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Old 10-23-2018, 07:57 AM   #1
T0XIX
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Question Performance Intake manifold for dohc

So as the title says I'm looking to see what my options are for a performance intake manifold if there is one.. I race dirt track in a 97 with a dohc engine and I'm hoping someone can point me in the right direction.

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Old 10-23-2018, 08:53 AM   #2
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Default Re: Performance Intake manifold for dohc

Pretty much only have what you can create with a welder and/or die grinder. I don't believe the stock PCM will net you much, if any, gains from doing any intake work but you might feel something with a CAI, DOHC Geo Storm TB & port matching.

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Old 10-23-2018, 10:42 AM   #3
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Default Re: Performance Intake manifold for dohc

The plastic manifold for the 3rd gens is supposedly better for performance.
Equal length runners, less heat soak, smoother surface inside.

It will take some modification to mount onto your head. The fuel rail and throttle cable will need tweeking too.

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Old 10-23-2018, 08:48 PM   #4
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Default Re: Performance Intake manifold for dohc

Thanks, is there anything I can do to the engine to get a few extra hp, the class I'm in stays it must be all stock or at least stock appearing. Nothing a coat of flat black paint can't fix

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Old 10-24-2018, 09:27 AM   #5
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Default Re: Performance Intake manifold for dohc

Look up deeb's build.
Flat faced valves, deck head, etc, etc.

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Old 10-26-2018, 06:34 PM   #6
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Default Re: Performance Intake manifold for dohc

Quote:
Originally Posted by AlexofNazareth View Post
The plastic manifold for the 3rd gens is supposedly better for performance.
Equal length runners, less heat soak, smoother surface inside.

It will take some modification to mount onto your head. The fuel rail and throttle cable will need tweeking too.
This is incorrect. The factory rated power output for 1991-1999 DOHC engines is 124hp @ 6,000rpms.

2000-2002 DOHCs are factory rated for 124hp @ 5,600rpms.

The stock, aluminum manifolds are sufficiently flowing up to 6,200rpms. They are a perfect port match to the cylinder head, on 1991-1998 DOHC engines, which is why there are no "performance" manifolds for the NA-build engines.

It is not needed, and is also why improvement to the intake side nets very little gains.

Porting a stock TB will allow the engine to make its peak HP at 6,200rpms.

The plastic manifolds will NOT interchange onto the wide(1991-1998) cylinder heads, due to port design and bolt patterns.

OP, if you are looking to boost performance, leave the intake side alone other than the TB and an aftermarket intake kit for the air cleaner.

This engine benefits more from exhaust porting and making the exhaust more efficiently flowing, as well as from compression increases by using flat-faced valves from the 1991-1992 cylinder heads, on your 1997 block.

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Old 10-26-2018, 06:37 PM   #7
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Default Re: Performance Intake manifold for dohc

And do NOT shave the block or the head, unless you want to go through trying to re-time your camshafts for the loss of performance with the retarded cam timing caused by shaving the head and block.

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Old 10-28-2018, 07:07 PM   #8
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Default Re: Performance Intake manifold for dohc

Quote:
Originally Posted by Saturn Night View Post
And do NOT shave the block or the head, unless you want to go through trying to re-time your camshafts for the loss of performance with the retarded cam timing caused by shaving the head and block.
I think you often confuse yourself by ignoring facts such as dyno runs posted by people that have actually done it. Some of the highest HP Saturn builds done in NA form include intake work and shaving the heads.

If you ignore all of that information you can convince yourself that it makes sense to engage in fearmongering about mods. But it really only makes sense if you ignore reality.

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Old 10-29-2018, 07:45 PM   #9
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Default Re: Performance Intake manifold for dohc

Quote:
Originally Posted by Saturn Night View Post
This is incorrect. The factory rated power output for 1991-1999 DOHC engines is 124hp @ 6,000rpms.

2000-2002 DOHCs are factory rated for 124hp @ 5,600rpms.

.
124hp@5600 rpm = 116.3 ft/lb torque
124hp@6000 rpm = 108.5 ft/lb torque

I would like to see the hp figure for the 91-99 DOHC at 5600, I bet it is a lot less than 124 hp.
Likewise I would like to see the hp figure for the 2000-2002 at 6000 rpm, I would guess it isn't far below 124hp.

I'll take the 116.3 ft/ lb torque. For what I do, it will get me moving faster.

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Old 10-30-2018, 11:10 AM   #10
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Default Re: Performance Intake manifold for dohc

I was also only referring to the manifold itself providing a performance benefit, not the 3rd gen cylinder head.

I'll be adopting a 3rd gen intake when I rebuild my next motor. Just make sure to perform the coolant line fix to avoid it cracking and leaking.

