I picked up a recently rebuilt 1970 455 with a comp 270h cam in it, how might this work in a motorhome with a gvwr of 10,500 ?

F block, V notch 398666 stock pistons, new rings and bearings (unsure on exact compression, cranking compression is 190psi)
E heads, all stock i believe
comp cams 42-308 270h cam
270/270 adv duration
224/224 @.050
.501/.501 lift
110 lobe separation
toro intake
tri-y headers to 3" single exhaust
holley sniper quadrajet with hyperspark ignition
th425/3.08 gearing (considering other gearing)

 

from Jegs

270H Series
Great for high performance driving in street machines. The 270H has a rough idle in small blocks and a noticeable idle in big blocks. This is the largest cam that can be used with a stock torque converter. The 270H should not affect power accessories, but should be used with headers and 4bbl carburetor.

I cant offer any thing beyond that

 

That’s a outdated old school cam, kinda small for a performance 455. It’s definitely an improvement over a stock cam, but modern cans would be worth the expense.

 

 

Ok, I need to revise my statement. That’s definitely TOO much cam for a motor home.

 

what might you suggest? im thinking the compression is somewhere around 9.5-10:1 (1970 455)
also different gearing is available for these motorhomes, 3.08 (stock) 3.21 3.42 3.73, as well as a different transmission chain drive ratio.

 

At 9.5 -10 CR you'll probably be feeding the motorhome premium fuel and with lower ratio than stock gear ratios additional fuel. This will notably affect the wallet and the driving range per tank. You'll also have a 455 constantly turning higher RPM's with lower gears.

Some of our members custom grind cams, I'd ask them to make a cam for maximum torque off idle through mid RPM range e.g. 3,500 rpm when the RV will use the torque.

Good luck!!!

 

I think "CANADIANOLDS" posted he had a similar set up in his motorhome. Perhaps check with him to see what he has. AppliedGMCMH (800) 752-7502 in California might also help you.

 

There are people here far more knowledgeable about camshaft theory and design, I’m perfectly content to back away and let the experts advise camshafts.


in the case of the Th425, there are aftermarket gearsets available for the 400 to lower the first and 2nd gear ratios. While a lower 1 gear sounds great, it also increases the spread between gear ratio changes.

I have taken apart many TH425 trans, internally they are very similar to the RWD 400. I don’t know if they are close enough to allow gearset changes, might be worth looking into.