HOT/A377

Can you use the "baby" LT! crank in a normal small block?

thanks

Vader

Other than the fact that it uses a different style balancer, it fits into a "regular" SBC like any other crankshaft.

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Later,
Vader
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GMTech

Your "baby" LT1 is called a "L99".

Dimensionally, they are almost the same. The difference is the stroke. The LT1 has a 3.480" stroke, and the L99 has a 3.00" stroke.

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[This message has been edited by GMTech (edited July 29, 2001).]

Vader

BCT,

You are correct. The L99 (VIN code "W") engine is a 265 CID version of the LT1 350 that has the same 3.48" stroke and a smaller 3.74" bore. Since the head chamber volumes are the same, it has a static compression ratio or just under 10:1 (9.93:1 to be exact) compared to the 10.3:1 ratio of the LT1. Main and connecting rod journals and con rods are identical for both crankshafts/engines. Cylinder heads and valves are the same on both engines, and the cast iron L99 heads actually outflow the cast aluminum heads on LT1 engines produced in 1992 and 1993, and are equal in flow to all but the 1996-later aluminum heads that had improved porting.

The L99 engines typically have a lower lift cam than the ir 350 inch counterparts to match more closely with the smaller bore.

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Vader
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GMTech

Not to be a geek, but the L99 has a 3.00" bore, not 3.48" and I think the LT1 compression is 10.4:1, not 10.3:1. I have a access to every measurement you could think of for just about any GM engine (gotta love the "net".) GM also reccomends that you torque the oil filter to 20 NM (yeah right)

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MRZ28HO

Both of you are right and wrong. The LT1 has a 4.00" bore with a 3.48" stroke yeilding 10.4:1 compression ratio by means of the 58cc combustion chambered heads. The L99 (baby LT1) has a 3.74" bore (same as the 305, but rounded up) and a 3.00" stroke. The bearings will interchange from both, but the rods on the LT1 are standard length 5.7" rods, while the L99 are 5.94" length rods. The difference comes from the fact that GM used the pistons (or left over stock) from the 305, but with a .24" shorter crank throw crankshaft. Hence why the rods are .24" longer than conventional SBC rods. You can make a "new" 1-piece 302 using the L99 crank in the LT1 assembly, but the crank will not (ever) with stand the high rpm use of the early forged 302 of the 2-piece design. The L99 is an economy cast crank. basically, you'll have a retro 302 using new technology, but it will be a dog since you wouldn't be able to drive it agressively.

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GMTech

I goofed, I said 3.00" bore and I meant stroke. Other than that, everything I said was correct.

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aquila

Is the L99 crank really weaker than theLT1 crank?

ATOMonkey

WOW! I can smell a budget 302 in the making! I don't suppose there are any aftermarket forged 4.3 cranks? That's been an idea of mine for about 2 years now. I want a long rod 302 TT that just screams. I want to show up with a V8 turning 10 grand, S2000 eat your heart out
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[This message has been edited by ATOMonkey (edited July 30, 2001).]

Chronos_Titan

What are the technicalities of this swap? What about the distributor drive? The water pump? Aren't the cranks different for the LT1 to a pre86? What about balancing? Is the LT1 completely internally balanced?

MRZ28HO

I know, I was just messing with you and Vader.

As far as aftermarket 4.3 forged cranks, nope. Unless you can afford to pay $2000+ for a custom one. The OEM 4.3 will never live to see 10K rpms, let alone under a twin turbo setup. The 4.3L (L99) crank is a direct swap into any 1-piece rear main seal block. You don't have to worry about direct drive or water pump, that's a camshaft issue, not related to the crank. All 1-piece rear main seal engines (L98, late LB9, LT1, LT4) are balanced the same, "externally" unlike a 400.

camaro6spd

humm, if you set up a 4.3 V6 and V8in the same manner what would the outcome the of the motors be? who has more power were?

zippy

that crank in stock form will handle 7k without a problem. as for the guy that would like to turn 10k, it's obvious you aren't an engine builder. running 10k doesn't happen just because you have a short stroke engine. at that point you've spent way more on valvetrain than that short stroke worthless engine will make. just because it rev's don't make it fast. the 302 was only made to pass the 305 cubic inch rule for the trans am series or gm would have never wasted their time on it.

aquila

My 305 already has more power than traction and I like the mustang guys not being able to whine about being stuck with only 302's(poor babies), they think only 350's and 383's can chew them up. I'm going to build a 302 chebbie and eat them up again.

