Need opinions on how to get back some low end torque on 400 with a big cam??

Joined: September 22nd, 2008, 10:06 pm

September 16th, 2012, 4:07 am #1

Ive got a 400 in a 78 bronco with a 4spd and 4.88 gears. I built it for hi rpm mud bogs and it runs good for what i built it for but i am wanting to drive it more on the road now. Its 10:1 with ported 2v heads, lunati cam with 245 deg dur @.05 int/exh .560 lift 108 lobe sep, price motorsport intake spacers, 351C edelbrock rpm air gap intake w/2" thick 4 hole carb spacer, demon 750 double pump carb, headers and msd dist (no vac advance). The air filter is plumbed into the cab with a spectra carb hat and 4" tubing. Pulls about 9" vacuum at idle and has best power from bout 3000 to 6500 rpms. I know the cam is the main reason for lack of low end power but im not interested in swapping the cam or swapping any internal parts. My first thougts were to put a 14" air filter on top of the carb, swap the 2" thick 4 hole spacer for a 1" thick 4 hole spacer, maybe swap the rpm air gap intake for a lower rise intake with smaller runners and a smaller plenum(maybe a edelbrock streetmaster or weiand 8010 dual plane??) and change the power valve in the carb to a 4.5(has the stock 6.5 power valve in it), and increase the shooter size cause its got a little dead spot if you don't rev it up a little before letting of the clutch on take off. Am i on the right track? What are some of your opinions? Thanks
Quote
Like
Share

Joined: November 18th, 2003, 6:49 am

September 16th, 2012, 5:23 am #2

Id work on the carby, maybe just needs some tweaking.
Maybe try a 650 instead, or even a 750 vac.
Last edited by xdclevo on September 16th, 2012, 5:24 am, edited 1 time in total.
Quote
Like
Share

Joined: April 10th, 2012, 7:09 pm

September 16th, 2012, 7:35 am #3

Ive got a 400 in a 78 bronco with a 4spd and 4.88 gears. I built it for hi rpm mud bogs and it runs good for what i built it for but i am wanting to drive it more on the road now. Its 10:1 with ported 2v heads, lunati cam with 245 deg dur @.05 int/exh .560 lift 108 lobe sep, price motorsport intake spacers, 351C edelbrock rpm air gap intake w/2" thick 4 hole carb spacer, demon 750 double pump carb, headers and msd dist (no vac advance). The air filter is plumbed into the cab with a spectra carb hat and 4" tubing. Pulls about 9" vacuum at idle and has best power from bout 3000 to 6500 rpms. I know the cam is the main reason for lack of low end power but im not interested in swapping the cam or swapping any internal parts. My first thougts were to put a 14" air filter on top of the carb, swap the 2" thick 4 hole spacer for a 1" thick 4 hole spacer, maybe swap the rpm air gap intake for a lower rise intake with smaller runners and a smaller plenum(maybe a edelbrock streetmaster or weiand 8010 dual plane??) and change the power valve in the carb to a 4.5(has the stock 6.5 power valve in it), and increase the shooter size cause its got a little dead spot if you don't rev it up a little before letting of the clutch on take off. Am i on the right track? What are some of your opinions? Thanks
I'd work with the carb first to see what improvements you can get. I used to run the edelbrock performer 2v and then went to the rpm air gap. Didn't notice a change on the low end, just a boost on the top end. A couple days ago I went from the 6.5pv to a 5.0, I didn't notice any change in performance either way, but it should improve mileage a touch. I've played with the squirters as well. Tried larger, but they dumped the fuel too fast and left a flat spot, so back to the original .031. It's definitely worth playing around with them as they are so easy to change. BTW in case you didn't know, the size regulates the duration of the pump shot, not the volume. Larger sizes = faster shot, smaller sizes = longer shot. Just depends on when you need more fuel. For my problem I needed a longer duration shot.
If you haven't already done so consider your advance curve. If you can increase the rate that the advance comes in without having preignition problems that should help out as well. Full advance at 2800-3000 rpm should do nicely. Have fun...........JP
Quote
Like
Share

Joined: May 20th, 2005, 4:48 pm

September 16th, 2012, 11:48 am #4

Ive got a 400 in a 78 bronco with a 4spd and 4.88 gears. I built it for hi rpm mud bogs and it runs good for what i built it for but i am wanting to drive it more on the road now. Its 10:1 with ported 2v heads, lunati cam with 245 deg dur @.05 int/exh .560 lift 108 lobe sep, price motorsport intake spacers, 351C edelbrock rpm air gap intake w/2" thick 4 hole carb spacer, demon 750 double pump carb, headers and msd dist (no vac advance). The air filter is plumbed into the cab with a spectra carb hat and 4" tubing. Pulls about 9" vacuum at idle and has best power from bout 3000 to 6500 rpms. I know the cam is the main reason for lack of low end power but im not interested in swapping the cam or swapping any internal parts. My first thougts were to put a 14" air filter on top of the carb, swap the 2" thick 4 hole spacer for a 1" thick 4 hole spacer, maybe swap the rpm air gap intake for a lower rise intake with smaller runners and a smaller plenum(maybe a edelbrock streetmaster or weiand 8010 dual plane??) and change the power valve in the carb to a 4.5(has the stock 6.5 power valve in it), and increase the shooter size cause its got a little dead spot if you don't rev it up a little before letting of the clutch on take off. Am i on the right track? What are some of your opinions? Thanks
Brent Lykins
B2 Motorsports, LLC






