Cam for 406 mud racer

General engine tech -- Drag Racing to Circle Track

Moderator: Team

mdabbott2009
Pro
Pro
Posts: 211
Joined: Mon Jun 24, 2013 1:16 pm
Location:

Cam for 406 mud racer

Post by mdabbott2009 »

Motor is
4.155x 3.75 13-1
Crower ultra light Molnar rods cp pistons
Has to run factory heads per rules soo vortecs with 2.05 flow 260@500 2700@600
Single plane 750 based carb per rules
4.56 gears in low side with tcase ratio of 2.72 and 31in tires 5500 converter
This is a lift rule class 550 can be solid roller etc.

We got the cam through the guy that set up the heads was post to be 268@.50 but when I got the cam yesterday from bullet it's 251/256. I was told this is better then the bigger one and would still rpm? Little confused

Customer is not happy about spending all the extra money for pretty much same cam that was in it before that wouldn't pull past 6500.soo would this cam even get us close peak power at 7500?
lefty o
Guru
Guru
Posts: 3445
Joined: Tue Oct 15, 2013 8:50 am
Location:

Re: Cam for 406 mud racer

Post by lefty o »

nope!
Walter R. Malik
Guru
Guru
Posts: 6353
Joined: Tue Jul 24, 2012 11:15 am
Location: Roseville, Michigan (just north of Detroit)
Contact:

Re: Cam for 406 mud racer

Post by Walter R. Malik »

mdabbott2009 wrote: Sat Apr 24, 2021 9:30 am Motor is
4.155x 3.75 13-1
Crower ultra light Molnar rods cp pistons
Has to run factory heads per rules soo vortecs with 2.05 flow 260@500 2700@600
Single plane 750 based carb per rules
4.56 gears in low side with tcase ratio of 2.72 and 31in tires 5500 converter
This is a lift rule class 550 can be solid roller etc.

We got the cam through the guy that set up the heads was post to be 268@.50 but when I got the cam yesterday from bullet it's 251/256. I was told this is better then the bigger one and would still rpm? Little confused

Customer is not happy about spending all the extra money for pretty much same cam that was in it before that wouldn't pull past 6500.soo would this cam even get us close peak power at 7500?
I would say that cam would be good to about 6,500 RPM. I think the first choice was near correct.
A camshaft of .367" lobe lift and about 268/276 duration @.050" on a 112 sep +2 would be OK with that gearing.

With those heads and 406 cubic inches it may get to 7,500 RPM but, peak power won't be near that high.
http://www.rmcompetition.com
Specialty engine building at its finest.
mdabbott2009
Pro
Pro
Posts: 211
Joined: Mon Jun 24, 2013 1:16 pm
Location:

Re: Cam for 406 mud racer

Post by mdabbott2009 »

Walter R. Malik wrote: Sat Apr 24, 2021 11:06 am
mdabbott2009 wrote: Sat Apr 24, 2021 9:30 am Motor is
4.155x 3.75 13-1
Crower ultra light Molnar rods cp pistons
Has to run factory heads per rules soo vortecs with 2.05 flow 260@500 2700@600
Single plane 750 based carb per rules
4.56 gears in low side with tcase ratio of 2.72 and 31in tires 5500 converter
This is a lift rule class 550 can be solid roller etc.

We got the cam through the guy that set up the heads was post to be 268@.50 but when I got the cam yesterday from bullet it's 251/256. I was told this is better then the bigger one and would still rpm? Little confused

Customer is not happy about spending all the extra money for pretty much same cam that was in it before that wouldn't pull past 6500.soo would this cam even get us close peak power at 7500?
I would say that cam would be good to about 6,500 RPM. I think the first choice was near correct.
A camshaft of .367" lobe lift and about 268/276 duration @.050" on a 112 sep +2 would be OK with that gearing.

With those heads and 406 cubic inches it may get to 7,500 RPM but, peak power won't be near that high.
That's what I thought

I need this thing pulling like a freight train at 7500 not like Prius
1980RS
Guru
Guru
Posts: 1636
Joined: Thu Oct 13, 2016 10:03 am
Location:

Re: Cam for 406 mud racer

Post by 1980RS »

If you can run a solid cam get an Elgin 1090-P cam you will like the power it makes. That cam has never let me down in any engine I have used it in. I know the exhaust lift is .557 so if that is a rule violator then get the same cam (1091-P) with a .500 lift and use 1.6 rockers to his your goal.
F-BIRD'88
Guru
Guru
Posts: 9802
Joined: Tue Mar 27, 2007 6:56 pm
Location: Ontario, Canada

Re: Cam for 406 mud racer

Post by F-BIRD'88 »

