can the SC handle it

BrentSC

Registered User
hey guys, i gotta 1990 thunderbird SC 5-speed with 180,000 kms on it. the motor is totally stock except for a magnum powers 3.5" cold air intake. im thinking about opening up the exhaust and putting one magnaflow muffler where the resonator is and getting rid of the stock mufflers. then getting a 10% od pully for the supercharger. maybe even a chip for the engine too. i wondering if i do these mods if i will blow a HG in 5 mins lol. and how much more horsepower will i get out of these mods??? thanks guys


brent
 
Opening up the exhaust will releive some of the pressure on your head gaskets.But I'd only put a 5% pulley on the blower since it's an early model.



Jay
 
From what I've read on the forum, installing a 10% pulley without also adding an upgraded intercooler is counter-productive. Supercharging is all about heat management.

JD
 
Opening up the exhaust will releive some of the pressure on your head gaskets.

Are the gaskets really that fragile? Headers and free-flowing pipes actually reduce compression? News to me... I thought these engines needed a proper balance of back-pressure to run right.

Cylinder pressure is cylinder pressure and until the exhaust valve opens, it shouldn't make any demonstrable difference to the HG's whether or not the exhaust scavenges better. Unless of course the cats are plugged, but that's another story :)

On a worn engine, I'd think that ring blow-by, valve stem leakage and carbon buildup would reduce compression to a point where increased scavenging would be a wash, if any effect at all.

Brent:
I'd study the engine a bit before taking steps towards mods. Do a compression test, etc. and make sure you have a good platform to work from. Might save some headaches in the long run.
 
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Are the gaskets really that fragile? Headers and free-flowing pipes actually reduce compression? News to me... I thought these engines needed a proper balance of back-pressure to run right.

Cylinder pressure is cylinder pressure and until the exhaust valve opens, it shouldn't make any demonstrable difference to the HG's whether or not the exhaust scavenges better. Unless of course the cats are plugged, but that's another story :)

On a worn engine, I'd think that ring blow-by, valve stem leakage and carbon buildup would reduce compression to a point where increased scavenging would be a wash, if any effect at all.

Brent:
I'd study the engine a bit before taking steps towards mods. Do a compression test, etc. and make sure you have a good platform to work from. Might save some headaches in the long run.

Everyone on these forums will recommend upgrading the stock exhaust. It's PUNY, with too many tight, restrictive bends. Not good for performance at all.
 
Everyone on these forums will recommend upgrading the stock exhaust.

...to take a load off the head gaskets? :confused:

I'm all for custom exhaust (if the engine is otherwise healthy), but this HG tip is news to me - please explain, thanks.
 
Are the gaskets really that fragile? Headers and free-flowing pipes actually reduce compression? News to me... I thought these engines needed a proper balance of back-pressure to run right.



I did not say anything about the exhaust lowering compression.As it doesn't compression is set by other factors i.e bore,stroke,combustion chamber cc,etc.But what a higher flowing exhaust system will do is reduce the backpressure in the exhaust and how hard the engine has to work to get the burnt mixture out.Which you'll also see by the drop in psi on your boost gauge after you open up the exhaust.Our stock exhaust is very restrictive at the exit of the resonater where it sends all your engines exhaust through a single crimped down outlet that probably less than 2.25 inches around.Not to mention the right angle inside of a cat thats made on one of our stock 1 7/8ths downtubes.Add to that the mileage on his car and it's pretty fair to say his cats etc have a high chance of being plugged up and worn out making an exhaust upgrade all the more wiser.Oh and roots blown cars aren't as sensitive to proper back pressure to run right.


Jay
 
I did not say anything about the exhaust lowering compression.

You said "Opening up the exhaust will releive some of the pressure on your head gaskets".
  • relieve: lessen/lower
  • pressure on head gaskets: cylinder compression
So, again, in what way does 'opening the exhaust' relieve pressure on the head gaskets? Is there another source of (less is better) 'pressure', other than compression, that you're referring to?

Sorry if I missed it - help me out, thanks.
 
