All Big Six Plans for a 300 rebuild: "Miss Melody"

Relates to all big sixes

Frank

Well-known member
Supporter 2021
I know the stock 302/351 TB is twin 49mm...with that you can do the numbers for potential airflow. I think I came up with around a single 65-70mm area once, long since forgotten. Only reason I know is my '88 5.0 truck now uses a BBK twin 61mm which flows around a single 90mm. Yes, I picked up the unit as a blem new in box unit to go for my Edelbrock intake for the Bent-8.

Also, I measured my stock 4.9 unit, but have forgotten. I think it was 41-43mm area, not much but the stock 4.9 does not make massive power at high RPM. Talking back in early April and that has been a while. :)

Recently I read the earlier EFI trucks had a larger plenum volume and runner length. So you should mind that.
Yes, twin 49's= 69mm single. Twin 61's= 86.2mm single. . I just measured the factory TB- it's smaller than I was visualizing in my head. 39.5mm X 2. Measured a YF carb@ 42.6mm. So my 1990 factory TB=a 55.8mm single bore. Roughing the figures to get a ballpark, I assumed the YF flows 200 CFM. (Someone correct me here if I'm way off.) That calculates to my twin 39mm TB flowing only 344 CFM. It's somewhat more, without venturi restrictions. If 344 CFM is close, that will max out a 305cu in engine @ 3900 RPM. I may need to go up to the twin 49's you referenced. Thanks for the input.
 

Pontus

Well-known member
Supporter 2021
Hey Pontus- Thanks. Yeah, I remember all that revamping you had to do, I was not impressed that a new product required nearly total reengineering. I was glad you caught it and didn't maul up your cam and who knows what. Thanks for the reminder! So the "stock" promaxx head has stock sized valves? You replaced the stock diameter EFI valves with stock carb head valves?
Yup, you'll need the stock carb sized valves (or longer SBC ones if upsizing valves) that are 4.81 instead of 4.75 EFI stock valves. I couldn't find the heavy duty valves in anything but Melling or Qualcast. The Melling ones were odd in that they were both a thousandth thinner stems, and the exhaust valve iirc had double grooves. The Qualcast ones were only available in .015 oversize stems. But if you have to redo the guides anyway, either will suffice. Heavy duty valves meaning they were stainless with chrome plating and stellite faced ex valves. If you want anything better quality, you're going to have to upsize to SBC valves.
 

HitmanX

Well-known member
Supporter 2021
In my parts the small block V8 throttle bodies are easy to find. I would venture to guess the 7.5L unit is probably the same size, but unsure. Some where I have seen a SBF throttle body installed on the I6, the throttle shaft was slightly different where the linkage attached. Made me wonder if one could swap shafts accordingly. 302HO had a single 60mm stock if that matters.

Happen to have any pics of the EFI plenum chopped open? I am curious!

Also, this may help to further convince you to keep the OE EFI:



You may be able to help 'efloth' to pull the data from a 4.9/E4OD ECU.
 

Frank

Well-known member
Supporter 2021
HitmanX, that ECM talk is a foreign language to me. For whatever reason, if it moves I can figure out how to fix or improve it. Computers just stay still and make that little gurgling noise and I don't have a clue what's going on. I grew up pre-computer, and when they were taking over in the 90's and 2000's I was on the road driving 25 days a month. All my focus was devoted to mechanical diesels, and I fell totally behind in the automotive electronics. I'm in pre-K with computers. This is a BIG step forward, planning this build around EFI rather than carb. But I'm willing to learn. Already learned by being proved wrong with this same truck. It got well over 20 MPG highway in stock EFI form. Being the hard headed ass I can too often be, I pulled that off. The Offy DP and correctly jetted Edlebrock 16 MPG highway is a banner run.
One further comment on the TB: I like the gentle off-idle accelerator pedal response of the factory 4.9 TB verses any single bore TB vehicle I've driven. The reason is two-fold, if I'm seeing this right. 1) Geometrically, smaller throttles must open more degrees for the same flow as a large single with a lesser opening. Also, the linkage is progressive on this TB. I hope to stay with the factory TB, even with the limited CFM airflow.
Took some pics of the upper factory manifold: . . hang on, I can't figure out how to attach them, even though I did it on here before. When my wonderful wife gets home I'll post them with her help. :banghead:
 