Howards Cams has the sft cam lobes you need to be .550" valve lift legal that have the durations for the higher rpm you are looking for. .343" (1.6 rr) or .367" (1.5rr).
Monza355
Expert
Expert
Posts: 504
Joined: Sat Dec 07, 2013 6:06 pm
Location:

Re: Cam for 406 mud racer

Post by Monza355 »

This lift rule. Is it measured at the valve or how do they go after it ? What cam was in it before and was that with the sam engine. Head work etc... ?
Walter R. Malik
Guru
Guru
Posts: 6353
Joined: Tue Jul 24, 2012 11:15 am
Location: Roseville, Michigan (just north of Detroit)
Contact:

Re: Cam for 406 mud racer

Post by Walter R. Malik »

mdabbott2009 wrote: Sat Apr 24, 2021 11:36 am
That's what I thought

I need this thing pulling like a freight train at 7500 not like Prius
With your specified combination, that is just not gonna happen; using ANY camshaft.
http://www.rmcompetition.com
Specialty engine building at its finest.
rustbucket79
Guru
Guru
Posts: 2151
Joined: Fri Apr 07, 2006 8:23 pm
Location:

Re: Cam for 406 mud racer

Post by rustbucket79 »

I feel Bullet has some knowledgeable people, perhaps what they provided will give the best average numbers within your given rules and components. More cam when the heads are the restrictions and the driveline is rules fixed can create an uncompetitive combination. (Without the torque to get the wheelspeed up where that extra few horsepower are you aren’t going anywhere quick) A peaky engine and a deep, sticky track will garner you last place.
rustbucket79
Guru
Guru
Posts: 2151
Joined: Fri Apr 07, 2006 8:23 pm
Location:

Re: Cam for 406 mud racer

Post by rustbucket79 »

Why would you bother with a flat tappet cam when you can run a solid roller?
User avatar
mt-engines
Expert
Expert
Posts: 857
Joined: Fri Sep 27, 2019 12:35 pm
Location: MN

Re: Cam for 406 mud racer

Post by mt-engines »

Considering you don't have enough CSA in the head to peak at 7500. You would probably need a cam in the 280@.050 range. But you would lose power everywhere. You could crutch it with a 6500 stall converter and gear.
Rick360
Guru
Guru
Posts: 1104
Joined: Sun Oct 03, 2004 9:55 pm
Location: Missouri

Re: Cam for 406 mud racer

Post by Rick360 »

Walter R. Malik wrote: Sat Apr 24, 2021 4:35 pm
mdabbott2009 wrote: Sat Apr 24, 2021 11:36 am I need this thing pulling like a freight train at 7500 not like Prius
With your specified combination, that is just not gonna happen; using ANY camshaft.
Exactly right.
mt-engines wrote: Sat Apr 24, 2021 10:50 pm Considering you don't have enough CSA in the head to peak at 7500. You would probably need a cam in the 280@.050 range. But you would lose power everywhere.
Also exactly right.

The lift limit is also limiting your rpm, you can't just add cam (duration) to an engine to get it to pull to whatever rpm you want.
CSA and entire induction sizing is the main thing that sets engine RPM range. Exhaust port and header sizing too. The duration of a cam should COMPLIMENT the rpm range the induction and exhaust sets.

Rick
PRH
Guru
Guru
Posts: 1501
Joined: Fri Sep 08, 2017 4:16 pm
Location: S. Burlington, Vt.

Re: Cam for 406 mud racer

Post by PRH »

Mud guys usually want high wheel speed.
A lot of stall...... buzz the motor pretty high.

The new cam seems short to me for the application.

406”, high CR, small heads, want some top end........

I’d have been looking more along the lines of the 268 cam.
Somewhat handy with a die grinder.
F-BIRD'88
Guru
Guru
Posts: 9802
Joined: Tue Mar 27, 2007 6:56 pm
Location: Ontario, Canada

Re: Cam for 406 mud racer

Post by F-BIRD'88 »

The larger duration cam will not move the horsepower peak rpm point up much b
F-BIRD'88
Guru
Guru
Posts: 9802
Joined: Tue Mar 27, 2007 6:56 pm
Location: Ontario, Canada

Re: Cam for 406 mud racer

Post by F-BIRD'88 »

The larger valve duration will not move the RPM point of peak horsepower up much, but what it will do is increase the power that is made UP AFTER peak horsepower, extemding the usable rpm range up. The tradeoff will be low rpm torque. You must keep the engine rpm way up.

Comp has a whole series if .323" lobe lift MA series sft cams that when used with 1.7:1 rr will be .550" lift rule legal.
Durations from BIG BIG thru small
You would have to A-B test it on track against your new Bullet/Ultradyne grind cam.
Post Reply