>>Yes, the heads had a little work on them.
>>Decked the block .050. Heads took off .015.
>>
>>I do know that the biggest expense was the special size
>>push rods. $178.00 Crane 9.035".
>>
>Ok, I have another question. I did a build of a 78 400. The
>shop milled the heads and decked the block but he said it
>wasn't enough to matter.
>The problem I am having is that it won't time. It back fires
>thru the carb. Nothing I do to change the timing helps.
>I have desassembled it down to removing the cam and putting
>it back making sure everything is right. It still does it.
>I used the stock push rods. How do I tell if I need special
>length rods? That may be what is holding the valve open and
>causing the backfire.
>Bob


Bob,

To get the proper length push rod, you either need a pushrod measuring tool, or get an adjustable pushrod and make one. You want a pushrod that is just snug between the lifter and rocker, then add the amount that you want for preload. Usually between .020-.050"

If you are backfiring through the carb, it sounds like there are greater problems here than pushrod length. Did you degree your cam? It sounds as though you may be 180deg out. Let us know what happens.

 

[updated:LAST EDITED ON 18-Dec-01 AT 05:19 PM (EST)]re: backfiring through carb. Push rod length could definitely be a problem. You might have used up all the preload with the milling. As you tighten down the rocker nut you should get about .030 preload past the point you contact the lifter. That leaves about .030 for cushion. Too little will bottom the lifter and hold the valves open. I don't rememer the "exact" clearances right now but if you took .030 off the heads and .010 off the block, hmmmmm. Changed valve geometry due to reuilding the heads can also contribute. In the past I obtained shorter push rods from Ford or get fulcrum shims from Crane Cams.

carb size: My 400 is a bit more radical but I've never had good luck with a 600cfm carb on it even when it was built milder. I've been building and modifing Holleys for........ well longer than I want to admit. The 600 has to open the primaries into the transfer slot to get enough air to idle and that's a catch 22. It also didn't perform as well as a 750. I'm running a Speed Demon 750 now and it isn't too much. A lot depends on the individual engine and driver.

Bear Tracks

 

Dan,

First off, congrats on your 400, nice job. And thanks for sharing the dyno experience with us. I hope it inspires more M-block owners to take the time to build up this great engine.

I ran the last 400 I built a few years ago on a dynamometer, a couple years before the HotRod article came out, and I got similar results with a little less cam and a little more head work. The cam is much cheaper, believe me. My engine put out 388 hp @ 5220 rpm and 485 lb-ft @ 4080 rpm.

Based on the dyno tuner's recommendation, I used the 650 cfm BG Speed Demon carburetor. It only took two jet and spring changes out-of-the-box to dial it in.

I have since met several other dyno tuners who swear by Demon carbs. Word is they are easier to tune and maintain more stable A/F ratio throughout the rpm range than either Holley or Carter AFB/Edelbrock carbs. I'm no expert on this. I'm just passing on info I've heard from guys that I believe are experts.

So along with seconding beartracks on the Demon carb, I just wanted to let you guys know that a 650 cfm carb can be adequate for getting serious power out of the M-block 400.

 

[updated:LAST EDITED ON 21-Dec-01 AT 10:10 PM (EST)]Sweet numbers on the dyno test!!!! Gives me reassurance that my "claims" for the 400 I have are actually realistic!!!! (hehe)

 

so what are your dyno figures?

 

I believe he posted his "numbers" in the very First post that initially started this thread!!!!fd:P

 

ooops. ok any one gonna guess on my build

400 bored 30 over
1970 4v heads
11.7 cr with flat tops
1 7/8 headers
and the standard stuff

 

>ooops. ok any one gonna guess on my build
>
>400 bored 30 over
>1970 4v heads
>11.7 cr with flat tops
>1 7/8 headers
>and the standard stuff

How much of torque, if any, did you lose by using the 4v heads?

 

the early word is maybe 20-45 tq down low, but when it builds, looks like it wont matter. desktop dyno point to 380 tq at 2k rpm and it builds to over 500. the hp looks like 475+. i just wish i knew what exactly to use on dd2k to get a good figure.

 

:-X12
Well here's what I come up with. I figured your not going to do much to the heads so I just plugged in unported canted valve heads with stock valves.Are you going with 2bbl or 4bbl intake?
my figures are with daul plane intake and 660 4bbl carb. 1 7/8" headers with mufflers. And a conservative 9.5 to 1 comp.
Depanding what cam you pick you can get some good numbers,
Fords roller cam # 51112 gives me 444 H.P.@ 5500 rpm 463# T.Q.@ 4500 rpm.
Crower roller cam #15481 gives me 438 H.P.@ 5500 rpm 457# T.Q.@ 4500 rpm.
The More comp. you give it the better your numbers get

:-X12 Merry Christmas

 

congrats on getting it stuffed in. Now, just look out for the others drivers. My truck got smoked by a careless 20 year old chick in a lumina w/ only 2500 miles on my truck.

As far as the CFM goes, these 400's will pull A LOT of air. It seems as much as you can give them. I too played with the 625's the 750's, and the bigger the better. It just takes a lot of tuning (at least with carter AFB's), and make sure you have a WIDEBAND O2 sensor to dial it in.

My 2nd ground up resto is underway, and this time I'm going with fuel injection. I'm gonna try a 900 cfm holley pro-jection throttle body w/ the Haltech ECU. My machine shop went out of business and sold it's dyno, so I won't have any numbers, but I'm sure I'll see some improvement over the last time.

My truck wouldn't "fry" the tires either, I don't know why. That is a lot of power, just goes to show how much engineering went into these trucks. I've noticed the '77-'79 ford trucks have different leafs in the rear and some how manage to make the rearends hook up. My 460 2wd should lite the tires for 2 blocks, and hooks up every time.

 

i have a 750carb, i had the heads ported, as far as i could.
wieand xcelerator 4v intake and plates ported as well. 2 inch headers

 

>ooops. ok any one gonna guess on my build
>
>400 bored 30 over
>1970 4v heads
>11.7 cr with flat tops
>1 7/8 headers
>and the standard stuff

looks exactly like what i'm planning, except compression is higher and my heads are the '71 4v's. i have the 1-7/8"x32" headers, a set of the exhaust "finger" plate fillers, and 351C intake adapters. i'm thinking about the 351C funnel-web intake & matching intake port "tongue" fillers. a little pricey though. cam will be hyd. roller, something big enough to really use those 4v ports. this will NOT be my daily driver!

as far as compression ratio, i can either go for the maximum possible for use with pump gas & MSD type ignition, or i can forget about running straight pump gas and get the flat tops.

can anyone give me an idea of the max compression ratio i might be able to run on pump gas, 50' above sea level, polished quench chambers and MSD?

any estimates of the difference in HP & torque between the "pump gas" CR and 12:1?

 

The first thing I would check is to pull the rockers off, and lay a straight edge across the tops of the valves and make sure they machined the valve stems when they worked the heads. This is a common problem, especially with cheapo head builders.

 

Your engine sounds like what I was TRYING to build.

My 400 has factory ignition with MSD coil, bored .30 with 9.5:1 pistons, balanced, ported and polished 2v heads, Edelbrock performer intake, HOlly 550 carb, RV grind cam, stock exhaust manifolds. I'm runnin 3.50 gears with 33 inch tires.

https://www.ford-trucks.com/user_gallery/displayalbum.php?&albumid=284

My 400 seems to runs well, but has never performed as well as I had hoped. I'm wondering if changing cams and adding headers would help? I wanted this thing to light the tires on demand when I built it.

Any good advice for me?

Tom