Cam choice for low compression motorhome 440

-
cpearce

cpearce

FABO Gold Member
FABO Gold Member
Joined
Sep 1, 2010
Messages
1,640
Reaction score
1,512
Location
Edson
I'm helping a friend with his 78 440 motorhome engine. This winter he has decided to do a cam swap. Since I have very little experience with 440's I though I'd seek advice from the group. He is looking for a nice boost in low to mid range torque, and would like a nice idle lope that isn't really choppy.

440
I think motorhome compression is 8.6:1
Factory intake
Thermoquad
Factory exhaust manifolds
Dual 2.25" exhaust
727 auto, stock covertor with shift kit.
3.23 gears
67 Sattelite

Looking for recommendations for hydraulic flat tappet cam to maximize a low compression engine.

This car is a daily driver in summer and often goes on road trips.

Thanks for the help FABO, and Merry Christmas everyone!!!!
 
Hughes Whiplash cam HUG SMC3245BL for low compression engine
 
I'm in search of a cam for a similar car ('67 Coronet daily driver,'74 440 smogger,727,2.94's,stock manifolds).The guy at Hughes recommended the SEH2428BL,the guy at Comp suggested their Extreme energy 21-222-4. The Hughes Whiplash cam sounds like it would also be a good choice but the xtra choppy idle is a dealbreaker for me.
 
I would look up threads by IQ52 and see what he did on his low compression Big block engine.
 
Post #2 nailed it. Simple and effective. No thinkin necessary.
 
21-222-4 comp cam. the hughes cam is silly with only 107 lsa and too much duration for low compression and mild rear gear, but it may sound like a funny car
 
Last edited:
21-222-4 comp cam will drop your DCR to about 6.8:1
 
The Hughes cam will have a DCR of about 7.9:1, that is where you want it for pump gas
 
I'd suggest something cut on a 106-108 LSA and install it at 100 or so.

You want to get the dynamic compression UP and installing it ahead will get that done. Similar to what the whiplash and comp thmper cams do.

Ignition timing, primarily initial will play a BIG role in how the car performs at idle and just off.
 
Last edited:
crackedback said:
I'd suggest something cut on a 106-108 LSA and install it at 100 or so.

You want to get the dynamic compression UP and installing it ahead will get that done. Similar to what the whiplash and comp thmper cams do.

Ignition timing, primarily initial will play a BIG role in how the car performs at idle and just off.
Click to expand...

Just a question, not arguing. I've always heard that a wide LSA (112?) is better when using exhaust manifolds. I understand advancing the cam to get the DCR up on a low compression engine but, why the tight LSA? Is it for a choppy idle?
 
crackedback said:
I'd suggest something cut on a 106-108 LSA and install it at 100 or so.

You want to get the dynamic compression UP and installing it ahead will get that done. Similar to what the whiplash and comp thmper cams do.

Ignition timing, primarily initial will play a BIG role in how the car performs at idle and just off.
Click to expand...
This is what I expected to hear, the tight LSA will also help the fact that we live at 3000ft elevation here. Thanks for the input, since it is a friends ride I don't want to make a bad choice for him.
 
crackedback said:
I'd suggest something cut on a 106-108 LSA and install it at 100 or so.

You want to get the dynamic compression UP and installing it ahead will get that done. Similar to what the whiplash and comp thmper cams do.

Ignition timing, primarily initial will play a BIG role in how the car performs at idle and just off.
Click to expand...
BAMM, this! ^^
 
Marcohotrod said:
21-222-4 comp cam. the hughes cam is silly with only 107 lsa and too much duration for low compression and mild rear gear, but it may sound like a funny car
Click to expand...

With the Whiplash cam, that's not true. If you look at the valve events as they happen, you'll see a wide split between the intake and exhaust. That wide split, coupled with the narrow LSA will bring cylinder pressure up, not down.

You cannot just say "that amount" of duration and "that lobe separation" will drop cylinder pressure. It's how it is ground. Crower made very similar grinds almost 50 years ago. They are nothing new, but the marketing sure is.
 
The OP said he don't want a choppy idle, so why a thumper cam ?
Id say comps 265deh cause of the manifolds.
 
In
273 said:
The OP said he don't want a choppy idle, so why a thumper cam ?
Id say comps 265deh cause of the manifolds.
Click to expand...
In truth, if a performance gain is to be had by the proper cam choice I'm sure he would take the idle with it. Lol, he always comments on the sound of my 408 which gas a definite cackle.
 
For the sake of comparison, how does the Comp Cams Thumpr fair against the Hughes Whiplash? Being in Canada, a fair amount of money can be saved by buying from our local speed shop who is a Comp vendor. (Exchange on dollar adds big expense). My friend is a retiree and so when recommending cams I must be mindful of cost. To me these cams appear similar with slightly less duration and lift on the Comp piece. Could this be run with power brakes in a 440? Thanks again everyone for the help, sharing your experience is appreciated.
Screenshot_20171219-082011.png
Screenshot_20171219-081914.png
 
Really guys? a Whiplash or Thumper cam?

There was a reason that the factory used a small duration, wide lobe separation cam in the low compression engines. I wonder if it had anything to do with engine vacuum?

What does Hughes say about the Whiplash cam?

"Your vacuum should be in the 9"-11" range using this cam." Uh-huh, should be.

"Idle: Very, very noticable (sic)."

"Vacuum: Medium to low." (italics mine)

Do you suppose the Thumper is any different?

You really want to gamble with a retiree's money? Do you?

P.S. I've never seen a motorhome engine above 8:1 compression.
 
IQ52 said:
There was a reason that the factory used a small duration, wide lobe separation cam in the low compression engines. I wonder if it had anything to do with engine vacuum?
Click to expand...
LOL! And I got a lot of flack for installing a cam with a 112 on a late ‘70’s 318.
 
IQ52 said:
Really guys? a Whiplash or Thumper cam?

There was a reason that the factory used a small duration, wide lobe separation cam in the low compression engines. I wonder if it had anything to do with engine vacuum?

What does Hughes say about the Whiplash cam?

"Your vacuum should be in the 9"-11" range using this cam." Uh-huh, should be.

"Idle: Very, very noticable (sic)."

"Vacuum: Medium to low." (italics mine)

Do you suppose the Thumper is any different?

You really want to gamble with a retiree's money? Do you?

P.S. I've never seen a motorhome engine above 8:1 compression.
Click to expand...
Thanks for the response IQ52,

I absolutely don't want to gamble with a retiree's money, especially a good friend, that is why I am seeking advise. This is a type of engine I am unfamiliar with, this is why I have approached the group. IQ52, might I ask what cam you would use in this application, I welcome your input as it seems you have had great successes with these engines. Thanks for your time.
 
You must log in or register to reply here.
-

Back
Top