Bottom End Rebuild Planning

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rich_mc

rich_mc

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Some of you I'm sure have seen my thread about my recent Sniper/Torqstorm Slant modification. It's running well as of now and I plan to take it easy on it this season. However, I did not do anything to the bottom end of the engine. My thought is that this winter I'll yank it again and rebuild the bottom end so that I can give it hell without worry of breaking anything and taking it off the road during cruising season. For that reason, I want to start gathering stuff and planning for what I'll get into this fall.

Car is a '76 Scamp.

Currently, it is configured with:
  • Torqstorm supercharger
  • Super Sniper 2300 2 Barrel
  • Aussiespeed intake
  • Dutra Duals
  • Gill Welding Fatpipe
  • TTI Single 2.5" exhaust
I have NOT:
  • Done anything to the head
  • Done anything to the bores
  • Adjusted ring gap for the supercharger
I want to:
  • Address the items that I have NOT done above.
  • Keep it on pump gas, though I'm fine with running premium.
I do have a set of forged pistons that I recently got through a group buy on the slant six site for it.

My question is what parameters would you all suggest I shoot for with a bottom end rebuild?
  • I know I want to use the new forged pistons.
  • Compression - from what I'm reading online, it sounds like due to the Torqstorm I should stay/shoot for a compression ratio around 8:1.
  • Head - Should I look at bigger valves and head porting, or does the boost more than compensate for increased flows I'd get by doing so? If valve work is suggested, thoughts on what I should shoot for?
  • Cam - ideas on what would be a good target?
  • Other things I should be looking at/planning for?

Thanks for the help/suggestions.

Rich
 
Power Nation did a build in a slant six with a turbocharger. You might want to see if you can look the episode up and watch it. They went through all of the particulars and told exactly what was needed to keep it alive.
 
rich_mc said:
  • or does the boost more than compensate for increased flows
Click to expand...
Boost multiples what your engine makes NA, a boost of 14.7 psi will basically double your NA, up to the blowers total hp ability, So say the blower can make 600 hp that's about the total output your engine can have, the more or less NA power you have the more or less boost you need to get desired up to Max hp.

Eg.. To get 600 hp, 200 NA hp x 29.4 psi = 600 hp, 300 NA hp x 14.7 psi = 600 hp, 400 NA hp x 7.4 psi = 600 hp. Obviously this is ballpark.
 
rich_mc said:
Some of you I'm sure have seen my thread about my recent Sniper/Torqstorm Slant modification. It's running well as of now and I plan to take it easy on it this season. However, I did not do anything to the bottom end of the engine. My thought is that this winter I'll yank it again and rebuild the bottom end so that I can give it hell without worry of breaking anything and taking it off the road during cruising season. For that reason, I want to start gathering stuff and planning for what I'll get into this fall.

Car is a '76 Scamp.

Currently, it is configured with:
  • Torqstorm supercharger
  • Super Sniper 2300 2 Barrel
  • Aussiespeed intake
  • Dutra Duals
  • Gill Welding Fatpipe
  • TTI Single 2.5" exhaust
I have NOT:
  • Done anything to the head
  • Done anything to the bores
  • Adjusted ring gap for the supercharger
I want to:
  • Address the items that I have NOT done above.
  • Keep it on pump gas, though I'm fine with running premium.
I do have a set of forged pistons that I recently got through a group buy on the slant six site for it.

My question is what parameters would you all suggest I shoot for with a bottom end rebuild?
  • I know I want to use the new forged pistons.
  • Compression - from what I'm reading online, it sounds like due to the Torqstorm I should stay/shoot for a compression ratio around 8:1.
  • Head - Should I look at bigger valves and head porting, or does the boost more than compensate for increased flows I'd get by doing so? If valve work is suggested, thoughts on what I should shoot for?
  • Cam - ideas on what would be a good target?
  • Other things I should be looking at/planning for?

Thanks for the help/suggestions.

Rich
Click to expand...
Definitely bigger valves.
Porting, yes.
Bearing clearances at .002-.0025
Better distributor gear
Good step header 1.5/1.62 to 2.5 pipe
Baffled pan
Scraper
 
What kinda oil pressure does it have?
 
Not knowing your final goal for HP, its difficult to make suggestions. But you should install better fasteners in the rods, mains and head. Several guys on .org have had parts failure in their bottom ends(stock connecting rods) even with ARP rod bolts at the 300-ish HP level. So Molnar rods may be a good consideration as an upgrade as well....
 
CNC-Dude said:
Not knowing your final goal for HP, its difficult to make suggestions. But you should install better fasteners in the rods, mains and head. Several guys on .org have had parts failure in their bottom ends(stock connecting rods) even with ARP rod bolts at the 300-ish HP level. So Molnar rods may be a good consideration as an upgrade as well....
Click to expand...

Thanks. In my reading I did see that the Molnars are only available for the forged crank, though it seems some people have machined the rods thinner to work with the cast crank. Mine I'm 99% sure is a cast crank so I'd either have to do that or to find a forged crank engine to rebuild instead and then drop in later.

I think I'd be reasonably content if I ended up in the 250-300 hp range when done.
 
Rich, find the Power Nation Video. They used a forged crank in an early block and they tell you exactly what is need and how to do it.
 
was that the group buy for wiseco high compression stock length rods? if you're looking at aftermarket rods anyway, I'd probably look at selling those pistons and then getting 198CID length rods (IIRC it's 7.005, vs. 6.7) and then using pistons intended for a chrysler 2.2L turbo. gives you a better rod ratio, a shorter compression height, very near 0 deck, a lighter piston, and more of a dish (IIRC the ones on the group buy were popups for up to 12:1 compression)
 
michiganpat said:
was that the group buy for wiseco high compression stock length rods? if you're looking at aftermarket rods anyway, I'd probably look at selling those pistons and then getting 198CID length rods (IIRC it's 7.005, vs. 6.7) and then using pistons intended for a chrysler 2.2L turbo. gives you a better rod ratio, a shorter compression height, very near 0 deck, a lighter piston, and more of a dish (IIRC the ones on the group buy were popups for up to 12:1 compression)
Click to expand...

Lol- now you've given me a lot more to research and contemplate...

The forged pistons set I got is from Icon (thread here: Forged pistons/pins - group buy - Pistons ordered on 1/31/24 - Slant Six Forum )
 
rich_mc said:
Lol- now you've given me a lot more to research and contemplate...

The forged pistons set I got is from Icon (thread here: Forged pistons/pins - group buy - Pistons ordered on 1/31/24 - Slant Six Forum )
Click to expand...
that was the group buy I was thinking about.

have you calculated what the CR will be using them as is vs. milling off the dome? (added cost)...guessing you'd want to keep your CR on the lower side if you plan on using a lot of boost.

the beauty with these pistons are they were designed for near 0 deck with stock rods. if you plan on building with aftermarket rods, there's no reason not to get the longer 7" rods and the lighter off the shelf forged pistons, which all seem like they're designed for the 7" rod.
 
michiganpat said:
that was the group buy I was thinking about.

have you calculated what the CR will be using them as is vs. milling off the dome? (added cost)...guessing you'd want to keep your CR on the lower side if you plan on using a lot of boost.

the beauty with these pistons are they were designed for near 0 deck with stock rods. if you plan on building with aftermarket rods, there's no reason not to get the longer 7" rods and the lighter off the shelf forged pistons, which all seem like they're designed for the 7" rod.
Click to expand...

I have not done any calcs yet. Kinda figuring I might have to remove the head and CC it to figure out what I'm starting with. As far as I know, it is factory and never pulled with 60k miles, but it is almost 50 years old so...
 
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