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Old 07-12-2011, 01:49 PM   #1
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Bowtie Vortec Heads-Exhaust Port Questions (GM #: 25534421)

Really need some help here from anyone who knows the details of the Bowtie Vortecs.

Want to replace my Gen1 sbc heads (pre ’87 versions on a 350) with the Bowtie Vortec small ports. While researching, I’ve come across several posts on various forums indicating differences between the exhaust ports on standard L31 Vortecs, Bowtie Vortecs and the Gen1 heads.
These posts talk about things such as": "the Bowties have raised exhaust ports", "the Bowtie exhaust port is moved out 0.250" in relation to other GM and aftermarket heads", "the Bowtie exhaust flange angle is different and your headers will not work, but if you have the standard Vortec heads your headers will work", "your headers will bolt up to the Vortecs but you may run into problems depending upon how close your primaries tuck in—the headers mount about ¼" higher on the Vortecs". Then there are others (several on this forum) that say none of the above is true and there are absolutely no differences. Very confusing to say the least!


Because of these differences of opinion, and at the risk of getting more, some specific questions:
  1. Are there any differences whatsoever in the Bowtie exhaust ports location, size, angle, bolt pattern, etc. when compared to Gen1 heads? If any differences, would appreciate details as to how they will affect header attachment/location.
  2. Will 1 5/8" headers (Dynomax ceramic coated-no emissions) for Gen1 heads work with the Bowties? If so, any plug/wire clearance issues due to different plug location, header not covering port, etc.? Have none of these issues now with the Gen1 heads. Again, would appreciate specifics.
Any pics would be great.

Thanks!
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Old 01-30-2012, 05:21 PM   #2
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Re: Bowtie Vortec Heads-Exhaust Port Questions (GM #: 25534421)

Bump! .....see if we can't get this answered. I've also wondered the same thing.
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Old 01-31-2012, 11:49 PM   #3
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Re: Bowtie Vortec Heads-Exhaust Port Questions (GM #: 25534421)

Abubaca – Thanks for raising this again. I reviewed many forums on this subject but got no concrete information, so decided to press ahead, bite the bullet and install the Bowtie Small Port Vortec Heads (GM #: 25534421) on my 350 (360ci) SBC.

In summary, there are exhaust port differences when comparing the Vortec heads to the older Gen 1 SBC heads. Below is what was learned. Some of this is hard to explain so please bear with me and apologies for the long post. I have headers so that reference is used in the explanation below, but the same should apply to exhaust manifolds:


