only1jp : engine swap questions?

Re: engine swap questions?
Post by elwenil on May 9, 2006, 11:54am


Quote: <TABLE class=bordercolor cellSpacing=1 width="90%"><TBODY><TR><TD width="100%"><TABLE class=quote cellSpacing=0 cellPadding=2 width="100%"><TBODY><TR><TD width="100%">Depends on the type of headers...shorty types do much better at low RPM...long tube ones work better up high...</TD></TR></TBODY></TABLE></TD></TR></TBODY></TABLE>

I think that is backwards. For example:

Quote: <TABLE class=bordercolor cellSpacing=1 width="90%"><TBODY><TR><TD width="100%"><TABLE class=quote cellSpacing=0 cellPadding=2 width="100%"><TBODY><TR><TD width="100%">You must first determine what is the lowest RPM your competition engine is being run at and what is the highest; where does the engine get pulled down to on the shift drop or each individual gear change, and how long will the engine be in any particular RPM range. As stated before, a shorter primary tube tends to make more power in the upper RPM range and a longer tube favors the lower RPM.

An example would be best stated that an engine spinning at 8,000 RPM might make its best power with a primary tube length of about 26", but this same engine while at its shift drop might make its best power with a primary tube length of 30". Therefore there is no true ideal length primary tube, as it's impossible to change this length as it's accelerating your racecar. This is where the trial and error method beats computer engine simulation in real world racing conditions.
The actual horsepower of a particular engine usually dictates primary tube size, and by the maximum RPM the engine is spun.

Engine basics teach us that an engine is nothing more than an air pump, the more air we put into the engine the more air must come out. Today's smaller high flowing intake ports require a high flowing exhaust port that can expel the spent gasses, which proves that it requires a certain amount of volume and flow to produce a certain amount of power. This same general rule of thumb can be used to dictate the size of the primary tube required to make a certain amount of power on a competition engine.

As previously stated, Performance Welding feels its best to use as small of a primary tube possible for your particular application, just as with the collector sizing.

Every Competition Engine does, although have its own inherit characteristics. Some engines use a small high flowing intake and exhaust port and some use a large high flowing port. Some classes require a stock intake port, and to obtain high volumetric effiency with the engine, excessive camshaft overlap and duration is required to help the competition header pull air through the engine, as the low flowing stock cylinder head cant perform this feat on its own.

So being very general, a low horsepower 350 CID V8 engine making only 1.5 horsepower per CID may only require a primary tube size of 1 5/8"stepped to 1 ?". This particular engine would only require a merged collector throat size of approximately 2 ?" with a 3" outlet. The primary tube length is dictated by what RPM the engine is run at to obtain these power levels, with the vehicle weight, transmission, torque converter, and type of racing playing a dominating role.
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http://performanceweldingheaders.com/primary.htm

With that said, typically this thinking is for full size headers and shorty headers don't really apply since they lack the long, equal length tubes needed for true exhaust "scavenging". Shortys are an improvement over most manifolds since they normally have larger tubes. In my experience a set of factory "high performance" manifolds work best in a typical small block 4x4, since the low gearing tends to make for a lot of crawling at higher then normal RPMs and a lot of heat build-up. This tends to warp and crack a lot of headers, especially the cheaper ones. There are exceptions to every rule, but typically a 4x4 rarely sees the RPM ranges where a set of good headers will really make some improvements unless you are running in mud, which I despise.

Re: engine swap questions?
Post by compexp on May 9, 2006, 12:43pm

I used these on my 725 with a sbc 350 from an 83 truck.

http://gearheadworld.com/itemDetail.asp?item=145

Re: engine swap questions?
Post by whydah on May 9, 2006, 2:10pm

below, a couple links to excellent header stories from Chevy High Performance Magazine. i know these guys and hold their opinion in high regard.

i did a set of sanderson block huggers during my SBC swap. if i could do it over again, i would have went with a longer design for greater power & torque. i'd also run a hydraulic clutch so linkage interference would not be an issue. there is quite a bit of room left with a SBC in that bay, regarding headers, it is the linkage you are getting around.

the quality from sanderson, though, is pretty impressive. they have no head/flange gaskets (never used that style before) and i've rec'd no leaks and no backed off bolts. can't stand header gasket problems, a pet peeve of mine.

http://www.chevyhiperformance.com/te...der/index.html

http://www.chevyhiperformance.com/te...178/index.html