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Old 06-20-2012, 09:52 PM
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LT1 build sugestions.

Well the times come to finally replace the Camaro's engine (not by choice). Last motor had a rod hanging out the side of the block snapped in half (H beam 4340) and a snapped crank and only 200 miles after Chevrolet did a valve adjustment to it. Long story short I'm a little ticked and just moving on, not wanting to go as extreme as the last build to maintain a little bit better street manners.

Goals for this build is 475 RWHP

Looking at the following for a new combo. Please keep in mind that the LT1 is reversed cooled and allows a lot more compression then traditional SBCs, Last engine was running 13.4:1 and a 292 cam on 93 octane pump gas.



LT1

383 forged stroker kit, 12.42:1 compression
230/236 @ .050 cam, 280/288 total duration, .652/.646 lift (hydraulic)
AFR 227cfm heads 2.100/1.600 valves (re-useable after 900 worth of parts (valves, guides, ect... )

Anyone see any issues (see above not on compression ratio)?

This is going into a street car (not daily driver but sees alot of street time). I run a T-56 transmission and 4.11 gears in a 9 inch rear end.

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Last edited by Eric63M; 06-20-2012 at 09:53 PM. Reason: Corrected Spelling
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Old 06-20-2012, 10:04 PM
How fast is fast enough?
 
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You better have damn good lifters pushrods springs and rockers for that lift. I'm guessing high ratio shaft mounts?

I know you don't want to hear it but dropping a point of compression would allow you more power on pump gas. What intake and ignition are you using? I presume this is a 4 bolt block? The heads and cubes will support that power the cam may be a hair low on duration. For 475whp you're looking at about 550fwhp, which is doable but not easy.

Btw the lt1 cooling system is not magic and your example engine put a rod through the block... I would seriously drop that compression down to about 11:1.
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Old 06-20-2012, 10:16 PM
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Quote:
Originally Posted by ap72
You better have damn good lifters pushrods springs and rockers for that lift. I'm guessing high ratio shaft mounts?
You're correct about the rockers running 1.7:1 roller rockers shaft mounted with girdle (old engines parts), and new push-rods. I replaced the valve springs with double springs, upgrading to the recommended lifter from comp (already contacted them about the rockers used).

Block is splayed 4 bolt (center 3) 2 bolt outer.

As far as the compression I know dropping back a bit more would be ideal, but a friend has the 383 kit unused and willing to sell for cheap. Makes it a bit easier to go back to high compression.

The compression wasn't the result of the failure (last motor lasted 71kmiles). Valve lash was improperly set and resulted in a nasty piston kiss. Already looked through the data log for the last 30 seconds before failure. there was no knock detected until it was to late (detecting the motor failure when oil press. hit zero and motor locked up)
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Old 06-20-2012, 11:17 PM
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lt1

Ive never seen 1.7 shaft rockers with a girdle? sounds interesting.Good luck with that combination. my engine uses shaft rockers without a girdle and its works great.Hope the camshaft is a premium billet?let us know how it works
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Old 06-21-2012, 06:29 AM
How fast is fast enough?
 
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I've never seen any shat mount rockers with a girdle. There's no point in running a girdle with shat rockers. Are you sure they're shaft mount? New pushrods and good pushrods are 2 different things, you can buy new crappy pushrods from a lot of places.

I don't understand how adjusting the lash caused your engine failure, especially if it was a hyd roller cam like this one. I don't understand why a chevy dealer was adjusting lash on your engine to begin with- since it was all aftermarket.
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Old 06-21-2012, 07:04 AM
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AP72 - fixed second post, not sure why i put shaft mounted... meant stud mounted.

Road Trip when the engine started ticking, took it there because it was all there was in the town. As far as how the lash caused the failure, not fully sure. I think they had too much pre-load on the lifters and when they pumped up the damage was done (passing a car on the highway when the motor gave). My machine shop can't find any reason for the engine to have failed the way it did, bearings were good, the rest of the rods inspected and other crank journals checked everything passed in their eyes.

As far as the push-rods, I'm running hardened chromoly. already learned the hard way about using "inferrior" push-rods in a LT1
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Old 06-21-2012, 07:20 AM
How fast is fast enough?
 
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Quote:
Originally Posted by Eric63M
AP72 - fixed second post, not sure why i put shaft mounted... meant stud mounted.

Road Trip when the engine started ticking, took it there because it was all there was in the town. As far as how the lash caused the failure, not fully sure. I think they had too much pre-load on the lifters and when they pumped up the damage was done (passing a car on the highway when the motor gave). My machine shop can't find any reason for the engine to have failed the way it did, bearings were good, the rest of the rods inspected and other crank journals checked everything passed in their eyes.

As far as the push-rods, I'm running hardened chromoly. already learned the hard way about using "inferrior" push-rods in a LT1
I'm hoping you have 3/8" pushrods? 5/16 chromoly pushrods won't cut it with that lift and required spring pressure. Do those 227 heads require offset rockers? I seem to remember they do but I could be wrong. Your lash shouldn't change on a hydraulic roller cam, indicating you had much bigger problems and the dealership was not at fault. How did the piston look on the bad cylinder? I wouldn't be surprised if you blew the ring lands- id kind of expect it.

I know your buddy is getting you a deal but if it were me id pay a little more to do it right this time instead of doing it all a third time...
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Old 06-23-2012, 06:21 AM
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Not sure how you want to run stud rockers on AFR 227 heads on the street. They don't recommend that at all. AFR 227 heads have 60/40 valve spacing which makes the intake valve slightly offset. You have to run special rockers on the intake side with the pushrod cups offset. Over time the rocker will want to spin off axis. That's fine for a drag engine that will have the valve covers off every week, but not on a street engine that is going to be run for 30+ minutes at a time. I run those heads along with Jesel shaft rockers. Here's a sample pic (not mine) of Jesel rockers on a 227 head with the PROPER offset on the intake:



Right from AFR's website:

Quote:
Requires shaft mount rockers or .050 offset rocker arms for durability and reliability of valve train components. With the .050 offset the intake rocker arm will be at a slight angle and the roller tip will not be perfectly parallel or centered on the valve tip. Not recommended for street use, unless shaft mount rocker is used
That cam is all wrong too. That is a lot of lift for the duration which means the lobe is going to be pretty aggressive. Aggressive= hard on parts. To feed 383 cubes with a big cylinder head like that you'll want something MINIMUM of 24x/24x duration. The Comp XFI 468 cam comes to mind, 242/248 .584/.579". Keep in mind that the factory pcm has a 7k rpm cap on it. You simply can't rev it any higher. You would want to run a single plane style intake on it as well, which means you'll need a custom one built for your engine. Try Advanced Induction and see if they have any laying around for sale.
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Old 06-23-2012, 06:37 AM
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There's nothing about this thread that makes sense to me.

OP, you list all these parts and combos but you say the engine failed because a DEALER adjusted the valve lash? Why didn't you do it?

Secondly, why are you building a high strung 383 when a rather mild big block will get you to your power goals?
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Old 06-23-2012, 11:46 AM
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Quote:
Originally Posted by cool rockin daddy
There's nothing about this thread that makes sense to me.

OP, you list all these parts and combos but you say the engine failed because a DEALER adjusted the valve lash? Why didn't you do it?

Secondly, why are you building a high strung 383 when a rather mild big block will get you to your power goals?
I'm going to say he's probably building a 4th gen Camaro that came with an LT1. Big-blocks don't fit without a TON of fabrication.
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