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moparman505
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Discussion Starter #1
The parts are coming in but I need some help please. For my 408 stroker comp cams has recommended thier 262.....480 cam.
Now the questions. What size injecters do I need? Will my old mopar performance computer handle the cam?
These parts will be swapped over from my 360 to the stroker.(bear in mind that the 95 5.9's came with 24.5 lb injecters) Headers--52mm throttle body--R/T heads(202-162 valves), 1.7 rr's,3" exhaust with highflow cat.
My 1.7's are going to push the vavles to about a 517 opening from 480 and the 408 is getting flat top pistons for a compression ratio of 10.2
This is a 1995 Ram. Thank you all in advance!:help:
 

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Ram Racer
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95 is obdI which isnt exactly mod friendly.
Cam your going with(will have .510lift w/1.7rr BTW) is pretty mild but with the 408ci & big heads still beyond what the mp pcm is able to control.
Stock inj the mp pcm will have you running dangerously lean
Bigger inj & mp pcm will have it running pig rich at idle & light throttle.(hard on cat & mpg)

Strongly suggest you contact B&G Chrysler & send them the stock computer to get flashed(better tune).
They need to know exact specs of what you have.
Probably best to get 28lb inj. to go with it.
Dont be surprised if it takes a couple flashes to get the tune right.
After getting the flashed pcm back, best to break in the motor by keeping the rpms down(dont go above 3k rpm) & throttle light(NO WOT) & varied.(no holding steady rpms).
Once you have 500miles on it, go to a dyno to get wideband o2 readings.
Be sure to make note of any ping & what rpms it happens at (if it happens)
If a/f ratio is in the 12.5-13.0 range then your good. Anything other than that (@WOT) will need to be reflashed.
B&G will want a copy of the dyno & w/b o2 results so they can give a better tune.
 

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OK let's start at the beginning and figure out how much fuel you will need.

ISFR (lbs/hr.) = Injector Static Flow Rate
BSFC (lb/HP x hr.) = Brake Specific Fuel Consumption. Good approx. 0.50.
HP = Estimated realistic engine output (assume at flywheel)
DC = Duty Cycle of injector. Maximum opening time of injector/cycle time. Max. Duty Cycle = 0.90

ISFR = (HP x BSFC/No of cyl.x DC of inj.

The HP you use is the est. HP at the crank.

Lets assume with the upgrades your 408 will be good for an extra 100 HP at the crank or about 350 HP (just an example I have no idea what you would be making).
350 x .5 (0.60 if you decided to add a supercharger) = 175/8 = 21.875/.90 = 24.30lbs./hr.

If you actually do make 350 at the crank, your stock injectors are border line OK. If you want however, you can go to the next size which I believe would be 30lb injectors.
 

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Ram Racer
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moparman505
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Discussion Starter #5
Thanks very much RM and Rattler. After reading your responses I have done a swing around on this engine.
One of the worst mods I did was put the big valve R/T heads on.( Got them cheap from a buddy and we all know they don't even start to work till about 4500rpm) And being here in Canada the truck would have huge down time waiting for tunes, plus the added expenses of trying to get it right.
So I am going to do an about face. I will clean up my old stock heads with a gasket match and a bit of a polish. Retain the 1.7 rrs and go with the stock cam. (Try and get a small block Mopar roller cam anywhere right now with a decent grind anyway)
So I might get away with the MP controller ( they can learn a bit) and stock size injecters. But it seems to me that the big heads and cam are turning this into one big hassle.
 

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Thanks very much RM and Rattler. After reading your responses I have done a swing around on this engine.
One of the worst mods I did was put the big valve R/T heads on.( Got them cheap from a buddy and we all know they don't even start to work till about 4500rpm) And being here in Canada the truck would have huge down time waiting for tunes, plus the added expenses of trying to get it right.
So I am going to do an about face. I will clean up my old stock heads with a gasket match and a bit of a polish. Retain the 1.7 rrs and go with the stock cam. (Try and get a small block Mopar roller cam anywhere right now with a decent grind anyway)
So I might get away with the MP controller ( they can learn a bit) and stock size injecters. But it seems to me that the big heads and cam are turning this into one big hassle.
low lift(.300)flow #'s on un-ported r/t's tell a diff story.... 200 cfm at .300 lift shows velocity is high...should translate in to nice low rpm power with right cam/intake combo...id run r/ts over stockers anyday...with 63cc chambers flat tops are a great choice or a quench motor....can try n save the stock heads but imo not worth the time or money as there going to be cracked...at the very least id run a set of EQ stock replacements...cheap and flow better then oem and wont crack...

edit....are the heads 4sale(cheap lol) if your not going to use them ?

for tuning id consider a megasquirt for obd1(sct not available)...its a diy standalone that has recieved great reviews...some assembly is required lol...it wouldnt be the heads that would give hassle its the performance cam....lower vac at idle gives the map sensor(speed density) a lower reading throwng pcm for a loop(run pig rich at idle/decel) even with stock injectors...
 

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D-pickup is right, I missed the OBD-I. An SCT tune won't work for you. In any case the point is, you have gone this far. It would be a shame to go back to stock. To reiterate what said before, I would bet you those stock head are probably cracked. That's what they do.
 

