Boxcar Posted January 2, 2014 Report Share Posted January 2, 2014 Just started to do the mental math on this build up. Am in the throws of a 620 4x4 build and am at the point where I should start thinking about power. As the truck has a fairly fresh L-20 in it now, and I like the robust nature of the L-20's bottom end, I'd like to run it. I will be running a carbed engine for simplicity and repairabillity on the trail. My thought was that an Eaton M-70 Supercharger coupled to a 5150 holly economaster carb might be just the ticket. Just wondering if anyone has run something similar, and with what results? Quote Link to comment
spudly13 Posted January 2, 2014 Report Share Posted January 2, 2014 The motor was rebuilt all stock? those pistons tend to break at the ringlands and skirts for various reasons when boost is added. The valve seals and valve guides tend to not last very long either. All my experience has been based off of turbo l's but fore the most part boost is boost. Quote Link to comment
datzenmike Posted January 2, 2014 Report Share Posted January 2, 2014 Most factory turbo fours... Chrysler, Ford, Nissan, Toyota (probably lots more) use the stock hyper-eutectic pistons but limit boost to 5-6 pounds. They can handle reasonably prolonged boosts at this level. For very short bursts you can run them higher and get away with it. It helps a lot if you have an improved cooling system, oil squirters, oil cooler, knock sensor/ignition retard system maybe water/alcohol injection. Now having said that and knowing that people are only human and know that if 5 PSI is good 10 would be better, and 15 great. Somewhere between good and better forger pistons are advised. There's nothing wrong with the L20B pistons, it's just that they were never designed for turbo use is all. Quote Link to comment
620Turbo4X4 Posted January 3, 2014 Report Share Posted January 3, 2014 My very first Datsun.. some 25 years ago... was a 620 with a turbocharged L18. The stock low compression L20b cast pistons were the weak link and is what eventually failed. Custom forged pistons have come down in price, somewhat, (I think I was quoted $400 each.. back in the day) and IMO would be well worth the extra investment. I was quoted about $650 for my ringed set of 4 from JE Pistons. O-ringing the head, and stainless valves with bronze guides, viton seals and ARP bolts would also be a good investment for reliability.I debated wether to supercharge, or turbo my 4X4 620 truck for quite awhile. My first choice engine was a 300ZX VG30DETT, but I don't see that fitting without major modifications. So I decided to keep the L engine since I have a few of them now, and boost/stroke that. Engine will be fuel injected running a TEC 3 system.1 concern that I would have with using a carburetor and supercharger, with a stock type distributer system would be cap crossfire... Out having a fun day splashing through puddles... little moisture in the cap, and... Ka-boom… Intake explosion/fire in the carb. A turbo can shrug this off, somewhat, as long as the fire goes out. Positive displacement superchargers, not so well. My L-18 turbo ran a .020 plug gap to avoid crossfire.How much power are to looking to achieve? Quote Link to comment
72240z Posted January 3, 2014 Report Share Posted January 3, 2014 Its a tricky thing to say how well its going to hold up when you compare with a l28et. It doesn't use forged or coated pistons and can reliably with no fmic or alc take 10 lbs of boost. That is with EFI though so the chances of issues are def lower. Besides the cross/mis fire issue mentioned I would be concerned with running lean and melting a piston or detonating and shattering rings. Also cylinder wash and premature wear could be an issue too depending on the set up. Whatever boost you choose your going to have to go the extra mile to keep it all reliable. Your end goals are going to dictate how far that needs to go... I am thinking of supercharging my Z this spring for fun. Mainly because you never see it though it does have its own benefits (and pitfalls). For me 10lbs would be the max, most certainly with efi and most likely with an fmic as well as oil cooler. Ideally I would also be going with a centrifugal type. Though roots is far cheaper centrifugal is beneficial in a bunch of ways. Quote Link to comment
d510addict Posted January 3, 2014 Report Share Posted January 3, 2014 Arent there supercharger kits for the KA24 platform? The motors are cheap as hell and easily fit the 620. Just a thought. Quote Link to comment
620Turbo4X4 Posted January 3, 2014 Report Share Posted January 3, 2014 Arent there supercharger kits for the KA24 platform? The motors are cheap as hell and easily fit the 620. Just a thought. Can't speak for boxcar, but on my truck I'm limited to a rear sump engine due to 12" of suspension travel, and the jeep SAS. Anything front sump would hit my axle, panhard bar and steering linkage. So I guess it would have to be out of a truck? From what I've read, aren't the truck blocks heavy and prone to cracks? I'm kinda regretting not looking into the supercharged Xterra VG33ER engine swap more…. Quote Link to comment