HitmanX

Well-known member
Supporter 2021
I learned to work with PCs on IBM 8088s and BASIC. The we graduated to DOS! So they are not too foreign to me...but like you, I build anything. I can build an auto trans easily as well as manuals. No big deal. Once I was tossed into Mac it was different, they are better machines if you use them to their full extent. I just use an old PC and a cracked screen smart phone.

I built the S5-47 ZF in my living room for the 7.3 :banana:

In any event, all I was trying to show was that the factory ECU can be tuned to compensate for essentially all modifications you are thinking about currently. The aforementioned member is far more knowledgeable on that front and the chap he recommended is just outside of Baton Rouge that offers remote tuning.

This build is similar to what I want to achieve, but I may just stick with the stock camshaft to not reinvent the wheel. Regarding the throttle body, it has two vacuum tits atop for some smog business, I would venture to guess these could be bridged together into a vacuum gauge to check if there is restriction maybe at high RPM or potentially use a vacuum tit on the back of the vac tree on the plenum. For all we know that stock twin 39mm may flow sufficiently!

Forgot to add, the 7.5L aka 460 EFI TB is a no go, it uses an external IAC.
 

THE FRENCHTOWN FLYER

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...You replaced the stock diameter EFI valves with stock carb head valves?
With valve seat inserts installed it could be a big act to upsize the valve diameters.

Which leads me to my next question. Why do the valves extend further into the combustion chamber, effectively shortening the length above the spring seats? especially since there was extra metal purportedly added for the installation of valve seats?
 

Frank

Well-known member
Supporter 2021
OK! Four pics of inside of the factory upper EFI manifold, circa 2/1990
Pic 1, looking down to the plenum floor. All 6 interior sides are the same, totally open plenum to 3 cylinders. There is no air channeling between the TB and the 3 runner heads. The center wall is solid, except for a 1/2" hole for the PCV inlet in the base of the center divider, and the vacuum supply port on the top, otherwise 1,2,3 is 100% isolated from 4,5,6. (Except the idle air valve just behind the throttles, which shares a 1/2" crossover port.) The volume of the plenum is significant, and nearly square in shape. 3 3/8" tall, 6" TB to runner head, 6" tapering out to 7" outside wall, 6" inside wall, for a total area of aprox. 130 cubic inches, feeding 150 cu in.
Pic 2- looking at the center divider and air inlet port. The shadow makes the floor look sloped, but it is flat, although the wall transition from the floor is not abrupt, but slightly curved. The entrance to the runners is very smooth. Round, with a correctly tapered transition, as is this supply inlet pipe. This supply port from the TB tapers out to 55mm, from the 39mm throttles. The 3 runners are 36mm each. I couldn't get the mic in there straight, so these #'s are aprox.
Pic 3- I posted this one because the angled TB produces a variation in volume and air flow characteristics between the two "banks". The distance from the front throttle plate to the plenum =3", while the rear throttle-to-plenum distance is 5". I knocked the casting plug out of the rear side that's not cut open, and the inlet for 4,5,6 is an inch away from the center divider, and aims more toward #5, where the 1,2,3 inlet (pic 2) is against the center divider, with the air routing along the wall toward #3. Because the engine draws air from the center out, the front side of this manifold will have a more stable, less turbulent air flow pattern:. Supply flowing toward 3, then turning to feed 2, and piling into the corner for 1, what's left circling back thru the static pocket into the incoming charge. The rear feed, being aimed at #5 has the air jumping from back to front (as seen from the TB). Of course this is moot on a low performance street engine, but I would like the manifold better if both inlet pipes were symmetrical, coming in straight, next to the center divider.
Pic 4) The 1,2,3 inlets. Note that they are not on the same plane. Also note the smooth, tapered transition from the plenum. I'm impressed. Note the narrow channel in the floor to collect PCV oil. It is sloped downward, back toward the PCV inlet in the center. Several ounces of oil can sit in this valley, and does on worn engines. There's a thread on here somewhere, young man had oil in his filter and TB. At least a quart could accumulate on the floor before reaching the bottom of the elevated runners.
I confess I wrote this intake off as mediocre engineering. It actually produces very equal flow to all 6 cylinders, and that through very long, gently curved runners coming into the head on the same plane as the valves. I look forward to using it again with the Schneider 131H cam and correct EFI programming.
 

