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Discussion Starter · #1 ·
To start off, I'm really sorry if this question (or a similar one) has been asked before, but I just searched through old posts for more than an hour, so I don't think that it has. My question is this:

I have PR3 pistons for raised compression, and I plan on getting either Crower 403 or 404 cams, along with AEM or Skunk2 cam gears. I don't want to mod too seriously, just get as much as I can out of mainly those mods, and keep it as a daily driver. What sized exhaust would you recommend, and what else, such as IM's and TB's would go well with that setup? Any info you can give me would be greatly appreciated.
 

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Discussion Starter · #3 ·
I'd rather not go for the ECU reprogram, I'm just trying to get the flow right, so I can get as much as possible without any big mods. My big concern is exhaust size. I'm not sure if I'd want to raise my redline or not, but I don't think so.
 

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Mike, recommending an ECU reprogram before cam optimization? i thought that was the last thing you do, after your package was complete.
 

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Of course he's not.

And I find one thing COMPLETELY HILARIOUS... you don't want to mod it heavily, yet you want to swap pistons, use the most powerful street cams for your setup (that require dual valve springs), and change the IM and TB? I would think that in comparison to those, ECU tuning wouldn't be that drastic...
 

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Discussion Starter · #6 ·
I don't mean I don't want to mod it heavily, just not much more serious stuff than I already have. IM and TB are bolt-ons, and that's basically what I was asking about. And I probably won't be using the 404's , because I've got a good deal pending on the 403's.
 

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an tunable ecu can be set now, and set again later. id agree that with the changes you plan for your engine, a real engine management system will help greatly. as exhaust goes, you should be fine with a 2" collector, 2.25" cat, and 2.36" exhaust. if price isnt a concern, talk to the guys at hytech or smsp. with all that and the IM/TB you should be puttin down some damn good times. a quaife for your new-found power might not be bad, either.
 

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you can't get the powerband to "firm up" with the IM /cam without an ECU reprogram...I assumed this is all you are doing to the fuel, and air delivery and will not proceed further than this in terms of mods. Then a reprogram is right. The stock 240 cc/min @43 psi injectors are fine for your needs...you won't need much bigger. an FPR can make a 240 injector go to 270 if you need that much more fuel during the reprogramming on a wideband at a dyno.
 

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Discussion Starter · #11 ·
Michael Delaney on Jan/13/03 said:
USDM DC 4-1 2 in. collector, 2.25 in. ID cat with a 2 3/8 in. OD exhaust is more than enough for a big 62404 with skunk2 IM LS.
That isn't changed by the raised compression of the PR3s? EDIT: If I would want the 2" collector header, does anyone know if that is probably what this guy is talking about?
 

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i thoguht that relationship was through horsepower achieved. or potential horsepower achieved since a restrictive exhaust would cause a significant loss. i figured the system would prevent any chance of reversion, and give him the extra high horsepower he seems to want with the 404's. what would be the correctly sized system? 2"->2.25"->2.25"?
 

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Greg,

2-> 2.25-> 2.25

OR

2 -> 2.25-> 2.375


both would work for a 1.8L with the 404 exhaust cam duration.

Remember....

1/3 of the way you make power is determined by the rule: in N/A, remove at least 80-85% of the volume of gas you take in...exhaust flow divided by intake flow volumes.

what goes in, must come out....

cams control "when" the volume comes in and leaves across the rpm range.

IM/headporting and exhaust sizing controls "how much" comes in and leaves.


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we can get into the relationships between cam timing and header & exhaust sizing a bit here.

there is a classic book on 4 stroke performance by Bell in which he describes the following formula for a 4-1 header sizing:


P = ([850 x ED] / RPM) - 3


P = header primary tube length in inches

ED = 180 crankshaft degrees + exhaust cam's valve opening spec BBDC

RPM = Tuned RPM for where you want the peak torque to occur

So exhaust cam's opening spec does determine the header length on a 4-1.

The formulas Bell describes to get the diameter of the tubing are further described here:

http://www.racecar.co.uk/btb/010102news.htm

where displacement also factors into determining optimal sizing in a 4-2-1 header.


if you look at the papers on 2 stroke motorcycle engines, where scavenging at overlap is even more of an issue compared to 4 stroke motors, you will see that they describe the relationship between header length and diameter with static CR.


As you may remember, on the intake side, we use static CR to recapture some cylinder pressure lost from intake reversion with a longer duration cam.

Similarly, on the exhaust side, static CR is used as a compensator for lost cylinder pressure when the diameter of the exhaust system increases.

Exhaust diameter can be increased to reduce backpressure up to a certain diameter. We push the limit or envelope of this diameter to "release" or free up some hp that was lost from inefficient exhaust gas removal from the cylinder. If you go past this limit and go too big, the flow speed dies or stagnates and the efficiency of cylinder gas removal dies with it. So it's a tight window we are aiming for: big enough to reduce backpressure to allow high exhaust flow speeds but not too big as to end up reducing the flow speed.


