Common performance-minded FAQs about 88-98 OBS trucks

[5point7joe]

can u use a dry shot system on the 96-99 vortecs or would u recommend against that?

[Red94Chev]

How do I install headers on my truck?
Well, you're in luck because I just replaced mine and I took some photos. Total install time was about 4 hours, but I'm sure some of you gear-heads could do it faster.

1. Unbolt exhaust manifolds. Easier said than done. Most of your time will be doing this step, so be prepared. Mark your sparkplug wires prior to removing them. This is also a good time to replace your sparkplugs since it can often be a difficult chore when headers are in place. Not all headers are equal mind you (as I quickly found out). The new Edelbrock headers I installed in place of the Flowtech ones had several design elements that make life easier: recessed area for wrenches, full length flat header flanges, notched outer bolts for easy removal/installation, slightly larger area for easy spark plug removal/installation. Together, these features made for easy installation.

Passenger side is pretty easy. Dipstick pulls right out and just one header bolt is securing it. 6 header bolts secure the exhaust manifold to the cylinder head. There are three bolts at the collector that need to be removed. Driver side has a spacer at the front of the engine near cylinder #1 that can cause some problems. It may be necessary to remove the bracket that attaches to the power steering pump. Depending on the amount of rust present, it would be a good idea to use a good penetrant spray available at your local automotive store a few days before tackling this (with a few applications on the nuts/bolts) to loosen things up a bit.

Some of you might be asking yourself why I'm taking my old headers off and installing new headers? Well, the pictorial below explains why.

Larger collector opening (minor issue) and larger space between header flange and header tubes to assist spark plug removal once the header is installed.


Header leaks!! See all the carbon deposits on the old header.


Perfectly flat flange. Any aftermarket gasket can be used.


Not a flat flange. For some reason, Flowtech decided to not completely flatten out the welds on the inner side of the header flange. The result? Very little material is available to seal the header. Change the stock heads to aftermarket ones like I have and you have a recipe for disaster.


Close-up of raised welds


Passenger-side header removed


Close-up of head surface showing poor fit. Even if I match gaskets to the header, the larger ports of my aftermarket heads leave little room for the gasket to properly seal the two surfaces.


2. Modify gaskets for easy installation. Essentially notch the area below the outer bolt holes of the header gasket, as shown below. Note that some aftermarket gaskets (ie. Felpro) will come with this modification already performed.





3. Install new headers. Start by putting the two end bolts on with the header loosely attached as illustrated below.



4. Drop modified header gasket over end bolts for a perfect fit everytime. Now the holes will line right up and you can insert the other header bolts. Leave everything slightly loose to allow for some movement when attaching the y-pipe to the collectors.



Want to make life easier for you. Get a set of ratchet wrenches that have adjustable wrench head angles. Way easier.





5. Loosely tighten collector bolts. Have your bolts already installed as shown below when you install your header. It can be difficult to get the bolts into the holes once the header is installed. This is a huge time-saving step and you will thank me many times over for suggesting it.



6. Tighten all bolts. Torque header bolts to 30 ft/lbs. Do not over-torque. I can't repeat this enough as over-torquing can warp the header flange and you'll get header leaks galore no matter how tight you tighten the bolts. Torque sequence should be inner to outer in a clockwise fashion.

Use a similar technique to tighten collector bolts. Go slow and tighten each bolt til you start to feel resistance. Then use a 3-stage torque sequence: 20, 50, 100 ft-lbs. This ensure even contact to prevent misalignment and leaks.



7. Reconnect sparkplug wires and other connectors and that's it, you're done.



Need more instructions? Here is a link to the instruction set from Edelbrock: http://store.summitracing.com/instructions.asp?File=edl%2D6566%2Dheaderfor88%2D9 5pu92%2D95su%2Epdf

[BagginA93chev]

wow great thread i have a feeling this will be helping me a ton this winter. i have a question for you, i have a rebuilt stock tbi 350 engine that i am looking to build. basically I am looking for something just like what your setup is, making about 350ho. If you dont mind me asking, about how mutch $ do you have invested into building your engine? i am just trying to figure out how mutch i am going to have to spend to get around 350hp out of my 350. thanks again for the great thread!