Quote
Like
Share

Joined: February 13th, 2006, 4:59 am

September 16th, 2012, 1:33 pm #5

I would imagine that being a bogger you have a. 35+ size super swamper style tire. With 488 gear in high range the motor will act a little lazy until it gets on the power. What about smaller rubber ( although those tires are pricy)? Only other option is advancing cam timing and trying a smaller vac secondary carb. I think you are on the right track by upping shooter size for bottom end stumble, every Cleveland I've had wanted extra shot! You can also adjust your cam to pump earlier.
Last edited by steve.k on September 16th, 2012, 2:07 pm, edited 1 time in total.
Quote
Like
Share

Joined: September 22nd, 2008, 10:06 pm

September 16th, 2012, 2:36 pm #6

The cam was installed straight up without being degreed in. It is a lunati streetmaster hydraulic cam 2500-6500 range 295 degrees advertised duration with 245 deg dur at .05" with .560 lift int/exh 108 lobe seperation. The tires are 35". I don't want to go smaller on the tire just for appearance. The timing is set a 16 deg at idle with 24 mechanical (40 total) all in by somewhere in between 2400 and 2800 i think. I'll have to look and see what color springs i changed in the msd distributor. So its worth messing with the carb a little before getting rid of the rpm air gap for a smaller intake?? Thanks for all the replys.
Quote
Like
Share

Joined: May 20th, 2005, 4:48 pm

September 16th, 2012, 2:53 pm #7

A big cam with a choked intake only compounds issues.

My advice is to degree the cam and put lots of advance into it if you think your gas can handle the extra pressure. That thing could be retarded, never can tell. Id try it on a 103-104 icl. Advanced cam timing is a blessing for street engines.

Brent Lykins
B2 Motorsports, LLC






Quote
Like
Share

Joined: February 13th, 2006, 4:59 am

September 16th, 2012, 3:49 pm #8

With that big rubber and your gears with the motor designed to pull and 2500 plus rpm your going to have lazy bottom end. Short of cam swap advancing cam like Brent suggests is your only option! A smaller intake will help marginally but Idont think you'll be happy with the performance per dollar. You probably mud race in low range which gives that bottom end pull?
Quote
Like
Share

Joined: December 16th, 2003, 1:59 am

September 16th, 2012, 10:08 pm #9

Ive got a 400 in a 78 bronco with a 4spd and 4.88 gears. I built it for hi rpm mud bogs and it runs good for what i built it for but i am wanting to drive it more on the road now. Its 10:1 with ported 2v heads, lunati cam with 245 deg dur @.05 int/exh .560 lift 108 lobe sep, price motorsport intake spacers, 351C edelbrock rpm air gap intake w/2" thick 4 hole carb spacer, demon 750 double pump carb, headers and msd dist (no vac advance). The air filter is plumbed into the cab with a spectra carb hat and 4" tubing. Pulls about 9" vacuum at idle and has best power from bout 3000 to 6500 rpms. I know the cam is the main reason for lack of low end power but im not interested in swapping the cam or swapping any internal parts. My first thougts were to put a 14" air filter on top of the carb, swap the 2" thick 4 hole spacer for a 1" thick 4 hole spacer, maybe swap the rpm air gap intake for a lower rise intake with smaller runners and a smaller plenum(maybe a edelbrock streetmaster or weiand 8010 dual plane??) and change the power valve in the carb to a 4.5(has the stock 6.5 power valve in it), and increase the shooter size cause its got a little dead spot if you don't rev it up a little before letting of the clutch on take off. Am i on the right track? What are some of your opinions? Thanks
Rhoads lifters ?

V-max flat tappet version doubles the effect over the original recipe
http://www.rhoadslifters.com/Pages/Products.html


http://www.summitracing.com/search/Bran ... Rank%7cAsc

there'll be phantoms, there'll be fires on the road... and the white man dancing
Quote
Like
Share

Joined: December 17th, 2003, 4:14 pm

September 16th, 2012, 10:42 pm #10

Just in case? I think they drop duration 6 to 10 degrees on the low end? Some love the tick sound, some dread it. They were pretty popular in the 80's.
Quote
Like
Share