GMTech

Why don't you just put a 350 in, and tell them is a 305. Most of the Mudstain guys lie about what they got anyhow, so why don't you beat them at there own game?

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'87 Trans Am
S/D TPI retrofit including functional PassKey,
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Whatever chip I feel like burning,
JET AFPR, Ported Plenum,
TB Coolant Bypass, Custom Cold Air,
SSM SFC, KYB Shocks, Boxed LCAs, Wonder Bar,
8mm Accel wires,
Flowmaster Exhaust,
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Summit 1-5/8" headers, 2.5" Dynomax catback.

Best 1/8: 9.519@72.74

'97 Bonneville SSE

steve8586iroc

I wish I still had the magizine article that had the 97 302 LT1 vs 69 302. It was GM exercise similar to the 302 LS1 version that GM did recently. From what I remember it had some pretty good performance numbers for a 302. Just mt .02

Steve

ATOMonkey

Oh I forgot that everyone is supposed to run exactly 350 ci and not be original. Sorry I'll try and get it right next time....

Vader

We need messing with once in a while. Since the data in the manual I checked (1996 Chilton's) says 3.48" stroke, I passed that along. In thinking about it, I see there is no way that bore could have a 3.48" stroke and net 256 cubes. (Doh!)

I've never opened a L99, since, IMHO, they should be left where they are found - either running in their respective cars or in the bone yard. Then again, I prefer the 4.16" crank with 4.316 pistons to a smaller, "high" revving engine anyway. Little engines are great for lawnmowers and import rockets, but not for true all-out performance.

I guess that's why I haven't seen many 3.0L Nissan twin turbos in Kenworths and Western Stars lately. The 3506 Cat diesels only make 300HP as well, so you figure out why I like more cubes. I also can't recall the last time I saw a five-second Nissan or Honda, regardless of how high the cliff is...

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ATOMonkey

Hey, it's not the size of your engine that matters. It's how you rev it, and what you have blowing it!


[This message has been edited by ATOMonkey (edited July 31, 2001).]

Ed Maher

You know what's funny....this is soo true. My budy's little brother had a screaming LX for a while then he got sick of breaking things and sold it. It ran low 12s off teh bottle, i don't think he ever made a strip pass on the 150 shot. Anyhow, i had always heard how it was stock based, only had TFS heads, intake, cam, etc. Well, found out a few months later that was the plan, but a built 347 shortblock somehow ended up in there instead. Sneaky bastard.

aquila

Does anyone realize you can put a 6.250 rod in with a 3.00 stoke crank. That will allow for more compression and make alot more torque than you would expect from a 302. It would even get decent mpg. I don't need 380+ hp, I drive this thing to work every day. Besides if what I have now ever gets a good bite on the road I'll have pieces of T-5 all over the road.

keithnh

Does anyone here know the metallurgy on the baby LT1 crank? I would ASSUME that it is most likely the same as a stock 350 crank. Why have 2 different raw materials? I would like to know exactly what material it is and havent found that information. Also, does anyone have experience with nitriding a factory crank as far as what it actually accomplishes in longevity, rpm limit improvement etc.? I believe I read the back in the day 302s used both main and rod journal variations as well as "tuff-coated" cast cranks and forged cranks. I dont believe they had crank issues with either. My 302 project is inching forward with a possible next step ion-nitriding the Autozone factory reman crank I bought. The machine shop looked it over, improved the oil passages and told me "it'll take whatever you put to it". It's not nitrided yet either. They're not enthusiastic about a 302 or maybe dont believe Ill ever finish it. I dont care its my dream, its going to happen and any motor I put together the crank will get some extra gravy on. I'll still wrap up under 400$ for a nitrided crank ready to go.