[ddawgnd]

My god this helped...TREMENDOUSLY! Lots of info, answered alot of unasked questions. Very good!

[Red94Chev]

Thanks. Another update for anyone with low voltage problems. I just fixed mine the other day. The original link is here: http://www.fullsizechevy.com/forums/...e-problem.html

[Red94Chev]

This little piece of software is going to be your new best friend. I often see a lot of questions in the performance section asking "which camshaft to use?" or "which are the best heads for my motor?". Use this program and you can find the best performing engine combination for your purposes, be it at the dragstrip or in your 1/2-ton truck.

Not convinced? Let's do an example using a dynoed engine. Horsepower TV on the Spike network did a "Best Bang for your Buck" series using a GMPP 350 290hp engine. The specs of the engine and dyno results can be found here: http://www.powerblocktv.com/sites/bang4buck/0602/. In summary, they turned the GM 350 crate engine with 290hp-326 ft/lbs into a 412hp-420 ft-lbs performance engine with a complete bolt-on top-end kit from Edelbrock. Looks like they partnered with Summitracing.com and you can even buy this exact combination for $2770.75 using the part# SUM-CBB2 at the Summitracing.com website. I wouldn't reccommend this combination for a truck, but for a lighter street car with a 3000 RPM stall and 3.70+ gears, this is a pretty wicked combination. Click on the video to see the actual build-up and dyno run. So what would be the predicted results using the DD2003 software? Let's find out...

STEP 1: You’re going to need to buy the software. Or alternatively, you can download a pirated copy of the software from sites like Torrentspy and Isohunt. You will need to be familiar with working with torrent files. An additional program is needed to help you download the file, like Bittorrent or Azureus. If you want more info on how to use these programs, search Google, go to the Bittorrent website, or read the Wikipedia link: http://en.wikipedia.org/wiki/.torrent

STEP 2: Install the software and start inputting the engine parameters. There are several sections shown in the figure below: Short block, Cylinder heads, Compression, Induction, Exhaust, and Camshaft sections.



STEP 3 - SHORT BLOCK: This one is pretty easy. If you have 350 engine, click the drop-down arrow and choose Chevy > 8 cylinder SB > 350 V8. The rest of the table is formatted for the standard 350 engine. Now if you have rebuilt your engine 0.030 over, you would change the bore size to 4.030. Notice when you do this, the cid calculated is now 355 ci. You can also choose a 383 V8 SB, a common upgrade for the 350 engine.

STEP 4 - CYLINDER HEADS: Here’s where things get a little more complicated. In order to get accurate simulations, it is best to look up the actual flow data from the manufacturers’ website. The program, depending on the software version and whether you actually paid for the software, comes with some cylinder head data for most common OEM production and aftermarket heads. You can select a particular head for your virtual engine to see the performance results. However, I prefer to enter in the head flow data. For the Edelbrock E-tec cylinder heads and others, the flow data can be found here: http://www.purplesagetradingpost.com...fo/heads1.html. In this section of the software, click the airflow button and enter the specs as shown below.



You will also need to enter the intake and exhaust valve size, in this case for the Etec heads, it is 1.94 and 1.5.

STEP 5 - COMPRESSION: In this case, the Horsepower TV video states the engine compression of 9.5:1, so we’ll enter that into the compression ratio area. If you need to calculate the CR of your engine, you can click on the CR button. Most pistons have valve reliefs, but you don’t need to click on the piston with valve reliefs. I find it more confusing since you cannot zero your piston to the deck height @ TDC. You just have to enter a number that is equivalent to the cc dish of your pistons. These are the common parameters: head chamber (58cc, 62cc, 64cc, or 76cc), gasket bore (4.000”, 4.030”, or 4.060”), gasket thickness (usually 0.028” or 0.051” for GM gaskets; you’ll need to look-up the thickness for Fel-pro gaskets), piston down bore (# in inches that is equivalent to piston cc valve reliefs). For my engine, I would enter 62cc, 4.000”, 0.028”, and 0.0874” to give me 18cc valve reliefs. My calculated engine compression ratio is 9.36:1. Entering this data allows you to calculate what your compression ratio would be if you: 1) changed cylinder heads (58cc for example), or changed engine displacement (either with a 0.030” or 0.060” rebuild or a 383 SB stroker engine. Using the same heads, compression ratio of would be 10.1:1 on a 383 short block with all parameters the same. This would be the max limit using pump gas and aluminum heads. 9.5:1 is roughly your limit with iron heads on pump gas.



