Tag Archives: Otto Cycle

Change of plans

I still haven’t made it to buy the butane and bolts. For some reason I just haven’t been able to get myself over there even though I have been able to get out of the house for other things. It’s even within walking distance, or what used to be walking distance until recently. What with the problem I have been having with my hip, and the problems I have been having not falling on my face when I get tired. So I don’t know what the problem is in getting butane and a few bolts. I plan on making a loop to the Lowe’s Wednesday after the Lab Rat Keeper to get the stuff, so no excuses.

I’m still tracking down why that one 383 build with the FIRST TPI manifold had such a steep drop-off of the torque curve. The data I have so far indicates the cam might be to blame because the guy that sells the manifold says the manifold does exactly what I saw in the video, but it can still make power at high RPM with even more displacement normally aspirated, and the heads were aftermarket aluminum so they should not be the source of the problem, either. That leaves only the cam in the Otto cycle (suck, squeeze, bang, blow) power equation unaccounted for. As I said in an earlier post the power output is fine, but the lack of power above 5000 RPM isn’t. So, more research on the cam specs is in order, and if it is a lift or a duration issue, or a combination of the two. Because head design does figure into it, how the intake port flows at low lift compared to high lift can dictate the cam specs. A combination that has relatively lower flow at low lift but greater flow at high lift (compared to another port design) requires spending less time at low lift and more time at high lift, so getting a cam with really high lift to get through the “bad” part of the flow as quickly as possible would be better than a longer duration cam with lift that wasn’t as high, Or given this manifold uses acoustic tuning for ram effect, maybe leaving the intake valve open longer would allow more ram effect and more air in the engine. Engines, like life in general, are a series of compromises.

I still don’t know what engine I will use on the Sprint-T, but I don’t seem to be able to let this problem go. I might end up with a Pentastar still, or a Subaru, or whatever I find that I can afford and get to the house. But right now I want to solve this mystery.

And I also need to get my fuzzy butt in a bed right now, so time to put the post to bed, unintentional pun.