall right between 470-480 on the pump gas tune and thinks that it will make 520rwhp and 500rwtq on race fuel.

That sounds very good, you have just about got it right now. Those numbers sound very promising, that car should be a blast to drive.

wow, that's huge power. Congratulations! Its a fire breather for sure.

I have to wonder why we are not seeing anywhere close to these kinds of numbers on the 347's that guys have dropped in to their Explorers? I know you went first class here, and paid great attention to detail, but still.......

Maybe you need to build another for an explorer and we can see what numbers you get.

Just for comparisons to the trucks, let's ask him this;

What exhaust system do you have on the Mustang? What size are the header primaries, the collectors, pipes to the mufflers, and tail pipes(plus how many mufflers)?

The power level should go in hand with the exhaust the vehicle has, you cannot expect to get 500hp out of half as much exhaust size.

 

[rjcooperss396]

I'm running Bassani egual length shorty headers which have a 1 5/8 primary and a bal collector. When I was putting the engine together I measured the diameter of the opening of the ball on the headers and was surprised to find that they were only 2 inch. Actually, they were ovaled from the heat but even the larger sides were only 2 1/4. So I took my die grinder and opened them up so that there was still enough material there for them to seal. I don't remember off the top of my head but I think they were still under 2 1/2 inches. The rest of the exhaust is 2 1/2 all the way. It consists of an X-pipe and Borla mufflers.

My tires are 255/45/17 and I have 3.55 gears and a T56 trans. All pulls were made in 5th gear (.80) because it kept spinning the tires in 4th.

 

[CDW6212R]

I'm running Bassani egual length shorty headers which have a 1 5/8 primary and a bal collector. When I was putting the engine together I measured the diameter of the opening of the ball on the headers and was surprised to find that they were only 2 inch. Actually, they were ovaled from the heat but even the larger sides were only 2 1/4. So I took my die grinder and opened them up so that there was still enough material there for them to seal. I don't remember off the top of my head but I think they were still under 2 1/2 inches. The rest of the exhaust is 2 1/2 all the way. It consists of an X-pipe and Borla mufflers.

My tires are 255/45/17 and I have 3.55 gears and a T56 trans. All pulls were made in 5th gear (.80) because it kept spinning the tires in 4th.

Those ball collectors are great for ease of use and to stop leaks, but as you know now, they are restrictive. That exhaust is typical for a street Mustang or any mild V8 car. You could gain a good bit by going a little bigger, but you know how much all of those parts cost you the first time.

Those 1.625" headers are good for a stock to mild 302, the bigger airflow you have now would like more. Given the exhaust that you have, those power figures are even better.

BTW, the ball collector that you measured, I read here that the Explorer thing is 2.125" there, which isn't good for a V8. I hope to use the V-band clamps to connect my exhaust when I do it. Those require welding the two mating pieces to the exhaust pipes, and the special clamp locks them together. They are pricey though, but worth it for a nice system that can be taken apart easily. Regards,

 

[rjcooperss396]

I'm sure that I could make a little more with some long tube headers but I live in CA and they are not legal so I'm stuck with what I have. But what I have seems to do all right.

I didn't measure the ones on my Explorer but I have a set of FRPP headers so I'll measure those to see how big the opening of the ball is. I think the Y pipe tubes are only 2 1/4 so my guess is that the opening of the ball on the headers will only be 2 inches.

 

[rjcooperss396]

I measured the ball collectors on the FRPP headers yesterday and they are 2 1/8.

 

[CDW6212R]

You mentioned long tube headers, those perform the best, but almost all of them hang down too low, plus they have 3-bolt flanges. I have a set I bought new for $75 around 1980, and if I finally get them into my Ranchero, I'll cut off the flange end and use a band or V-band clamp.

 

[rjcooperss396]

Unfortunately there aren't any legal long tubes here in CA for my car or I would be running them. But like I said before what I have seems to work well.