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Vortec L31 MARINE MANIFOLD project! Q&A
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Post Vortec L31 MARINE MANIFOLD project! Q&A 
Preface:
In 2004 several members of the Pacific Performance Engineering Forum began brainstorming about the possiblity of adapting the true MPFI intake manifold from the Marine version of the Vortec 350 (L31) for use on the street version of this engine. Around the same time TunerCATS OBD-II was released and supported the 96-97 and 98-00 Vortec trucks giving us, for the first time, the ability to calibrate the "black box" PCM for larger injectors ourselves. This manifold has the distinct advantages of supporting all OEM smog equipment and eight individual standard fuel injectors. Because the throttle body is in exactly the same place as the street L31 manifold, most aftermarket supercharger and cold air intake kits can bolt right on the same.

There are now many forum members that have done this swap with the help of the information assembled here. The number continues to grow!

The original text:
Thanks to the resourcefulness of Matt "Pecos" and the collaboration of several others, we have learned a great deal about the Vortec L31 Marine Intake Manifolds we have each had in our possessions for the past few months. We consciously choose to keep a lid on this project because of the limited availability until feasibility for use with our L31 trucks could be proven. Over the past few months over 100 emails have been exchanged in our collaborated effort to identify and overcome the dozens of issues that exist with this piece. With the new PPE forum up and running so well it's time to bring our project into public domain. The editable format the forum now has will provide the means to post updates to the information and pictures as we progress.

Thank You Pecos, NJCKZ71, Speeder, White350, Cannon, RCFast, and Hog for your contributions both past and future.



Here is our information!

1. The Marine Intake Manifold has no provision for a thermostat bypass like the stock manifold. (See PIC)
SOLVED
The manifold casting does have the appropriate internal structure and enough metal to drill through. (See PIC) Some creative use of cold weld or epoxy is required inside to make sure the tapped hole is a sealed passageway through and into the internal structure. (See PIC)

2. The included injectors are Delphi EV6 24lbs/hr. @ 43.5psi. units with USCAR connectors. (See PIC) They work out to about 27lbs/hr. at this fuel pressures of about 53psi. These connectors are used on some Ford SVT models and the LS2 and LS7 engines. They are high impedance (~14ohm) and the same physical dimensions from o-ring to o-ring as standard Bosch type injectors. (See DIAGRAM)
USEABLE
...for naturally-aspirated L31's. Anything blown or having more cubic inches will want more of an upgrade in flow than the OEM Marine injectors can provide. (The whole point of this swap is that be able to put any size injectors in there you want!)
Standard EV1 injectors will also fit the rails and a harness must be made anyway. Connectors for the "oval" USCAR connectors are available.

3. There is no hole for the water temperature sensor.
SOLVED
There is a boss for it in the manifold, and in the stock location. (See PIC) Simply drill and tap it for 3/8" sensor. (See PIC)

4. There is no EGR valve mounting flange like the stock manifold. (See PIC) There is an internal passage for it (See PIC) with an inlet in the stock location matching the stock size. (See PIC)
SOLVED
Using the divorced EGR flange block from a Gen-III engine (See PIC) it is possible to cut and splice into the stock EGR pipe and have EGR. A piece of angle iron drilled to mount between the compressor and its accessory braket can serve as an attachment point for the Gen-III EGR flange. (See PIC) The two stainless steel tubes from the flange need to run behind the compressor in the location taken up by the stock upper radiator hose. It is necessary to reroute the hose forward using a 45-degree thermostat housing and an upper hose from a TBIā„¢ truck. (See PIC) The valve will sit higher than before, but the harness will reach and the hood clears with plenty of room to spare.

5. The Marine Intake Manifold throttle body (See PIC) does not have the EGR diffuser plate (lip) or the hole to diffuse the EGR coming up under the butterfly. (See PIC) This is fine because the pipe inside is directed toward the rear, not up like the stock manifold.
NOT USEABLE
This TB does not have the proper connections on it for throttle and cruise control cables making it unusable anyway. Also, the TPS and IAT are not the same parts as stock even though they appear to be at first glance. (See PIC) The return spring rate is also all wrong. The blade used in the TB would seem to have desirable qualities but the holes in it holding it to the shaft in in different places than the stock unit. The marine TB also has different bearings for the shaft which prevents any interchang eability between the Marine and stock units.

6. Throttle Body sits forward on the intake like the stock unit meaning that aftermarket intakes will work with this manifold. The TB mounting flange of the marine manifold is exactly in the same position and height as the stock manifold. This makes the L31 Marine manifold the ONLY true MPFI intake manifold compatible with bolt-on superchargers and cold air induction kits.