Not sure why you think a different rod length will raise compression or improve torque noticeably. The piston starts and stops at the same spot regardless of rod length combo although the speed between the 2 points varies. Nominal deck height 9.025 - 6.250 -(3.0/2) means a piston with a compression height of 1.275 . Not much room for rings with only .786 above the pin . Im running a 6.0 rod and 350 piston that will need to be shaved up to .035 to get a zero deck. It will still have over 1.0" above the pin.

302(311+.060) becomes 604 with 14.7 pounds of boost ... with a R/S of 2.0 to 1 and B/S of 1.35 to 1 . I dont know if those specs actually mean much. Hopefully I'll find out.

Vader

The LT1 and L99 cranks were cast nodular iron.

Rod length would not affect the static compression of the assembly, but could affect the dynamic compression, depending upon valve timing.

Further, rod length will affect dwell time at the ends of stroke slightly, potentially increasing effective cylinder pressure and resultant torque production. Longer rods also tend to reduce side thrust on pistons, potentially lowering the internal drag of the assembly.

keithnh

Did some searching and found the baby LT1 crank is considered to be a standard crankshaft made from the same materials as the 350. It is not a cheap or economy crank made from lesser materials or with any lesser process. I dont know whether LT is the moniker for "Light truck" and that indicates a heavier duty part ... but the LT1 series was supposed to be a change for higher performance and better fuel economy which was acheived with LT1 parts. Nodular iron lends itself well to nitriding I believe, which I visualize like the skin on a hotdog. Providing a slightly harder barrier and helping retain original shape under stress. Worth doing on a crank I want to pound on a bit. I just dont know how far it actually gets you.
Longer rod stays at the top longer and is more prone to detonation and the lesser rod deflection would also move the pin pivot point higher so skirt side loading especially on the bottom would be a toss-up if not going the other way. I know I was comfy having a combo that uses a standard 350 piston (shaved a little). Increasing dynamic compression seems like would be a minor miracle if timing actually matched for that to occur. People argue alot about about rod length, I believe a longer rod moves slower and pushes down straighter. I dont know how many horses that equates to tho.

InfernalVortex

iTrader: (4)

LT1 was a production code that got latched onto for marketing purposes. Much like the LS1 engines. They say "LS1 brakes" or "LS engine" and so forth. Just a production code that became an easy identifier. LS became an easy identifier for Gen III+ small block chevys and LT became an easy identifier for Gen II small block chevies. Trucks never got an LT anything.

If a 302 is good then a 283 is even better. Why stop at 302? I mean if you really want to be fast, build a 265!

This is from a published article by David Reher of Reher Morrison racing engines, and he is clearly way smarter than I am, so here's what he said about it:

This is a pretty interesting read, also.

http://www.rustpuppy.org/rodstudy.htm

keithnh

I believe I can make a 302(311) exhibit enough low end torque in the hole its going in to keep me happy even being a novice and putting together my first non-standard motor. Its pretty straight-forward really and not that expensive. Thats as low as I want to go right now. Was just reading an article in the current "Super Chevy" entitled "LS Slugfest" in which the 4.8 and 5.3 LS motors were compared stock and similiarly modified and both neared 500HP and 400ft-lbs with the peaks slightly higher on the lower displacement motor. I will be modifying my motor similarly and expect same ballpark results. Ive heard people say you cant compare LS to Gen 1 or II sbc as there is no similiarity. To me that sounds like nonsense. Displacement is displacement, a V8 is a V8. Newer motors are light with better heads cam and electronics but not that different. I did a chart showing actual air displacement and find that my 311 @7000 rpm displaces an equivalent amount of air as a 400 @5500 and more than a 350 @6000rpm. That is most likely the real crux of the biscuit with most engines, the efficiency of the various parts adds and subtracts small percentages with fuels held constant. Then a matter of keeping it together.

