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393/GT40 heads/GT Cam Performance Questions

gclauson

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Nov 17, 2007
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It has been a while since posting here, but now I am finally replacing the trusty 289 and seek information.

I'm on a restricted budget, so I am building a solid 393 short block that can be upgraded later with better heads and camshaft.

I am looking for inputs from people that have similar builds, regarding low-end and high-end performance. I know the 393 will be flow-restricted with my cam and head choice, but I plan to swap them for better parts in 1-2 years.

Engine specs:
- 351 roller block bored .030
- Eagle stroker kit with cast crank, I beam rods, and hypereutectic pistons
- Balanced
- GT40 heads (non "P") with OEM rocker arms and valve springs
- 94-95 Mustang GT roller cam
- about 9.5:1 compression
- GT40 (Lightning) lower with Explorer upper intake
- 1993 Mustang harness and ECM (C3W1, similar to A9P) (already running on 289)
- 90 mm Lightning style PMAS MAF
- 70 mm throttle body and EGR spacer, upper intake opened to 70mm
- fuel injectors not yet purchased
- Explorer front dress
Other relevant specs:
- I have a Tweecer RT to tune the engine but have not used it yet
- NV4500, 4:56 gears, 35" tires

1. What is the max rpm it will run? I need high rpm for winter snow bashing. Will it go to 5500 rpm? Less? More?
2. Will it run smoothly and basically idle along when rock crawling in first gear? I believe this small cam in large engine will do well, but want first-hand experience, especially from those running manual transmissions.
3. I need new fuel injectors. 30# should supply enough fuel for my limited HP, but it would nice to buy a larger set now, to support future cam/heads. Has anyone seen low-end / idle issues with injectors in the 36-50# range?
4. Any other useful information????

Thanks in advance!
---Gary
 

sykanr0ng

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Aug 11, 2014
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5,363
Your planned injectors are way too big, for that engine build 24 lb would be more than you need.
Even for any reasonable upgrades you may do later 24 lb injectors will supply plenty of fuel.

Remember that it is a Bronco not a drag racing Mustang, so don't go by the Mustang forum info.
 
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gclauson

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Thanks for injector info

Sykanr0ng,
Thanks for that info. I agree that 24 will be fine with where I will start, but if I go with 30 or 36#, do you think I will have driveability issues? Perhaps my thinking is warped, but if I had really good heads and little larger cam, I would need bigger injectors which would still need to work at low RPMs with a short duty cycle. Or are those mutually exclusive objectives?

Gary
 

sykanr0ng

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Aug 11, 2014
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24 lb are bigger injectors for the 351w based engines.

Unless you are going to put a supercharger or turbochargers on it you will not exceed their ability to feed enough fuel to your engine. Those are far from a 'budget build' item.
 

pcf_mark

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Jun 11, 2010
Messages
3,574
I think you will see 5,500 rpm, but I suspect it will slow its race to 5,500 around 4,000. I bet it will really light the tires down low. A smallish cam and head on a bigger engine is always snappy down low. The only recommendation I would make is a forged piston not hypereutectic. If you have any tuning problems or get a bad tank of gas forged give you a nice safety margin. I am sure I will be flamed for this point of view! EFI with spark retard you can squeak by in hypereutectic. No spark retard I would use a forged slug.
 
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gclauson

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Thanks, guys!
Looks like I will go with 24# injectors and expect not much more than 5500 rpm until I can get a bigger cam and better heads into it (if ever).
The shop has already received the stroker kit and balanced it, so I think I am stuck with the hypereutectic pistons.:cry: I will have to ensure I do a conservative tune or have a second tune with less advance if I get a tank of low-octane gasoline.
Gary
 

EFI Guy

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I would run 30#'s at a minimum. I'm tuning a 393 right now that is hitting 74% duty cycle on the 30# injectors, and there is more power to squeeze from it still. I consider 80% to be about the max. Granted, this one has Trick Flow heads and a slightly larger cam, but it is not a drag car. 24#'s might support it, but you'd be very close to 100% DC and you get no warnings if you run out of injector, you just go lean and hurt things.