7. The upper intake manifold does not have an integrated gasket for the throttle body like the stock manifold does. Instead the Marine setup has this seal integrated into a channel in the throttle body. Since the Marine TB cannot be used, a gasket is needed between the stock TB and the upper manifold. (See PIC)
SOLVED
The stock L29 Vortec 454 uses a TB gasket between its TB and upper intake. Part number 12570168. (See PIC)

8. The fuel rail has 3/8" and 5/16" quick-connectors like a Gen-III manifold. (See PIC)

9. Entire fuel rail is stainless steel and brazed together as a single unit with no possibility of leaking. Fuel pressure regulator has a lower pressure than stock at about 50-55psi instead of 60-63. (See PIC)

10. There is no port for a vacuum brake booster.
SOLVED
There is a boss in the upper (aluminum) portion of the intake that can be drilled and tapped out for it.

11. PCV routing is a little different but will work. (See PIC) I heated up the stock plastic tube to straighten it out. The tube connects to a 90-degree checkvalve that PCV needs with forced induction.

12. There are no ports for all the EVAP stuff. An existing nipple can be tee'd and external divorced adapters can be fitted to the various EVAP parts and plumbed in.

13. The lower manifold is cast iron. (Yes, really, and very very heavy.)

14. There are mounting points miscellaneous stuff like the coil, but they are in a different place. The coild can be mounted directly to the intake manifold between the two pair of injectors. The drilled holes in the manifold are about 1/16" closer together than the holes on the coil - the coil holes can be enlarged to fit. The forward ear of the coil assembly needs to be cut down to clear the #4 fuel injector if wide-body injectors are used. Also, the module and heat sink need to be unscrewed from the coil bracket and flipped over to put the harness connector toward the rear. The wiring harness can not reach it otherwise.

15. The stock wire harness bridge will not fit.

16. There is no drain hole in the bottom of lower manifold because it's flat with no cavities. This is a good thing.

17. Stock heater-hose quick-connector will thread right in.

18. Stock distributor and hold-down will work, however it may be necessary to clock it one tooth off counter-clockwise so that the driver-side plug wires clear the fuel line depending on how you choose to run them..

19. Stock Vortec-style thermostat will work. (See PIC)

20. Stock Thermostat Housing will work if you do not intend to run EGR. The lower manifold also has holes for clocking the housing. (See PIC)

21. MAP sensor is different. (See PIC) Marine unit is 5-pin with integrated IAT.
SOLVED
The stock unit can be adapted with a custom hold-down bracket. (See PIC) The sensor needs an o-ring over it to seal to the hole in the upper manifold. (See PIC)

22. Stock GM Vortec intake manifold gaskets work. GM Part# 89017465 (See PIC)
If a conventional paper-type gasket is desired, Flepro 1255 can be used. (See PIC)

23. Fuel lines with Quick-Disconnects are needed. (See PIC)
MULTIPLE SOLUTIONS
There are a few companies making QD to AN to O-Ring adapters and lines. (See PIC) The line used for OEM installations of the Marine Intake are about 34" long with o-ring and QD ends. (See PIC) It is possible to cut off the o-ring ends and clamp onto the stock hardline under the footwell where the stock hardlines make the transition to flexible line.
PREFERRED SOLUTION
Pure Choice makes quick-disconnect to -6AN Male Flare adapters. Part# 5800 (See PIC)
For the lines on the firewall two female o-ring to -6AN male flare adapters are needed from Pure Choice, one 14mm 1.5 thread and 16mm 1.5 thread. These are part numbers 5860 and 5870.
Two -6AN fuel lines with female flare on both ends are needed, one 6" long the other 7" long.
The optimal solution is to use 45-degree -6AN fittings at one end of each fuel line. This solution ends up needing one line 2" long between fittings and the other 1.5" long. (See PIC)

24. The proprietary connector for the CPI injection assembly is most practical to simply cut off and replace with a spliced in custom built harness. The new harness can be loomed and zip-tied to the fuel rails. (See PIC)

25. Throttle-Body height. The cruise control peg on the throttle body hits the passenger side fuel rail.
SOLVED
Use a throttle body spacer or any type to obtain the needed clearance to the fuel rail.
(See PIC)

26. Programming.
SOLVED
Use Stan Weiss's Injector Calculator to figure out what your injectors will flow at with the 50psi fuel pressure the Marine regulator puts out. (See PIC) TunerCAT can convert lbs/hr to gm/sec with its built-in calculator. The "Injector Flow Rate" in the "Fuel System Constants" section of the tuning needs to be updated with the new value. The Marine Intake Manifold flows a great deal better in the upper RPMs than the stock piece. Over time the Long-Term Fuel Trims will reflect this greater volumetric efficiency. The VE table can be updated youself through trial and error to get those trims dealed in perfectly. The alternative is dyno-tuning. If you opt to go this route, make sure the tuner is not just changing the IFR number to get the trims to zero out. The difference in flow characteristics are similar to installing a cam with a higher-rpm band but not losing any low-end torque - it needs VE tuning.

