[oldman]

Originally Posted by Eldi Z

What do you mean in terms of Big?

What is the Lift/Duration on the LT1 and what is it on the LT4?

LT4 Cam Specs
Part Number 12642245
Duration @ .050 in. (int./exh.) 189°/223°
Valve Lift (int./exh.) 0.492 in./0.551 in.
Lobe Separation Angle 120°

tiny in fact.


L86 Camshaft Specs
Part Number 12629512
Duration @ .050 in. (int./exh.) 200°/207°
Valve Lift (int./exh.) 0.551 in./0.524 in.
Lobe Separation Angle 116.5°

LT1 Cam Specs
Part Number 12629512
Duration @ .050 in. (int./exh.) 200°/207°
Valve Lift (int./exh.) 0.551 in./0.524 in.
Lobe Separation Angle 116.5°

LT2
204 / 219
.551 / .551
Revised Cam Profile And Phasing
Now that the exhaust flows about as freely as the intake, the exhaust valve lift is increased by 1mm to match the intake's 14.0-mm lift, which improves exhaust valve flow rate from 122 to 125 grams/second. Duration is also increased, and the range of authority of the cam phasing is now 62 degrees (though the controller seldom orders more than 50 degrees).

It would be my opinion that power is related to intake duration and lift.

[Eldi Z]

Originally Posted by oldman

LT4 Cam Specs
Part Number 12642245
Duration @ .050 in. (int./exh.) 189°/223°
Valve Lift (int./exh.) 0.492 in./0.551 in.
Lobe Separation Angle 120°

tiny in fact.


L86 Camshaft Specs
Part Number 12629512
Duration @ .050 in. (int./exh.) 200°/207°
Valve Lift (int./exh.) 0.551 in./0.524 in.
Lobe Separation Angle 116.5°

LT1 Cam Specs
Part Number 12629512
Duration @ .050 in. (int./exh.) 200°/207°
Valve Lift (int./exh.) 0.551 in./0.524 in.
Lobe Separation Angle 116.5°

LT2
Revised Cam Profile And Phasing
Now that the exhaust flows about as freely as the intake, the exhaust valve lift is increased by 1mm to match the intake's 14.0-mm lift, which improves exhaust valve flow rate from 122 to 125 grams/second. Duration is also increased, and the range of authority of the cam phasing is now 62 degrees (though the controller seldom orders more than 50 degrees).

It would be my opinion that power is related to intake duration and lift.

Excellent data here.

So the L86 and LT1 share the same stock Cam...

I wonder why the LT4 cam exhibits a smaller intake lift
What are the advantages of this Cam spec in an FI setup? Vs. the LT1/L86?

[oldman]

The 120 LSA cuts down on overlap, don't want to be blowing boost out the exhaust... bad for smog too.

I think OEM valve springs are very weak, GM wants 200,000 miles out of these so cut down on lift helps the larger intake that is also fighting against boost. Less guide wear too. GM wants to use the SMALLEST cam posible for any HP target, and the least lift. So the Lt4s cam is the most dependable, best on smog for the application, the LT1 cam should make more power.

[Tim M]

Heater: Great feedback on you experiences. Not sure about the comment, "produce a little more power due to heat." Possibly I took that out of context, but more heat will produce less power. Possibly the LT1's cam may produce more boost than the LT4...but I'd chalk that up to not an ideal blower cam.

I'm not an expert, but I'd think the cam is not such a benefit to the LT1 with a blower. Yes the intake lift/duration is greater than the LT4, but you have boost benefiting the inflow. Notice the exhaust is less for lift and duration on the LT1 compared to the LT4 - an area that the blower does not help. In other words, the LT4 has a blower cam and the LT1 has a NA cam. How does this impact long term longevity of the engine/cats...

I'd suggest (as others have) the 1.5 point of compression increase on the LT1 is the source of any 'extra' power...I'm not sure a LT4 blown LT1 makes anything more than the LT4. Doing so means the power is made differently with a weaker piston design. Why does Chevy go with a lower CR...reliability, no doubt-just like oldman states on minimal cam actuation/valve springs.