Doesnt make sense to me that differences in rod length would make no difference at all in the "adds and subtracts" as they mean measureable differences in piston speed which should affect head flow and chamber efficiency which I believe is a very delicate balance and perhaps more important than the other effects. The greater angle the shorter one travels must make some difference ... Im no racing engine builder. Different rod lengths probably weigh differently. I dont think there is any dispute that affects engine rpm capability. I guess try and see

InfernalVortex

iTrader: (4)

Your volumetric efficiency will be NOWHERE NEAR what those motors do. The Gen III heads are 18 degree heads vs Gen I 23 degree heads. The port design is different. The exhaust design is different. Literally the only the similarity is bore spacing. Just looking at LS head ports will show you the difference. Factory LS heads flow as much as $1500 aftermarket Gen I heads. To make a 302 make that much low end torque you will need to use a pretty small cam and VERY nice cylinder heads.

Cubic inches is cubic inches is a terrible argument. Displacement is nothing, airflow is everything.

keithnh

Well my heads are fastburns 12464298 with matched GMPP RPM dual plane. The cam I have my sights on is a CC 268 Magnum solid roller, .525 lift just below where the fastburns flat line according to the flow diagrams Ive seen. Top shelf heads I believe ... I will be reducing the chamber volume for the 302(311) to approx 52cc to get a static CR of about 10.75 with coated flat-top pistons. Things that will help this ratio be runable on pump gas are aluminum heads, shorter stroke, the ramps on the cam according to the CC rep, the coating on the piston tops ala Rousch/Yates and some detailing to remove any sharp edges in the chamber area. The heads and intake will become a 302 only set I think because for a match I will have to angle mill ... Im not really sure how that works. I'd like to keep it so I can go back to 350 if I desire but 52cc chambers will be a little tight I think.

I know there are alot of enhancements on LS motors I was thinking they might have 4 valve heads but it doesnt look like it in the Super Chevy ads for LS cams ... they have 16 lobes in the picture ... unless there are 2 cams in an LS ???? That Super Chevy mag did a comparison some time ago 302 vs 327 vs 350 Ill have to find it again and compare the LS numbers.
Not sure I agree displacement is nothing ... it is what is creating the airflow. A certain displacement will need a certain amount of airflow ... larger displacements will need more to populate the cylinder ... when they have to struggle to get it, I think, is where rpm starts to choke. This may be a limiting factor on fastburns as I see they dont increase in flow above .540 or .550 lift. Under that they are one of the highest flowing Chevy heads I believe. I was figuring cam just under that and enjoy. But when the rpm starts climbing there will be a point where that no more flow is hit even with a .525 lift. Im not sure where that will be .... I would think not before 8000 but I could be wrong. It would be lower with a higher displacement motor I think. Was think last night of expanding my displacement vs RPM chart to include air flow requirement in CFM through the head in a way that is comparable to results when heads are flowed. I think a basic ballpark will be straightforward ... will work on it.

ASE doc

I have to say something here. Having built motors with cast cranks before, I am concerned when I hear 8,000 rpm and nodular crank mentioned in the same context. First of all, what keeps a crank shaft alive at high revs is not rigidity. Nitriding a shaft increases rigidity and hardens the surface against wear. It will increase the base torque handling capacity but once that line is crossed, the nitrided shaft will actual shear or crack sooner due to the same rigidity. At even 6,000rpm, there is no way you are going to keep a crankshaft rigid. Consider the reason for the harmonic balancer. It's necessary because the crankshaft is twisting and flexing under quickly changing torque loads as the cylinders compress and fire. Therefore, a harmonic balancer is needed to absorb the constantly changing harmonics that this twisting and flexing produces.

The reason a forged steel crankshaft stands up better at high revs is not because it's harder but because it takes rapid flexation and extreme force better. The forged material, especially a material like Chrome Moly steel alloy, has a grain structure that accepts the flexing and high torque loads and can handle the high rate twisting and flexing without cracking. I'm afraid that if you you try to run that cast crank anywhere near 8,000rpm, especially nitrided, you will find out why forged cranks are the standard in high rev applications.

I personally salute your efforts at building a high revving, short stroke, big bore, long rod motor. However, rather than throw good money into a crank shaft that is completely wrong for your intended purpose, contact a machinist with the capability to turn and balance a crankshaft and talk to them about setting up a 3.00" stroke steel crank that will fit your block. If you really plan on pushing 8,000, I would strongly suggest a 4130 Chrome Moly forging with 1/8" fillets on the rod journals.