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Pontus

Well-known member
Supporter 2021
With valve seat inserts installed it could be a big act to upsize the valve diameters.

Which leads me to my next question. Why do the valves extend further into the combustion chamber, effectively shortening the length above the spring seats? especially since there was extra metal purportedly added for the installation of valve seats?
I'll be getting my promaxx stock head back from the machinist today finally. :banana: I'll take measurements soon to confirm if the valve seats are lower or if the spring seats are higher or both. I had started that process earlier but wasn't confident of my results, and then I had to give it to the machinist. I'll post my results in my project thread.
 

Frank

Well-known member
Supporter 2021
I learned to work with PCs on IBM 8088s and BASIC. The we graduated to DOS! So they are not too foreign to me...but like you, I build anything. I can build an auto trans easily as well as manuals. No big deal. Once I was tossed into Mac it was different, they are better machines if you use them to their full extent. I just use an old PC and a cracked screen smart phone.

I built the S5-47 ZF in my living room for the 7.3 :banana:

In any event, all I was trying to show was that the factory ECU can be tuned to compensate for essentially all modifications you are thinking about currently. The aforementioned member is far more knowledgeable on that front and the chap he recommended is just outside of Baton Rouge that offers remote tuning.

This build is similar to what I want to achieve, but I may just stick with the stock camshaft to not reinvent the wheel. Regarding the throttle body, it has two vacuum tits atop for some smog business, I would venture to guess these could be bridged together into a vacuum gauge to check if there is restriction maybe at high RPM or potentially use a vacuum tit on the back of the vac tree on the plenum. For all we know that stock twin 39mm may flow sufficiently!

Forgot to add, the 7.5L aka 460 EFI TB is a no go, it uses an external IAC.
The 39mm TB flowed fine. I have a manifold vacuum gauge on the steering column, and used the TB ports you referenced as the source. It must have been close to 0 at WOT, or I would have remembered it. At this point, I will begin with the factory TB, and if it's starved we can go from there. I don't expect it to be. I will rarely exceed 3000 RPM, and never exceed 4000. . . As for my computer ignorance- I still use a flip phone. lol. The pics above I took with a cheap camera.
 

Frank

Well-known member
Supporter 2021
I'll be getting my promaxx stock head back from the machinist today finally. :banana: I'll take measurements soon to confirm if the valve seats are lower or if the spring seats are higher or both. I had started that process earlier but wasn't confident of my results, and then I had to give it to the machinist. I'll post my results in my project thread.
Pontus, I don't want to miss your results. Post them here if you like. I don't want to waste $900 if the HP head is unnecessary, but I D sure don't want the headaches you had getting the stock head to function. My time is more valuable than $, and stress I will attempt to avoid "at all cost", no pun intended.
 