620Turbo4X4 Posted January 3, 2014 Report Share Posted January 3, 2014 Its a tricky thing to say how well its going to hold up when you compare with a l28et. It doesn't use forged or coated pistons and can reliably with no fmic or alc take 10 lbs of boost. That is with EFI though so the chances of issues are def lower. Besides the cross/mis fire issue mentioned I would be concerned with running lean and melting a piston or detonating and shattering rings. Also cylinder wash and premature wear could be an issue too depending on the set up. Whatever boost you choose your going to have to go the extra mile to keep it all reliable. Your end goals are going to dictate how far that needs to go... I am thinking of supercharging my Z this spring for fun. Mainly because you never see it though it does have its own benefits (and pitfalls). For me 10lbs would be the max, most certainly with efi and most likely with an fmic as well as oil cooler. Ideally I would also be going with a centrifugal type. Though roots is far cheaper centrifugal is beneficial in a bunch of ways. The L28et has a lower compression ratio vs a N/A L28. The et's have dished pistons, and heads with raised combustion chambers (shorter valves). Totally agree about the cylinder washing and lean issues with a running a carb. Especially on the off camber/hill climbs done while off road-ing. I notice the difference in my truck on steep hills and descents. Carburetors only work well when kept somewhat horizontal. The Rotrex centrifugal superchargers are supposed to be really compact and efficient. I don't care for the extra separate oiling system it involves though…. Quote Link to comment
72240z Posted January 3, 2014 Report Share Posted January 3, 2014 Actually it depends which L28 your talking about. The N42 block from a 280z uses dished pistons stock and with either the N47 or N42 heads compression is only about 8.2, which is just fine for boost. Event he flat top F54 block and P79 head only yields 8.5-8.8 compression. You can drop a turbo head on the flat top block with a HKS head gasket and have compression under 8 if inclined. I'll prob just toss a P90 on my F54 flat top with a felpro and head studs and call it a day, under 9:1 is fine. Anyway back on task I thought the comp for a 620 L20b was like 8.3-8.5 ish? Thats good for boost imho, too low and you loose engine responsiveness. Quote Link to comment
Boxcar Posted January 9, 2014 Author Report Share Posted January 9, 2014 Thanks for the response guys. Had the flue so was slow in getting back to this. Thanks for the tech. Like I sed , just starting to think about this build. Sounds like fun to me though. 1 concern that I would have with using a carburetor and supercharger, with a stock type distributer system would be cap crossfire... Out having a fun day splashing through puddles... little moisture in the cap, and... Ka-boom… Intake explosion/fire in the carb. A turbo can shrug this off, somewhat, as long as the fire goes out. Positive displacement superchargers, not so well. My L-18 turbo ran a .020 plug gap to avoid crossfire.How much power are to looking to achieve I'm looking for the high 100's. to low 200's And will be building a large cap dizzy using Ford components. If I decide to go this route. Quote Link to comment
620Turbo4X4 Posted January 10, 2014 Report Share Posted January 10, 2014 Sounds like fun to me too… You've got me looking for a supercharger for my truck now that I nearly have my cutdown 280z efi manifold done.. Have you came up with a pulley/drive belt, supercharger combination yet? I found BHJ Dynamics sells 8 rib serpentine pulleys for 240-280z's.. Wonder if it could be used on the L20b? Why not go fuel injection? More complicated to initially install, but, is well worth it in power and reliability... A used Electromotive TEC 2 runs about $200-250 on ebay… With That, you won't even need a distributer. You can either cut down the oil pump shaft and plug the hole, or if you spend the extra for a TEC 3 system, use it for a cam sensor for sequential injection. I used a modified ford ranger cam sensor for mine. My turbo L18 Pickup even with 17lbs. boost was probably around 140hp at best.. Modern day fuel injection and intercooler could have added another 40 - 50? That's really pushing stock pistons to the max and beyond!!! Quote Link to comment
Boxcar Posted January 13, 2014 Author Report Share Posted January 13, 2014 Not going to run stock pistons. I have several sets of forged after market pistons and H-beam rods on the shelf. Some times being an older builder has it's advantages. I tend to hord cool shit. The news: Picked up a rebuilt Camden 9" supercharger from a Toyota 20 R , $75 from a buddy. It's not what I origanaly wanted, But can't beat the price. I'll post pics as soon as I get it in the shop. So it begins: I will probably machine my pulleys in house and run a cog belt. Still in the planing stages , so I haven't ruled out EFI yet. But I am leaning toward the carb set up. I'm a big fan of simplicity on the trail. Quote Link to comment
Z-train Posted January 13, 2014 Report Share Posted January 13, 2014 ANy carb but a Holley...... Quote Link to comment
EricJB Posted January 13, 2014 Report Share Posted January 13, 2014 I race with the guy who sells those blowers. He also makes all the pulleys and brackets, or complete kits for them. www.Atkinsrotary.com Quote Link to comment
Boxcar Posted January 14, 2014 Author Report Share Posted January 14, 2014 The 5150 is just a Weber converted to run Holly jets. Makes jetting very simple. I race with the guy who sells those blowers. He also makes all the pulleys and brackets, or complete kits for them. www.Atkinsrotary.com Thanks for the link, I'll look into it...... :thumbup: Quote Link to comment
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