[DFW1LE]

How much boost does the ZL1's LT4 make in stock trim? Given that the LT4 has 10:1 compression while the LT1 is at 11.5:1, how much boost can be run on a supercharged LT1 to maintain the same margin of safety that you would have on the LT4 given its lower compression? I would assume that you would need to run a lower boost level on a FI LT1 to maintain that margin of safety as designed by GM for the LT4.

[ADM PERFORMANCE]

Originally Posted by DFW1LE

How much boost does the ZL1's LT4 make in stock trim? Given that the LT4 has 10:1 compression while the LT1 is at 11.5:1, how much boost can be run on a supercharged LT1 to maintain the same margin of safety that you would have on the LT4 given its lower compression? I would assume that you would need to run a lower boost level on a FI LT1 to maintain that margin of safety as designed by GM for the LT4.

We run 8-9 on our cars when using lt4 supercharger. Fueling is a bigger issue.

We have 2.6" pulleys for stock cars , 2.38" for our cammed,header,lt4 fuel system cars

[DFW1LE]

Originally Posted by ADM PERFORMANCE

We run 8-9 on our cars when using lt4 supercharger. Fueling is a bigger issue.

We have 2.6" pulleys for stock cars , 2.38" for our cammed,header,lt4 fuel system cars

Thanks for the reply, so can I assume a stock LT4 is ~ 8 psi. If you add your LT4 SC to a stock LT1 is it reasonable to expect equivalent engine longevity vs stock LT4 engine at that boost level.

I am contemplating some mods within the next 12 months and trying to decide between SC vs heads/cam/headers, so starting my homework now. I do not have much knowledge when it comes to SCers. I like what you have done with the LT4 SC parts, but also wonder would I be better off with a Heartbeat. My car use is just enjoying some added power on the street, while doing some track days down at MSR, no plans to run at ennis.

[jessrayo]

Originally Posted by DFW1LE

Thanks for the reply, so can I assume a stock LT4 is ~ 8 psi. If you add your LT4 SC to a stock LT1 is it reasonable to expect equivalent engine longevity vs stock LT4 engine at that boost level.

I am contemplating some mods within the next 12 months and trying to decide between SC vs heads/cam/headers, so starting my homework now. I do not have much knowledge when it comes to SCers. I like what you have done with the LT4 SC parts, but also wonder would I be better off with a Heartbeat. My car use is just enjoying some added power on the street, while doing some track days down at MSR, no plans to run at ennis.

There is a lot more difference between the LT4 and the LT1 than the piston size and corresponding compression ratio. The LT4 has titanium rods and forged pistons, it was designed from the factory to handle 650 HP. The LT1 was designed to handle about 460 HP. So to ask if it will handle it about the same, no, the LT4 is a more robust engine, it can handle a lot more power than the LT1. Can the LT1 handle a supercharger, most generally yes. There is always a risk for failure and even though the quality and consistency of engine production has improved tremendously over the last few decades, occasionally an engine will fail. Really it has more to do with the consistency of the metals in the engine components than the engine design.

As far as stress on the engine, there is some debate between individuals on what I'm about to say but after running different superchargers on the same engine I would predict that the LT4 supercharger will have less stress on the engine than the Heartbeat because it runs a smaller supercharger with less mass. The smaller supercharger will generally require less power to spin it even though it must be turned faster. The smaller superchargers are generally taking less power to drive them and this has an overall reduced stress on the engine.

[DFW1LE]

Thanks for your comments jess. Yes, I realize there are other differences beside compression, but crank,rods, and piston materials aside, what I am trying to understand, is what is a safe boost level for a LT1 SC conversion considering the LT1s compression is higher. I had a 372 stroker motor in my C5 with a bullet proof bottom end, so I appreciate that, but it would be difficult to quantify the margin of safety for the other LT4 components vs the LT1. Certainly if I was planning on a lot of racing, I would upgrade the bottom end as well. Nevertheless, I thought considering the CR difference, that might be something that could be quantified to possibly reduce the boost to avoid excessive cylinder pressures.