This is a PROVEN solution to the Vortec L31 fuel problem! Congratulations to RCFast for being the first one up and running on this research!
Watch the Quicktime Video of John's truck running!

Here's a Video of my truck at idle, revving, and accellerating with the Marine Intake.



Last edited by James B. on Sun Aug 28, 2011 9:08 am; edited 11 times in total
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I ended up getting some svo 30# injectors off ebay for 150 brand new so i figured that would be better for me since cleaning would cost around 100 and these where brand new and bigger for 50 more. Anyways, i should get the injectors and i plan on getting the manifold installed after i get out of school which is about a month if money permits.. Its almost sounding like i might be the first to get it on but im not sure, if so it looks like i will be a geni pig for everyone else which i have no problem with. I look forward to getting it on and helping in any way i can to get everyone else goin on it. Hopefully i will be able to give some tuning advice once i get it on for i have been reading for the last 2 months on tunning and asking tons of tuning questions (yes some are quite idiotic now that i look at them but its all good information that i have learned off of).

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RE: Item 25 programming the injectors

Some time back I was looking at the 8.1 manifold from Arizona Speed and Marine. They have this aeromotive injector regulator.

http://www.azspeed-marine.com/aea1inbyre.html

Would something like this unit be of service in "conditioning" the computer program? I'm thinking that you might find mechanical adjustments more beneficial than electronic. I don't know, maybe I'm not thinking hard enough. This is interesting stuff James. Good work.

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Honestly, I think it's going to be easier to dial in the fuel with the computer rather than a regulator. Of course this stupid Vortec FMU that shoots my fuel pressure up to 100 psi has left a bit of a bitter taste in my mouth. Also, this would be just one other thing in the fuel system to have to rely on. Computer tuning with some SVO 30lb injectors seems like the best bet for me right now. Just my thoughts.....

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James pointed out the SVO injecors are high impedence (well, some of them). You want standard Bosch EV1 injectors if at all possible, as they will be easiest to source in varying sizes. Don't skimp now to save a buck, as it may cost you more sourcing out new injectors when these eventually fail.

I'm going to do some injector research and get back to all of you. From my experience there are several styles of injectors. Single pintle style is one I know of, and another is a multiple pintle style with a good atomizing spray pattern. Some injectors spray different angles of degrees, different patterns of atomization, etc. Injector technology has really taken off and is very good.

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White 350 wrote:
Honestly, I think it's going to be easier to dial in the fuel with the computer rather than a regulator. Of course this stupid Vortec FMU that shoots my fuel pressure up to 100 psi has left a bit of a bitter taste in my mouth. Also, this would be just one other thing in the fuel system to have to rely on. Computer tuning with some SVO 30lb injectors seems like the best bet for me right now. Just my thoughts.....


SLP has these,

http://www.lmperformance.com/3502/27.html

and maybe they'd program better being GM oriented?

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Post More info 
James - Excellent job! Wonderful resource for all to work from. Thank you.

With regards to your #2 above, the stock marine EV6 body/USCAR connector injectors are "rated" at 24 lbs/hr, not 29 lbs/hr. The injector rating is determined with the standardized 43.5 fuel psi. These injectors will actually flow 28-29 lbs/hr as you mentioned only when operated with the 58 - 60 psi the stock L31 truck regulators put out. If I recall correctly, NJCKZ71 somehow confirmed the marine fuel regulators produced a similar 58 - 60 psi.

Here is a link for more information on the differences between the Bosch EV6 body/USCAR connector injectors used on the GM Marine (these are also used on the Ford SVT, GM LS2/LS7 applications), and the much more common Bosch EV1 body/Jetronic connector injectors used many other places.

http://www.redpulsar.us/~coldfusion/injectors.html


Another source of information is the Five O Motorsports site below, the USCAR connectors in the FORD section are called "oval", and the Jetronic are called "rectangle".


XR3E-24lb* - "Cobra" - Oval
8/Set: $266.

http://www.fiveomotorsport.com/Injector_Sets.html

If one was going to deviate from the stock marine injectors, changing to the more common EV1/Jetronic injector makes good sence. The EV1 injectors offer many more flow rates to choose from, and much better availability.