I've asked about better valve springs when going from NA to blower and was told, not necessary. I used to change valve springs out seasonally on my 7200 rpm LT4 (Gen II) motor as they were consumable. I'll probably address in the future as boost on the backside of the valve reduces the resulting spring pressure - I do like to hear those 6500 rpm shifts!

I'm interested in the discussion only because I will be putting the stock LT4 blower on my LT1...may not be the best idea for my application, but can't deny the need for 650 HP!

I'm at 1100 feet elevation so will report back what boost it runs with an OEM LT4 blower/pulled as well as OEM intake setup.

Thanks!

[Eldi Z]

Originally Posted by Tim M

I'm interested in the discussion only because I will be putting the stock LT4 blower on my LT1...may not be the best idea for my application, but can't deny the need for 650 HP!

I'm at 1100 feet elevation so will report back what boost it runs with an OEM LT4 blower/pulled as well as OEM intake setup.

Thanks!

Same plan here. I am at sea level here. Where are you located?

When do you plan installing the LT4 blower on your motor? Are you sourcing the necessary parts and adaptation elements from ADM or WeaponX?
Who will be tuning?

[KingLT1]

Originally Posted by Tim M

Heater: Great feedback on you experiences. Not sure about the comment, "produce a little more power due to heat." Possibly I took that out of context, but more heat will produce less power. Possibly the LT1's cam may produce more boost than the LT4...but I'd chalk that up to not an ideal blower cam.

I'm not an expert, but I'd think the cam is not such a benefit to the LT1 with a blower. Yes the intake lift/duration is greater than the LT4, but you have boost benefiting the inflow. Notice the exhaust is less for lift and duration on the LT1 compared to the LT4 - an area that the blower does not help. In other words, the LT4 has a blower cam and the LT1 has a NA cam. How does this impact long term longevity of the engine/cats...

I'd suggest (as others have) the 1.5 point of compression increase on the LT1 is the source of any 'extra' power...I'm not sure a LT4 blown LT1 makes anything more than the LT4. Doing so means the power is made differently with a weaker piston design. Why does Chevy go with a lower CR...reliability, no doubt-just like oldman states on minimal cam actuation/valve springs.

I've asked about better valve springs when going from NA to blower and was told, not necessary. I used to change valve springs out seasonally on my 7200 rpm LT4 (Gen II) motor as they were consumable. I'll probably address in the future as boost on the backside of the valve reduces the resulting spring pressure - I do like to hear those 6500 rpm shifts!

I'm interested in the discussion only because I will be putting the stock LT4 blower on my LT1...may not be the best idea for my application, but can't deny the need for 650 HP!

I'm at 1100 feet elevation so will report back what boost it runs with an OEM LT4 blower/pulled as well as OEM intake setup.

Thanks!

The LT1 indeed makes more power then a LT4 at the same PSI of boost. As you mentioned, The LT1 has a lot more compression which contributes to the increase. Honestly the LT4 supercharger works better on the LT1 because it doesn't need spun as hard to make power which equals lower blower temps. LT1's tend to dyno around 600whp on 9 psi and not 550whp like the LT4 on 93. The down side is the LT1 runs into a octane wall on pump gas around 10psi. So you need to supplement with Ethanol blend or Meth. LT4 can potentially make a lot more power on 93 octane with it's lower compression.

It's a good swap if you don't plan to go very far. I personally would run a larger 7psi pulley and run a blend of ethanol(E60) with LT4 fuel system. It will soften the hit since the little 1.7 makes a boat load of torque down low and still make the same if not a little more power up top as the 9 psi pulley on 93.

[Eldi Z]

Originally Posted by KingLT1

The LT1 indeed makes more power then a LT4 at the same PSI of boost. As you mentioned, The LT1 has a lot more compression which contributes to the increase. Honestly the LT4 supercharger works better on the LT1 because it doesn't need spun as hard to make power which equals lower blower temps. LT1's tend to dyno around 600whp on 9 psi and not 550whp like the LT4 on 93. The down side is the LT1 runs into a octane wall on pump gas around 10psi. So you need to supplement with Ethanol blend or Meth. LT4 can potentially make a lot more power on 93 octane with it's lower compression.

