Possible 5.3L (lm7) build....newbie to LS engines.
04-12-2015, 03:46 PM
#1
Teching In
Thread Starter
iTrader: (1)
Join Date: Apr 2015
Posts: 11
Likes: 0
Received 0 Likes
on
0 Posts
Possible 5.3L (lm7) build....newbie to LS engines. Hi all,
I have been lurking the sites for a little while and decided to make my first post. Hopefully I do not get flamed to harshly for the questions that I am about to ask.
I am currently building/restoring a 240sx (I come from an import world) and have a 5.3L I am throwing in it. My thing is, I really do not care for high horsepower, so setting a HP limit is not what I am going for. What I really would like to do is build a 7-7500 rpm LM7 with Jenvey ITBs. I am more into engine response than anything. The car is not a track car, just simply something I am building for myself. I know people say "high rpm is costly" etc. Personally, I do not mind saving, buying a part that I need and repeating the process. Car already has a large amount invested into it and basically, its still a shell. So this definitely is not a budget build.
What I was thinking is keeping the stock bore and stroke and mostly work on the heads etc to support the 7-7500 rpm or possibly go to the largest bore possible (3.903) and keep the stroke the same. I know some might suggest to throw the 4.8L crank in but I would like to reduce the rotating mass as well while I am at it. Seems like K1 makes a stock 5.3L stroke forged crankshaft over at Texas Speed website. Plus the 5.3L is already close to a 327ci engine, which I assume would be a plus.
I know that the valvetrain has to be as light as possible to achieve this with Gen3 engine "reliably". I definitely do not mind spending the extra for hollow valves (heck, even titanium if need be).
My questions (that I can think of right now):
1) At such RPM, is a dry sump really required?
2) Would keeping it at stock bore/stroke be reasonable for the RPM that I am thinking of?
3) Would it be better to go with a 3.903 bore and 4.8L forged crank and make it a 312ci?
3) Any recommendation for the type of spring specs I would need? Shaft mount rockers?
4) Rod Length?
5) Could this possibly be done with a 383 LM7 build?
6) Is this a dumb idea?
I know I will need taller valve covers to support the extra lift. I was thinking of having Total Engine Airflow CNC the stock heads. Cam profile I will probably discuss this with a company that builds cams but if you have a recommendation then feel free to chime in on the cam subject.
Again, not looking for huge power and I know people may shun this idea but I would like to do something different for this.
Thanks and sorry for the long, first post.
I have been lurking the sites for a little while and decided to make my first post. Hopefully I do not get flamed to harshly for the questions that I am about to ask.
I am currently building/restoring a 240sx (I come from an import world) and have a 5.3L I am throwing in it. My thing is, I really do not care for high horsepower, so setting a HP limit is not what I am going for. What I really would like to do is build a 7-7500 rpm LM7 with Jenvey ITBs. I am more into engine response than anything. The car is not a track car, just simply something I am building for myself. I know people say "high rpm is costly" etc. Personally, I do not mind saving, buying a part that I need and repeating the process. Car already has a large amount invested into it and basically, its still a shell. So this definitely is not a budget build.
What I was thinking is keeping the stock bore and stroke and mostly work on the heads etc to support the 7-7500 rpm or possibly go to the largest bore possible (3.903) and keep the stroke the same. I know some might suggest to throw the 4.8L crank in but I would like to reduce the rotating mass as well while I am at it. Seems like K1 makes a stock 5.3L stroke forged crankshaft over at Texas Speed website. Plus the 5.3L is already close to a 327ci engine, which I assume would be a plus.
I know that the valvetrain has to be as light as possible to achieve this with Gen3 engine "reliably". I definitely do not mind spending the extra for hollow valves (heck, even titanium if need be).
My questions (that I can think of right now):
1) At such RPM, is a dry sump really required?
2) Would keeping it at stock bore/stroke be reasonable for the RPM that I am thinking of?
3) Would it be better to go with a 3.903 bore and 4.8L forged crank and make it a 312ci?
3) Any recommendation for the type of spring specs I would need? Shaft mount rockers?
4) Rod Length?
5) Could this possibly be done with a 383 LM7 build?
6) Is this a dumb idea?
I know I will need taller valve covers to support the extra lift. I was thinking of having Total Engine Airflow CNC the stock heads. Cam profile I will probably discuss this with a company that builds cams but if you have a recommendation then feel free to chime in on the cam subject.
Again, not looking for huge power and I know people may shun this idea but I would like to do something different for this.
Thanks and sorry for the long, first post.
04-12-2015, 05:29 PM
#2
TECH Veteran
What your horsepower goals?
What is the car go be used for?
