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428cj vs 428pi, dyno and timeslip

February 11 2018 at 6:12 PM

WerbyFord  (Login werbyford)

Response to weight difference

The 428cj-iron vs 428pi-aluminum saga.

This is long - I think the jury is still out.

First a note on weights:
Every time I’ve weighed the 428pi I get 29 lbs.
I’ve not weighed a 428cj, but FMP (Ford Muscle Parts) says +55 lb.
I have in my notes, 81 lb for the 428cj which would be +52 lb.
Brent weighed one and said he got 78 lb which would be +49 lb.
Either way, call it +50 lb and that’s pretty close.

On performance:
Right about now I wish I had bought a 428cj-iron back when they were $100 or so, which to me was high even then, maybe because we only gave $75 for our 1st 428pi intake. Well ok that $75 is like $300 today if you count inflation. I would like to include the 428cj-iron when I FINALLY get back to doing intake shootouts on the car.

For now, all I can do is offer a comparison of these intakes, based on my own data which is not dyno but a combination of GTECH, stopwatch, and timeslips, plus inputs from Jay B’s dyno, Ford Muscle Parts, and Royce P’s timeslips.
SM=Streetmaster, unported, 1” open spacer in my tests (ran best that way)
Z=Z-code iron, what Jay calls the C4 intake

I like the FE Forum format because it’s fast, and doesn’t gobble up my laptop’s memory or CPU like eg Ford Truck or the memory hog of all time, Facebook. However, the downside is, it is hard to post tables or photos.
Much easier to read a single metric on our forum, so as that single metric I will use “Ponies” or approx. (T+P)/2, whether those are peak T and peak P or average T and P as in some of Jay Brown’s tables.

So here goes –
Let’s compare these intakes 6 different ways:
J428=Jay’s TGFEIC 428cj410 average Ponies from average T and P
J445=Jay’s TGFEIC 390stroker average Ponies from average T and P
W396=Our old stopwatch and timeslips from our L6 vs PI runs in the car circa 1977
W421=My GTECH from a 421/320hp build
W440=My GTECH form a 440/410hp build
F428=Ford Muscle Parts Book 1969
R427=Royce P’s Cougar timeslips (428cj iron better by .20sec and 2mph)
To get T, P, and Ponies=(T+P)/2 from my GTECH runs, or from Royce’s Cougar, I take a base Gonkulator run and change T and P to match the changes in one GTECH or strip run to another.

Here is what I am seeing. I am setting the base ponies as “zero” for the 428pi intake. The number shown is the ponies gained or lost vs the 428pi.

(I’m trying to use dots to make the columns line up on the forum, that is taking some editing!)

PI vs L8: My 428pi does a lot better than Jay’s vs the LR-8v setup.

PI vs SM: My 428pi does a little better on average than Jay’s vs the unported Streetmaster.

PI vs CJ: I have not run this. Ford said the 428pi was better, Jay shows the 428cj comes out a little better, Royce shows the 428cj comes out a lot better, like 30 Ponies better. That’s like a 390cid vs a 428cid.

PI vs L6: Our 428pi came out about the same vs. the LR-6v setup given our old mixed data, back when gas was 59c a gallon. Jay’s 428pi came out about 3 Ponies better than the LR-6v. Pretty consistent.

PI vs Z: My 428pi was better than the Z-code iron across the board, about 7 Ponies better on average. In Jay’s testing, the Z=C4 iron actually beat out his 428pi intake in one series, but lost badly on the other engine, down by 19 Ponies. This is significant since it shows the variation we can see between the same two intakes, on the same dyno, just with two different “street” engine buildups. Compared to this, the other three 4bbl intakes, PI and CJ and SM, kinda look all the same.

W396: PI vs L6
Back in the 1970s, the 428pi was in vogue for sure. When we built our car, Clyde Dietrich raved about the 428pi intake (and the c8ax-c cam) to us so we bought one. Clyde’s iron ran pretty good out at Milan as I recall, so we took his word for it, and the $1.00 each Ford Muscle Parts book agreed. Iron CJ parts were junkyard items back then, so I’m sure we would have gone with that if the feeling was it was better. So we went with the pricey ($75) 428pi intake, until I found a complete 6v Ford setup, complete with polished Tbird air cleaner, for $100. The bling factor demanded we try that setup. The two setups ran “about the same” on the buttmeter, stopwatch, and different days at the strip, on this approx. 396cid / 360hp setup.

W421: PI vs Z vs SM
When I started the shootout project, I started with basically a stock 7-Litre equivalent, with a loose 40-over 410, and since it ended up a lot like a 421ho Pontiac I figured, well, Ford often added an inch or two to their engines so I would so the same and call this a 421. This also made sense since the car is heavy like a Pontiac at 4400 lb. With just over half that weight right over the 3.00 gears, traction is not an issue. So, 421cid/320hp approx. This is where I compared the Z, PI, SM intakes.