Exhaust Port/Header Issues
  • With the Vortec heads mounted on the block, the horizontal and vertical position of the headers will be identical to their position when mounted on conventional Gen 1 heads (if no adjustment to the header mounting position is made – see below). That means there should be (note – should be) no clearance problems or issues with steering columns, heater boxes, etc. if the heads are installed/swapped and the headers just bolted on.
  • The exhaust ports on Gen 1 heads are centered on the centerline of the exhaust bolt holes. That is, 50% of the Gen 1 exhaust port is above the bolt hole centerline and 50% is below.
  • On the Vortec heads, approximately 60% of the exhaust port is ABOVE [now stated correctly] the bolt holes’ centerline and 40% is BELOW [now stated correctly] it. This design change apparently aids in improved exhaust flow. But it means that the inside diameter of the header pipe is not centered on the exhaust port if no mounting adjustments are made. See the attached pic. It shows how my header (Dynomax 1 5/8”) aligns with the Vortec exhaust port. The circle labeled ‘Stock’ in the pic represents the inside diameter of the header pipe and how it aligns with the Vortec exhaust port if the headers are installed without modification. The ‘Adjusted’ circle represents the alignment if the header flange bolt holes are modified (slotted) to allow the headers to mount 1/8" [now stated correctly] higher on the heads so as to center the header pipes on the exhaust ports.
  • I chose to mount the headers without slotting them, so nothing would change regarding header alignment/clearance. This was important as clearance is tight in a couple of spots. Slotting the header flanges to allow them to mount ¼” higher would appear to optimize exhaust flow as the ID of the header pipe would be centered over the exhaust port. How much HP would be gained in doing this is unknown unless dynoed. Likely not significant unless an all-out race car. Also, raising the headers to center them on the exhaust port would cause alignment problems of the header collectors with the rest of the exhaust system. Not something I wanted to address.
Other Important Considerations
  • Header Gaskets – The Vortec exhaust ports are essentially square with rounded corners (1 5/16” x 1 5/16”, or 1.31” x 1.31”). With the Gen 1 heads, used Mr. Gasket #5917 (1.82”W x 1.50”H). That gasket will not seal at the top on the Vortecs with 1 5/8” (my) headers. Had to use Mr. Gasket #1404 (1.5”H x 1.5”W). The headers sealed without leaking using this gasket. The Dynomax are well made with a protruding lip on each pipe that is larger than the ID of the pipe itself which causes a good seal around a larger exhaust port. Other 1 5/8” headers lacking this lip may not seal at the top (again, look at the pic), and may require 2 different size gaskets for a good seal. 1 3/4” headers should seal with the appropriate gasket.
  • Head Gaskets – With Gen 1 heads, previously used FelPro 7733PT2 head gaskets (4.125” bore, 039” compressed thickness [8.700cc]) to ensure piston clearance with the .060 overbore. This is a good gasket because it can be removed without anything sticking. No scraping required. However, on the Vortec heads, wanted to reduce the quench area, so used GM# 10105117 (4.100 bore, .028” compressed thickness [5.94 cc]). No retorquing has been required.
  • Spark Plugs – With the Gen 1 heads, used Delco R45TS. The Vortecs require a longer reach plug for optimum spark, so used Champion RS12YC (.708” reach). With the Champions, if you don’t like the ‘12’ heat range, ‘09-14’ is available.
  • Intake Manifold – A Vortec style intake is required. Selected the Scoggin Dickey (SD) Vortec TPI Intake #3816 ($399 at the time). The Edelbrock intake is identical to the SD except for the Edelbrock logo, but costs $100 more. I was told by SD that they licensed their design to Edelbrock. Other literature supports this. The top of the TPI plenum (both front and back) is at the same height as previously with the stock TPI manifold. Note that you may need to make a couple of block-off plates if you’ve removed EGR, etc. (Edelbrock includes the plates, perhaps for the extra $100). Aluminum plate (1/8”+) works fine with RTV as a gasket. Also may need a few NPT plugs to fill holes depending you’re your hoses, accessories, etc.
  • Intake Gaskets – After a lot of research, chose to use the more expensive GM # 89017465 (approx $45 – Wow!). But am told by the round track guys that they are reusable a few times because of the raised rubber/neoprene seals around each port and water jacket. The Vortec intake seems to have more space between the bottom of the manifold and the front and back lifter valley ridges on the block than does the stock TPI manifold. Because of this, plan on using about 1/4”+ thick bead of RTV sealer to seal the front and back of the lifter valley – nothing on the gaskets themselves perhaps except right where they join the lifter valley.
  • Intake Manifold Bolts & Installation – The old Gen 1 bolts won’t work. They are 3/8”-16 course thread bolts (16 bolts). Rather, must use 5/16”-18 x 1½” course thread bolts (8 bolts). I chose not to use the new GM self-bottoming bolts many recommend. These bolts, along with the intake gaskets above, were apparently released sometime after the release of the Vortec heads to solve all too many coolant leaks due to improper torquing and/or gasket deterioration. Because the fit of the intake is so critical, make four, 2” long threaded studs to aid in manifold installation. Bought 4, 2” long 3/8” bolts from Home Depot and cut off the heads with a Sawsall. Took 5 minutes. Screw the studs a few turns into the front and back holes on each side of each head, install the gaskets, lay down the RTV and carefully drop the intake manifold down using the studs for alignment and press/wiggle it around to seal the RTV. Remove the studs and install the bolts.
    Snug all 8 bolts initially to 2 ft lb.{24 in/lb}, then second pass to 8 ft-lb.{96 in/lb} and last pass to 11-12 ft-lb {132-144 in/lb} Below is torque sequence; ‘o’ = bolt location:
    7 1 / 3 5
    o o / o o