Frank

Well-known member
Supporter 2021
Gentlemen, good Sunday afternoon. I have firmly decided to use the factory intake manifold with factory port injection hardware.
I NEED PARTS. Pretty much everything that attaches to the intake manifold: sensors, fuel injection lines, injector and sensor plugs/ wires, manifold to block support bracket. and maybe etc, etc. Yes these valuable items have been discarded years ago. . If someone has a complete upper/lower intake with everything that goes on it, I'll take the whole package. give me a price. Thanks.
I'm posting here because I remember one of you mentioning in passing that you had this stuff, if anyone wanted it. I can't remember who or find the thread. Well, now someone wants it.
MAP ERA EFI (1990)
 

THE FRENCHTOWN FLYER

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Supporter 2021
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Gentlemen, good Sunday afternoon. I have firmly decided to use the factory intake manifold with factory port injection hardware.
I NEED PARTS. Pretty much everything that attaches to the intake manifold: sensors, fuel injection lines, injector and sensor plugs/ wires, manifold to block support bracket. and maybe etc, etc. Yes these valuable items have been discarded years ago. . If someone has a complete upper/lower intake with everything that goes on it, I'll take the whole package. give me a price. Thanks.
I'm posting here because I remember one of you mentioning in passing that you had this stuff, if anyone wanted it. I can't remember who or find the thread. Well, now someone wants it.
MAP ERA EFI (1990)
Frank, PM sent.
 

Frank

Well-known member
Supporter 2021
UPDATE-
I'm still mostly in the planning and holding phase, due to waiting for other things in life to roll into place in due season. Namely, getting another (non Ford) vehicle running first. Promised my wife, so I've been working on it. Also, we're selling a house, which will finance this project, hoping by year's end we can close.
1) Will be going to the machine shop later this week. Gary had a good 300 block/ crank/ rods last time we spoke, if he still has it I will purchase it and do the build with it. It's also a '90 vintage, out of his dad's truck, known history. Building from a different block is practical since the only hardware to transfer that is now in service is the exhaust manifolds, lifter and valve covers. Want to enjoy the build process without pressure from down-time. Miss Melody is still my daily driver.
DECIDED:
1) Returning to factory-based EFI and ignition system, and have located and purchased the factory intake and hardware. Very thankful for that, and thank you FTF.
2) Changing rear gear to 4.10:1 with Ford gears and Eaton Torsen differential
3) Fresh E4OD with Fairbanks shift kit upgrade.
4) Original EFI exhaust manifolds
UNDECIDED
5) CAM- I spend probably unhealthy amounts of time dwelling on the cam selection. (Yet another symptom of gear-head insanity). There is a sweet-spot where the correct overlap duration combined with the long runner intake will produce instant, very strong torque. I missed the mark with the Crower cam that's in it now- don't want to miss it this time. Since Schneider does custom grinds, I've been calculating every scenario. The .006 duration is dependent on the SCR and LSA, but I expect to be close to stock @268* +/- . Target lift .5" (Scorpion pedestal 1.73:1)
As for .050 duration: We've not heard an update from Mojoworkin (Tractor Motor thread). He's running 204/270 @112 LSA, with stock ECU. Hope we get an update soon, as to if he's had to retune the ECU. seemed to be running good in his video. That grind is close, but I'd like to squeeze it a bit more. Mojoworkin's is-20* overlap. Stock is -28*. I am looking at -14 to -16* or so. The big question is will this spook the stock ECU at idle. If it does, I'll deal with it, but not willing to sacrifice torque for fear of out-camming the stock ECU. Pmuller9's recommendation of the 131H is -16 overlap, and that cam is very close to my target. May need more .006 duration, depending on head and piston selection. I would like to 0 deck the block and work backward from there toward DCR.
3) Head questions: In scouring multiple threads, there's a couple of things that need untangling in my head.
1- Someone reported that the Promaxx ported head killed the swirl pattern by unshrouding the intake. Is this correct? If so, that won't do, since I would rather not reprogram the ECM for more spark advance., and want maximum fuel efficiency. I was leaning toward the ported head for the larger combustion chamber, since I plan on 0 deck height, plus already being ported, larger valves, and ready to go.
2- Stock Promaxx head. Hand port. Valve size. Although this is not a race build, 1.94" 1.60" undercut valves still seem reasonable. It's a big cylinder to fill. Have Gary cut it for Chevy valves, then remove slight amount of shrouding to match original distance, as Pmuller9 described in post #6. Feedback appreciated.
 

