Square port to cathedral port adapters
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Teching In
Joined: Dec 2023
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Square port to cathedral port adapters Hey all,
Do square port to cathedral port adapters work for NA applications? Best answer I've seen is that they aren't great but, I've not been able to find many people who have tried it, only to bolt blowers on, and that's a whole different story.
There is also the issue of the intake maybe not fitting under the hood.
Do square port to cathedral port adapters work for NA applications? Best answer I've seen is that they aren't great but, I've not been able to find many people who have tried it, only to bolt blowers on, and that's a whole different story.
There is also the issue of the intake maybe not fitting under the hood.
Hey all,
Do square port to cathedral port adapters work for NA applications? Best answer I've seen is that they aren't great but, I've not been able to find many people who have tried it, only to bolt blowers on, and that's a whole different story.
There is also the issue of the intake maybe not fitting under the hood.
Do square port to cathedral port adapters work for NA applications? Best answer I've seen is that they aren't great but, I've not been able to find many people who have tried it, only to bolt blowers on, and that's a whole different story.
There is also the issue of the intake maybe not fitting under the hood.
It won’t work nearly as good as the LS6 intake will. The adaptors disrupt flow. A good way of looking at this is knowing that the intake port actually starts at the bell mouth of the intake port in the intake. Having the wonky adaptor and the abrupt deviation halfway will only hurt performance. It’s a great discussion starter however.
Teching In
Joined: Jan 2024
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From: South-East U.S
I did it no problem, and will do it again. If needed. Background and why: I sold my LS1, and was having a L76 built. Well it was taking the machine shop longer then, I wanted. My cousin gave me a 4.8 (1999 or 2000/ estimated 400K miles) to use. I had the L76 intake, but the 4.8 was cathedrals. So I brought the adapters.
I drove the messed out of it. Probably 10,000 miles, ran amazing (Holley Terminator ECU). Before taking the 4.8 out of the car, I took it to the track. It was a 2002 Pontiac Trans Am in full street trim, 4.8 with built 4L80e w/ 3800ish stall /trans brake, S60 4.10, and street tire 275/60/15 Cooper Cobras . Ran a 14.5 on NA and on Nitrous it ran a 13.2 (or 13.5 IIRC) on a 75 shots.
For a Video check out my Youtube:
I drove the messed out of it. Probably 10,000 miles, ran amazing (Holley Terminator ECU). Before taking the 4.8 out of the car, I took it to the track. It was a 2002 Pontiac Trans Am in full street trim, 4.8 with built 4L80e w/ 3800ish stall /trans brake, S60 4.10, and street tire 275/60/15 Cooper Cobras . Ran a 14.5 on NA and on Nitrous it ran a 13.2 (or 13.5 IIRC) on a 75 shots.
For a Video check out my Youtube:
TECH Fanatic
Joined: May 2016
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From: St. Louis
I had a 4.8 swapped in a stock 2002 Z28 at one point, 4.8 long block swap with the OE LS6 intake and Camaro exhaust manifolds a 212/ 218 comp. Cam, stock converter stock 2.73 gear car. My car ran 14.30"s @ 104mph at 3000 da 95° heat with 2.3 60ft times
I don't think That intake was doing you any favors
I don't think That intake was doing you any favors
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Teching In
Joined: Jan 2024
Posts: 3
Likes: 1
From: South-East U.S
I had a 4.8 swapped in a stock 2002 Z28 at one point, 4.8 long block swap with the OE LS6 intake and Camaro exhaust manifolds a 212/ 218 comp. Cam, stock converter stock 2.73 gear car. My car ran 14.30"s @ 104mph at 3000 da 95° heat with 2.3 60ft times
I don't think That intake was doing you any favors
I don't think That intake was doing you any favors
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This is an example of the 305 Paradox. It feels like its flat out running well, but in truth its only running as well as it can.
For comparison, my factory stock 07 mustang GT ran the same 14.5 with literally every component in the car being supplied by the Ford factory. The only modification was pulling the air cleaner. A cammed 3800 stall, re-geared, trans brake 4.8 should run harder than that.
For comparison, my factory stock 07 mustang GT ran the same 14.5 with literally every component in the car being supplied by the Ford factory. The only modification was pulling the air cleaner. A cammed 3800 stall, re-geared, trans brake 4.8 should run harder than that.
Teching In
Joined: Jan 2024
Posts: 3
Likes: 1
From: South-East U.S
This is an example of the 305 Paradox. It feels like its flat out running well, but in truth its only running as well as it can.
For comparison, my factory stock 07 mustang GT ran the same 14.5 with literally every component in the car being supplied by the Ford factory. The only modification was pulling the air cleaner. A cammed 3800 stall, re-geared, trans brake 4.8 should run harder than that.