It's a good swap if you don't plan to go very far. I personally would run a larger 7psi pulley and run a blend of ethanol(E60) with LT4 fuel system. It will soften the hit since the little 1.7 makes a boat load of torque down low and still make the same if not a little more power up top as the 9 psi pulley on 93.

Good points.
For instance, my personal goal is no more than 570-580 RWHP tops. I do not plan on drag racing - just to increase my daily "fun factor" a little.

I guess that for such power goal the sweet spot for a clean pump 93 (no E and no Meth additions), would be 8 PSI of boost on moderate and safe timing advance?
From most of the information posted, so far the weakest link is the tight ring gap on the LT1 pistons, which calls for extra care when boosting.

[oldman]

Intake duration directly increases power period 189 duration is just TOO small. exhaust duration indirectly increases power by reducing pumping losses.

Look at the smallest cam Cam Motion makes for the PD: 220 /236
"to be used in completely stock vehicles"
That is an intake change of 31 degrees and an exhaust change of 13.

Somebody has Camdoctor and can give a figure on how much a LT1 cam add in HP or not. IMO the LT1 cam produces more HP i.e. the ingestion of more intake charge. Would be interesting to find out...

Since there is so little here on either cam, I consider this angles dancing on pins. I am NOT saying the LT1 is an optimal supercharger cam, obviously it is a NA cam.

[oldman]

Originally Posted by Tim M

I've asked about better valve springs when going from NA to blower and was told, not necessary. I used to change valve springs out seasonally on my 7200 rpm LT4 (Gen II) motor as they were consumable. I'll probably address in the future as boost on the backside of the valve reduces the resulting spring pressure - I do like to hear those 6500 rpm shifts!

what you wrote is gospel truth. I too consider valve springs consumable. In general over the past 32 years race 4 valve engines. So boost over the valve head did NOT require stronger springs (heads really small). I'm of the opinion now with these huge valves that boost does require stronger springs or you subject the intake valve to bounce as the related lifter overshoots the lobe and deceleration ramp and impacts on the cam. Think of it as a motocross overshooting the landing. This fails either the lifter or the valve (probably the hollow intake), in my case the lifter. I think this problem is further complicated by dual valve spring harmonics (should have gone conical), fast lobe lifts (add HP and brings customers in), and extended RPM, and most importantly large valve lifts (customers like that too). Try 7000 RPM sifts... OMG sounds great. Especially with a near stock exhaust that you can actually hear the metallic engine sounds.... not just loud exhaust. I posted an idle rev video on the NA section of large cam and stock exhaust.

BTW always luved the LT4 as the final evolution of the SBC.

Originally Posted by Tim M

I'm interested in the discussion only because I will be putting the stock LT4 blower on my LT1...may not be the best idea for my application, but can't deny the need for 650 HP!

Price seems good, performance better than stock LT4, looks bad action. It was my first choice.

[oldman]

The octane limit of about 10 PSI on 93 is a good rule of thumb, there is some flex of course because we all know boost is related to restriction. So 10 PSI of boost on stock engine is not filling the chamber up as much as 10 PSI of boost on a heads, cam, header engine. Same goes for where the boost happens, 10 PSI on a twin turbo big cam engine reaching this boost at say 5500 RPM has far less detonation potential than 10 PSi on stock lt1 with a 1.7 PD pullied at 2800 RPM, there is going to be more fuel, air, and much slower piston speed, all of which contribute to detonation (charge heating too adds to detonation). Gut feeling and I don't want to test the limits here, the 1.7 PD on stock engine is about 1 psi lower than this rule of thumb and a twin turbo, large cam built engine is 2 PSI above (assuming relatively lazy turbos). That 3 PSI swing, added to better flowing build engine does equal a WHOLE lot of HP when all is said and done. .i.e 11.5 CR is octane limited, but within this limit different builds probably vary by say 70 HP or so (granted it is expensive HP).