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i think ur reading too much into it, KMT. i think that the headgasket problem on ours cars is caused more by detonation than a poor exhaust. when ppl run 10% OD and blow HG's its becuase that pulley is making more heat than the IC can remove. So u have hi intake air temps that leads to detonation. i think the crap exhaust system has a little bit to do with it but detonation is much more detrimental. ppl have blown HG's even WITH a full exhaust. my experiences are that a poor exhaust system results in high boost not blown headgaskets, unless it was just their time :rolleyes:

im running about 14psi on a cool nite and thats with no OD using a 94 blower, FMIC, ported heads and intake, full exhaust, intake, 76 MAF, UD pullies.
 
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'i think that the headgasket problem on ours cars is caused more by detonation than a poor exhaust.'

Right, detonation - me too. Poor fuel...need for tune-up...overheating...etc.

'When ppl run 10% OD and blow HG's its becuase that pulley is making more heat than the IC can remove. So u have hi intake air temps that leads to detonation.'

Right, detonation again, of course.

'i think the crap exhaust system has a little bit to do with it'

Ok. In what way? In your opinion, what pressure detrimental to HGs is being relieved that can be helped by a custom exhaust?

'...but detonation is much more detrimental.'

Right. Detonation again. Couldn't agree more. Moving on.

'ppl have blown HG's even WITH a full exhaust.'

Right - so why would someone say that custom exhaust helps to not do that?

'my experiences are that a poor exhaust system results in high boost not blown headgaskets'

I'm with you all the way.:) Thanks for the reply & helping make my point.
 
hey guys, i gotta 1990 thunderbird SC 5-speed with 180,000 kms on it. the motor is totally stock except for a magnum powers 3.5" cold air intake. im thinking about opening up the exhaust and putting one magnaflow muffler where the resonator is and getting rid of the stock mufflers. then getting a 10% od pully for the supercharger. maybe even a chip for the engine too. i wondering if i do these mods if i will blow a HG in 5 mins lol. and how much more horsepower will i get out of these mods??? thanks guys


brent

Why would you have a 3.5" cold air intake on a totally stock engine. Are you using some kind of adapter coupler to hook to the stock TB and MAF? Increasing your exhaust is all about reducing restrictions for better flow. If you have a lot of miles on an engine than you are looking to blow HG some where down the road. Regardless of exhaust improvements. I had 145,000 miles on mine, a huge exhaust system and a blower pumping out 19.5lbs of boost and they went in a big cloud of white smoke on the dyno. Over time, many WOTs they tend to blow out. Increasing exhaust size will see a nice increase of HP and a drop in boost. I went from 13.5lbs of boost to about 10lbs of boost when I did my exhaust but felt a large increase in acceleration. Thats when it becomes necessary to put a smaller pulley on to gain some of that boost back. Too much boost and you increase the heat factor and the car will pull timing on the top end, thus you need a bigger IC to manage the heat. When I started working on my car years ago the word was More boost means blown headgaskets. Now it is about detonation, heat and head gasket that are old and ready to blow.


Ken
 
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One of your first mods could be change out the head gaskets.. You don’t have to wait for them to blow to change them out.
 
One of your first mods could be change out the head gaskets.. You don’t have to wait for them to blow to change them out.


Thats what I was thinking. You can improve a known problem before you get stuck having to deal with it by surprise. When they go, you usually get coolant in the crankcase which is harmful to the bottom end.

I now have 98 mustang V-6 fel-pro headgaskets and arp head studs with a comfortable 15-17 lbs of boost.
 
'i think the crap exhaust system has a little bit to do with it'

Ok. In what way? In your opinion, what pressure detrimental to HGs is being relieved that can be helped by a custom exhaust?

'ppl have blown HG's even WITH a full exhaust.'