For comparison, my factory stock 07 mustang GT ran the same 14.5 with literally every component in the car being supplied by the Ford factory. The only modification was pulling the air cleaner. A cammed 3800 stall, re-geared, trans brake 4.8 should run harder than that.
Now I do agree, I would think it should have netted 275ish hp. Do I think that intake was hurting it 25 hp, probably not.
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https://www.michiganmotorsports.com/...fa2b2bb4e05285
Trailblazer SS Intake, for your engine probably 30hp and and torques, if not more.
Trailblazer SS Intake, for your engine probably 30hp and and torques, if not more.
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https://www.michiganmotorsports.com/...fa2b2bb4e05285
Trailblazer SS Intake, for your engine probably 30hp and and torques, if not more.
Trailblazer SS Intake, for your engine probably 30hp and and torques, if not more.
revisiting an old thread. Anyone actually use these types of adapters with NA setups and run into obvious performance issues. I run a set on a set of ITB’s as for some reason the ITB intake for a square port were half the price at the time. I have no doubt I could throw a TBSS On here an pick up power. That’s not really the question. I was just curious if anyone had glaringly obvious issues with the adapters.
My setup is JY 5.3. milled 706’s .100. Around 13:1*ish with a small (228/232 .550"/.550" 110+5) cam. With the above mentioned ITB’s. Setup acts like a diesel, lol. Pretty much the exact opposite of what I was shooting for. Pulls like crazy from say 2k to 4600 or so. Done at 5600 and falls off a cliff at 6k and above. Fun to drive and sounds pretty neat which is all I was really going for. But I’m thinking the adapters may be to blame here.
Don’t believe I can toss on a factory intake to test with this much milled off the heads. Was just curious if anyone noticed performance above 5k pretty much being neutered with the adapters.
My setup is JY 5.3. milled 706’s .100. Around 13:1*ish with a small (228/232 .550"/.550" 110+5) cam. With the above mentioned ITB’s. Setup acts like a diesel, lol. Pretty much the exact opposite of what I was shooting for. Pulls like crazy from say 2k to 4600 or so. Done at 5600 and falls off a cliff at 6k and above. Fun to drive and sounds pretty neat which is all I was really going for. But I’m thinking the adapters may be to blame here.
Don’t believe I can toss on a factory intake to test with this much milled off the heads. Was just curious if anyone noticed performance above 5k pretty much being neutered with the adapters.
revisiting an old thread. Anyone actually use these types of adapters with NA setups and run into obvious performance issues. I run a set on a set of ITB’s as for some reason the ITB intake for a square port were half the price at the time. I have no doubt I could throw a TBSS On here an pick up power. That’s not really the question. I was just curious if anyone had glaringly obvious issues with the adapters.
My setup is JY 5.3. milled 706’s .100. Around 13:1*ish with a small (228/232 .550"/.550" 110+5) cam. With the above mentioned ITB’s. Setup acts like a diesel, lol. Pretty much the exact opposite of what I was shooting for. Pulls like crazy from say 2k to 4600 or so. Done at 5600 and falls off a cliff at 6k and above. Fun to drive and sounds pretty neat which is all I was really going for. But I’m thinking the adapters may be to blame here.
Don’t believe I can toss on a factory intake to test with this much milled off the heads. Was just curious if anyone noticed performance above 5k pretty much being neutered with the adapters.
My setup is JY 5.3. milled 706’s .100. Around 13:1*ish with a small (228/232 .550"/.550" 110+5) cam. With the above mentioned ITB’s. Setup acts like a diesel, lol. Pretty much the exact opposite of what I was shooting for. Pulls like crazy from say 2k to 4600 or so. Done at 5600 and falls off a cliff at 6k and above. Fun to drive and sounds pretty neat which is all I was really going for. But I’m thinking the adapters may be to blame here.
Don’t believe I can toss on a factory intake to test with this much milled off the heads. Was just curious if anyone noticed performance above 5k pretty much being neutered with the adapters.
706's are also the worst flowing ls head and the cam is way too small if you were looking for a high rpm screamer
put 243/799 on it and a cam that makes power up top and then adjust itb runner length from there
Not sure I agree. Esp. for a low buck small bore motor setup. People hype up the 799’s too much IMO.
706’s flow 230CFM 799’s only flow 20cfm more. Which is why swapping 706’s for 799’s picks up power on most mild NA applications. I knew I wasn’t going to need the additional 40CFM on a cheap little cam only 5.3. So I didn’t see the 799’s being worth the inflated cost.
I paid $500 for the motor and sold the 799’s for $400. Picked up the 706’s for $100.