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Old 10-31-2018, 12:06 PM   #11
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Default Re: Performance Intake manifold for dohc

Quote:
Originally Posted by Signmaster View Post
I think you often confuse yourself by ignoring facts such as dyno runs posted by people that have actually done it. Some of the highest HP Saturn builds done in NA form include intake work and shaving the heads.

If you ignore all of that information you can convince yourself that it makes sense to engage in fearmongering about mods. But it really only makes sense if you ignore reality.
Team sCR only netted 5hp from re-timing the camshafts, after they shaved their head to get 10.0:1 compression, which gave them 151bhp. You gain a static compression ratio of 9.8:1, with flat faced valves and stock camshaft timing.

For building compression, using a longer connecting rod would be better than shaving the head or decking the block. Use of a longer rod would give higher compression, by allowing the piston higher travel upward in the cylinder.

It is no different than using a larger lifter ratio, on your valves, to boost lift over swapping in a new camshaft(such as dropping a 1.5:1 lifter for a 1.6:1 lifter).

Camshaft lobe lift x lifter ratio = total valve lift

Example: Cam lobe lift .250" x 1.5 = .375" at the valve

.250" x 1.6 = .400" at the valve

There are many way to make cheap power out of just about any engine, if you actually know what you are doing and what the limitations of the engine are.

And ironically, when I try to find a link to the Bill Deeb's build website, my browser gives me an HTTP 403 Forbidden error, and I notice that nobody can seem to post a working link and hasn't done so since I have been on this site.

However, I CAN post a link to the Team sCR build results on their 1992 Saturn to confirm that there is very little gained from the expense of shaving the head and re timing the camshafts.

http://www.teamscr.com/motorsports/t...owall=&start=2

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Old 10-31-2018, 12:12 PM   #12
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Default Re: Performance Intake manifold for dohc

Quote:
Originally Posted by laser3kw View Post
124hp@5600 rpm = 116.3 ft/lb torque
124hp@6000 rpm = 108.5 ft/lb torque

I would like to see the hp figure for the 91-99 DOHC at 5600, I bet it is a lot less than 124 hp.
Likewise I would like to see the hp figure for the 2000-2002 at 6000 rpm, I would guess it isn't far below 124hp.

I'll take the 116.3 ft/ lb torque. For what I do, it will get me moving faster.
Until you account for the gear ratio, when changing gears. The MP3 transmission drops about 1,300rpms with each gear change, which means running the engine beyond 5,600rpms is over revving(this is how you float valves and burn your engine up), to shift back to peak torque rpm(4,800), and if you shift at peak HP rpm(like you are supposed to), you drop BELOW peak torque rpm(4,800) and then you are lugging the engine for a few milliseconds as the engine gets back to its most efficient speed and into the power band.

This concept is WHY the automatic-equipped Saturn S-Series are almost a full second slower in the -mile, versus their manual-equipped brothers and sisters. The automatic, at WOT, will shift from 6k, back to 4,200, in every single gear.

And it is quite noticeable when you are going down the track.

This is also one of the reasons that older 1st/2nd Gen Saturns put up better 0-60mph times over the third gen S-Series. You also don't have to worry about cracking your aluminum manifold, from everyday driving, like the cheap, plastic 3rd Gen manifold.

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Old 10-31-2018, 08:34 PM   #13
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Default Re: Performance Intake manifold for dohc

Quote:
Until you account for the gear ratio, when changing gears. The MP3 transmission drops about 1,300rpms with each gear change, which means running the engine beyond 5,600rpms is over revving(this is how you float valves and burn your engine up), to shift back to peak torque rpm(4,800), and if you shift at peak HP rpm(like you are supposed to), you drop BELOW peak torque rpm(4,800) and then you are lugging the engine for a few milliseconds as the engine gets back to its most efficient speed and into the power band.
in this argument, I guess you're saying revving a motor with a aluminum manifold to 6000 rpm won't float the valve and burn your engine up , but if you take the same motor and install a plastic manifold and rev it to 6000 rpm, the it will float the valves and burn up the motor?
point being the basic long block with head, cams, pistons, rod, crank etc, will rev will past 6000 rpm with out problems.
Show me the actual, realistic torque and horsepower curve for the same engine combination with each manifold.
Theoretically, the plastic manifold could be making 123 horsepower at 6000, but that wouln't be a "peak" number

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Old 11-01-2018, 06:52 AM   #14
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Default Re: Performance Intake manifold for dohc

Quote:
Originally Posted by laser3kw View Post
in this argument, I guess you're saying revving a motor with a aluminum manifold to 6000 rpm won't float the valve and burn your engine up , but if you take the same motor and install a plastic manifold and rev it to 6000 rpm, the it will float the valves and burn up the motor?
point being the basic long block with head, cams, pistons, rod, crank etc, will rev will past 6000 rpm with out problems.
Show me the actual, realistic torque and horsepower curve for the same engine combination with each manifold.
Theoretically, the plastic manifold could be making 123 horsepower at 6000, but that wouln't be a "peak" number
What rpm the bottom end can survive up to and the rpm that the valve train can with stand are capable of being different.