[parish8]

The current consensus is the lt1 can handle 700rwhp safely if you have the right fuel and tune. For whatever reason some people/shops start breaking pistons above this level.

Durability has more to do with the fuel you are running and the tune.

[DFW1LE]

Originally Posted by parish8

The current consensus is the lt1 can handle 700rwhp safely if you have the right fuel and tune. For whatever reason some people/shops start breaking pistons above this level.

Durability has more to do with the fuel you are running and the tune.

Thats good to hear, after all, the LT1 does have forged crank and rods, but as I understand it, the LT4's crank and rods have a bit more machining which provides additional strength. ADM also noted the importance of fueling.

[ADM PERFORMANCE]

LT4 has Powder Metal Rods just like the LS1,LS2,LS3,LSA,LT1. LS7 AND LS9 have Titanium Rods and Intake valves.


LT4 TECH SPECS
Part Number:
19332621 or 19332702
Pistons (P/N right hand 12674094 and left hand 12674093):
Forged aluminum with internal ribs; flat-top crown
Engine Type:
Direct injection spark ignition Gen-V Small-Block V8
Displacement (cu. in.):
376 (6.2L)
Bore x Stroke (in.):
4.06 x 3.62 (103.25 x 92 mm)
Block (P/N 12619171):
Cast aluminum with 6-bolt nodular iron main bearing caps
Crankshaft:Forged steel
Connecting Rods:Powdered-metal steel
Camshaft Type (P/N 12642245): Hydraulic roller
Maximum Recommended rpm:6600
Camshaft Lift (in.): 200° intake / 212° exhaust
Valve Lift (in): .492 intake / .551 exhaust
Camshaft Duration (@.050 in.): 189° intake / 223° exhaust
Cylinder Heads (P/N 12646959):
A356-T6 rotocast aluminum
Valve Size (in.):2.13 intake / 1.59 exhaust
Compression Ratio:10.0:1

SOURCE - http://www.chevrolet.com/performance...gines/lt4.html

[SGDM]

Originally Posted by DFW1LE

How much boost does the ZL1's LT4 make in stock trim? Given that the LT4 has 10:1 compression while the LT1 is at 11.5:1, how much boost can be run on a supercharged LT1 to maintain the same margin of safety that you would have on the LT4 given its lower compression? I would assume that you would need to run a lower boost level on a FI LT1 to maintain that margin of safety as designed by GM for the LT4.

I run 20 pounds of boost...NOT. I would say 8-9 is safe on stock heads and 10-12 if ya open up the heads to reduce yer compression. I am running stock fuel with no issues thus far and plan to leave it that way, making over 600 with the little blower.

[DFW1LE]

Originally Posted by ADM PERFORMANCE

LT4 has Powder Metal Rods just like the LS1,LS2,LS3,LSA,LT1. LS7 AND LS9 have Titanium Rods and Intake valves.


LT4 TECH SPECS
Part Number:
19332621 or 19332702
Pistons (P/N right hand 12674094 and left hand 12674093):
Forged aluminum with internal ribs; flat-top crown
Engine Type:
Direct injection spark ignition Gen-V Small-Block V8
Displacement (cu. in.):
376 (6.2L)
Bore x Stroke (in.):
4.06 x 3.62 (103.25 x 92 mm)
Block (P/N 12619171):
Cast aluminum with 6-bolt nodular iron main bearing caps
Crankshaft:Forged steel
Connecting Rods:Powdered-metal steel
Camshaft Type (P/N 12642245): Hydraulic roller
Maximum Recommended rpm:6600
Camshaft Lift (in.): 200° intake / 212° exhaust
Valve Lift (in): .492 intake / .551 exhaust
Camshaft Duration (@.050 in.): 189° intake / 223° exhaust
Cylinder Heads (P/N 12646959):
A356-T6 rotocast aluminum
Valve Size (in.):2.13 intake / 1.59 exhaust
Compression Ratio:10.0:1

SOURCE - http://www.chevrolet.com/performance...gines/lt4.html

Its funny that GM does not use the same terminology in their engine descriptions. On the LT1, they state rods as being "forged powdered metal", yet above they just say powdered metal steel.