2.32…..6.56…..10.06…..69.66mph Z
2.32…..6.60…..10.08…..70.47mph SM
2.30…..6.51…..…9.99…..70.39mph PI
You can see that the Z is slower than the PI all the way. The PI gives nothing away even down low. The SM is a dog down low, a dog all the way up to 330 ft. After that, it stays with the PI in e.t. and pulls ahead in MPH. Per the old 1mph=10hp rule, this means in the 1/8 mile that 1mph=12.5mph, so a rough estimate is the SM is making 10hp more than the PI.

W440: PI vs L8
This is the 427/400 H&M Marine clone I build for my dad to match his H&M valve covers, and he got to enjoy it for 3 summers and about 90 car meets so I’m glad I finally finished it in time. It’s actually 440cid so call it 440cid/410hp approx. This is where I compared the PI vs L8 intakes.

2.25…..6.30…..9.52…..77.27mph PI=428pi
2.23…..6.22…..9.48…..77.11mph L8=LR-8v
It is pretty clear here that the L8 has the edge down low, but the PI is gaining by the 330ft mark and pulls ahead in MPH, implying it has a little more of both midrange and top end here. The 428pi is just a few Ponies better than the LR-8v on average overall.

This is Jay Brown’s 428cj engine from TGFEIC, about 400hp peak typically. Numbers here are taken from Jay’s averages on pg 164-166.
This is Jay’s 390 stroker engine from TGFEIC, about 480hp peak typically. Numbers here are taken from Jay’s averages on pg 172-173.

Ford Muscle Parts just says the 428pi intake adds 6 hp over the 428cj intake. It’s hard to compare torque because they don’t mention it, and the unlabeled curves in the book also include the “C” cam and headers.

Royce says his car ran .20 sec and 2mph better with the iron 428cj boat anchor on there vs the wimpy aluminum 428pi – even WITH the added 50lb on the front end! I pulled out an old Gonkulator file for one of Royce’s cars (not sure if this was the 428cj-vs-428pi car) and “swapped intakes” in the Gonkulator.

2.37…..6.21…..9.35…..78.91…..14.30…..99.32mph PI=428pi
Then I added 50lb in the Gonk file, no other changes. This is how the car would run if the 428cj ran exactly the same as the 428pi in power and traction:
2.37…..6.23…..9.37…..78.63…..14.34…..99.04mph CJ=428cj
So that’s .04 and .28mph slower (rule of thumb would say .05 and .50mph slower).
Then I cranked up ponies across the board until the Gonk was better than the 428pi by .20sec and 2mph.
Adding 7% across the board gave
2.36…..6.13…..9.21…..80.62…..14.06….101.27mph CJ=428cj
Ok, about right on the MPH+2, but a little too quick.
Well, 50 lb more on the front end would mean about 2% less G’s on the rear, so I did that:
2.38…..6.17…..9.25…..80.55…..14.11….101.24mph CJ=428cj
So the Gonk had to add about T=32 ftlb and P=28hp or about 30 Ponies to match that .20sec and 2mph better in Royce’s car. To me, this was either super-slow 428pi intake or a super-fast 428cj intake, or something else changed? Weather? Tuning?

I still think Ford had things backwards in using aluminum on the 428pi and iron on the 390gt and 428cj. From 1961-65 they did it the right way; the PI got the iron, and the hipo cars got the aluminum. After that, aluminum should have at least been an option. I used to cast metal in college so I know it costs more, but so does a Holley and LeMans rods! Back in 1969, retail on a Ford aluminum intake was $95, compared to $45 for iron. So for the same $50 on say a 390 Super-GT (SGT?) or a 428 SCJ you could have a 50 lb lighter nose. It was $21 for the battery kit, just to move 40 lb from front to rear, with no actual weight reduction, so the price seems sensible at least to us hipo folks. If the 428pi intake was such a dog (I am not yet convinced), the 428 SCJ should have run the Medium Riser or Sidewinder intake. Or, make a real “copy” of the 428cj iron in aluminum. Maybe not on ALL the 390gt or 428cj engines, but at least as a step-up OPTION, with added bling factor. Oh well.

FINALLY – The 428cj intake design is 2 years newer than the 428pi design, so it seems it could and should be better. But the results are mixed. The battle of the 428cj vs 428pi is not over, based on these conflicting results. I would encourage anybody who has the chance to get dyno or GTECH or dragstrip results in a comparison of the 428pi vs 428cj intakes on their own build! The results on this pair are all over the place. This is as exciting as the Super Bowl or the Olympics, isn’t it?

This message has been edited by werbyford on Feb 11, 2018 6:59 PM

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