Right - so why would someone say that custom exhaust helps to not do that?

an exhaust is always helpful on any car. the SC's exhaust is a terrible design from the downtubes to about the rear axle. the worst parts are the downtubes, small and with bad angles. then the resonator, its small and has pinch points. the rest of the exhaust is ok cuz the stock mufflers are not that restrictive.

i think an exhaust helps to prevent detonation, not blowing HG's(on SC's). with an exhaust that has flows and breathes better, the motor is able to get the burnt mixture out easier b4 the next mix comes in. this reduces the amount of hot, combusted gas left in the cylinder to raise the temp and lead to detonation.

hope that made sense :)
 
Are the gaskets really that fragile? Headers and free-flowing pipes actually reduce compression? News to me... I thought these engines needed a proper balance of back-pressure to run right.
It seems you are thinking in N/A terms... This is a forced induction engine. We're cramming air into the cylinders while it fights to get it out. When exhaust backs up in the cylinder, dynamic compression ratio rises, and soo does cylinder pressure during the cycle.

Cylinder pressure is cylinder pressure and until the exhaust valve opens, it shouldn't make any demonstrable difference to the HG's whether or not the exhaust scavenges better. Unless of course the cats are plugged, but that's another story
Once again, this motor is forced induction. Scavenging is irrelivent.

On a worn engine, I'd think that ring blow-by, valve stem leakage and carbon buildup would reduce compression to a point where increased scavenging would be a wash, if any effect at all.
I'm just quoting this because I'm an a$$hole, and know that the valve seals aren't going to do anything but possibly bleed off a small amount of pressure while the next charge waits.

I'd study the engine a bit before taking steps towards mods. Do a compression test, etc. and make sure you have a good platform to work from. Might save some headaches in the long run.
I back this statement completely, though the spark plugs aren't very accessable on these motors to remove for a propper compression test.

I'm all for custom exhaust (if the engine is otherwise healthy), but this HG tip is news to me - please explain, thanks.
The spent charges from these motors will stack in the exhaust system as it is not adequate enough in the velocity department. It backs up all of the way back to the collectors/heads. Eventually, you can't expell as much spent gasses as you are pushing in with that little nifty supercharger of yours. Cylinder pressure rises, putting stress on the gaskets and causing the motor to be more knock sensative; heat rises, also contributing to the issue. Want proof? Look at the readings on a boost gauge before and after a GOOD exhaust. Less pressure, eh? Remember, you're metering it on the intake side. HMMM, Now what was getting in the way of that air which was previosly stacking in the intake???? Could it be exhaust backup? :p

Detination, Detination, Detination, BLAH BLAH FRIGGEN BLAH
Once again, I'm being an ~~~~. Yes, detination can be hard on the headgaskets. That's obvious. The flamefront contacts the piston before the crankshaft is in a position allowing enough mechanical advantage to relieve the pressure by converting it to mechanical energy... If too extreme, it can put a considerable amount of pressure on the cylinder walls, rotating assembly, AND headgaskets. This isn't an "OMG Shez gunna BLOW! (and not in the good way)" type thing thought (EDIT: For the head gaskets... You still need to stop the knock as it still overstresses the internals)... The surface area of the head gasket that are exposed to the burn is very minimal, as well as the overall design of it. As long as the pressure rises moderately evenly on all 'sides' (its round) of the cylinder, this isn't that bad of a thing. The only thing the gasket can TRY to do is expand to a larger radius; though the tensile strength of a good gasket won't allow much expansion.

'my experiences are that a poor exhaust system results in high boost not blown headgaskets'
I'm with you all the way. Thanks for the reply & helping make my point.
More boost = more backpressure in the intake caused by restrictions infront of it. I've covered this. If you don't understand by now, you probably won't get it.

