What will make a big cam work?
08-26-2007, 10:31 AM
#1
What will make a big cam work? Question is, is there any combination to make a large cam work with a turbo set up.
Reason for this is, I have a chance to pick up a rear mount turbo kit for very little money. I am in the process of building a LSX 427 that will be turbo charged. That engine will get a good "turbo cam" grind. This set up will not be completed for a year. For the minimal money for this rear mount as offered to me, it is something I can not pass up on. I am going to pick it up and would like to try it on my pressent combo with tunning changes. Here is my updated present combo:
MS3 cam at 113LSA 237/242 .603/.609 13.5 overlap
Larger injectors
Valve Springs and pushrods for the MS3
Hooker long tube headers
Off rode Y pipe "No Cats"
4000 Staull converter
3.73 gear
Nitrous
I will remove the nitrous when the turbo is installed.
I am wondering if the 4000 staull will help the turbo/MS3 combo. I know the MS3 is not what most would consider a good turbo cam.
What are your thoughts on this and has anyone tried this on a rear mount turbo, what was your results.
Again, I do not plan to change the cam in the 346, and I am sure someone will tell me to just use the nitrous and forget the turbo. I am bored with the juice, and will not change the ms3 in this engine. I am wanting to know if you think the high staull, long tube headers, no cat (minimal backpressure), rear mount turbo will be enough to compensate for the valve overlap the ms3 has in it?
Reason for this is, I have a chance to pick up a rear mount turbo kit for very little money. I am in the process of building a LSX 427 that will be turbo charged. That engine will get a good "turbo cam" grind. This set up will not be completed for a year. For the minimal money for this rear mount as offered to me, it is something I can not pass up on. I am going to pick it up and would like to try it on my pressent combo with tunning changes. Here is my updated present combo:
MS3 cam at 113LSA 237/242 .603/.609 13.5 overlap
Larger injectors
Valve Springs and pushrods for the MS3
Hooker long tube headers
Off rode Y pipe "No Cats"
4000 Staull converter
3.73 gear
Nitrous
I will remove the nitrous when the turbo is installed.
I am wondering if the 4000 staull will help the turbo/MS3 combo. I know the MS3 is not what most would consider a good turbo cam.
What are your thoughts on this and has anyone tried this on a rear mount turbo, what was your results.
Again, I do not plan to change the cam in the 346, and I am sure someone will tell me to just use the nitrous and forget the turbo. I am bored with the juice, and will not change the ms3 in this engine. I am wanting to know if you think the high staull, long tube headers, no cat (minimal backpressure), rear mount turbo will be enough to compensate for the valve overlap the ms3 has in it?
08-26-2007, 10:56 AM
#2
The problem with cam'ing a turbo car is the high exhaust pressure versus low intake pressure. The concern is excessive overlap allows reversion of exhaust into the intake port. A rear-mount turbo inherently has higher exhaust pressure than a front-mount. Add long-tube headers, and the situation gets even worse since they cool the exhaust gas. Now, consider that the turbo you're getting is a T76 at the biggest, but probably a T67, and put it on a 427 and the backpressure is going to go through the roof.
It's just not a good kit for 427 cid engines, let alone those with big camshafts.
Mike
It's just not a good kit for 427 cid engines, let alone those with big camshafts.
Mike
08-26-2007, 11:48 AM
#3
I am not looking to put this turbo kit on my 427. That engine will not be completed for a good year and it will have a cam speced for turbo. The engine I am looking at installing this rear mount on is my presently running 346. As for the turbo size in the kit, I have not found out for sure what it is. All the guy can tell me at present is it is a T3-T4 turbo speced for rear mount, and the cost was about $700 for the turbo. He is going to call me back today with the rest of the turbo info.
My thinking was that with the 4000 staull, it would help the turbo work with my present ms3 cam in the 346? I have no idea for sure, but I am thinking the overlap would not be much of an issue at 4000 rpm and above. Wouldn't the cooling of the exhaust gasses lower the backpressure in the exhaust? I was under the impresion that is one of the reasons the rear mounts have a different AR then a front mount, to compensate for the cooler/lower velocity/lower pressure exhaust pulse. The main restriction should be the turbo, so it will still have at least 2:1 exhaust/intake ratio if not higher.
I don't know, just asking for input. I guess I will have to try it and just let everyone know.