When you buy injectors, stick to Ford Racing only. No, Accel, Holley, etc... The little extra money spent will come back to you in ease of tuning. The only exception to that would be Seimens Deka 60 or 80 pounders. They are what Ford Racing rebrands as their own. Contrary to popular belief, they will not over fuel down low. The injector technology behind them has come a long way since the green 42's that gave everyone problems. They are expensive though, and the cheap ones on Feebay or Amazon are often Chi-com fakes. If you plan on building bigger later or adding boost, they might make sense to buy now.

That build will still spin to 5k, but HP will start to drop like a rock somewhere around 4000-4500 rpm. Lowend torque should be very impressive though. Throttle response should be great in a crawler. I'd do the "Viperwolf progressive throttle mod" on it if you plan on crawling.

PMAS makes great stuff. But you could save a few bucks and have more MAF stability and resolution running an OE Ford slot MAF in an aftermarket 75-80mm housing. You can find that MAF in any Ford V-6 or V-8 from 2005-2010.

Personally, I'd sell the Tweecer and buy a Quarterhorse. The Tweecer will do what you want though. If you keep it, I'd upgrade the software. I'm not a fan at all of it's native software.

Lastly, while I'm spending your money... Since you're running Explorer front dress and have the ability to tune, I'd consider running EDIS-8 instead of a TFI distributor. You can find most of the parts cheap at the junkyard and it's so much more reliable. The guy with the special cam sensor collars is only about a 30-minute drive from you and comes up your way often. =)
It does require a longer oil pump driveshaft, something to consider before you bolt the oil pan on.

If you get to the point that you need help tuning it, just give me a shout.
 

pcf_mark

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EDIS is solid! I took the OEM distributor and cut the top off. Then I drilled and tapped the body for a bolt, washer and oil drain plug gasket into the body where the shaft was sticking out. Then I shortened the drive shaft so it would not touch the bottom of the "bolt" and put the whole thing back in. This gets me oil pump drive problem free. I was going to use the OEM Explorer cam position sensor but I was too cheap and lazy.
 
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gclauson

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Thanks for those new replies!
Good advice to go with QH over Tweecer and how to mod the 351 distributor.

Garry, I have more questions about EDIS.
1. After PMing with you several years ago (yes I am slow to do new projects!), I believe I need to run two new wires to my ECM, plus patch in the EDIS, crank position, cam position, and the coil packs. Am I missing anything? My main pain point is unravelling my nicely loomed harness to run the two ECM wires, but I suppose I can overcome that :^)
2. If I bite the bullet, I'm to hear you still have the cam sensor collars!
3. I have had a TFI failure on the trail and it was miserable (didn't know what was wrong was for several hours), so I had bought the TFI relocate kit from Fat Fox, but I think as long as the engine is out, I may want to spend the time to do EDIS or go all the way to OBDII. I need to refer to your Explorer harness rework instructions to compare harness rework difficulty.

Regarding Ford Racing injectors, there are several ebay sellers that are refurbishing Volvo turbo 30# injectors that they claim are the same Bosch PN that Ford Racing uses for their product. These are much cheaper than a brand-new set of official Ford Racing. Do you know if these are acceptable to use and have the same tuning parameters?

BTW, I got the 393 parts back from the machine shop yesterday, so now the engine assembly fun begins!

Gary
 

nvrstuk

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X2 what Garry said. Im running about everything he said - Moates, EDIS, 63# SD injectors, custom cam (that needs to have more duation for my 418) but ridiculous torque...I shift at 6K and i love snow bashing...more fun than any other wheeling IMO...you either need to crawl or you need 50mph wheel speed while you're moving at about 5 mph...

My cam was custom built as per my own specs...I was a bit conservative and now want/need more 3k to 6K HP...

I swapped in a 4r70w with 300M parts...you'll love the torque but if you havent built your drivetrain for it..
well, start collecting HD parts!!
 
