Another "Which Cam" Thread

[plovett]

My thoughts:  The thing that stands out to me is the 31" tall tires with 3.89 gears.  A 3.89 gear sounds low, but with 31" tall tires it's not.  That would be like a 3.50 gear with 28" tires or a 3.25 with 26" tires.  Not very low and not very high.  So, I think I'd lean toward something like a 270S with 224@0.050".

That said, cam, compression, and octane have to match.  So as has been said already find your true compression ratio.  If it's low enough I'd say go with a smaller cam like the 270S.  If it's not then go with a bigger cam and just live with the reduced low end power, or get lower rear gears. 

That's just my opinion.  It seems that I always recommend smaller cams than Ross does for trucks and I recommend bigger cams for cars (assuming they're not super heavy).  Ross actually has an FE powered truck and I don't so take my opinion with a grain of salt.

JMO,

paulie

[R-WEST]

Thanks for the input, guys.

We should have the actual CR determined sometime next week.  The guy doing the engine does a lot of dirt track engines, and the season is winding down here, so he can devote more time to getting going on mine.  It'd probably help if I'd quit vacillating on cam choice..   

He already checked the deck and confirmed it at 10.15.  I'd originally done the engine back in the late '70's, and the decks had been squared up then.

I read Barry's write-up with great interest.  That 390 rocks!!

[My427stang]

My thoughts:  The thing that stands out to me is the 31" tall tires with 3.89 gears.  A 3.89 gear sounds low, but with 31" tall tires it's not.  That would be like a 3.50 gear with 28" tires or a 3.25 with 26" tires.  Not very low and not very high.  So, I think I'd lean toward something like a 270S with 224@0.050".

That said, cam, compression, and octane have to match.  So as has been said already find your true compression ratio.  If it's low enough I'd say go with a smaller cam like the 270S.  If it's not then go with a bigger cam and just live with the reduced low end power, or get lower rear gears. 

That's just my opinion.  It seems that I always recommend smaller cams than Ross does for trucks and I recommend bigger cams for cars (assuming they're not super heavy).  Ross actually has an FE powered truck and I don't so take my opinion with a grain of salt.

JMO,

paulie

Paulie, your advice is good.  IMHO though, these little bump side trucks are pretty light.  Mine is a 4x4 and tips the scales at 4200, every body style after these got heavier and heavier, but the little 67-72 short bed 2WDs are car weight

Even so, nothing wrong with a 270S either, I'd say he could use either depending where static compression ended up

[plovett]

True. The original post does say 3500 pounds which is quite light for a truck.  And he says he will use up to 3000 stall so it's all good for a bigger cam there. I think I get hung up on the word "Truck" and think it needs "Dumptruck" like low-end.  Like you said the true compression ratio is the kicker.

Now I'm looking for short bed F100's on craigslist!   Thanks a lot guys!   

paulie

edit:  added "will".

[turbohunter]

Now I'm looking for short bed F100's on craigslist! 

Woohoo

[R-WEST]

Now I'm looking for short bed F100's on craigslist!   Thanks a lot guys!

   

Totally swamped at work - still waiting to talk to the engine guy to see what CR numbers he's come up with..

[My427stang]

If he didn't measure chambers or deck height, ask him to.  Estimating isn't accurate enough

[R-WEST]

If he didn't measure chambers or deck height, ask him to.  Estimating isn't accurate enough

Hi Ross - He already checked the decks when I dropped the engine off some time ago and asked him to look it over - 10.15".

The guy's very thorough - a number of champions in various dirt track racing classes use his equipment.  That's also one of the downsides, he's really in demand.

As soon as I get the numbers from him I'll post up.