johns84bird

For a daily driver car with weekends at the track. I am looking at comp cams High Energy 268H, because it is one of only five street legal cams that I can find for my 350 in their huge catalog. I want to optimize for low and midrange torque. Also, I was wondering how well that cam would match with edelrock performer aluminum heads, and either the edelbrock performer intake manifold or the weiland action plus(need street legal and egr). The car will have everything my signature PLUS slp 1 5/8 headers, catco 3inch in/out hi-flow cat, and hooker cat-back. (please don't flame me about the headers being too small for a 350 if you are going to respond, because I am following advice in John Lingenfelter's book, although I will accept CONSTRUCTIVE criticism because I don't know everything about performance yet). Thanks in advance guys.
John

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• 84 Firebird w/ T/A gfx
• 350 4bbl (LM1)
• Automatic
• Non-leaking T-Tops (new rubber all around)
• Working headlights (new parts)

Mods: K&N, 180* stat, ram-air hood, flowmaster muffler (ugh), Accel cap & rotor, MSD Super Conductor Wires, 24mm solid rear & 36mm hollow front sway bar w/ PST polygraphite bushings and endlinks.

Mods Coming Soon: new gray interior, Spohn SFCs, more PST bushings, front WS6 springs and an entire exhaust.

http://www.homepagez.com/350thirdgen/

RatMtrs

I would say don't waste your money on the performer heads get the RPM's or some cheap irons. Even s/r torquers ported/polished. You can pick em up for about $650 at Northern auto parts.com go with the XE268. I don't know much about egr but as far as street legal that's a pretty broad statement, I've seen pratically race motors run street legal in a first gen.

Your gonna want that size headers or even Thorley tri-y's for low/mid power. If you really wanna go for low/mid power go with a cam like the comp XE262 with some good heads like 180cc Dart Iron Eagles but you might want a bigger cam like the xe268.

johns84bird

The only reason I didn't mention performer RPMs is because I thought they weren't emissions legal for my car. Also, I have the comp cams catalog and it says the xe (extreme energy) cams are for off road use only. First gens are exempt from emmisions testing arent they? I still have to get an annual check and I live in PA where they are d**ks. I definitely want aluminum cause I'm trying to save weight off the front of my car. I believe performers are 170cc, so you think I should go a bit bigger with both heads and cam? Thanks for replying. Anyone else?

88IROCs

While I respect Lingenfelter's opinions on engine building his theories on headers contradict the experience of those people who are only in the business of building headers.

<u>To wit:</u>
"Primary pipe diameter is far more important to ultimate engine power than pipe length."(page 130, para 2)
Actually pipe length is equally important to pipe diameter, in determining the rpm at which the most efficient scavenging occurs(resonance). For a given resonant rpm: if you decrease the diameter, you have to increase the length or if you decrease the length, you have to increase the pipe diameter. With the thirdgen's limited and obstructed engine bay, you are limited to relatively short pipe length's. Thus you need to increase the diameter to reach a certain resonant rpm. Keep in mind too that, although the SLP 1 3/4's have a larger pipe inside diameter than the factory manifold's, their longer pipe length will develop a stronger scavenging pulse(which would be true of almost any header, as the factory manifold's pipe length is too short to develop much of any scavenging action). Also, there is restriction to flow posed by the numerous bend's in the typical thirdgen header. These bends reduce the velocity of the exiting exhaust plugs, which ultimately decrease the effectiveness of the scavenging wave. The larger pipe diameter has the effect of decreasing the restriction posed by these bends(though, admittedly, this becomes more of a factor as rpm's increase.)

In a larger, less obstructed engine bay, 1 5/8" primaries would be ideal for a 350 cid engine - if sufficient room exists to utilize a full-length header. But the room needed can be significant. For example to tune the resonant point for the above engine, so that it occurs at 3500 rpm, a primary pipe inside diameter of 1 5/8" would need a primary pipe length of approximately 30" and a collector of approximately 12". Needless to say these pipe length's are impractical in a thirdgen, but shortening the length's requires an increase in inside pipe diameter.

By the way, with their LS1 pipes, SLP has acknowledged that pipe length plays a critical role in developing "ultimate engine power".