On my 11.5 CR build, the most knock retard I've seen to date is like 1 degree and Texas can get heck of hot.. all on 93. I'm on E85 tune now.

[Eldi Z]

Originally Posted by oldman

On my 11.5 CR build, the most knock retard I've seen to date is like 1 degree and Texas can get heck of hot.. all on 93. I'm on E85 tune now.

So if you look back to the days of your LT1 being in its stock form (Incl. exhaust End-to-End) and you would go with the LT4's Eaton 1.7 PD blower setup, but adding all of the LT4 fueling parts (Injectors, HPFP, LPFP-InTank & Related Fuel lines) on "pure" 93 Pump, that does not contain any E at all, nor would you add meth! -
At which boost levels would you feel "safe" not damaging the motor (I.E.knowing that the top ring gaps are tight).

What would you expect the perfectly "detonation free" RWHP to be at such boost level?

[oldman]

My engine still has cam and ported heads as well as a slightly lazy centri (d1x), I'm comfortable at 10 PSI on 93 with forged pistons.

I have not looked into pullied 1.7 on a stockLT1 engine, I think the LT4's stock boost is in the high 9 range, so we know what GM believes. I would look at a shop or somebody that has the car and see what they think. There have to be many guys now with this setup. IMO I like only builds capable of 100,000 miles. My first build was temp till I retired and even then within 5k or so miles I had a lifter failure. No bigs as I was going to change the cam and lifters on the rebuild, but scary it could have taken out the engine. My pistons look fine... mint in fact, don't know if I was lucky. Nut shell even at stock LT4 boost, you are starting with an engine with higher CR and cast pistons, at some point getting rid of pumping losses makes more sense vs boost.

I do think the front cats are very restrictive and will be putting in CA front cat deletes with Borla 60608 twin resonator mid-pipe (hope this keeps the sound near stock. If this does not work, I will put two high flow cats into the system, bringing the total to 4 cats, two resonators, two crush pipes, stock exhaust pipe. At some point, it has to be quite? I have tried 20 different combinations to find something I'll be happy with over the life of the car (1 to 20 years).


IMO this would be my first mod after blower; my only issue with any upgrade to the exhaust is my M6 car with my mods sounds terrible with no cats and just plain heck of loud with LT and cats. I'm looking for something fast but near-stock at 45 MPH or completely stock.

[Eldi Z]

Thanks for the insight oldman.
Yes, best thing is to ask around people running this setup for a while. Assuming GM is comfortable with ~ 10 PSI on an engine with 1 point lower C/R and with forged material, then my guess for a "safe" boost on a 1 point higher C/R with non-forged material should be ~ 7-8 (Max.) PSI - and yes, no less than 100K reasonable use (not "beating on her") miles longevity is the target.

[oldman]

Originally Posted by Eldi Z

Thanks for the insight oldman.
Yes, best thing is to ask around people running this setup for a while. Assuming GM is comfortable with ~ 10 PSI on an engine with 1 point lower C/R and with forged material, then my guess for a "safe" boost on a 1 point higher C/R with non-forged material should be ~ 7-8 (Max.) PSI - and yes, no less than 100K reasonable use (not "beating on her") miles longevity is the target.

IMO that is conservative, I like that. I'd do GM's high 9s (on 93) and work on the exhaust with either CA cat deletes move the 02 behind the second cats, or for an auto LT with cats. I know I'm "avant garde now" Also RotoFab, both mods reduce pumping losses so it is stress-free HP, which is longevity HP, ported tb and snout too. I figure the blower is probably optimized for high 9s and a 6.2 liter engine (never saw an efficiency map on it), I figure the aftermarket is doing plus 70 to plus 100 on a LT4 so dunno 12 to 14 PSI which has to be WAY off the efficiency map. We are dealing with a temp rise in either case, either before the intake valve or mechanical compression.

I hope others with the actual build will chime in. I would expect the build to be very responsive and fun.