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EricLar80

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Just get the Siemens Deka 60 lb injectors and be done with it. They are plenty big to support any changes you are ever likely to consider, yet are NOT too big. They are a newer style injector that has superb low volume accuracy - they will actually be more accurate at low volumes than the old 24 lb bosch style injectors. It will idle butter smooth, and rip roar when needed, if it's built well and tuned correctly. Get a Moates Quarterhorse chip.

EDIS is a nice to have, not a requirement, to get the thing up and running. It would be easy to install if you are doing everything new anyways.

Check out my 393W install if you want to see the parts I used. Wish I has bought the SD injectors since I am running close max flow on my 30's.
http://classicbroncos.com/forums/showthread.php?t=174611
 
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gclauson

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That's good to know that the SD 60 work well! I had wondered how modern LS and Hemi motors get all that OEM power yet retain perfect driveability with huge injectors.
Eric, I have your 393 tuning thread bookmarked and plan to follow it as I go thru this! Thanks for your engine build link- I am reading it right now.

Regarding massive torque and breaking drivetrain parts, I am concerned about the D20 output and will get the AA heavy duty output kit. And will get an anti-wrap for rear axle. But do I need to upgrade the driveshafts to larger size and larger U-joints?
 

nvrstuk

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D20 was made for stock engines, 28" tall skinny tires, limited slip not locked axles front and rear...its a tough little tcase but the output ahaft is only one of the very inherent weak spots in the D20. I finally gave up and went Atlas now I run a 205. Thr dear teeth are 2 ti.es wider than a D20...I'll look for my comparison pics.

Tell us the type of rig you have, its use and your driving style...these are 3 big factors to the longevity of the little D20.
 
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gclauson

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I agree that an Atlas should be part of my plan!

I rock crawl and snow bash with most of the street driving just to get from my home to trails. It is not a daily driver!

I never worried much about breaking things with the 289, but now I'll be on an upgrade escalation cycle!

Truck has 35" MTRs, 4:56 gears, Detroit in the rear 9" and ARB in the front D44. Cromo axles all-around and CTM u joints in the D44. Stock drivelines. NV4500 trans, too.

I don't have a real heavy foot- I try to drive with more finesse than craziness, at least.
 

nvrstuk

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Just a Bronco driver for over 50 yrs!
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I think we think alike... :)

Rocks = Finesse

Snow and Sand = Very heavy right foot... :)

Start saving for the Atlas... I upgraded to a 300M output shaft almost 20 yrs ago...then I twisted the teeth off a low range gear set....then I went thru 4 cases... cracked them all...that got old...
 
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gclauson

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Atlas and Deka injectors

Maybe I should just avoid the carnage and get the Atlas now.
I was going to get good heads next, but I hate breakdowns on the trail, so the transfer case may be more important.

However, the D20 will probably live thru the snow bashing season due to lack of traction, I suppose, and i could get the Atlas in the spring.

Does anyone else have inputs on the Siemens Deka injectors? I see 60s ranging from about $220 to almost $400 for a set of supposedly genuine injectors. I also see the obvious knock-offs for around $120 a set, so those are off the table. Has anyone dealt with the lower-cost Siemens on ebay? Are they okay?

Thanks!
 

sykanr0ng

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No personal experience with those, but from what it looks like to me neither eBay or Amazon have any interest in keeping copies, forgeries or counterfeits off their markets.
 

nvrstuk

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I picked up a set off one of the Stang forums... don't go counterfeit...you'll be wishing you hadn't upgraded to the 205 or Atlas and spent the extrq 200 on the real injectors...

Hi tech= more crappy, knock off, guaranteed to break SOON parts...

I'm not pleased with some heims that are only 2 yrs old and have 5x the slop in them than the 12 yr old heims I replaced...absolutely serious...vendor sells a LOT of fab parts...
 
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gclauson

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Definitely don't want counterfeit! I will look around for some genuine used and if I can't find any, I'll get new ones that are genuine!

It is not worth it to save a few bucks and possibly damage a new engine.
 
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