THE FRENCHTOWN FLYER

5K+
VIP
Supporter 2021
Supporter 2020
Supporter 2018
UPDATE-
I'm still mostly in the planning and holding phase, due to waiting for other things in life to roll into place in due season. Namely, getting another (non Ford) vehicle running first. Promised my wife, so I've been working on it. Also, we're selling a house, which will finance this project, hoping by year's end we can close.
1) Will be going to the machine shop later this week. Gary had a good 300 block/ crank/ rods last time we spoke, if he still has it I will purchase it and do the build with it. It's also a '90 vintage, out of his dad's truck, known history. Building from a different block is practical since the only hardware to transfer that is now in service is the exhaust manifolds, lifter and valve covers. Want to enjoy the build process without pressure from down-time. Miss Melody is still my daily driver.
DECIDED:
1) Returning to factory-based EFI and ignition system, and have located and purchased the factory intake and hardware. Very thankful for that, and thank you FTF.
2) Changing rear gear to 4.10:1 with Ford gears and Eaton Torsen differential
3) Fresh E4OD with Fairbanks shift kit upgrade.
4) Original EFI exhaust manifolds
UNDECIDED
5) CAM- I spend probably unhealthy amounts of time dwelling on the cam selection. (Yet another symptom of gear-head insanity). There is a sweet-spot where the correct overlap duration combined with the long runner intake will produce instant, very strong torque. I missed the mark with the Crower cam that's in it now- don't want to miss it this time. Since Schneider does custom grinds, I've been calculating every scenario. The .006 duration is dependent on the SCR and LSA, but I expect to be close to stock @268* +/- . Target lift .5" (Scorpion pedestal 1.73:1)
As for .050 duration: We've not heard an update from Mojoworkin (Tractor Motor thread). He's running 204/270 @112 LSA, with stock ECU. Hope we get an update soon, as to if he's had to retune the ECU. seemed to be running good in his video. That grind is close, but I'd like to squeeze it a bit more. Mojoworkin's is-20* overlap. Stock is -28*. I am looking at -14 to -16* or so. The big question is will this spook the stock ECU at idle. If it does, I'll deal with it, but not willing to sacrifice torque for fear of out-camming the stock ECU. Pmuller9's recommendation of the 131H is -16 overlap, and that cam is very close to my target. May need more .006 duration, depending on head and piston selection. I would like to 0 deck the block and work backward from there toward DCR.
3) Head questions: In scouring multiple threads, there's a couple of things that need untangling in my head.
1- Someone reported that the Promaxx ported head killed the swirl pattern by unshrouding the intake. Is this correct? If so, that won't do, since I would rather not reprogram the ECM for more spark advance., and want maximum fuel efficiency. I was leaning toward the ported head for the larger combustion chamber, since I plan on 0 deck height, plus already being ported, larger valves, and ready to go.
2- Stock Promaxx head. Hand port. Valve size. Although this is not a race build, 1.94" 1.60" undercut valves still seem reasonable. It's a big cylinder to fill. Have Gary cut it for Chevy valves, then remove slight amount of shrouding to match original distance, as Pmuller9 described in post #6. Feedback appreciated.
Frank, PM sent regarding your cam.

As far as unshrouding the EFI chamber, the numbers that the Power Nation folks quoted on their dyno test for WOT spark was very nearly the same as a carbed head - about 36 degrees. While I don't deny that unshrouding the intake valve will enhance flow this confirms what I learned at R&D that all the fast burn characteristics will go away if the valve gets unshrouded beyond 3mm.
 

Frank

Well-known member
Supporter 2021
Frank, PM sent regarding your cam.

As far as unshrouding the EFI chamber, the numbers that the Power Nation folks quoted on their dyno test for WOT spark was very nearly the same as a carbed head - about 36 degrees. While I don't deny that unshrouding the intake valve will enhance flow this confirms what I learned at R&D that all the fast burn characteristics will go away if the valve gets unshrouded beyond 3mm.
Thanks, I remember that too. Having to recurve the spark in the ECU partially defeats my purpose, and since this is a low speed torque/ economy build, don't need the extra unshrouded flow, or lost economy. 3mm, that's good to know.
 