Here are a few additional sources for replacement injectors -

http://www.witchhunter.com/variousfuelinjectors.htm

http://www.injectors4u.com/tbi_injectors.htm


Also, here are some on-line calculators for sizing injectors. Using one of these should confirm the marine injectors rated at 24 lbs/hr at the standard rating pressure of 43.5 psi should flow 28 lbs/hr at the 60 psi the L31 trucks typically run.

http://www.csgnetwork.com/fiflowcalc.html

http://www.rceng.com/technical.htm



Last edited by Pecos on Fri Jun 02, 2006 6:26 am; edited 1 time in total
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Post Intakes 
Those intakes are so hot they are actually red.
Secrecy sucks.

Peace
hog

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Post Re: Intakes 
Hog wrote:
Those intakes are so hot they are actually red.
Secrecy sucks.

Peace
hog


Well, the idea was to not get everyone's hopes up until it was known whether or not it would be viable. Better to wait till it was reasonable to assume that it would work than put it out and find out it wouldn't. I think the announcement should have waited till one was up and working myself, but seeing as I'm not one of the main investors (almost was) it wasn't up to me. Still and all, as soon as one is proven to work we should see the L31 emerge as one of the hot engines to have. Either way, these boys deserve some real thanks for ponying up near a grand apiece plus labor on a project that was not a sure thing. Wish I could have participated, but the wife and kids must take priority over hot rod projects. Bummer, but them's the facts.

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Post Don't beat yourself up.... 
You have the right order for your priorities.

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Post Good work 
Awesome guys, I'm glad we have some able people around here to finally figure out how to fuel our L30's and L31's. The marine intake should,all else considered, be better flowing than the L31 just by not having the poppet assemblies hanging in the airflow inside the manifold. Sealing the marine intake to an iron head will be better than the stock lower due to it also being cast iron. The marine intake with a set of those large port iron vortec heads would work great.

Awesome work guys. I have no doubt that all of the hangups will be overcome.

Peace
Hog

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Post Re: More info 
Pecos wrote:
...With regards to your #2 above, the stock marine EV6 body/USCAR connector injectors are "rated" at 24 lbs/hr, not 29 lbs/hr. The injector rating is determined with the standardized 43.5 fuel psi. These injectors will actually flow 28-29 lbs/hr as you mentioned only when operated with the 60 - 65 psi the stock L31 truck regulators put out. If I recall correctly, NJCKZ71 somehow confirmed the marine fuel regulators produced a similar 60 - 65 psi....


Excellent point Matt, the original post has been edited for accuracy.

-James

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Sounds awesome guys. Great work. Can't wait to see what results could come out of these intakes on our engines. Btw how did you guys come up with four of them. Did you get them from whipple from customers that swapped their intakes?

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Nice Work Guys, I am sure you will all see gains far beyond the expense, once your tuned for the new injectors.

Boosted

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If I get all my parts in I should have the intake installed hopefully in 2-3 weeks. I am going to buy a $600 sandblasting cabnet this friday to clean everything. I am then going to send my parts out to be ceramic coated. I will be purchasing accel 32# injectors, Intake gasket set, Dont know about the fuel lines yet (Do they make a line that will go from the stainless rail and screw directly into the lines coming over the trans?). My intake gasket is shot and im leaking coolant and sucking oil into my #8 and #6 cylinder so its a win win situation for me. I also need to pull my distributor due to one of the ears breaking off. Stupid Cap and Rotor set came with screws that had blue locktite stuff on them. When I started tighting the screw it stopped and snapped the ear off. Cap held on by Zip straps and one screw for now.

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Here's what I did for my fuel lines, same situation as you guys-

Pure choice LS1 quick disconnect to -6AN, -6AN aeroquip socketless hose connector:


Aeroquip socketless hose connector, -6AN to 16mm male saginaw fuel filter fitting, -6AN to 14MM female saginaw fitting for return. Pure choice carries these too I think:


Ended up being about $75 I guess.

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I sandblasted my lower intake. Just painted it this evening.









Last edited by James B. on Wed Apr 19, 2006 9:32 pm; edited 1 time in total
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I found this from pro choice: http://www.performanceplumbing.com/FuelLineKits.html . Im not sure who's a dealer for them

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James, Can you post a picture of the bottom side of the upper portion of the intake, I would like to see what the runners look like.

Thanks

Boosted

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Boosted-Z71 wrote:
...Can you post a picture of the bottom side of the upper portion of the intake...


It's sort of like the stock manifold on the inside, same runners, but without all the extra debris in the way and the deep cavity in the center.





Last edited by James B. on Sun Jan 24, 2010 9:47 pm; edited 1 time in total
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