My thinking was that with the 4000 staull, it would help the turbo work with my present ms3 cam in the 346? I have no idea for sure, but I am thinking the overlap would not be much of an issue at 4000 rpm and above. Wouldn't the cooling of the exhaust gasses lower the backpressure in the exhaust? I was under the impresion that is one of the reasons the rear mounts have a different AR then a front mount, to compensate for the cooler/lower velocity/lower pressure exhaust pulse. The main restriction should be the turbo, so it will still have at least 2:1 exhaust/intake ratio if not higher.
I don't know, just asking for input. I guess I will have to try it and just let everyone know.
08-26-2007, 11:59 AM
#4
Originally Posted by Texas_WS6
...The engine I am looking at installing this rear mount on is my presently running 346. As for the turbo size in the kit, I have not found out for sure what it is. All the guy can tell me at present is it is a T3-T4 turbo speced for rear mount, and the cost was about $700 for the turbo.
Originally Posted by Texas_WS6
... Wouldn't the cooling of the exhaust gasses lower the backpressure in the exhaust? I was under the impresion that is one of the reasons the rear mounts have a different AR then a front mount, to compensate for the cooler/lower velocity/lower pressure exhaust pulse.
For front versus rear-mount energy comparison, I'm running a T76GTS front-mount in a 388 LTx with AFR heads and a 224 cam. My Tial 40mm wastegate is wide open and it still makes 17 psi boost. I've been as high as 23 psi and I'm sure it can go higher. Zombie has a similar 76 R-trim turbo but rear-mount on his 346 LSx, stock heads, and a mild cam. Early on, he couldn't get over about 13 psi out if it with the wastegate totally blocked off. He has since re-installed cast iron manifolds, ran a smaller intermediate pipe, and insulated everything, and now he can get up to about 18 psi boost tops. Exhaust heat is very important to a turbo.
08-26-2007, 01:19 PM
#5
I just got off the phone with the guy. All he could find on the turbo is t3-t4 AR .58 M56. I have no idea what brand of turbo or the trim. Were he got it from told him it was good for 700hp and could make 25psi.
I am buying the entire kit for $1000. It has the upgraded oil pump system, and a few little add ons. When I finish the 427, I could upgrade the turbo in this kit for it. Maybe I should replace the turbo now with something that will work with both engines.
Can you change the ar with a housing swap? Maybe I can modify the turbo to make it more acomidating for the 346 and ms3 I am running. I deal with an industrial turbo remanufacturing shop here locally that could take care of any turbo modifications. With the 4000 staull I do not think the .58 AR will work good. Any ideas? The .58 AR also sounds like it will not work with my cam and I bet with the fact I run the engine from 4000 rpm to 7000rpm it will restict the engine drasticly.
All I was hoping to achieve with this turbo is 500hp so I can take my nitrous off, not change the present cam, and upgrade the system when the 427 was completed.
I am buying the entire kit for $1000. It has the upgraded oil pump system, and a few little add ons. When I finish the 427, I could upgrade the turbo in this kit for it. Maybe I should replace the turbo now with something that will work with both engines.
Can you change the ar with a housing swap? Maybe I can modify the turbo to make it more acomidating for the 346 and ms3 I am running. I deal with an industrial turbo remanufacturing shop here locally that could take care of any turbo modifications. With the 4000 staull I do not think the .58 AR will work good. Any ideas? The .58 AR also sounds like it will not work with my cam and I bet with the fact I run the engine from 4000 rpm to 7000rpm it will restict the engine drasticly.
All I was hoping to achieve with this turbo is 500hp so I can take my nitrous off, not change the present cam, and upgrade the system when the 427 was completed.
08-26-2007, 02:17 PM
#6
Housings are easy to swap in 10 minutes. However, that's not what you need to be worrying about. The wheel size will be your issue. I don't think you can do much with a T3/T4 to make it work well. That's a common turbo for 4-cylinder imports that want quick spoolup.
Secondly, if you're serious about going turbo, then you need to re-think the whole 427 cid choice. You see, you'll need a pretty big turbo to work well with an engine of that size. A mid-frame turbo will be marginal, but a large-frame would work best (T91+). Many folks pick a good 76 mm (TC76 or 76GTS) because it's physically small. That turbo works best in the 300 - 350 cid range, so you limit the engine size to match.
Mike
Secondly, if you're serious about going turbo, then you need to re-think the whole 427 cid choice. You see, you'll need a pretty big turbo to work well with an engine of that size. A mid-frame turbo will be marginal, but a large-frame would work best (T91+). Many folks pick a good 76 mm (TC76 or 76GTS) because it's physically small. That turbo works best in the 300 - 350 cid range, so you limit the engine size to match.
Mike
