What boost would you expect from this combo?

S_Mazza

Registered User
Hi all. I want to know how much boost you guys think my car should make, and then I will tell you what I am actually getting.

I recently had a leaky snout seal on my SC, so I swapped the blower with one that I rebuilt and ported on my own for fun. (I didn't take the rotor pack apart, of course.)

FYI, the stock blower was making about 11 psi.

So, I ported the inlet as far as I could without cutting and welding. I included small flares on the inside of the case like an S-port. I also ported the outlet a little - really just filleting the lip on the underside of the exit, and cutting the bolt bosses back a little.

Next, I coated the rotors (yep, myself) with a spray-type epoxy coating. (Consider this a durability test for the club. Results to follow in a few thousand miles.)

Finally, I swapped the pulley to a 10% overdrive steel pulley. I thought I was going to need a new belt for this, but the stock one seems to fit ok with the tensioner still within its range.

And my exhaust is still stock (don't worry, not for long ...), so I am not losing boost because of a non-restrictive exhaust.

So, what would you expect it to make? Thanks!
 
15ish

depending on your porting and the coating you could have made it worse. Also you are going to blow hg's, or heat soak really fast with a stock ic. you should really invest in a dbl ic or at least a fan if money is tighter!!
 
I was pushing 15-16 with a 10% underdrive and no mufflers. After new exhaust system i was at 14-15 psi. And a few weeks later blew my HG. I had FMIC 75mm TB 3Intake 80mm MAF.


I would guess 15-16 psi.
 
im making 14psi with headerback exhaust no res 10% pulley and ic fan.. hopefully the ic fan only keeps me trouble free and no hg failures..

i want a dbl ic soon though
 
Thanks for the replies, everyone. Drum roll, please ...

It is making just over 13 PSI of boost.

I am generally happy with the results. I wasn't really sure what to expect - I guess I thought it would make a little more. This is really my first performance mod to this car! So I am a little bit excited about that, anyway. The blower makes more boost, it rises faster, and it certainly changed the tone of the blower sound. It is higher-pitched and a little louder. It sounds more like the blowers I heard on the cars at the Beaver Valley SC meet this past fall. (You guys have some fierce cars out there.)

So, it seems like it's more or less on par with the general opinion. That's good. I knew I didn't screw it up too badly because it was still more boost than stock. I guess I could have figured out that overdriving the blower a certain percentage should only give about that same percentage more boost, and maybe a little less because of drag. 11*1.10 = 12.1. So maybe my porting and coating increased the effectiveness another 10-15%. I'll settle for that - it only cost me maybe $25 and a lot of elbow grease.

I wonder how it will react when I go to a CAI, MAF, TB, and matched plenum?
 
Thanks for the replies, everyone. Drum roll, please ...

It is making just over 13 PSI of boost.

I am generally happy with the results. I wasn't really sure what to expect - I guess I thought it would make a little more. This is really my first performance mod to this car! So I am a little bit excited about that, anyway. The blower makes more boost, it rises faster, and it certainly changed the tone of the blower sound. It is higher-pitched and a little louder. It sounds more like the blowers I heard on the cars at the Beaver Valley SC meet this past fall. (You guys have some fierce cars out there.)

So, it seems like it's more or less on par with the general opinion. That's good. I knew I didn't screw it up too badly because it was still more boost than stock. I guess I could have figured out that overdriving the blower a certain percentage should only give about that same percentage more boost, and maybe a little less because of drag. 11*1.10 = 12.1. So maybe my porting and coating increased the effectiveness another 10-15%. I'll settle for that - it only cost me maybe $25 and a lot of elbow grease.

I wonder how it will react when I go to a CAI, MAF, TB, and matched plenum?

The blower is sensitive to inlet restrictions and the CAI, MAF and TB will help but only a little. I think your money would be better spent on a upgraded blower and inlet plenum...it will make more power with the stock MAF & TB on an MPII or S port than a ported early model with bigger MAF, CAI and TB.

Early model will require extensive rework to blower inlet and plenum to get much more out of it....even then it's no match for an MPII or an S port. You can overdrive it harder, and it's going to make more boost, spin the tires easier and feel stronger, but it will lose power on the top end and nose over like you dropped an anchor, because it's generating too much heat and pulling more power off the crank to turn the blower.

You can make a very large improvement by going with an MPII or S port and the MP inlet plenum. Remember, that more boost doesn't always mean more power....more oxygen molecules makes it possible to burn more fuel and that's where the power comes from. Cooler more dense air contains more oxygen.

David
 
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I would like to have an S-port, but I don't think that expenditure is going to happen any time soon. The thing is, I already own the TB and MAF, and I have the parts to make the CAI. So I think I will at least finish the project. I have a 190lph fuel pump and exhaust to install as well.