LS can be built to take 7k plus rpm but you'll NEED the best of the best valvetrain components and a great oiling system..
What is the car go be used for?
LS can be built to take 7k plus rpm but you'll NEED the best of the best valvetrain components and a great oiling system..
04-12-2015, 05:35 PM
#3
Teching In
Thread Starter
iTrader: (1)
Join Date: Apr 2015
Posts: 11
Likes: 0
Received 0 Likes
on
0 Posts
Car will be a weekend cruiser/show car. Its just a personal build for me. I am mostly an enthusiast. Not a track car or anything so mostly street use. Not building it to race on the street either. Simply just to enjoy the time and money invested into it.
I know that they can do high RPM but I just want to do it fairly reliably since I am new to LS engines.
If I need to invest in quality valvetrain, then so be it but my biggest thing is can it be done with stock bore and stroke on the LM7.
04-12-2015, 05:56 PM
#4
TECH Veteran
Well, as stated before, not shooting for a HP goal. In the end, whatever HP I get, I get.
Car will be a weekend cruiser/show car. Its just a personal build for me. I am mostly an enthusiast. Not a track car or anything so mostly street use. Not building it to race on the street either. Simply just to enjoy the time and money invested into it.
I know that they can do high RPM but I just want to do it fairly reliably since I am new to LS engines.
If I need to invest in quality valvetrain, then so be it but my biggest thing is can it be done with stock bore and stroke on the LM7.
Car will be a weekend cruiser/show car. Its just a personal build for me. I am mostly an enthusiast. Not a track car or anything so mostly street use. Not building it to race on the street either. Simply just to enjoy the time and money invested into it.
I know that they can do high RPM but I just want to do it fairly reliably since I am new to LS engines.
If I need to invest in quality valvetrain, then so be it but my biggest thing is can it be done with stock bore and stroke on the LM7.
It's so many ways to get horsepower out of a 5.3...
Do you want to spin the motor high constantly?
04-12-2015, 05:59 PM
#5
Teching In
Thread Starter
iTrader: (1)
Join Date: Apr 2015
Posts: 11
Likes: 0
Received 0 Likes
on
0 Posts
Yes, I agree. You can make power with them. I have read the Modern Mouse article from Super Chevy and they made very good numbers from a 383 stroker.
I would like to do 7-7500rpm reliably with me shifting in that range if I have to.
04-12-2015, 06:08 PM
#7
TECH Veteran
A 383 would be nice. It will help the torque curve and pull you back in the seat!!
After all tho you may want to look into better heads. A ported 243 is nice but no comparison to a aftermarket head.
Cubes only do so much but they not everything. Get a great set of heads and a cam to match. No need in having cubes and not taking full advantage of them. Look into link bar lifters over drop in lifters. Spinning a motor north of 7K requires a good stable valvetrain!! As far as the crank goes.... callies has the best!! Wiseco pistons is great too.
After all tho you may want to look into better heads. A ported 243 is nice but no comparison to a aftermarket head.
Cubes only do so much but they not everything. Get a great set of heads and a cam to match. No need in having cubes and not taking full advantage of them. Look into link bar lifters over drop in lifters. Spinning a motor north of 7K requires a good stable valvetrain!! As far as the crank goes.... callies has the best!! Wiseco pistons is great too.
Trending Topics
04-12-2015, 06:12 PM
#8
Teching In
Thread Starter
iTrader: (1)
Join Date: Apr 2015
Posts: 11
Likes: 0
Received 0 Likes
on
0 Posts
A 383 would be nice. It will help the torque curve and pull you back in the seat!!
After all tho you may want to look into better heads. A ported 243 is nice but no comparison to a aftermarket head.
Cubes only do so much but they not everything. Get a great set of heads and a cam to match. No need in having cubes and not taking full advantage of them. Look into link bar lifters over drop in lifters. Spinning a motor north of 7K requires a good stable valvetrain!! As far as the crank goes.... callies has the best!! Wiseco pistons is great too.
After all tho you may want to look into better heads. A ported 243 is nice but no comparison to a aftermarket head.
Cubes only do so much but they not everything. Get a great set of heads and a cam to match. No need in having cubes and not taking full advantage of them. Look into link bar lifters over drop in lifters. Spinning a motor north of 7K requires a good stable valvetrain!! As far as the crank goes.... callies has the best!! Wiseco pistons is great too.
Anybody with more input?
04-12-2015, 11:51 PM
#9
Moderator
iTrader: (4)
Join Date: Jul 2014
Location: My own internal universe
Posts: 10,446
Received 1,835 Likes
on
1,145 Posts
It can be tempting to go aluminum rockers to lighten the valve train. Don't. Aluminum flexes and has lower fatigue. Light valves, good springs, titanium keepers are all good ideas.
