Hey guys, I've been lurking in the shadows for a couple years now. Used to have tons of time to modify and fix my old trucks but work family and new house got my time...

Anyhow I'm back to my pulling truck build. "Zeus" below... 351w build zf542 3.55 gears 4x4

Here is what's been done so far.
1.) .030 over bore flat top hypertunic pistons 9.5-9.8 compression ratio
2.) Headman LT headers
3.) Comp cam 35-255-5 (sad motor so I couldn't go to crazy)
4.) No cats and high flow exhaust. Probably 2.5" single. Not for sure yet on exact configuration yet but will be way more open than stock
5.) stock rebuilt heads


Pretty simple build, just want to know where my power numbers might be. Hoping Paul (conanski) might chime in here. Pretty sure I had some #'s on this setup before but can't find all my old info and forgot 1/2 of what I learned.

I have considered the gt40 heads but they have been hard to find at junk yarss here and not sure if that would overload the SD computer. Would be willing to trade some 300 i6 performance parts if anyone has some heads and they would work for me... I have dual plane offey intake, 390 4bbl holly carb, efi manifolds and a hotter cam and lifter kit.

 

Should make 250-260hp but even better you'll have 380-400tq if your CR estimates are accurate.

 

Yea I'm pretty sure that was the #'s I'm remembering. A couple years back when I was doing the engine build I was looking for the upgrades that would work with the SD computer to get more power. I got the higher domed hypertunic pistons when I did the rebuild b/c I believe you suggested it to bump the CR in the engine. From what I recall the stock CR was like 8.5:1? I know the new estimated CR with the pistons I bought was at least 9.1:1 or higher.

 

Stock CR is 8.8:1 on an 5.8EFI motor, stock pistons have a 20cc dish IIRC, Assuming your flattops have valve eyebrows that works the same as a small dish so CR should not exceed 10:1, but if they are truely flat then CR could be as high as 11:1 which is not good.

 

I'm pretty sure I calculated it before I put them in the basket...

I think I got SLP-H336CP30 from Summit. Couldn't find my old receipt to be 100% sure.

What is my compressed gasket thickness and deck clearance?

 

I believe standard gaskets are 4.100" bore, 0.035" compressed thickness, and pistons are 0 deck height.

 

I'm using the summit compression ratio calculator and it says 19.63:1?!?!?! Wtf?

4.030 bore (30 over bored)
3.5 stroke
20cc head volume
12cc dish on piston
0.0 deck clearance
0.035 gasket
8 cylinders

I'm thinking my cylinder head volume is off for stock 351w f250 heads?

 

Yep looks like the e7 heads were 64cc. That calculates to 9.78:1 ratio.

I've got the die grinders and carbide burs and everything to slick up the e7 runners too. If I can find a cheap valve spring compression tool I'll probably port match and slick them up some...

 

I'm sorry to hi-jack the thread, but why whould this not be good?

 

The higher the CR and the heavier the vehicle the more difficult it is to prevent detonation. With a gas truck that will likely have oversized tires and fuel milage focused gearing and possibly see duty towing loads the practical limit for CR is around 9.5-10:1 with available pump gas, but even at the upper limits of that the thing would likely be a premium fuel only vehicle without a really fancy ignition control system.