[DFW1LE]

Originally Posted by SGDM

I run 20 pounds of boost...NOT. I would say 8-9 is safe on stock heads and 10-12 if ya open up the heads to reduce yer compression. I am running stock fuel with no issues thus far and plan to leave it that way, making over 600 with the little blower.

Thats significant power if you are talking at the wheels. Not sure I need that much, but who knows whether I'd want more if I didn't have it. Here is what I am thinking at this point, any comments/suggestions would be appreciated:

Objective: achieve 500-525 HP at the wheels with a broad power curve, and doing that on a fully catted exhaust. Would prefer to run straight 93 vs E85. Want an engine that will provide good reliability (e.g. 75-100K) miles, although it will never see that much mileage.

Options:
1) IM/Heads/cam/LT
Concerns: do not want cam to cause emission or valve train problems, want good street drivability and broad power band. Can LTs be mated to the stock cats. The GM performance heads and cam might be a good way to go.

2) SC (and LT if it helps)
Concerns: do not want to create excessively high cylinder pressures given the 11.5 CR, will back pressure from a fully catted system cause problems, do not want to add too much weight to front of car and upset the cars balance on the race track.

Lastly, which of the above is the most cost effective way to go?

[jessrayo]

Originally Posted by DFW1LE

Thanks for your comments jess. Yes, I realize there are other differences beside compression, but crank,rods, and piston materials aside, what I am trying to understand, is what is a safe boost level for a LT1 SC conversion considering the LT1s compression is higher. I had a 372 stroker motor in my C5 with a bullet proof bottom end, so I appreciate that, but it would be difficult to quantify the margin of safety for the other LT4 components vs the LT1. Certainly if I was planning on a lot of racing, I would upgrade the bottom end as well. Nevertheless, I thought considering the CR difference, that might be something that could be quantified to possibly reduce the boost to avoid excessive cylinder pressures.

I could be wrong again here, as I was in the connecting rod metallurgy previously, but I just don't think the compression ratio corresponds to cylinder pressure as directly as the horsepower reading does. If you increase compression ratio you generally can get a little more power (and fuel efficiency) out of the same amount of fuel but if you add more fuel you get more power and cylinder pressure. Ultimately it is the horsepower that indicates how much pressure you have in the cylinder. I'm with parish8 in that people have found if you go over 700 HP you are risking trouble.

Boost is also in many ways not the best way to measure engine performance. In your last post you describe two alternative methods to gain horsepower. The first with intake, cam and head work, is completely designed to open up all of the air restrictions going into the engine so it can naturally get more air in. The second method is adding a supercharger which pumps air through the restricted passages. The end result is, however much air/fuel you can get into the engine is how much power you can make. The end result is if you make say 500 hp running 3 pounds of boost or if you make 500 hp with a cam that allows more airflow, you have roughly the same amount of air/fuel in the engine and roughly the same amount of cylinder pressure.

Originally Posted by ADM PERFORMANCE

LT4 has Powder Metal Rods just like the LS1,LS2,LS3,LSA,LT1. LS7 AND LS9 have Titanium Rods and Intake valves.


