LT1 Crank Strength

[HighMileage]

How much power have any of you guys thrown at an LT1 crank with success? Rods are eagle SIR with forged blower pistons. Crank is stock nodular iron cast. Should be good to at least 500 at the crank, I have heard upto 550 - 600. Want to know any real world experience. Plan is to either step up boost to 12 pounds or leave it near 8-9 pounds and do the heads and cam. I think either path gets me close to 600 at the crank, 500RWHP. My setup is crank limited, so there is a place I have to stop. I see the C5 guys making sick power on stock bottom ends in the 600+ ranges.

[mnstrlt1]

I've also heard about 600... I've heard that certain heat-treating and shod-pin methods can strengthen the existing crank. I am assuming these methods have not been employeed?

Why did you leave the crank stock on a blower application when you had the engine assembly apart? I mean, you did the pistons and rods, what made you leave the stock crank in the build?

What's your setup anyway?

I would leave the boost at 8-9psi and go with the top end build. With work wonders for you in the future. More boost = more stress (IMO).

[BrianCunningham]

I went forged, but I plan on road racing my car.

You should be OK

[HighMileage]

Originally Posted by mnstrlt1

I've also heard about 600... I've heard that certain heat-treating and shod-pin methods can strengthen the existing crank. I am assuming these methods have not been employeed?

Why did you leave the crank stock on a blower application when you had the engine assembly apart? I mean, you did the pistons and rods, what made you leave the stock crank in the build?

What's your setup anyway?

I would leave the boost at 8-9psi and go with the top end build. With work wonders for you in the future. More boost = more stress (IMO).

Actually, I am not the original owner. I bought the car with the work done and a pile of receipts. Seems he had more money than brains. I talked to the shop that did the work and he cracked 6 pistons on stock shortblock by leaning it out. SO, he spent 5K getting bottom done.

They did some strange things I would have done differently:
1. As you noticed, they did everything bu the crank. For another $500 it could have been a forged 383. Left at least 30HP on the table

2. Put a new LT4 cam in to replace the LT1 cam. With a 1.5 rocker, its actually milder than the LT1 cam. The LT4 gets more thift through the stock 1.6RR.

3. Did not key the balancer.

Total setup is Forged lower end (except crank as noted), stock heads, LT4 cam. ATI procharger pushing 7 to 7.5 pounds - no detectable belt slip either via dust or erratic boost readings.

So I need to figure ourt how far to go with it. I am not in a hurry to tear down and replace bottom end. So I have two paths:

1. New brackets and smaller pulleys and go to 12 pounds. May be do rocker arms and throttle body

2. Keep existing boost and do heads, cam, rockers, and throttle body.

Believe it or not the costs will be similar and the power levels look to be similar based on my calculations.

Doing the braket and pulleys is simple bolt on and easy to get going.

Heads and cam really may be better, less heat, less chance of detonation, but need to tear into whole engine, pull a recently done bottom and start over.

What is your setup like?

[yzfr1mike]

Hi - I have done a similar job, but with AFR 190cc heads and a comp cam with a 114 LSA and 220/230 Deg. at 0.050. This cam is set up at 0 degrees and has 0.544 lift with 1.6 rockers.

My car made 496 rear wheel after the dyno tune and with an auto trans. I haven't had any trouble in 20,000 miles driving. (Except for frequent belt replacements)

This would be about 650 crank HP, allowing 30 HP for the blower. I don't know what they absorb as far as HP goes, so 30 HP is a "swag"

Bottom line, I think I would run it and enjoy!

Mike

[HighMileage]

Originally Posted by yzfr1mike

Hi - I have done a similar job, but with AFR 190cc heads and a comp cam with a 114 LSA and 220/230 Deg. at 0.050. This cam is set up at 0 degrees and has 0.544 lift with 1.6 rockers.

My car made 496 rear wheel after the dyno tune and with an auto trans. I haven't had any trouble in 20,000 miles driving. (Except for frequent belt replacements)

This would be about 650 crank HP, allowing 30 HP for the blower. I don't know what they absorb as far as HP goes, so 30 HP is a "swag"

Bottom line, I think I would run it and enjoy!

Mike

Mike,
So are you using stock nodular cast crank?

How do you like that 305 cam? I have been considering upgrading to the 304 or 305 but wonder how the 305 plays with stock heads?

Did you ever run boost without the headwork? The AFR heads are nice pieces. Its good to know that heads and good cam can take m into that kind of power level. What is your boost level?

[mnstrlt1]

Well, if you bought it that way that the rule of thumb is to mod it until it blows up! lol... then build bigger/better.

[HighMileage]

Originally Posted by mnstrlt1

Well, if you bought it that way that the rule of thumb is to mod it until it blows up! lol... then build bigger/better.

MnstrLT1,
Would love to build bigger and better, but would prefer to do it down the road. So I am trying to figure out a good reliable level and run it to that point. I have put close or over 200K miles on 3 different C4's:
1986 - 215K
1990 - 190K
1992 - 170K (Not one oil leak, no oil usage - is still going!)

Would like to get a good solid boosted car with 500-600 CHP to run over a 100K.

Hope that doen't sound funny!