    Front / Rear

    o o / o o
    8 4 / 2 6
  • Head Bolts – The Vortec heads use the same number and length bolts as used with Gen 1 heads, but sometime later GM introduced a new design with a small flange under the bolt head. Since it’s thought best to not over re-use head bolts, I chose to use the new bolt design (GM complete bolt set #: 12495499). These bolts are pre-coated with a Teflon sealer, but very sparsely. Initially chose to not add additional sealer, but paid the price with a couple of the bottom (shortest) bolts not totally sealing. Fortunately no under-the-rocker-cover bolts leaked. So removed the leaking bolts one at a time, coated with Permatex 80632 Thread Sealant, retorqued and problem solved. Suggest coating all water jacket bolts with this or something similar.
  • Head Water Jacket Plugs – Like the Gen 1 heads, the Vortecs have a NPT threaded hole in the water jacket. If you have a thermocouple or something else that must install in one of these holes, you need to ensure that the headers will bolt on. Why? Because the top of the NPT hole is very close to the bottom of the header flange on the Vortecs. It’s 1/4+” lower on the Gen 1 heads. This is possibly because the exhaust manifold/headers are designed to mount 1/4” higher on the Vortec heads (again, see the pic). I only needed to use plugs in the holes, but because of the closeness of the top of the plug to the bottom of the header flange, a NPT plug with a hex head could not be used because the hex head is larger than the diameter of the NPT plug itself, and it interfered with the header flange. Naturally grinding was possible; but for me, a better solution was to use NPT plugs with a 4-sided head that is smaller than the diameter of the plug itself. These plugs worked without any grinding.
  • Head Accessory Bracket Mounting Holes – This was one of the principal reasons the more expensive Bowtie Vortecs were chosen over a cheaper aftermarket clone. If you review various posts and carefully question some of the Vortec clone manufacturers, some will admit that not all accessory brackets will fit without modification because of slightly varying GM bolt hole patterns over the years. Some of the head manufacturers pick one pattern and use it without regard to the others. My serpentine system moved from the Gen 1 heads to the Vortecs perfectly.
  • Push Rod Guide Plates – The Bowtie Vortecs assume you will be using self-aligning rocker arms. If you don’t, you’ll need pushrod guide plates [CompCams Flat Guide Plates (8) 5/16" #4808-8, approx $17]. Removed screw-in studs, installed guide plates and torqued studs to 35 ft/lb.
  • Pushrods – Pushrod length was measured with the Vortec heads installed using the old .039” gaskets (granted having an 0.011 compressed thickness difference between the old and new 0.028” gaskets to be used – this difference was determined to be immaterial). The measurements indicated that the stock length Gen 1 push rods were the proper length. The same is not true for some of the cloned Vortec heads. Because of the valves they use, many require at a minimum 0.100 longer pushrods for proper alignment of the valve train.
  • Head Condition When Received – Chose to order the heads from Jegs in case there was an issue requiring a return. There was. The heads come wrapped in an oil impregnated paper. However, when the heads were received, there were all manner of rust and pit marks on the machined surfaces, as if they had been stored in a very humid area for some time without any oil coating. Took pics, emailed pics to and called Jegs; and to their credit, they immediately issued a pick-up ticket and the heads were returned. Thanks Jegs! But when the second pair arrived (had to wait a few days because they were backordered so the second set was from a different manufacturing lot), they too were similar to the first but not as bad. Some minor filing and sanding took care of everything, but seems strange they would be in that condition. This is not Jegs fault. They buy all GM parts from a local Chevy dealer for resale as required by GM. Clearly the manufacturer is using less than adequate quality control and/or storage techniques. Go figure!
  • Valve Cover Height - One other issue to be aware of is that the top of the valve covers will sit higher with the Vortecs. How much, don’t know; but estimate 1/2”+. Just forgot to measure this before installation. It’s apparently due to the head’s raised upper lip for better oil control and leak reduction/elimination.
Bottom line – The head change was worth it. The seat of the pants difference from the old 76cc GM # 332882 heads to the Bowtie Small Port Vortec 65cc heads was massive. Static compression ratio increased from about 8.4:1 to just under 10:1. Also reduced the timing tables significantly and still have much more power and pull than before at all RPMs. Started with the stock AUJP timing tables and reduced every entry by 4-5* while retaining approximately the same shaped curve. Had to go to Plus fuel from Regular to avoid minor knocks, but well worth it.

Hope this helps.

Last edited by 84Elky; 07-11-2013 at 04:48 PM. Reason: Correction-Pic Change 7/11/2013 to Correct Header Realignment Distance
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Old 02-01-2012, 08:46 AM   #4
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Re: Bowtie Vortec Heads-Exhaust Port Questions (GM #: 25534421)

Are you references to "Vortec" dimensions (in your diagram and text) aimed at the Bow-Tie version or the stockers (pn 12558060) ?
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Old 02-01-2012, 12:27 PM   #5
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Re: Bowtie Vortec Heads-Exhaust Port Questions (GM #: 25534421)

Quote:
Originally Posted by skinny z View Post
Are you references to "Vortec" dimensions (in your diagram and text) aimed at the Bow-Tie version or the stockers (pn 12558060) ?
skinny z – Thanks for your question. It caused me to look at some of my notes and resulted in my making a correction to the original post to correct an error and to repost the diagram pic for clarity. Apologies to those who may have already read/printed this.

