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Porting the Driveline LP 421?


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My past experience was a 421 Serval dune ported by cam on race gas w/ 35’s.  Usable power far surpassed my expectations but I couldn’t carry enough gas for the big dunes. Hindsight I should have experimented with different carbs.

I had a used driveline LP 421 as cast fall in my lap and I used 33’s. Pulled 78hp on the dyno at 5000’ so maybe 85hp sea level. Fuel economy has been exceptional but you know, “just a little more would be perfect” haha.

So the engine is at Cam’s shop for a freshen up, pro mod etc. I need to decide soon to have him port it or not. My fear is loosing considerable fuel economy? Anybody play with these cylinders that can share experience? Thanks!

 

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My past experience was a 421 Serval dune ported by cam on race gas w/ 35’s.  Usable power far surpassed my expectations but I couldn’t carry enough gas for the big dunes. Hindsight I should have experimented with different carbs.
I had a used driveline LP 421 as cast fall in my lap and I used 33’s. Pulled 78hp on the dyno at 5000’ so maybe 85hp sea level. Fuel economy has been exceptional but you know, “just a little more would be perfect” haha.
So the engine is at Cam’s shop for a freshen up, pro mod etc. I need to decide soon to have him port it or not. My fear is loosing considerable fuel economy? Anybody play with these cylinders that can share experience? Thanks!
 
More power= more fuel ;-)

Envoyé de mon SM-N975W en utilisant Tapatalk

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2 hours ago, gusto said:

Desert tank makes a big difference. What pipes are you running? Im asking because there is hp to find there, Shearers would make a nice difference on that engine.

What Claude said, porting is going to kill your gas mileage. 

Thank you for clarifying what I believe too but you have far more experience than me.  Cam has built a couple engines for myself and the wife in the past and there is no builder I respect more.  At the same time, he is thinking more efficient horse power and little change in economy with carbs being the much bigger factor.  I'll likely talk through the driveline design with him, change what we believe should be improved then leave it closer to "as cast" but with some fundamental changes.  Tank is yfz450 IMS 3.6 gallon.  Pipes ... um ... kind of shear .... mostly one off, longer body hoping for more torque but very free flowing too.  will share the 15+ month creation soon!

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12 hours ago, WALZ said:

Thank you for clarifying what I believe too but you have far more experience than me.  Cam has built a couple engines for myself and the wife in the past and there is no builder I respect more.  At the same time, he is thinking more efficient horse power and little change in economy with carbs being the much bigger factor.  I'll likely talk through the driveline design with him, change what we believe should be improved then leave it closer to "as cast" but with some fundamental changes.  Tank is yfz450 IMS 3.6 gallon.  Pipes ... um ... kind of shear .... mostly one off, longer body hoping for more torque but very free flowing too.  will share the 15+ month creation soon!

Sounds like your building something special. I had Cam do my engines, the last was a 421 and i had the same concerns. We went with 28s and a desert tank for mileage, its better on gas but i cant tell you by how much because its the only carbs ive ever used on it and its been riden sparingly. I just ordered 33s for it due to its hard to tune between pipes with these carbs.

I am currently building another 421 serval and i am not convinced i should. I kind of toying with the idea of a 347 or 358 cub or a 392 serval or driveline setup. A guy out here has a 392 DL set up by the guy at DL and its real impressive. The guys at Driveline would do my next build over anyone else if i was using their cylinders, they have done some experimenting and i thought the results were excellent.

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Having both 421 Serval and Driveline  though not identical builds I think the Serval is far more thirsty.  
 

I was wishing I got 28’s over 33’s but was worried about exactly what you experienced. Thanks for confirming!
 

The driveline incredibly small boost ports seem odd and I can’t say I’m drinking the kool aid for the huge windows in piston skirt. Standard pistons should work but I don’t think lane would install them. So many great builders with different opinions. 

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17 minutes ago, locogato11283 said:

What's a few gallons here and there? Power = get bitches.

I’m not worried about $6.50/gal race fuel. It’s distance. Glamis and St Anthony you burn so much getting to the good stuff.  Oregon, Utah and Michigan it’s not a problem. I think I’m going to keep as-cast. You guys pointed out some good threads and the DL as-cast actually has mild porting compared to CP cast.   Mid 80’s hp is nothing to sneeze at when it’s getting the fuel economy.  I am going to ditch the 10 pound heavier LSR +4 for a shorter aluminum one then ditch the hipers for less rotation weight.  Stick a fork in it! This build has taken way too long.

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On 12/2/2020 at 6:07 PM, WALZ said:

I’m not worried about $6.50/gal race fuel. It’s distance. Glamis and St Anthony you burn so much getting to the good stuff.  Oregon, Utah and Michigan it’s not a problem. I think I’m going to keep as-cast. You guys pointed out some good threads and the DL as-cast actually has mild porting compared to CP cast.   Mid 80’s hp is nothing to sneeze at when it’s getting the fuel economy.  I am going to ditch the 10 pound heavier LSR +4 for a shorter aluminum one then ditch the hipers for less rotation weight.  Stick a fork in it! This build has taken way too long.

Pics, we need pics

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Final assembly is coming quick.  All parts are at  powder/cerakote, due back this week and hopefully my engine comes this month.  I will post up in YFZ-Banshee category just to see if people like some of my ideas or not. 

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