Forcefed86

iTrader: (4)

Anyone have this? I was seeing a solid 1.4:1 on my S480 1.32 T6 on a 370” motor @ 20lbs. Throwing in a spare Gen4 4.8 to play this season while a build a “real” motor. Figured I’d toss a cam in and I’m torn on going for a more NA oriented grind with a tight LSA, or a more typical wider LSA turbo grind. Running the small 862 truck head, around 7k. I’m assuming this thing will be close to 1:1 but I’m really not sure.

Also have some 1.8 roller rockers I can use.

1CAMWNDR

iTrader: (21)

If the 370 only had 1.4:1 I imagine the 4.8 will have NONE LOL. But how long will it take to spin the damn thing.....hmmmm.

Forcefed86

iTrader: (4)

No idea... But I'm gonna find out! Not opposed to smacking it around with a 100 shot to get it lit if I have to.

1CAMWNDR

iTrader: (21)

I am interested to see what the driving characteristics are going to be.

JoeNova

If all factors are equal, X amount of HP produces Y amount of exhaust volume regardless of engine size.

Since X HP in a 4.8 will mean more PSI than X HP in a 370, backpressure ratio will always be lower.

Forcefed86

iTrader: (4)

I’m sure it will be lower, but all factors won’t be equal. Not sure how much more RPM I’ll squeeze out of the 4.8 but I ran the 370 to a whopping 6200 rpm. That’s around 531cfm NA flow wise. 292 cubes at 7500 rpm is around 507… so pretty close. 4.8 will have the baby heads VS the 317s on the 370.

Little worried about the valve train health with 1.8 rockers. Need to go pretty conservative lobe wise… Think I’ll limit it to .600 lift (with the 1.8 adjustment) and keep it under 220 with a tight LSA. No idea where to find a nice lazy lobe with those specs.

SethU

In that case, the Turbine will have to produce more shaft power to produce the additional boost pressure, elevating the back pressure too. Wouldn't it?

JoeNova

You're thinking into it too hard. More force on the shaft = more boost. The ratio is largely unaffected.

SLOW SEDAN

iTrader: (13)

I think it will be fine a 1.32 T6 S480 spooled up faster on my 5.3 then a .96 T4 88mm. Only problem was the gen 4 rods couldn't handle the S480 on 27lbs. Was a quarter second faster to the 1/8th though!

Forcefed86

iTrader: (4)

Hope it’s easier on the rods at a 3100lb race weight.

Also was going to play a bit with the boost by RPM function. Try to limit it around 20lbs below 5500 and then ramp it up to “big boost” above there. Or just drop the *** out of it timing wise at pk tq and keep the boost up might work better. Hoping to rev it cleanly over 7k. If I can get 8.XX consistently I’ll be happy. Last 4.8 combo did 9.0x @ 151 with the S476 on 19lbs.

SethU

That's what I was getting at.

67Firebird455

iTrader: (27)

LOL @ "Drop the *** out of it" comment. I love your way of thinking. We've talked about this before, I'm kind of with you on the limiting timing/boost below 5500 and let it eat 25-30psi up to just above 7k (depending on cam). It'll probably love it.

JoeNova

I'm talking about the force to spin the shaft, not the difference due to displacement.

3 window

iTrader: (1)

How much timing are you guys pulling from your total ad how do you determine that number? Let's say it likes 12 degrees at 20 psi, what do you pull it down to under 5500?

LJMSJohn

I've done 2 of those so far. Given the data we gathered... the cam can be pretty rowdy.

and there are plenty of lobes out there slow enough to be stable with an aftermarket 1.8 ratio rocker.

Worrying about staying under .600 lift is pointless.

Forcefed86

iTrader: (4)

I figured If I went with a short duration and .630 lift or something it would beat the valves up too much. What would you suggest? I have a 9.5 PTC with a 14 stator. So Im a little worried it wont get up on the converter and make boost on the brake without some power down low. Will have LS6 intake and the small valve 706 head.

Previously ran the JFR trip12 on a 4.8 with the 1.24 T4 s476. It barely lit off. With the ls1 intake I had on it originally, it wouldnt light off at all. The ls6 intake put it over the edge and gave it just enough to lite off an make boost on it's own.

LJMSJohn

You can't look at duration alone in making that determination. a 14-0 stator behind that little motor is way too tight. You should look at adjusting that versus trying to cam to the converter. This setup isn't going to work unless the motor can flash and make some RPM. Or you spray it 100 shot from 2000 to 3500.

Forcefed86

iTrader: (4)

Its the same converter I ran with the 4.8 previously and it built boost fine. That was with a 2.5" "T" merge hotside. Now I have a fully divided 2" hotside and 1.32 T6 s480. Id like to keep the converter as tight as possible since this motor will only be in for a year... maybe less. This is just a temporary thing till the bigger engine goes in. So Im not looking to change the driveline combo any. Just to get a cam in here that will help as much as possible. Its only a weekend warrior toy.

ddnspider

iTrader: (26)

I would love to see a more na oriented cam too as opposed to the turbo style. Something more like the triple 12 on steroids like a 212/218 108 with 600 life. I'm NOT a big fan of the big heavy roller rockers even if they have the benefit of rolling over the valve tip, so much weight. I noticed a significantly quicker valvetrain and cleaner Rev when I got rid of my Harland Sharps.

LJMSJohn

The one I did looked pretty N/A ish... on a 110 lobe sep.