Pro's & Con's of porting the LT1/LT4 intake
05-11-2004, 09:36 PM
#1
Registered User
Thread Starter
Join Date: Sep 2002
Location: kitchener/Ontario
Posts: 1,942
Pro's & Con's of porting the LT1/LT4 intake
Is there any real power to be found in porting your intakes ...
what people have done and gain's or just leaving them alone and making the same power,.....
what people have done and gain's or just leaving them alone and making the same power,.....
05-11-2004, 09:44 PM
#3
Registered User
Join Date: Oct 2002
Location: Lancaster, PA
Posts: 55
I've heard that if you port your LT1 head to that of something along the lines of a LT4 head you'll get yourself around 330hp as long as you get the right springs and rockers, think its 1.6, not sure though. Also the 330 comes considering that your running stock, with stock hp and all that jazz. If i had the money right now i'd be doing the porting, springs and rockers right now.
05-11-2004, 10:09 PM
#4
Registered User
Join Date: Feb 2002
Location: Houston, TX USA
Posts: 706
I guess you can decide for yourself...
on the left is a ported LT4 intake (opened up to the GM "race" LT4 intake gasket)
on the right is the stock LT4 ports.
Which one you think will flow better???
on the left is a ported LT4 intake (opened up to the GM "race" LT4 intake gasket)
on the right is the stock LT4 ports.
Which one you think will flow better???
05-12-2004, 05:56 AM
#6
Registered User
Join Date: Nov 2001
Location: In a house by the bay
Posts: 2,985
Having talked with some guys who have flow tested and dynoed ported LT intakes I'd have to say.... yes, it's well worth the effort. Even on your more-typical 400 rwhp builds people are aiming for.
If you ever want to see just how restrictive the intake is... have your porter flow the cylinder head with the intake. A very minor loss is to be expected due to friction but it should be minor, like 5%.
-Mindgame
If you ever want to see just how restrictive the intake is... have your porter flow the cylinder head with the intake. A very minor loss is to be expected due to friction but it should be minor, like 5%.
-Mindgame
05-12-2004, 10:06 AM
#7
Registered User
Join Date: Jul 2002
Location: Philly, PA
Posts: 292
Somewhat of a dumb question, I am wondering with a ported intake, what gaskets should then be used?
I just ordered the typical GM placement for my upcoming cam swap, BUT--I am thinking that while the manifold is off, I could easily swap on a nicely ported one and make the most of this project.
Any thoughts? I am not worried about power increase, just simply whats different for installation as opposed to simply reinstalling the stock intake.
Thanks
I just ordered the typical GM placement for my upcoming cam swap, BUT--I am thinking that while the manifold is off, I could easily swap on a nicely ported one and make the most of this project.
Any thoughts? I am not worried about power increase, just simply whats different for installation as opposed to simply reinstalling the stock intake.
Thanks
05-12-2004, 10:34 AM
#8
Registered User
Join Date: Nov 2002
Location: Indiana
Posts: 30
On a stock LT1 the intake manifold ports are bigger than the head intake ports so unless your heads are ported also I dont see were the gains would be. Unless you port the TB opening and run a bigger TB but then also the 48mm TB will flow plenty for a stock car and even pretty well for a slighty modded car. Until you get into the heads I dont see why the intake would make a difference. If the intake port will flow say 250cfm but the head will only flow 210 whats the adavantage. 
05-12-2004, 11:15 AM
#9
Registered User
Join Date: Feb 2002
Location: Houston, TX USA
Posts: 706
Originally posted by BadBirdLT1
On a stock LT1 the intake manifold ports are bigger than the head intake ports so unless your heads are ported also I dont see were the gains would be. Unless you port the TB opening and run a bigger TB but then also the 48mm TB will flow plenty for a stock car and even pretty well for a slighty modded car. Until you get into the heads I dont see why the intake would make a difference. If the intake port will flow say 250cfm but the head will only flow 210 whats the adavantage.
On a stock LT1 the intake manifold ports are bigger than the head intake ports so unless your heads are ported also I dont see were the gains would be. Unless you port the TB opening and run a bigger TB but then also the 48mm TB will flow plenty for a stock car and even pretty well for a slighty modded car. Until you get into the heads I dont see why the intake would make a difference. If the intake port will flow say 250cfm but the head will only flow 210 whats the adavantage.
And so far as which gasket to match it to, use the ones you plan to run and do both the intake and heads.
05-14-2004, 11:53 AM
#11
Registered User
Join Date: Mar 2000
Location: Louisiana
Posts: 435
I just tested this on an LT4 intake last week. I used a factory LT4 head that I'm about 90% done with for 95Bird. On the head I've worked the intake side to 205cc and it flows 275 @ .600
With the unported intake bolted up to the head on the bench it flowed 230.5 @ .600
After fully porting the intake (includes raising the runner) the combo flowed 251.8 @ .600
Peak gain 21.8 cfm.
Link for the flow graph:
http://www.thunderracing.com/users/s...ke%20chart.jpg
Intake on bench:
http://www.thunderracing.com/users/s...imH_LT4002.jpg
Is it all worth doing... sure is if you want to go fast
Steve...
With the unported intake bolted up to the head on the bench it flowed 230.5 @ .600
After fully porting the intake (includes raising the runner) the combo flowed 251.8 @ .600
Peak gain 21.8 cfm.
Link for the flow graph:
http://www.thunderracing.com/users/s...ke%20chart.jpg
Intake on bench:
http://www.thunderracing.com/users/s...imH_LT4002.jpg
Is it all worth doing... sure is if you want to go fast
Steve...
05-14-2004, 03:39 PM
#12
Banned
Join Date: Oct 2002
Posts: 6,518
Same thing happens on LS1's, the heads flow 300+cfm and the flow gets killed 10%+ with the intake on. But if you get more flow out of the heads, say going from 300cfm to 330cfm the motor will make more power and go faster, even if the flow with the intake on the heads is the same. The intake manifold should be as little a restriction as possible but the more important feature is the runner length and area, that will make or break the power curve vs. the flow. If you can get both, well that's going to make you even more power.
The LT4 intake is a great intake for porting, but in stock trim leaves more to be desired than the LT1 intake. That intake is at least close to the LT1 heads. The only real advantage of the LT4 intake is that they have .200 more material on top of the runners where the intake meets the head. In the case of the LT intakes, you can just try to get as much out of it as possible, that's all you can do, welding them up and then raising the roof with straight and parallel port walls is about the max you can do without cutting the thing open and doing open heart surgery.
Most of the work done to a LT4 intake is to increase the flow and make the port consistant rather than having a changing cross sectional area like it does in stock trim. That's why a ported intake makes more power.
Bret
The LT4 intake is a great intake for porting, but in stock trim leaves more to be desired than the LT1 intake. That intake is at least close to the LT1 heads. The only real advantage of the LT4 intake is that they have .200 more material on top of the runners where the intake meets the head. In the case of the LT intakes, you can just try to get as much out of it as possible, that's all you can do, welding them up and then raising the roof with straight and parallel port walls is about the max you can do without cutting the thing open and doing open heart surgery.
Most of the work done to a LT4 intake is to increase the flow and make the port consistant rather than having a changing cross sectional area like it does in stock trim. That's why a ported intake makes more power.
Bret