You'll remember from my exhaust article that as diameters increase, the peak torque shifts to a higher rpm.

The goal of our engine package is to have the highest area under the torque curve or a broad torque powerband in which:

1. the torque curve is at peak torque for the longest time (widest rpm range) as possible

2. this wide powerband is located over an rpm range that is usable by our tranny gear ratios.


So to widen things up, a higher CR on the exhaust stroke will have higher cylinder pressures earlier to assist in pushing the exhaust gases out at a faster speed. The faster exhaust flow at an earlier rpm is a counter to the bigger diameter exhaust effect.



People also discuss exhaust port shapes and exhaust cam duration as other factors that determine whether you need a higher static CR on the exhaust stroke.

Exhaust cam spec can determine something called the blow down period (not blow-by). Blow down period is the number camshaft degrees the exhaust port is open by itself without any overlap with the intake port. Longer blow down periods need higher static CR as it relates to cylindr pressure.

Exhaust port shapes can be changed by headporting. Some people raise the height of the exhaust port roof during porting so that the piston "sees" the exhaust port earlier on it's way up during the exhaust stroke to remove more exhaust gas. When you raise the exhaust port's height, the combustion chamber volume also changes. The static and dynamic CR is decreased. To compensate for this loss in cylinder pressure from porting, a higher static CR is used.

So we change the static CR not only to improve burn efficiency but also use it as a "fix" for situations when unwanted loss of cylinder pressure occurs due to an increased cam duration causing intake reversion or due to a large diameter header-exhaust.
 

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if you read that article in the Nov. or Dec. 2002 (can't remember which) Turbo Magazine on Burns headers, they throw out this simple line: "we change the length of the header primary when cam specs are changed."

if you talk to John Grudynski at HyTech, he'll tell you his longer than stock hybrid 4-2-1's like a little higher static CR than the USDM ITR's stock 10.6:1...

now you know why....
 

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good stuff. i completely missed that point before. i never would have considered that cam timing and static compression could affect your header specs like that. bah, looks like i need to go to the bookstore and get some of corky's stuff...
 

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You'll notice that at the Virginia Battle of the Imports, the all motor Street Stock Class winner was Fred Highland who runs on Crower race cams in his GSR.
They're not bad import cams: VTEC or nonVTEC.

You won't regret using PR3 pistons and nonVTEC 62403's. If you plug in the Intake Cam's ABDC closing spec [ from the 2nd page of the B18B Cam thread in the Performance Forum's COMMoN TOPICS ] into the Dynamic CR Calculator [see COMMoN TOPICS from this forum], you'll see how much of change (or gain) in cranking pressures you'll get along with the added cylinder filling. It's a good package.

You really do need a 4-1 with 2.25 in. cat and 2.375 in. exhaust to efficiently scavenge those cams.
 

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I already have a 4-2-1 header. Do you think it would make a huge difference going to the 4-1 (assuming I go with the 2.25" cat and 60mm exhaust)?

Also, while we're speaking on this, what other things would you recommend to have installed while doing a cam install without pistons?

I'm thinking FPR, Cam Seals, Valve Cover Gasket, Cam Gears, of course springs/retainers... anything else that I am missing that would help the cams operate, or just simply be stupid not to do while they're off?

And can you explain why an FPR will help the cams work well? I believe MD, you said that it would help with the idle...
 

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bigger lift duration & overlap cams make their power in the upper powerband.

this is where all the "serious" N/A power is made for these 1.8L (i.e. low displacement) inline 4's.

VTEC, a 4-2-1 layout, dual stage IM runner lengths, and adjusting the cam gears for a wider LSA/less overlap all try to recapture the lost power in the midrange once you go to high powerband location modifications like "wilder N/A cams". They try to make the engine more streetable or flexible or driveable in the rpms where you spend the most time at , in a daily driver.

In race cars, streetable is not a consideration. only performance is. Performance (faster times) means a no-compromise high powerband location. Driveability is "sacrificed at the cross". So a 4-1 header works in conjunction with or "tows the party line" with a package that aims for maxing out the upper powerband location "performance only" motor.

So the trick in this game is to strike a balance between the 2 states of existence: streetable vs race only.

when you choose more of one end, you sacrifice the other. You want it to be driveable in your daily commute? then don't expect to do high 12's to low 13's with no reliability issues at the same time...it's just not going to happen...that's the reality of physics. These N/A 4 bangers go faster only if you juice the upper end powerband (i.e. make it wide and big up there).

if you really want a 12's daily driver, stop dicking around and get FI or bore out to 2-2.1 L then...that will give you low end and high end at the same time...N/A can't do both if you keep the same displacement.
 
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