A few reasons that American automakers began experimenting with OHC designs in the 1970s:
Allows for high rpm limits to the valve train
Allows for better positioning of the spark plug in the combustion chamber
Better valve train geometry

Now, with that being said, engines produce power by burning fuel. To do this, the engine needs so much time to atomize the fuel, ignite it, burn it, and repeat.

When you go past your peak torque rpm, the engine has already started losing power from loss of thermal efficiency, or achieving the best mix and burn of fuel within the cylinder, which generates the highest cylinder pressures, hence the PEAK TORQUE.

To create peak HP, you spin the engine faster than its most-efficient speed, however, the power being made is still better than the constant losses of power associated with the increased engine speed.

Once you pass the peak HP rpm, torque output drops at an exponential rate because now the engine is losing power from BOTH inadequate pressurization of the cylinder and poor atomization AND increasing rotational speeds(which increases friction).

Valves do not just "close" on their upward motion between engine strokes. They actually bounce a few thousandths of a inch, when closing, because they are on a spring. Valve float can occur at a lower rpm than the maximum rpm the bottom end can handle. Valve float damages the valve seats, because the valve doesn't have time to close and seat, before the cam lobes begins opening it again.

The bottom end is unaffected by this dynamic, because it is a rotational motion, not a reciprocating motion. Thus, the only frictional destructive force is centrifugal force.

While running a 3rd gen head to 6,000rpms may not float the valves, the torque curve between a 3rd Gen from 5,600-6,000rpms has a sharper drop to it, than the 1st Gen/2nd Gen heads would have between the same rpm range.

The older heads have a better designs, better manifolds for power output, hence why those that do race them build the older engines and don't use the plastic manifold.

However, I realize some of you are simply trolling to see how long I will debate this topic.

So, go ahead, try to even get that 3rd Gen manifold to fit the older head.

And post a dyno test to back up your claim.

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Old 11-01-2018, 09:07 PM   #15
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Default Re: Performance Intake manifold for dohc

that's a great write up Saturn Night! I am sure someone will find it useful.
Now - take a deep breath and relax.
You ended up trolling yourself.
This started out with the OP asking for a performance intake manifold for a oval track car.
A couple of people gave viable suggestions. The one using a late model plastic manifold even had the disclaimer
Quote:
It will take some modification to mount onto your head. The fuel rail and throttle cable will need tweeking too.
Then it turned to what engine made horsepower and at what rpm - that has nothing to do with whether manifold "A" will work better for the OP on his motor over manifold "B", ( also see above mention disclaimer)
Then, every other suggestion was poo-pooed. Most of which are tried and proven to help the OP achieve his goal of
Quote:
Thanks, is there anything I can do to the engine to get a few extra hp, the class I'm in stays it must be all stock or at least stock appearing.
Then it turn to gear ratios and how shift gears is bad yada-yada-yada. I have never seen a stock car "shift gears" while at race speed - so that argument is out. Then it was how detrimental the plastic manifold would lead to
Quote:
running the engine beyond 5,600rpms is over revving(this is how you float valves and burn your engine up),
your words -
Then you state the engine with the aluminum manifold is good to 6200.
Quote:
The stock, aluminum manifolds are sufficiently flowing up to 6,200rpms.
Quote:
Porting a stock TB will allow the engine to make its peak HP at 6,200rpms.
Thus, disproving your own statement.

Then more distraction about fundamentals of engine theory - none address the basic question whether the plastic manifold would help, his motor, on a dirt track (while not shifting gears).
All during this exchange I have asked for power charts you keep referring to to uphold your assertions, and of course which, have not appeared. Even a link to another site would be appreciated.
So- You trolled yourself into this mess, used several unconnected straw-man arguments, poo-pooed on everyone's attempt to help the OP and ended up with this rebuttal.
that's it for now - I refrained from punctuation with smiles, that seems to upset people.

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Old 11-02-2018, 09:23 AM   #16
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Default Re: Performance Intake manifold for dohc

lulz. Saturn_Night got told.

The consensus over on the sphere is that yeah the AL manifold works, but it flows like garbage. With supplementary injectors and boost, cylinder #4 would lean out because the flow to it was so poor and it didnt receive enough fuel.

Anyone who was serious about making power would have their own intake welded up. So before making claims about how great the AL manifold is, do a bit of reading to see what's been done in the past.