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moparman505
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Discussion Starter #9
Love the input here. Ok,so I'll continue to use my R/T heads and 1.7 rr's and just make my engine 48 cubic inches bigger with a stock cam. Seems to me now that the only change I might need then is bigger injecters while retaining my MP ECU.
 

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i'd like to add my 2 cents from experience. arent the obd1 rams running 19lb injectors at 39lb fuel rails? i set up a buddy w/ a 95 on bosch III's corvette 24lb injectors and his truck runs them fine. few mods though it runs perfect. the pcm learned OK. w/ mods and a stroker the fuel rail pressure may need to come up. bosch 24s are easy to find and 28s. i have heard complaints w/ 30lb injectors on the non turbo non super charged blocks.
any ways i just wanted to be part of this conversation!
 

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Also the stock fuelpump may not flow enough at WOT so be sure it's up to the job.
The stock fuel pump by design has enough flow to feed a modest upgrade in fuel injectors say anything less than 35 lb. So unless there is something wrong with the fuel pump or if the fuel filter is clogged you should be alright. If you are making serious engine modifications I would just buy a fuel pressure gauge that you would mount inside the cab (electronic). That way you can see at WOT if the pressure changes. With my 2000 Dodge Ram it stays at 48 psi if it is at idle or at WOT. If it drops, say with 30 lb. injectors, than either the fuel filter is clogged or the fuel pump is bad.
 

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moparman505
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217 Posts
Discussion Starter #13
So I guess I'm looking for a definitive answer on injector sizing. Going with stock cam,big valave R/T heads and 1.7 rr's. Along with my headers,cai,high flow cat with a 3" single exhaust(Flowmaster). Will stock injector size handle this with the 48 more cubic inches?
 

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The only way to know for sure would be to run it on a chasis dyno and measure the A/F ration with a wide ban O2 sensor. If you are less than 13, you should be OK. If you are exceeding 13 you are running lean and need more fuel.
 

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moparman505
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Discussion Starter #15
Rattler, I am going to go back to your original post and the formula for calculation of injector size.
I'm thinking that with the add ons I have that I am really not going to be far off the 350 horse mark after we add another 48 cubic inches. The 30 lb'ers are looking like the injector of choice.
Some of the Mustang 5.0 strokers around here are running 30's and 34's with mild to moderate cams. With no problems.
 

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Ram Racer
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30lb inj & only an MP PCM, good luck indeed :ugh
 

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as long as the mp pcm has its original tune, it will not take full advantage of the injectors & does not have adjustability. a 30lb will operate at a very light duty cycle. a 28lb may operate at an average cycle, and a 24lb can handle up to 350 hp. the mp box tune may not be sophisticated enough for the build up and may lean the a/f mixture. the only way my stock truck could run the mp tune was burning high octane gas. are you willing to fill up on cam2 / purple gas every time? these posts are very technical and seem to get complicated quick. i would continue to research. obd1 engines have 1 o2 sensor, would a sim card from fastman help richen up the mixture? dunno?
 

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Ram Racer
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MP PCM only has adjustablity for about 3% variance max, with 30lb inj & the 408 this will be well beyond its abilities.

Another option beside the B&G flash is either the Megasquirt or SMT7.
I ran an older SMT6 for a while, with 24lb fms injectors. Figure I saw about 10-12rwhp more than what the MP PCM was giving on its own(laptop tuned it myself). Couldnt run with the fms24lb on the mp pcm straight up & that was making 270rwhp, 52tb, m1/2bbl, rt+ cam & 1.7rr. Stock injectors had me running excessively lean (WOT 14.0 from 3k-4k, 14.8 by 4500rpm) .
 

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moparman505
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217 Posts
Discussion Starter #20
I threw the 30lb injectors in for feedback. Realisticly this is where we are at.
The block is out getting machined. I am not looking to juice up my truck. I am looking for torque not a revving horsepower monster. I want my power to be from idle to 4400 to 5000.
We are putting a stock cam in with the 1.7's and R/T heads. This set-up is mild. I do have the throttle body,cai, and exhaust to handle the extra cubes.My tranny was recently rebuilt with the Transgo kit, kevlar bands and HD clutches. My rear-end was rebuilt at the same time. The truck is ready.
I am old school ..change cam...new jets..metering rods.. or springs then job done. It was and is critical to me that I come here where so many of you are so much more knowlegable(sp?) than myself and others in my small town.
This is what we are going to do...The engine will be put together as above with stock intake and injectors. We will flash it up using the MP ECU. Realisticly I believe this engine will be in the 320 to 330 horse area. There is every possiblity that the stock 24.5's will handle the extra 6 cubic inches in each cylinder.We will do fuel ratio readings as we gently break in the engine.And allow the MP ECU a little time to adjust somewhat to the extra inches.
If bigger injectors are needed they would probably be 26 or 27 lbs. And on a real positive note I found my stock ECU (thought I had thrown it away) which can be sent to B&G as necessary.
Do you guys figure my expectations are where they should be? Thanking you all!
 
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