2270(or so) Build |
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2270(or so) Build |
yeahmag |
Jan 8 2021, 12:47 PM
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#1
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Advanced Member Group: Members Posts: 2,421 Joined: 18-April 05 From: Pasadena, CA Member No.: 3,946 Region Association: Southern California |
I'm starting to get the case(s) machined and inspected and parts ordered for my next generation engine. The car is mostly used for autocross.
78x96 96mm piston with 22mm wrist pin (stroker) 5.4" Type 1 Rod, 22mm wrist pin WebCam 86b/86c David Finch heads (from Len Hoffman many moons ago) 9.5:1 CR running on 91 octane pump gas CB Dry Sump (heavily modified) or Thorsten Piper dry sump pump Front mounted oil cooler There are a few crank options out there now: * DPR offset grind Type 1 journal * AA Performance Forged Type 1 journal * FAT Performance Forged Chevy journal I've read about a few 80mm DPR cranks breaking, so I was planning on staying under 80mm as I like the car to be able to rev. I was considering Chevy journals for ease of assembly, but the two cranks I've read about breaking were 80mm/Chevy journals. Is there any new information on cranks out there? Any input on the config? |
Blown59 |
Jan 13 2021, 10:55 PM
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#2
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Member Group: Members Posts: 66 Joined: 21-July 19 From: St Louis Member No.: 23,315 Region Association: None |
Curiously... As a noob when it comes to T4 builds... Why not run the 2.0 rod journal and not reduce the cam base? Isnt the crank strong enough and the reduced cam circle weakening the cam?
If my idea is wrong, can someone please educate me as to why? |
Dave_Darling |
Jan 14 2021, 07:08 PM
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#3
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914 Idiot Group: Members Posts: 14,981 Joined: 9-January 03 From: Silicon Valley / Kailua-Kona Member No.: 121 Region Association: Northern California |
Curiously... As a noob when it comes to T4 builds... Why not run the 2.0 rod journal and not reduce the cam base? Isnt the crank strong enough and the reduced cam circle weakening the cam? I'm not sure what level you are asking that question from, and the other replies require a bit more knowledge than a total noob would likely have, so I will try to fill that in. When we talk about making the stroke of an engine longer, that is generally done by swapping in a crankshaft where the rod journals are farther away from the main bearing journals. Specifically, the center of the rod journals are farther than the center of the main journals. Because the piston is directly connected to the rod journal, that means the piston travels further up and down (or side to side in a 914 engine!) which is a longer stroke. When you do that, you are going to take up more space inside the engine. Due to the layout of the internal bits, there is one place in the cam and crank rotation where a connecting rod on a long-throw crank will try to occupy the same space as a cam lobe. Whether or not this happens is influenced by a bunch of factors, very much including how long that stroke is, how big the big end of the rod is, how tall the cam lobe is, and so on. It's not really feasible to move the cam down, or the crank up, so you try to make room by carefully taking material off the outside of the rod (which then needs to be balanced again along with the rest of the rods) and possibly by making the cam's base circle (the part that doesn't open the valves) smaller. This latter means that you can get the same lift from the cam but the edge of the lobe will be closer to the center of the camshaft, so it takes up less room in the case. This is a simplification of what's going on, but I hope it helps. --DD |
Blown59 |
Jan 17 2021, 03:38 PM
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#4
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Member Group: Members Posts: 66 Joined: 21-July 19 From: St Louis Member No.: 23,315 Region Association: None |
Curiously... As a noob when it comes to T4 builds... Why not run the 2.0 rod journal and not reduce the cam base? Isnt the crank strong enough and the reduced cam circle weakening the cam? I'm not sure what level you are asking that question from, and the other replies require a bit more knowledge than a total noob would likely have, so I will try to fill that in. When we talk about making the stroke of an engine longer, that is generally done by swapping in a crankshaft where the rod journals are farther away from the main bearing journals. Specifically, the center of the rod journals are farther than the center of the main journals. Because the piston is directly connected to the rod journal, that means the piston travels further up and down (or side to side in a 914 engine!) which is a longer stroke. When you do that, you are going to take up more space inside the engine. Due to the layout of the internal bits, there is one place in the cam and crank rotation where a connecting rod on a long-throw crank will try to occupy the same space as a cam lobe. Whether or not this happens is influenced by a bunch of factors, very much including how long that stroke is, how big the big end of the rod is, how tall the cam lobe is, and so on. It's not really feasible to move the cam down, or the crank up, so you try to make room by carefully taking material off the outside of the rod (which then needs to be balanced again along with the rest of the rods) and possibly by making the cam's base circle (the part that doesn't open the valves) smaller. This latter means that you can get the same lift from the cam but the edge of the lobe will be closer to the center of the camshaft, so it takes up less room in the case. This is a simplification of what's going on, but I hope it helps. --DD I sort of understand what youre saying... I get that fundamentally there is a shift where at one point the outer edge will be further away in the rotation. What Im not understanding is what the differences of each are. For example, I was going to use a 78mm welded crank with a 2.0 rod journal, 2.0 H beam rods (5.325) 22mm pin, and KB 96mm pistons with 80mm stroke. My understanding is this allows to run in the case of my build a 163/86b without a reduced cam base. I was under the impression a reduced base with this cam would weaken the cam. So, to keep things as robust as possible on the top and bottom end, this was the route we were going. What I dont understand is how that is any worse than the type 1 or Buick?? FYI the rods will be lightened and balanced by my builder. Just looking to understand something maybe I just cannot see or that isnt computing for me... |
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