The bottom line is that the plastic manifold is better for the following reasons:
1. Its lighter
2. It has more even flow to each cylinder
3. There's no need to extrude hone out casting marks to smooth the runners.
4. Plastic is an insulator and doesn't heat soak as bad.

The main downsides are that it takes some work to bolt onto the 5 bolt heads and the coolant port/egr need to be dealt with to make it work. If that's OK with the OP, then that's the route I would suggest going.

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Old 11-02-2018, 01:39 PM   #17
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Default Re: Performance Intake manifold for dohc

Quote:
Originally Posted by laser3kw View Post
that's a great write up Saturn Night! I am sure someone will find it useful.
Now - take a deep breath and relax.
You ended up trolling yourself.
This started out with the OP asking for a performance intake manifold for a oval track car.
A couple of people gave viable suggestions. The one using a late model plastic manifold even had the disclaimer

Then it turned to what engine made horsepower and at what rpm - that has nothing to do with whether manifold "A" will work better for the OP on his motor over manifold "B", ( also see above mention disclaimer)
Then, every other suggestion was poo-pooed. Most of which are tried and proven to help the OP achieve his goal of

Then it turn to gear ratios and how shift gears is bad yada-yada-yada. I have never seen a stock car "shift gears" while at race speed - so that argument is out. Then it was how detrimental the plastic manifold would lead to

your words -
Then you state the engine with the aluminum manifold is good to 6200.



Thus, disproving your own statement.

Then more distraction about fundamentals of engine theory - none address the basic question whether the plastic manifold would help, his motor, on a dirt track (while not shifting gears).
All during this exchange I have asked for power charts you keep referring to to uphold your assertions, and of course which, have not appeared. Even a link to another site would be appreciated.
So- You trolled yourself into this mess, used several unconnected straw-man arguments, poo-pooed on everyone's attempt to help the OP and ended up with this rebuttal.
that's it for now - I refrained from punctuation with smiles, that seems to upset people.
Very well put.

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Old 11-03-2018, 09:58 AM   #18
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Default Re: Performance Intake manifold for dohc

Quote:
Originally Posted by laser3kw View Post
124hp@5600 rpm = 116.3 ft/lb torque
124hp@6000 rpm = 108.5 ft/lb torque

I would like to see the hp figure for the 91-99 DOHC at 5600, I bet it is a lot less than 124 hp.
Likewise I would like to see the hp figure for the 2000-2002 at 6000 rpm, I would guess it isn't far below 124hp.

I'll take the 116.3 ft/ lb torque. For what I do, it will get me moving faster.
If one was to take the HP and torque vs RPM numbers posted above, and then applied the incorrect bolded below....


Quote:
Originally Posted by Saturn Night View Post
The MP3 transmission drops about 1,300rpms with each gear change, which means running the engine beyond 5,600rpms is over revving(this is how you float valves and burn your engine up), to shift back to peak torque rpm(4,800), and if you shift at peak HP rpm(like you are supposed to), you drop BELOW peak torque rpm(4,800) and then you are lugging the engine for a few milliseconds as the engine gets back to its most efficient speed and into the power band.
....then the debate would be over, since the later engines don't require over revving to make power. Who would want to float the valves and burn up the motor?




In reality and back to the OP's original question, often in dirt track racing it's an advantage to have the gearing to take advantage of your power band. Since gearing options for the S Series are essentially limited to tire sizes, the inverse must take place, that being moving the power to where your gearing can take advantage of it.

This often means higher revs, and moving the torque curve up if possible. But that depends on the track.



In regards to the question posed by laser3kw, SPS did dyno runs and couldn't find 124 HP at 5600 RPM on the earlier head car. But then again, they weren't afraid of blowing up engines by going beyond 5600 revs either, so they did testing up to just shy of 6500 RPM IIRC. And the extrude honed intake combo was tested at some point, but not without mods unavailable to most.

But they did do testing with combos the OP might find useful, including removing mufflers/cats and adding intake stuff. With basic bolt ons (and bolt offs ) they made max power in the 6300-6300 RPM range. I guess all that valve float cost them power.

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Old 11-03-2018, 03:50 PM   #19
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2001 SC2
Default Re: Performance Intake manifold for dohc

Dirt track guys swap in Auto PCM's to their 5spd's for a reason...no moving rev limiter so they can keep it in 2nd or 3rd for another 300rpm and make it to the corner without wasting time/speed shifting gears. I *think* someone actually tested for valve float, found it closer to 7500rpm than 6500rpm.

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Old 11-03-2018, 05:29 PM   #20
OldNuc
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Join Date: Apr 2008
Location: Far Southwestern Iowa
Posts: 65,006
 

1998 SC2
Default Re: Performance Intake manifold for dohc

For almost every model year the DOHC valve spring, one or both, were changed. No telling where a given model year experiencing valve float.

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