Budget 350 RV build

[travis]

This is kind of a generic question...

350 sbc in a early 80’s class C motor home, TH400, 4.10 gears. WAG it’s somewhere in the 7-8k pound range by itself, and will be towing a small trailer with a couple of Harleys.

I’m guessing that it’s got a broken piston or 2, as the owner said it ran fine (gutless, but mechanically ran ok), then lost power and now has a ton of blow by and a definite miss. It only has about 70K miles on it. I will have a better idea what’s going on once they bring the engine to me sometime this week.

My question is...what would be a better approach to building a low budget engine for this application. Keep the compression low (8.0-8.5-ish), and use a small cam on a tighter lsa (more bottom end torque), or a little more compression (say 8.7-9.0 or so) and a slightly larger cam on a tight lsa, or a small cam on a wider lsa?

Fuel economy is important, but more important for the owner is the ability to climb rolling hills at better than 40mph uphill with his foot buried in it, and the ability to maintain better than 62mph on flat ground without having to drive at WOT.

The motor home has a small dual exhaust system...I’m trying to talk him into a set of headers.

[lefty o]

a budget 383 or 400 is a better start.

[rustbucket79]

8.75:1 383 with budget alloy or possibly Vortec heads and a mild cam.

[dynoflo]

a few years ago i built a 383 for towing. 1 ton with 400 and 4.11s. It made 500 tq and only 275 hp. Fellow loved it. Tried several inakes and carbs 2101 with a quadrajet was the best. It had truck heads with sodium filled exhaust valves. I dont remember the cam but it was specd by comp. He towed with it for several years before selling it. He bought a new 3/4 ton chevy and said it ran just like the 383 but at much higher rpm with same gas milage. I remenber the duration was much higher than i thought it should be. Could find out cam specs as he is a old friend who probably kept it or remembers.

[novadude]

a few years ago i built a 383 for towing. 1 ton with 400 and 4.11s. It made 500 tq and only 275 hp. Fellow loved it. Tried several inakes and carbs 2101 with a quadrajet was the best. It had truck heads with sodium filled exhaust valves. I dont remember the cam but it was specd by comp. He towed with it for several years before selling it. He bought a new 3/4 ton chevy and said it ran just like the 383 but at much higher rpm with same gas milage. I remenber the duration was much higher than i thought it should be. Could find out cam specs as he is a old friend who probably kept it or remembers.

Would love to hear the cam specs... that's a crazy amount of tq.

[dynoflo]

found the dyno sheet. I dont know how to transfer to here but gt hold of fellow i did engine for and he will call this evening with cam cars specs. It had older truck heads only found on larger than 1 ton with 1.750 and 1.5 sodium filled exhaust. at 2000 it had 483 tq. at 3500 had 503 tq. peak hp was 357 at 4000. egt only went to 1244 max. It was 9.2 compression on pump gas.

[dynoflo]

cam specs are 212 218 at .050. lift is 447 454 on 110 lobe sep. comp 12-234-2 . grind iscsxe25614-10

[novadude]

cam specs are 212 218 at .050. lift is 447 454 on 110 lobe sep. comp 12-234-2 . grind iscsxe25614-10

Thanks for sharing the details!

[travis]

A 383 isn’t happening, judging by the whining after I told him it has to go to the machine shop

One piston had a sizable portion above the top ring groove missing. The ring was still intact, but that cylinder has some pretty good sized scratches in it, and a slightly bent intake valve.

[PRH]

What heads are on it?

Some of those factory 80’s heads leave a lot to be desired.

If the owner doesn’t want to part with much $$$$, I’d say the power gains will end up being pretty small.

[travis]

The heads are 882 castings with the 1.72/1.50 valves. I believe this era 350 should have had 624 castings on it, but I’m not completely sure on the heavier applications.

[RevTheory]

Can you at least talk him into some iron Vortecs? They're probably ~$500 or so a pair from Scummit or Jegs.

[PRH]

I’d probably see if he was willing to spring for some of the SR type Dart heads with the 1.94/1.50 valves.

Do some very minor clean up in the bowls, and recut the seats, hone the guides, etc.

[mt-engines]

The heads are 882 castings with the 1.72/1.50 valves. I believe this era 350 should have had 624 castings on it, but I’m not completely sure on the heavier applications.

just do a basic rebuild. cut for larger valves, get the compression above 9:1 and throw a $70 summit 1102 camshaft in it. he will be happy. it will make a bunch more power in the low end.
that cam is like 204/214 112 lobe sep

[turbo camino]

I wouldn't do anything other than fix what's broken if he's not willing to do the 3.75" crank. (actually if it was me I'd probably turn it down altogether)