Your question will be address in a moment, but first to the correction. The original post stated that 60% of the Vortec exhaust port was below the bolt holes’ centerline and 40% above. That is incorrect and backwards. 60% of the port is ABOVE the centerline and 40% BELOW it. Again, apologies for the error as it’s key to the whole issue.

Now to your question. All references in my post apply only to the Bowtie Small Port Vortec Heads (GM#: 25534421). However, I have every reason to believe now that the logic can be applied to the original Vortecs you reference. Here’s why. Most of the Vortec clone manufacturers will admit that they used the initial Vortec head as their pattern to clone. Given that, plus my personally measuring both the cast iron and aluminum versions of the Patriot heads during a visit to their plant, I now realize that the Bowtie and Patriot cast iron exhaust port measurements are identical. I did not realize this until checking my notes to respond to your question.

Below are my notes on the Patriot heads made in June, 2010:



Measurements
  • Intake port
    • Cast Iron #: 2151-- 2 5/16h x 1 1/4w (MY MEASUREMENTS)
      • Per Patriot (2.315 x 1.175)
    • Aluminum (Not sure if the 185cc, or 190cc blended) – 2 1/8h x 1 1/4w
    • TPI Intake (OEM) = 1.96 x 1.20
    • Edelbrock/SD Intake = 2.05 x 1.23 (per Edelbrock Tech article)
    • The aluminum heads are not a Vortec clone. Have different combustion chamber
  • ExhaustPort
    • Cast – 1 5/16h x 1 5/16w (Sq w/rounded corners) [My Measure]
      • Per Patriot (1.342 [1 3/8] x 1.467 [1 15/32])
    • Aluminum (Not sure if the 185cc, or 190cc blended) - 1 5/16h x 1 7/16w
    • On both Cast and AL, all ports are slightly above the centerline of the bolt holes (approx 1/2” below and 3/4” above).
Note the last line above. I had forgotten about this, but believe it answers the question and concludes that ALL Vortec heads (GM & cloned) will have the stated exhaust port characteristics. These notes also indicate that the size and orientation of the Bowtie Small Port Vortec exhaust ports and those of the Patriot cast iron clone heads (and thus the original GM Vortecs) are identical at 1 5/16 x 1 5/16.

I guess the only unknown now is the architecture of the Large Port Bowties. Exhaust ports likely slightly larger, but bet they have the same centerline characteristic.
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Old 02-01-2012, 01:11 PM   #6
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Re: Bowtie Vortec Heads-Exhaust Port Questions (GM #: 25534421)

While I agree on the 1 5/16" square shape, I can't comment on the raised port.
I've been running Vortecs for years and have always used a conventional Gen 1 SBC header gasket. This isn't to say that I've been using a misapplication all this time however, of all the header gasket I've researched only once have I come across a Vortec specific part number. This was referenced to a 96 Chev 1/2 ton (with the OEM Vortec engine) and the gaskets was by Percy's.
I can say this, I've got those same gaskets on delivery at this time and am invloved in a head swap on my sbc. I'm replacing the factory Vortecs with the RHS ProTorker version.
I'll have plenty of data in the next month or so.
Thanks for the excellent write up.
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Old 04-15-2012, 08:52 PM   #7
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Re: Bowtie Vortec Heads-Exhaust Port Questions (GM #: 25534421)

I'm using the RHS vortec 2.02/1.6, no issues with header fit that I know of- using Eddy TES old style heders 1989 k1500. Having a problem with an intake valve and am looking at replacing with Fast Burn- but the LT4 style exhaust won't work for me I think.

Last edited by dfarr67; 04-15-2012 at 08:56 PM.
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Old 04-16-2012, 10:02 AM   #8
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Re: Bowtie Vortec Heads-Exhaust Port Questions (GM #: 25534421)

Quote:
Originally Posted by skinny z View Post
While I agree on the 1 5/16" square shape, I can't comment on the raised port.
I've been running Vortecs for years and have always used a conventional Gen 1 SBC header gasket. This isn't to say that I've been using a misapplication all this time however, of all the header gasket I've researched only once have I come across a Vortec specific part number. This was referenced to a 96 Chev 1/2 ton (with the OEM Vortec engine) and the gaskets was by Percy's.
I can say this, I've got those same gaskets on delivery at this time and am invloved in a head swap on my sbc. I'm replacing the factory Vortecs with the RHS ProTorker version.
I'll have plenty of data in the next month or so.
Thanks for the excellent write up.
The RHS ProTorker Vortecs have exactly the same exhaust port configuration (relevant to the header flange bolt holes) as the OEM Vortecs.
What I find odd is that ANY 1.5" round port header gasket fits. There is no distinction among part numbers or application (other than the aforementioned Percy's) between a traditional SBC Gen 1 head and the Vortec castings.
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Old 04-16-2012, 10:52 AM   #9
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Re: Bowtie Vortec Heads-Exhaust Port Questions (GM #: 25534421)

http://catalog.remflex.com/category_s/159.htm
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Old 04-16-2012, 11:51 AM   #10
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Re: Bowtie Vortec Heads-Exhaust Port Questions (GM #: 25534421)

This why the headers I make all have the raised port configuration, to accommodate the new heads.