EDIT: Sorry, I was thinking of a different alloy. The crankshaft alloy I was thinking of is 4340.

keithnh

My real thought was to set up the 302(311) to be capable of using an rpm the same % higher than the displacement is lower than a 350(355)... 12% ... and that 6500 was about where a stock 350 redlines. So about 7200 with a little safety margin to 7500. My mention of 8000 was in reference to the fastburn heads choking with the smaller displacement. I wasnt really thinking of using the motor in that region. I was being optimistic about the heads most likely. I know I will most likely be in for some doses of reality here ... wasn't thinking of nitriding being a negative for high rpm ... dont think Ive ever heard that before. I do know it is only so deep and doesnt change the metallurgy of the crank below that depth. It makes the surface much harder so it cant be scored as easily I would think it would improve rigidity and make it harder for a crack to start because of that but then if it interfered with the irons ability to flex and flex back it might truly be a negative. I have a nitride guy ... who does mostly airplane cranks in Lowell MA, I will talk that over with him. I am using this chevy motor as a precursor to several ponchos I intend to build and steel cranks for them are few and far between ... I dont like the idea of buying a Chinese one. I think I can get the performance and reliability I need with iron cranks and need to test the waters a bit. This 3" crank I have has larger mains/rods than the original and smaller stroke than a 350. I may let the roush/yates guy push me into selling my Mahle no frills pistons and going up to a set of Power-packs that are about 110 grams lighter figuring a slightly smaller weight might help rev and be less of a crank burden. When balanced I believe the weight reduction is matched in the counterweight for 220 gms per piston ... 4 lbs less in rotating assy. Not sure yet on that.

1gary

I cringe everytime a poster "tries" to use "comic book" test results and make it worse compare one against the other.

The real street advise is here from selected members.A good guy forging crank is going to cost ya.$$$$$$$$$$$$$$$$$

keithnh

Not sure exactly what you're trying to say but if you had some information to share other than derogatory comments it might be helpful. Dyno results and testing in Super Chevy is bunk? And you know better ??? You know not everybody is interested in just copying someone else or making decisions based solely on a forum conversation or a magazine article for that matter. Or buying alot of fancy parts just to say they bought them or because somebody else did. I am not building a car for drag racing although I might test it a few times ... its gonna be a worker bee with license plates that will get whipped every once in awhile when I "feel the need for speed." SBC has alot of nice parts for reasonable cost with varying levels of performance and reliability available. I believe alot more high compression high performance engines came off the assy lines with nitrided cast cranks than forged back in the day ... maybe cost was a factor I dont know. I had heard that when a forged crank goes it breaks and causes more catastrophic damage than an iron one that just bends. Early 60's Pontiac racers claimed the nodular iron cranks were more resilient than 1140 forged steel cranks. I have a 67 Arma-steel (nitrided iron) 428 poncho in my basement right now ... 46 years old and straight as an arrow. I have machinist friends and acquaintances who have been my friends for many years who can do whatever I need done to a crank steel or iron thank you. Honestly I havent heard or seen of many crank failures and have never had one myself except the 455 crank I bought cheap on Ebay that was bent not cracked and one rod journal was trashed. To be honest my experience is mainly Pontiac street stuff not race (although Ive enduro'd 2 poncho 400's and not lost them) I had heard cast chevy cranks bend easier than ponchos. Mainly at the rod journal fillet which can be helped with the right grinding wheel contour. My next motor planned is a destroked, indexed and fillet manicured 350 Pontiac, with an iron crank I will also have nitrided and fitted with BME 500 rods and possibly chevy pistons. Maybe the first to repower my 64 GTO convertible thats been sitting too long. I have to finish one at a time tho. I come to forums to share ideas and get alot of enjoyment out of them and do learn alot. I dont claim to be Joey expert on anything but if I have an opinion your likely to hear it I dont have alot of time in between work shifts tho so sayonara for now.