I wanted the smaller chamber head to get the most compression possible out of the mill job. Since you get roughly 4% NA gains off each point of compression the 706’s make a better choice to get the most bang for your buck.
Similar deal with the cam. I went with a lower lift and duration to keep PTV issues down. According to the 5.3 test mule at TSP this cam made 428@ 6500RPM at 10:1. With 706’s It would have made more.
I’m was curious if anyone had actual before and after data with and without the adapters.
A friend linked me to the Holdner video below.
He dyno’d them back to back with a cathedral headed 6.0. LS2 intake VS LS3 intake with adapters. .
The LS3 with adapters made more power to PK TQ, then lost 10ish hp at a peak near 6500. So a 2% power loss past pk TQ isn’t bad at all IMO. I know the car would pick up a ton with a stock intake, but I was going more for sound and driving experience with this setup.
706’s flow 230CFM 799’s only flow 20cfm more. Which is why swapping 706’s for 799’s picks up power on most mild NA applications. I knew I wasn’t going to need the additional 40CFM on a cheap little cam only 5.3. So I didn’t see the 799’s being worth the inflated cost.
I paid $500 for the motor and sold the 799’s for $400. Picked up the 706’s for $100.
I wanted the smaller chamber head to get the most compression possible out of the mill job. Since you get roughly 4% NA gains off each point of compression the 706’s make a better choice to get the most bang for your buck.
Similar deal with the cam. I went with a lower lift and duration to keep PTV issues down. According to the 5.3 test mule at TSP this cam made 428@ 6500RPM at 10:1. With 706’s It would have made more.
I’m was curious if anyone had actual before and after data with and without the adapters.
A friend linked me to the Holdner video below.
He dyno’d them back to back with a cathedral headed 6.0. LS2 intake VS LS3 intake with adapters. .
The LS3 with adapters made more power to PK TQ, then lost 10ish hp at a peak near 6500. So a 2% power loss past pk TQ isn’t bad at all IMO. I know the car would pick up a ton with a stock intake, but I was going more for sound and driving experience with this setup.
im with you on selling stuff off and replacing with cheaper stuff to recoup cost but a 799/243 head will make more power everywhere and carry higher rpm than a 706 will with the same comp ratio, that cam is never gonna want to turn much more than 6500 either so i would bump the cam up, you could check PTV on your current setup to see how much more you could get away with or flycut the pistons
make sure your port alignment with the adapters is spot on as well as the turbulent air from them not being lined up perfectly is what kills power
and then after all that whether you want to do it or not i would test with different runner lengths on the itb's as that plays a huge role in the usable rpm range, there are a few engine masters episodes covering this, Holdener has some videos i believe and garage4AGE on youtube has a bunch of videos covering it on toyota 4 cyls but the theories are the same
make sure your port alignment with the adapters is spot on as well as the turbulent air from them not being lined up perfectly is what kills power
and then after all that whether you want to do it or not i would test with different runner lengths on the itb's as that plays a huge role in the usable rpm range, there are a few engine masters episodes covering this, Holdener has some videos i believe and garage4AGE on youtube has a bunch of videos covering it on toyota 4 cyls but the theories are the same
im with you on selling stuff off and replacing with cheaper stuff to recoup cost but a 799/243 head will make more power everywhere and carry higher rpm than a 706 will with the same comp ratio, that cam is never gonna want to turn much more than 6500 either so i would bump the cam up, you could check PTV on your current setup to see how much more you could get away with or flycut the pistons
make sure your port alignment with the adapters is spot on as well as the turbulent air from them not being lined up perfectly is what kills power
and then after all that whether you want to do it or not i would test with different runner lengths on the itb's as that plays a huge role in the usable rpm range, there are a few engine masters episodes covering this, Holdener has some videos i believe and garage4AGE on youtube has a bunch of videos covering it on toyota 4 cyls but the theories are the same
make sure your port alignment with the adapters is spot on as well as the turbulent air from them not being lined up perfectly is what kills power
and then after all that whether you want to do it or not i would test with different runner lengths on the itb's as that plays a huge role in the usable rpm range, there are a few engine masters episodes covering this, Holdener has some videos i believe and garage4AGE on youtube has a bunch of videos covering it on toyota 4 cyls but the theories are the same
This was just a super mild NA build to see if I could find some extra "free hp" with cheap high compression and E85 on an SBE JY motor. Was hoping for something that sounded more "exotic" and less classic mild SBC is all. Really wanted the exotic exh note more than anything.
Just a fun daily commuter. Was surprised when It fell on its face well before 5.3 tested by TSP though. I could live with it pulling to 6500rpm as they show.