Future plans involve a cam and maybe ported heads, but I think that will have to wait until a full engine rebuild. I just don't think I can take the downtime on this car to open the engine that far unless it's broken. So I'll probably build a fresh longblock (mostly stock, but done right) and swap it in in the next couple years. (IE, when I have a garage.)

Edit:

Ok, one more question: How much boost does an S-port typically make at 10% OD?
 
Yours turned out better than mine.. I went from 13/14psi stock with a 5% blower pully to 11psi with a 5% blower 5% js when i ported my blower... plus it has no balls off the line anymore.
 
ive gotten 15 lbs from a stock blower and enough heat to grill hot dogs with 10% over drive with 15 % over drive I got same but at lower rpm and way more heat and way way less hp toooooooo much heat!!!!
 
Jacob, you ported your heads too, right? So that would certainly explain part of your boost loss.

Manny, I wonder how much heat mine is making. I never really get on it for more than 5 seconds at a time (can't find enough road to "play" in a manner that I would call safe). I am thinking I might piggyback my digital voltmeter onto the IAT sensor with some extra-long leads so I can check it while driving. (Or maybe I will farm that task out to my wife so I can actually watch the road. :) )
 
I can pretty much asure you that without an upgraded IC, and even with a fan on the stock IC, you would not complete the 1/4 mile without ACT's climbing high enough to pull timing, which starts at 120F... thats with a 10% on a 32F day.

Run a 5% and be safe. Remember that not only do you lose HP with higher ACT's, you also increase the chance of detonation... which will have you building that extra motor faster ;)

FT
 
I haven't actually been to the track, so I think I am safe for now. I don't mean to ignore what people are saying. My thinking is, it's only 13 psi. We have people out there with way more than that on a stock motor. I think I will check the IATs, though, as I said, because I do want to know what my margin of safety is. One other thing to consider is, the 13 psi is after the intercooler. The hotter the air going into the IC, the more effective the IC becomes. So a 30 degree temperature gain at the blower hat may only be a 20 degree gain at the engine.
 
I haven't actually been to the track, so I think I am safe for now. I don't mean to ignore what people are saying. My thinking is, it's only 13 psi. We have people out there with way more than that on a stock motor. I think I will check the IATs, though, as I said, because I do want to know what my margin of safety is. One other thing to consider is, the 13 psi is after the intercooler. The hotter the air going into the IC, the more effective the IC becomes. So a 30 degree temperature gain at the blower hat may only be a 20 degree gain at the engine.

Not neccessarily in our case. The IC we have is already useless so to speak at stock levels. I have datalogged my car totally stock and watched ACT's go over 120 within a few seconds at WOT on a cold day. On a hot humid day our cars are useless as it feels like the 94lx 3.8 I drove around, and I know alot of folks can confirm that.

Since then, I have upgraded to a 94 blower and OD it at 3% with a stock 90 pully. With datalogging on a 32F day at WOT within 15 seconds I was hitting an ACT of 120F and I actually saw my spark timing being pulled.

You can't just think of its only 13psi.... Heck you can run 5psi and still see 200F for ACT's.

Its your car, do as you see fit ;).
 
Boost seems a little low but most likely that's due to your homebrew coatings. A properly ported early style blower with coated rotors (such as GTP rotors) will make over 14psi at stock drive. It can also be driven up to 15% over without issue but you really need a better IC.

The stock IC is not useless, in fact it is very efficient. Outlet temps from a stock IC are normally about 300 deg assuming 65 deg inlet temps and normal non overdriven ACT's usually run in the 125 deg range. 300 deg - 65 deg inlet = delta 235 deg @ 12psi. To bring that down to 125 less 65deg ambient (60 delta) requires short term efficiency around 75%. After repeated full throttle blasts the inlet temps will climb to about 140 deg but even so that is still almost 70% efficiency. Heat soak will eventually reduce that even more but if you have a shortened AC condenser you will be able to maintain at around 70% efficiency quite easily.
 
Ok, a couple of things.

1.) I checked on the homebrew coating, and it seems to be holding up perfectly. Less than 1,000 miles on it so far, but I am pretty confident in it.

2.) I think my belt is slipping. When I first installed the OD pulley, it seemed like the belt had enough tension, but I went back and looked this weekend, and the tensioner is resting at the end of its range. Maybe the belt stretched. Anyway, I will fix that and see what happens.

3.) I "datalogged" my car this weekend with the voltmeter. It was about 50 degrees outside. That corresponds to a IAT sensor voltage of about 3.5 V. The car was warmed up, but not heat soaked. As I was accelerating uphill onto the highway at full blast, my IAT voltage dropped from 3.5 V to 2.7 V. That is about 80 - 90 degrees total, or a gain of about 30-40 degrees. I topped out at about 60 mph as I didn't want to get too crazy on the public road. So, it seems likely that I could get IATs over 120 on a 1/4 mile run. Well, c'est la vie. I might get an IC fan, but I don't think I will spring for a double IC in the near future.

I'll post pics of my porting when I remember to bring the camera to work.
 
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