Frank

Well-known member
Supporter 2021
Scorpion 1.73 pedestal rockers ordered y'day. Summit says BO till February. They charged my card, so I'll get them.

I measured the length of the intake runners from the inside, and they are even longer than I thought- just over 18" intake plenum-to-head, with less than an inch variation. I ran some sonic numbers and the return pulse is nicely matched for this low RPM engine. Point at which the pulse math "tuned" best = 2100 rpm. Balanced echo points: 1050 rpm, 1400 rpm, 2750 rpm, 3450 rpm, 4200 rpm (numbers rounded off). With all 6 runners 100% isolated from the others, the tuning effect is not diluted (or outright destroyed) as with pretty much any other intake for this 6. Nice!

I keep increasing the overlap duration target, because I believe the combination of components will take more overlap before loping, and "smooth out" and start breathing sooner than other intake/head configurations with the same cam specs. Are there others who have used the full factory intake and EFI head with the fast burn swirl undisturbed, with a longer duration cam? Other than tiptoeing around the stock cam specs? This one will be noteworthy for our books perhaps, I don't know.

New stock bare EFI head, Promaxx with the thicker casting and VG upgrade. I will clean up the ports. 1.90" I, 1.60" E valves from Ferrea. 11/32" stem, 4.91" length. (feedback welcome about valve head sizing and the Ferrea brand. I'll ask about installed height, shimming rockers and longer push rods later.) I will not be unshrouding the intake valve, to keep the fastburn design. I'm calling Jason tomorrow.

DCR will be 7.3- 7.35:1. I know this will work on midgrade gas and the factory ECU. The engine currently has at least 7.75:1 DCR. I say at least because I am conservatively estimating how much head volume was lost with the extreme milling it arrived with when purchased online. Bottom half of the casting #'s are gone. IV closing is 58* ABDC. (Compression check= 210 lbs.) Ran it thru a calculator, = 7.75:1 DCR. Stock ECM/ intake it ran perfectly on 93 gas. (Crower 192/252 cam- I'll be glad to see it gone.)


Silv-o-lite 1186H pistons (is this a trustworthy brand?)
68cc EFI head (will verify cc with Jason when I call)
26.1cc D dish (EFI factory design)
0 deck. This is not up for debate. I'm leveling the deck.
.039 thick / 4.108" Felpro 1024 head gasket
Intake closing @ 65* ABDC
EQUALS 9.1 SCR, 7.32 DCR

Back to camshaft. Will be Schneider custom grind, obviously. Hope they have cores. It's time to pick a number and call them ASAP.
I've settled on -10* overlap @ .050. Here are the options @ -10* OL, IVC 65* ABDC:
206/274 @ 108 LSA
208/272 @ 109 LSA
210/270 @ 110 LSA
212/268 @ 111 LSA
214/268 @ 112 LSA
Yes I'm upping my power goals since my first post. Yes I will have to tune the ECM. The factory intake gives me reason to believe this cam profile will not be as chunky at idle as short, shared plenum intakes with the same grind. And even if it is, it will be totally smooth and pulling by 1050 rpm. IMO

I saw Gary (local machine shop) last Thursday. He still has (his dad's) 300 in the back of the shop. Bored .030, polished crank and bottom end parts. Wants $700 for it. I may go this route, so I keep Miss Melody in service, and can enjoy the build process without time pressure. (Also, the odometer is at 97000 miles, and it would be great to do the swap at 200,000 even (00000 on the dash.) Gary and I go back to HS days. He went to work for the local m shop out of HS, later bought them out, and has had a thriving business for almost 50 years. He's a good guy and I trust his work. We had a blast talking about the L6, reminiscing about some of the performance builds he's done. (I remember his '67 Camaro in HS. Would lay rubber all the way across the parking lot, 230 L6 with Clifford 6=8 build.) He is excited to help me with another L6 build- it's been a while.
 
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