STEP 6 – INDUCTION: For the horsepower TV build, they are using a single plane intake so that is what is selected. They are also using a 800 cfm 4-barrel Edelbrock carb (@ 1.5 inHg), so that is entered as well. Flow data for 2-barrel carbs are usually at 3.0 inHg. The exception to this rule is the TBI throttle body, which flows 490 cfm at 1.5 inHg. A modded TB from CFMTech (aka ultimate TBI mods) would flow 590 cfm with the injectors or 620 cfm without the injectors. The TBI engine uses a standard dual plane intake. An air-gap performer RPM intake from Edelbrock would be equivalent to the high-flow, dual plane intake manifold type.

STEP 7 - EXHAUST: If you have the stock log-type set-up, choose “stock manifolds and mufflers”. “HP manifolds and mufflers”, according to the user manual, corresponds to the ram-horn style manifolds. Shortie and long-tube headers are grouped together as “headers”, but separated into small tube and large tube headers. Small tube headers typically have 1-5/8” primaries or smaller, whereas the large tube headers have 1-3/4” primaries or larger. You can model with or without mufflers. There is no parameter for catalytic converters unfortunately. You could assume very little obstruction of flow when two 3” catalytic converters are being used. For the Horsepower TV engine build, small tube headers were used with 1-5/8” primaries. Mufflers were also installed on the engine during dyno runs.

STEP 8 - CAMSHAFT: Here is another place where it is best to look up the specs from the camshaft manufacturers. There is two ways to enter the data; either using valve timing open/closing angles or camshaft duration angles (advertised seat-to-seat or specs at 0.050). You will also need to know the camshaft’s LSA and intake/exhaust centerline angles. DD2003 can use both advertised duration and 0.050 specs to calculate the ramp rate and therefore provide a better simulation when using aggressive high lift camshafts. Here is the cam card for the Comp cam in my ride to illustrate these values: http://www.compcams.com/Technical/Se...umber=08-502-8.

For the horsepower TV engine, the camshaft used is a hydraulic roller retrofit camshaft #2201. The specs for the 2201 camshaft are: duration at 0.006 - 296/300, duration at 0.050 - 234/238, Lift w/ 1.5 rockers - 0.539”/0.548”, lift w/1.6 rockers - 0.575”/0.585”, LSA 112, intake centerline 107, exhaust centerline 117. The figure below shows the entered specs. In the video, the horsepower guys mention they are using 1.6 ratio roller rockers, so I’ll enter the higher lift data.



Do I use the data based on advertised duration (0.006) or the specs at 0.050? According to the user manual for the software, seat-to-seat duration is the most accurate, but occasionally I’ve found that with higher duration camshafts, using valve opening based on 0.050 specs produce more accurate simulations (particularly in the low RPM torque estimates). In this case, the simulation using the 0.050 specs produced a result closer to the actual dyno results.

STEP 9 - THE RESULTS: Shown below is the simulated dyno curve using DD2003 and the specs of the Horsepower TV 350 top end build. The program estimates 409 hp at 6000 RPM and 407 ft-lbs at 4500 RPM. The yellow block highlights the same RPM range given in the actual dyno results, the actual peak data being 411.8 hp at 5800 RPM and 419.8 @ 4500 RPM. Pretty dam close as you can see.

[Red94Chev]

Here is a useful tool from Comp Cams: http://www.compcams.com/Camquest/.