I'd run a cam that allowed me to run stock rockers with a trunion upgrade, say .610 lift max. Pick springs that are about .050" away from coil bind at max lift or close to it. If your cam has .612" lift, then springs that bind between .660-.700" lift are good. Shim to about .050" for stability and longevity. Dual springs can give extra insurance in case of a break.
There is a sticky on valve train stability you should study.
All that said, your opportunities to go 7400 rpm on the street might be limited. It would be worth your time to talk to some vendors about head and cam combinations. One of the best for head design is tony mamo. For cam selection, I lean towards tick, but cam motion and eps are also very good cam designers.
I think best bang for buck might be to punch out to a 5.7 and basically build an iron ls1. Cubic inches determines potential power and torque, but power is made or lost in the heads. An iron ls1 would have a stroke short enough to rev really high and a bore wide enough and proven to make lots of power. Plenty of cranks, rods, pistons available. You'd gain more from a well thought out and designed ls1 than you would spending the extra money for a 383, based on your goals.
I'd run a cam that allowed me to run stock rockers with a trunion upgrade, say .610 lift max. Pick springs that are about .050" away from coil bind at max lift or close to it. If your cam has .612" lift, then springs that bind between .660-.700" lift are good. Shim to about .050" for stability and longevity. Dual springs can give extra insurance in case of a break.
There is a sticky on valve train stability you should study.
All that said, your opportunities to go 7400 rpm on the street might be limited. It would be worth your time to talk to some vendors about head and cam combinations. One of the best for head design is tony mamo. For cam selection, I lean towards tick, but cam motion and eps are also very good cam designers.
I think best bang for buck might be to punch out to a 5.7 and basically build an iron ls1. Cubic inches determines potential power and torque, but power is made or lost in the heads. An iron ls1 would have a stroke short enough to rev really high and a bore wide enough and proven to make lots of power. Plenty of cranks, rods, pistons available. You'd gain more from a well thought out and designed ls1 than you would spending the extra money for a 383, based on your goals.
04-13-2015, 07:37 AM
#10
Teching In
Thread Starter
iTrader: (1)
Join Date: Apr 2015
Posts: 11
Likes: 0
Received 0 Likes
on
0 Posts
It can be tempting to go aluminum rockers to lighten the valve train. Don't. Aluminum flexes and has lower fatigue. Light valves, good springs, titanium keepers are all good ideas.
I'd run a cam that allowed me to run stock rockers with a trunion upgrade, say .610 lift max. Pick springs that are about .050" away from coil bind at max lift or close to it. If your cam has .612" lift, then springs that bind between .660-.700" lift are good. Shim to about .050" for stability and longevity. Dual springs can give extra insurance in case of a break.
There is a sticky on valve train stability you should study.
All that said, your opportunities to go 7400 rpm on the street might be limited. It would be worth your time to talk to some vendors about head and cam combinations. One of the best for head design is tony mamo. For cam selection, I lean towards tick, but cam motion and eps are also very good cam designers.
I think best bang for buck might be to punch out to a 5.7 and basically build an iron ls1. Cubic inches determines potential power and torque, but power is made or lost in the heads. An iron ls1 would have a stroke short enough to rev really high and a bore wide enough and proven to make lots of power. Plenty of cranks, rods, pistons available. You'd gain more from a well thought out and designed ls1 than you would spending the extra money for a 383, based on your goals.
I'd run a cam that allowed me to run stock rockers with a trunion upgrade, say .610 lift max. Pick springs that are about .050" away from coil bind at max lift or close to it. If your cam has .612" lift, then springs that bind between .660-.700" lift are good. Shim to about .050" for stability and longevity. Dual springs can give extra insurance in case of a break.
There is a sticky on valve train stability you should study.
All that said, your opportunities to go 7400 rpm on the street might be limited. It would be worth your time to talk to some vendors about head and cam combinations. One of the best for head design is tony mamo. For cam selection, I lean towards tick, but cam motion and eps are also very good cam designers.
I think best bang for buck might be to punch out to a 5.7 and basically build an iron ls1. Cubic inches determines potential power and torque, but power is made or lost in the heads. An iron ls1 would have a stroke short enough to rev really high and a bore wide enough and proven to make lots of power. Plenty of cranks, rods, pistons available. You'd gain more from a well thought out and designed ls1 than you would spending the extra money for a 383, based on your goals.
Thank you Darth_V8r. All of your points definitely make sense. I was thinking the same about punching it out to a 5.7 and then focus most of my work into the heads/cam combo. Gives me something to think about and research.
I will study the valve train sticky as you suggested as well.