LT4 TECH SPECS
Part Number:
19332621 or 19332702
Pistons (P/N right hand 12674094 and left hand 12674093):
Forged aluminum with internal ribs; flat-top crown
Engine Type:
Direct injection spark ignition Gen-V Small-Block V8
Displacement (cu. in.):
376 (6.2L)
Bore x Stroke (in.):
4.06 x 3.62 (103.25 x 92 mm)
Block (P/N 12619171):
Cast aluminum with 6-bolt nodular iron main bearing caps
Crankshaft:Forged steel
Connecting Rods:Powdered-metal steel
Camshaft Type (P/N 12642245): Hydraulic roller
Maximum Recommended rpm:6600
Camshaft Lift (in.): 200° intake / 212° exhaust
Valve Lift (in): .492 intake / .551 exhaust
Camshaft Duration (@.050 in.): 189° intake / 223° exhaust
Cylinder Heads (P/N 12646959):
A356-T6 rotocast aluminum
Valve Size (in.):2.13 intake / 1.59 exhaust
Compression Ratio:10.0:1

SOURCE - http://www.chevrolet.com/performance...gines/lt4.html

Thanks for the clarification Andy. I'm still learning about this LT4. I couldn't see from the web site you referenced but do the rods in the LT1 and LT4 have the same part numbers? Are they literally the same rods or is there a difference in construction?

Originally Posted by DFW1LE

Thats significant power if you are talking at the wheels. Not sure I need that much, but who knows whether I'd want more if I didn't have it. Here is what I am thinking at this point, any comments/suggestions would be appreciated:

Objective: achieve 500-525 HP at the wheels with a broad power curve, and doing that on a fully catted exhaust. Would prefer to run straight 93 vs E85. Want an engine that will provide good reliability (e.g. 75-100K) miles, although it will never see that much mileage.

Options:
1) IM/Heads/cam/LT
Concerns: do not want cam to cause emission or valve train problems, want good street drivability and broad power band. Can LTs be mated to the stock cats. The GM performance heads and cam might be a good way to go.

2) SC (and LT if it helps)
Concerns: do not want to create excessively high cylinder pressures given the 11.5 CR, will back pressure from a fully catted system cause problems, do not want to add too much weight to front of car and upset the cars balance on the race track.

Lastly, which of the above is the most cost effective way to go?

I think cylinder pressure is corresponding to the amount of horsepower and these LT1 engines are pretty good to 700 hp. I think you get the most bang for your buck from the supercharger and it is pretty safe. A supercharger will add some weight but the performance gains far outweigh anything you can feel on the track.

[Speedy1975]

If you're worried about longevity, warranty, additional maintenance, etc then LEAVE THE CAR STOCK. Modified cars are just that, modified. They require more maintenance and more attention to the systems by the owner.

There's a huge thread started by Janetty on FI, etc. Good read.

Pray and EFI have been fooling with bolt ons and have relatively cheaply added like 70RWHP/70RWTQ for right at $2,000 with E85 flex, ported IM and TB, and tune. That's about $30 per HP. A supercharger, while still awesome, is about $50 per HP considering an intercooled Magnuson unit adding 160RWHP and assuming you don't save the install fee by doing it yourself.

On my Challenger it was a simple decision to do the blower and built motor. Nothing else gave that kind of bang for the buck. This Camaro seems to respond VERY well to bolt ons so the decision is a bit more difficult.

[DFW1LE]

Originally Posted by jessrayo

Thanks for the clarification Andy. I'm still learning about this LT4. I couldn't see from the web site you referenced but do the rods in the LT1 and LT4 have the same part numbers? Are they literally the same rods or is there a difference in construction?


I think cylinder pressure is corresponding to the amount of horsepower and these LT1 engines are pretty good to 700 hp. I think you get the most bang for your buck from the supercharger and it is pretty safe. A supercharger will add some weight but the performance gains far outweigh anything you can feel on the track.

Jess, I thought I read some where that LT4 rods and crank were similar, but some addition machining went into the LT4's components, so if true, I suspect the P/Ns to be different.

When I say track, just to avoid mis-understandings, I am referring to road courses. Could I perhaps start out with a SC with a different pulley size to make a lower boost (e.g. 6-7) and then change it up down the road if more power is desired?