"Most authorities agree that equal-length headers are important, but mainly when applied to finely-tuned race engines"(page 130, para 1).
I'll agree that equal-length tubes will have more effect on a race engine(no big surprise there), but they can also have a measurable effect on a milder street engine. If the pipe length(along with pipe i.d.) determines the resonant rpm, then using different length's will cause the resonant rpm to vary by cylinder. Because the scavenging effect is critical to drawing the fresh intake charge into the cylinder, unequal-length pipes will cause a variance in cylinder-to-cylinder filling efficiency(VE). Balancing VE between all cylinders, is extremely important to "ultimate engine power". When a header manufacturer tries to downplay the importance of equal-length tubes, what they are really saying is that: making the tubes equal is difficult(darned near impossible in a thirdgen)and not worth their bothering for the money involved.

Lingenfelter has some considerable experience in the engine building game(more so for race engines that those meant for the street), but too often in his book he plugs his own products - at the expense of competing product's which are equally, or more, capable. When he does that, his book becomes nothing more than a glorified catalog, and should be taken as such.

Caveat Emptor

SLP 1 3/4's will not decrease your low-end torque, in fact they will probably increase it(vs stock manifolds). But the ultimate question becomes: how much low-end torque do you want or need? Short of major suspension upgrades or Sportsman II's, most 350's can generate enough torque to smoke 'em at will. But going up in smoke doesn't win races(at the track or on the street).

[This message has been edited by 88IROCs (edited May 21, 2001).]

johns84bird

Thank you for your very objective reply about the headers. I will take it into serious consideration. So basically what you're saying is go with the 1 3/4" headers and optimize more for midrange and high end power with less focus on low end torque because in our cars, the traction isn't there. that is a very good point and it makes sense. what about the street-legal cams and heads? any recomendations? I thought I had a plan picked out but now I'm second-guessing it. I am going to be buying some performance parts for my car soon, I just dont know which.. can anyone help me pick out a logical package for my application? Maybe someone could explain this emmisions thing to me better also. I was under the impression that if you dont have a c.a.r.b EO # on the part that you cant use it on the street. Thanks guys.
John

88IROCs

Can't tell ya too much 'bout emissions, as there ain't no testin' for it where I live. No visuals, no sniffer, nuthin'. Hell, the cops can't even do nuthin if ya remove thet cat and thet there pump fer air. All the same tho', I'll do what I can ta keep thet hole in za ozone layer from gittin bigger. I figger all them eemission deevices ain't steelin thet much power, so I keeps them workin'. 's the least a feller can do.

Now 'bout them heads,...

For the money($950 - $1000), you can do a lot better than the older Edelbrock heads(Performer and Performer RPM). They don't flow that much(compared to similiarly priced heads) and the combustion chamber design is practically paleolithic. For this price range you should be looking at either TFS 23° heads or something from Canfield. However, both of these heads are a little weak on the exhaust side(nothing that a mild port and polish can't cure though).

Another option might be the Edelbrock E-Tec aluminum heads, though I haven't seen any prices for them yet. The 170cc version of this head has very good flow(for an intake runner of this size) and coupled with a very good combustion chamber, these heads should make good power over a wide rpm range. Keep in mind though, that these heads require a "Vortec"-type intake manifold(which Edelbrock will be happy to sell you).

This is getting to be an old saw for me but, I think the weight savings from aluminum heads(about 80 lbs) is overrated. This weight only represents about 2.5% of the average thirdgen's weight(3400+ lbs) and won't do much for transfering weight onto the rear axle during acceleration. This of course is really the job of the chassis and suspension. While the torque arm/control arm arrangement did an acceptable job with the low power thirdgen's of the early eighties, it is quite inadequate for L98's or any engine capable of making some real torque. Because of the length of the torque arm, the instant center tends to be too far forward to generate much rearward weight transfer. Further, flexing in the torque arm, control arms and chassis works against weight transfer onto the rear end.

My recommends: buy a set of cast-iron Vortecs(and a matching manifold) and spend the money you save(over aluminum heads) stiffening the suspension and chassis. Aftermarket torque arms and control arms are a good place to start. Later subframe connectors, adjustable shocks, variable rate springs. That way as you make more power later on, you can shred asphalt and not rubber.

It's been a while since I've looked at flat tappet cams(all four of my current vehicles have roller blocks) but the cam you mentioned seems a little big for the motor you have in mind. Additionally, I believe this cam has around 50° of overlap - which means it will release a lot of unburnt mixture into the exhaust at lower rpm's and could make passing the sniffer test difficult. As mentioned above: the 260H(or even the 252H) might be a better choice for all-around drivability and emissions compatibility.

With a 350, Vortec heads and manifold, a 625 cfm carb, free-flowing exhaust and the 260H cam: 400 lbs/ft and peak hp at 5000 rpm, or higher, is quite doable.

Hope some of this helps and Good Luck!

[This message has been edited by 88IROCs (edited May 22, 2001).]