Camquest version 6 is a FREE software download that uses the Desktop Dyno software engine and matches the proper camshaft to your engine combination. Very cool tool. You can also input the flow data from aftermarket heads just like Desktop Dyno and sim the hp/torque levels of your engine with different Comp Cams camshafts. There is also a video tutorial of how to use the software listed on the website. Check it out.

[hunt4240dw]

I am new to this Forum. But it is awesome! I have a 99 Tahoe 4x4 with 5.7, 3.42. Fram Air Hog, Flowmaster 50 SUV, and a custom tune from MGS Custom. All in all, I think I have gained 60 HP on 91 octane tune. I am thinking of adding Edelbrock Headers to add HP/TQ.
How should should I expect?
I tow a 6400# travel Trailer. I am getting 11 mpg in 3rd but would like to stay out of the throttle a little more. I have a ScanGauge II to monitor my engine preformance.

David

[350 sbc ftw?]

Originally Posted by hunt4240dw

I am new to this Forum. But it is awesome! I have a 99 Tahoe 4x4 with 5.7, 3.42. Fram Air Hog, Flowmaster 50 SUV, and a custom tune from MGS Custom. All in all, I think I have gained 60 HP on 91 octane tune. I am thinking of adding Edelbrock Headers to add HP/TQ.
How should should I expect?
I tow a 6400# travel Trailer. I am getting 11 mpg in 3rd but would like to stay out of the throttle a little more. I have a ScanGauge II to monitor my engine preformance.

David

get 3:73 or 4:10 gears..

[Red94Chev]

Time for another update as I am re-tuning my engine after I converted the PCM to PFI mode and installed larger 29#/hr injectors since replacing my short block and converting to a hydraulic roller cam setup. I am running Edelbrock's MPFI for TBI trucks and a larger TB from CFM-tech that I bought several years ago. Thought I'd share some useful tips I've learned.

When do I need to adjust TPS and IAC?
I can hear it already, "I thought you said, 'TPS is non-adjustable. Just leave it alone.'". Yup, I did say that and that's true for stock or mildly modified TBI engines. However, once you start upgrading major components like camshafts and cylinder heads, you change the characteristics of the engine. More specifically, you need to recheck your setup for proper operation.

The key is setting the idle set screw to correct the IAC for proper operation, which will require you to remove the plug by drilling a small hole in it to get enough leverage behind it to remove it. It is located on the front of the TB near the throttle linkage. Once the plug is removed, you will see a hex screw behind it. The end of the screw serves as the stop pin for the throttle linkage. In order to adjust the idle screw, you will need the assistance of a handheld scantool or your laptop running TunerPro or DataMaster connected to the PCM via the ALDL port so you know what the IAC counts are. A small change in the idle screw will affect the IAC counts, despite no apparent change on engine operation. This is why you need a scantool to see the results.

At idle and in the "park", you will need to adjust the screw in or out until the IAC counts read between 10-15. The engine should be at operating temp for this and it shouldn't change your idle RPM if done correctly. The IAC itself will be able to open/closed to provide a controlled air leak and therefore provide a smooth idle at the desired RPM setting programmed into the PCM/ECM (via the "Target Idle RPM vs Coolant" table). Then turn off the engine, wait a few secs, and then turn the key on (but not with the engine running). Wait for the fuel pump to finish its cycle and turn the key off. Wait ~30 secs. Turn the key on and restart the engine. This will reset the TPS sensor for the 0% position.

Keep in mind, you have now changed the throttle blade position relative to the TPS sensor. If you turned the idle screw in, the TPS voltage will be higher and it will need to be adjusted back to spec. This is probably why GM installed the idle screw plug on the TB in the first place to prevent dodos who don't know what they're doing from screwing stuff up. You may need to modify your TPS sensor by enlarging the holes so you can rotate it (usually counter-clockwise to lower the sending voltage). Some older or aftermarket TPS sensors may be adjustable BTW, especially if they have elongated oval mounting holes. Mine wasn't adjustable and I had to elongate the holes to allow me to rotate the sensor. Again, this is easy to do and you can verify TPS output with your scantool or a handheld volt meter. Voltage at 0% TPS should be between 0.53-0.57V. Just remember to do the key on-off-on cycle trick to reset the 0% TPS position in the PCM.