Increasing exhaust size will see a nice increase of HP and a drop in boost. I went from 13.5lbs of boost to about 10lbs of boost when I did my exhaust but felt a large increase in acceleration. Thats when it becomes necessary to put a smaller pulley on to gain some of that boost back.
Sorry Ken, I have to comment on this. The horsepower gain is from you getting more burnable fuel into the chamber rather than spent exhaust gasses. Its like running a car at WOT with EGR wide open... It fills the cylinder, but not all with burnable gasses :D Obviously, the fresh air is going to make more power, and a noticeable increase in acceleration. The boost decrease.... "Boost" is backpressure in the intake side. Your boost went down when you did your exhaust because you could now fit more in the combustion chamber (and possibly lost a little bit out of the exhaust depending on your cam (NOTE: NOT A BAD THING!!)), and it didn't stack in the intake and build up in heat. The blower still output just as much as it did before, and you technically shouldn't need to put a smaller pulley on. There is no need to gain boost back.

'ppl have blown HG's even WITH a full exhaust.'
Right - so why would someone say that custom exhaust helps to not do that?
People blow their HG's N/A. What's your point? There are MANY possible reasons to blow headgaskets. You can't assume that the exhaust doesn't greatly help simply because people can still blow the headgaskets with a good exhaust system.

NOW, I'm done being a douche for a little while atleast.... So here's my thoughts on the original post... Around KC, We've got quite a few SCs with 10%s, gutted cats, and good exhauts. The cars do tend to heat soak after a few runs, and pull timing from charge temps, but we haven't had any with issues with detination. It's definately do-able, but a double intercoolelr or something to that effect would help.
 
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dont run 10% without exh work done I ported my heads and did exh and my boost went from 13 to 8 lbs then added 15% over drive to the early blower and make 15 lbs boost stock ic car runs like a bat outta hell .

the problem is with resictive exh the boost is high and it comes i a low rpm causing detonation this eats away at the gaskets the chips available well most lean out fuel mix and add timing great on a stock sc but makes it worse witha modified engine lean is not good on a moded engine. most stock sc's run rich so he chips make it run leaner and its a noticeable thing but to lean out a overdriven blower is suicide.

now before anyone starts in on me about the ic unit mine does not need a bigger unit yet temps are still ok in itake track and i make all kinds of parts so its not just me being cheap its i dont need it yet hell my other sc ran 13;22 with stock ic stock exh manifolds ported .
 
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Most of what you say is true. Not sure where you were going with not needing a bigger pulley to make up the diffrence. Like I said its about reducing restrictions to increase flow. Intake flow is increase by going larger on the intake side of the blower so the blower can move more air along. Porting the blower to make increaseing flow as well as removing restrictions that cause turbulence. A better nonrestrictive IC ported and polished heads, bigger valves, better exhaust. Everytime you remove a restriction you get better flow, more HP and a drop in boost. I dropped from 19.5lbs of boost to 17lbs of boost when I installed ported heads with bigger valves. If I want to run the same boost the blower has to turn 15% faster. I ported the hell out of the blower so I hope to be 20lb at least. Sure Im getting more air and fuel in the chamber with a less restrictive exhaust but if I want max performance far exceeding stock specs one needs bigger boost numbers on a free flowing intake and exhaust and the way to do that is spin the hell out of a M90 or get a bigger blower;) If I stayed with the same blower and pulley did everything else I have done on my car I bet my boost would be around 6lbs and Im sure I wouldnt be putting down the numbers I want

Ken
 
Ok, I understand what you're getting at now Ken.

Hypothetical situation -- Basically what Manny said (but assuming the car has a good tune) -- You run 15psi stock with a 10%. You modify the exhaust so that it drops you to 11 psi. What you've done is allow more air to get into the cylinder, where it matters, and not stacking in the lower intake plenum (Where your boost gauge is reading). You didn't loose anything. Actually, you gained everywhere, so there really is nothing you need to make up.

In this scenario, you COULD put a 15% on the stock m90, but that's at the price of blower efficiency, more heat, and more parasitic loss from the belt. Would you gain power? maybe, maybe not.

I thought the reason you went to the m112 was so that you didn't have to spin it as fast to make power. I don't know nearly enough about the m112 as I should so educate me if you don't mind... Isn't it quite a bit more efficient at lower rpms?

EDIT: Specified "Lower intake plenum" because "Intake pipe" was ambiguous. (Two intake sides... the blower's intake side, and the motor's)
 
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