They still work fine with the older heads.
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Old 04-16-2012, 12:45 PM   #11
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Re: Bowtie Vortec Heads-Exhaust Port Questions (GM #: 25534421)

Quote:
Originally Posted by dfarr67 View Post
I find the dimensions given very small even for the Vortec exhaust port. Interesting to see a seperate listing though. Also interesting is that the gasket has a rectangular opening as opposed to what I ususaly get and that's round.http://catalog.remflex.com/CHEVROLET...t_p/rf2011.htm

Quote:
Originally Posted by Dyno Don View Post
This why the headers I make all have the raised port configuration, to accommodate the new heads.

They still work fine with the older heads.
What is your preferred gasket?

Last edited by skinny z; 04-16-2012 at 12:51 PM.
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Old 04-16-2012, 01:44 PM   #12
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Re: Bowtie Vortec Heads-Exhaust Port Questions (GM #: 25534421)

I ordered a set of the regular vortec and they are very square- perfect for the RHS exhaust.
Dyno Don- I've almost set my sights on a used set of FastBurn's but the headers are pre vortec- but work on the RHS, is the mounting hole elongation trick worth doing?
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Old 04-17-2012, 11:29 AM   #13
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Re: Bowtie Vortec Heads-Exhaust Port Questions (GM #: 25534421)

Quote:
Originally Posted by skinny z View Post


What is your preferred gasket?
I prefer the Earl's 29DD3BERL
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Old 04-17-2012, 11:30 AM   #14
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Re: Bowtie Vortec Heads-Exhaust Port Questions (GM #: 25534421)

Quote:
Originally Posted by dfarr67 View Post
I ordered a set of the regular vortec and they are very square- perfect for the RHS exhaust.
Dyno Don- I've almost set my sights on a used set of FastBurn's but the headers are pre vortec- but work on the RHS, is the mounting hole elongation trick worth doing?
Not sure on that, never tried it.
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Old 04-17-2012, 02:05 PM   #15
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Re: Bowtie Vortec Heads-Exhaust Port Questions (GM #: 25534421)

Yes- when the exhaust is working right- you don't think about it. Eddy even discontued their gaskets, which I no trouble with.
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Old 07-11-2013, 04:44 PM   #16
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Re: Bowtie Vortec Heads-Exhaust Port Questions (GM #: 25534421)

Posted a corrected pic in Post #3 on 7/11/2013 showing the proper distance headers designed for pre-Bowtie heads need to be adjusted to be centered on the Bowtie head exhaust port (was prevoiusy shown as 1/4"; corrected to 1/8") . Also corrected the text of that post to reflect the proper 1/8" distance.

Thanks to RPO-whuh for catching this error.
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Old 07-12-2013, 08:38 AM   #17
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Re: Bowtie Vortec Heads-Exhaust Port Questions (GM #: 25534421)

I thought I'd post up with my findings regarding the RHS Vortec Pro Torker heads.
A recap of what I'd discovered earlier was that despite there being separate listings for a typical gen 1 SBC and the L31 (Vortec), the gaskets are identical. When overlaid, there are no visible difference. These are the 1.5" round port versions.
The attached photos show that the gaskets fit perfectly with no overlap into the ports and ample area around the port for sealing. The same applies to the headers I'm using.
I suppose from this and what you're documenting is that the Bow Tie version of the Vortecs and the more pedestrian (and by extension) the RHS heads are cast differently. Yours being raised more that that of the L31 castings.
Something to be considered with the Bow Ties.
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Old 07-13-2013, 12:40 PM   #18
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Re: Bowtie Vortec Heads-Exhaust Port Questions (GM #: 25534421)

Generally, you want the header ports to be slightly larger than the head port size, but more importantly, when selecting headers you need to make sure, whether straight or angle plug design, that you'll have enough room between the pipes and your spark plugs with boots installed.
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Old 07-13-2013, 12:40 PM
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350, bowtie, exhaust, head, headers, heads, l31, location, port, ports, problems, raised, sbc, size, small, timing, vortec
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