I’ve installed larger/smaller tires and/or different rear end gears on my truck. Is there anything I need to change on the chip? How do I correct my speedometer?
You can thank HaulnA$$ for this one. The PCM needs this value to be correct to properly calculate MPH. It has nothing to do with your speedometer, which is controlled independently by the DRAC module. I’ll get to that in a minute.

Speedometer correction: The simplified formula for calculating the ratio for the DRAC is ((Tire Rev's/mile) x Rear end Gear Ratio)/3200 using 40 pulses/rotation. You can get tire revs/mile from the tire manufacturer’s website. Please note that you may come across a website from 614streets about DRAC info. The chart listed has errors in it from 0.707031 down where the numbers have been reversed: http://614streets.com/drac.html. Another good website for DRAC info is here: http://www.tbichips.com/drac/. It explains the modifications to the DRAC very well and its table is accurate. Another resource is this PDF doc: http://pswired.com/misc/pacaudio/drac2.pdf. Good resource, but pay attention to the legend if you use it. The table is accurate but the 1’s and 0’s are reversed!! 0 is pin in place and 1 is pin removed. The pin nomenclature is reversed too: 12345677654321 instead of 76543211234567. Just to make it more complicated with the whole mirror image thing, hey?

I prefer looking at tables to set up the pins, but you may come across an online DRAC calculator: http://www.philter.com/cgi-bin/drac.pl. Don’t use it!! Using tire size for the calculation is inaccurate. You can use tire circumference to calculate DRAC settings. Just take 63360 (inches/mile) and divide it by your rev/mile number from the tire manufacturer’s website to get the inches/rev (i.e. tire circumference in inches). It says it uses the tables from 614streets, so I question its accuracy. A quick test and it looks like the pin connections are reversed (i.e. “connected” should be “not connected” and vice-versa). Just stay away from it because it might only confuse you more.

To give you an example of the calculation, I will use my setup. I went from the stock tire size (P235/75R15) to a larger size (P265/75R20). As expected, my speedometer was out of spec. My stock DRAC is set up the same way as the pic below and translates to an input ratio of 0.781738.




According to the Nitto website, my tire revs/mile is 682. I take 682*3.42 (rear gear ratio)/3200 = 0.7288875. The closest pin input ratio is 0.731446. The pins (using the 76543211234567 nomenclature listed on the TBIchips website and 1 = pin connected and 0 = not connected) would translate to 1100010//1011100. The table lists the second half pin connections. Rearrange the appropriate pins or use the DIP switches and ta-da, back on track. Unfortunately, there is a wide gap between input ratios in this region of the table, but it is still way more accurate than before!! The best way to test your new setting is to verify speed using one of those GPS nav systems (TomTom, Garmin, etc.).

PCM correction: You will need to change the constant for RPM/VSS ratio. The formula for that is ((Tire Rev's/mile) x Rear end Gear Ratio)/60. This calculates speed accurately for the transmission-related tables. Again, for my truck = 682*3.42/60 = 38.874. Change the constant for this, burn the chip. You’re done.

I'm using TunerProRT and datalogging. How do I tune my VE tables?
Oh man. You're in luck because I’m creating an average BLM/VE table calculator similar to pfk’s AFR calculator…but you’re going to have to wait while I test it. pfk’s thread is here: http://www.fullsizechevy.com/forums/...t-anymore.html. His files and instructions are listed at post #91. The catch is it uses some of the new functions of Excel 2007, but it does a great job. For the few times I’ve used it with my setup, it corrected things fast after a couple of cycles. This will provide the same functions as the histogram table used in Datamaster. I’ve also added color-coded 3D surface graphs to compare VE tables easily and a function to give you an idea of how many data points are used for each cell population. Smooth as you go in Excel or in TunerPro and perform another datalog. There is also one for the near-idle table as well to finetune that table. It won’t be as accurate as using a WBO2 sensor, but it is another tool for tuning. Definitely better than trying to eyeball it. Stay tuned…pun intended!!