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Setting up a stock efi motor to run on 91 octane

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Wesman07
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Setting up a stock efi motor to run on 91 octane

Post #1 by Wesman07 » Sun Nov 19, 2017 9:25 am

What if you were to take a stock efi 300, and put flat top pistons in to raise the compression up to the 9.2 ish range? Or a level safe for 91 octane.

Would this have similar results to putting a smaller cam in that raises the dynamic compression?
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pmuller9
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Re: Setting up a stock efi motor to run on 91 octane

Post #2 by pmuller9 » Sun Nov 19, 2017 9:37 pm

You would accomplish 9.3ish by zero decking the stock piston. Flat tops increase the compression ratio by 2 full points.
Anyway depends on what you mean by similar results.

Increasing the static compression ratio increases the expansion ratio during the power stroke which means there is more work being done and more energy is extracted.
The result is more torque throughout the power band.
Engine is more efficient and fuel mileage should increase.

Changing the cam timing more importantly the intake valve closing point in this case, affects the cylinder fill or volumetric efficiency versus rpm.
Generally speaking an early closing intake valve builds torque at low rpm and the torque curve moves upward in rpm as the intake valves closes later after BDC.
This is more of a function of the intake valve closing based on the .050" duration spec.

The Dynamic Compression Ratio is based on the advertised duration spec (SAE .006" lift standard) and is mainly used as a value for detonation for a given engine.
It can affect off idle performance.

What result are you looking for?

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Re: Setting up a stock efi motor to run on 91 octane

Post #3 by Wesman07 » Sun Nov 19, 2017 10:42 pm

I'm looking for a reliable, simple and strong motor for my truck. The area I'm trying to improve is the highway cruse... 2500 down to 1800 rpm.

I was considering the 260 degree crane cam, but I really like the characteristics of the factory cam set at zero degrees. Knowing that going to a smaller cam could require a higher octane fuel... why not set the motor up to run 91 octane with the stock cam?
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Re: Setting up a stock efi motor to run on 91 octane

Post #4 by pmuller9 » Mon Nov 20, 2017 12:13 am

There is a good amount of performance gained with the EFI head by increasing the valve lift.
Limit the lift to the .450" range for the sake of the stock rocker arms.
I don't like the Crane 260 cam for that reason where the exhaust lift is .487".
Also there is no need to have that more much exhaust duration over intake duration (204/216) especially if you are looking for improvements mainly in the low end of the power band.

If you raise the compression by decking the block so the stock pistons are at zero deck, the increased quench will lower the tendency for detonation.

I would go for it all, up the compression and use a cam with higher lift, longer than stock advertised duration and a short .050" duration.

Howards cams has a list of "stock replacement" lobes that would fit the bill. It is their 1HS series
Crower cams also has a similar series of cam lobes.

I would talk to both of them about a single pattern cam for your project.

Advertised duration 270 or more.
.050 duration 200 to 206
Valve lift near .450"
110 degree LSA

I was looking at Howards 1hs20627 lobe.
It comes with either a 270 or 288 .006" lift duration.
.050" duration is 206
Lobe lift is .278" which is .444" valve lift with 1.6 ratio rocker

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Re: Setting up a stock efi motor to run on 91 octane

Post #5 by Wesman07 » Mon Nov 20, 2017 4:32 pm

Very cool. I like the direction this is going. So hypertec Pistons set at a zero deck hight. 9.2:1 compression, and 91 octane.

I'll gladly take your cam advice... I filled out the form on Howard's website to get their recommendation.

Would this factory fuel system handle this? I remember reading the factory fuel system won't run lean until 3800 rpm. Being that I want to keep the same working range, I shouldn't have a problem?

Will I be able to adjust spark enough by just the base timing to account for the higher compression?
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Re: Setting up a stock efi motor to run on 91 octane

Post #6 by pmuller9 » Tue Nov 21, 2017 9:40 am

Wesman07 wrote:Will I be able to adjust spark enough by just the base timing to account for the higher compression?


If the cam has a longer advertised duration than the stock cam that will help with detonation
Adjusting the base timing moves the entire timing curve. If you retard the base timing you will lose power.
The plan was to use a higher octane pump gas (91 octane) to compensate for the higher compression.

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Re: Setting up a stock efi motor to run on 91 octane

Post #7 by Wesman07 » Tue Nov 21, 2017 11:06 am

?[/quote]
If the cam has a longer advertised duration than the stock cam that will help with detonation
Adjusting the base timing moves the entire timing curve. If you retard the base timing you will lose power.
The plan was to use a higher octane pump gas (91 octane) to compensate for the higher compression.[/quote]

It absolutly is. I read that I would still need to retard timing.... I guess that is not true?

I could not find the cam you were talking about. Do you have a link?
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Re: Setting up a stock efi motor to run on 91 octane

Post #8 by pmuller9 » Tue Nov 21, 2017 11:53 am

Wesman07 wrote:It absolutly is. I read that I would still need to retard timing.... I guess that is not true?
I could not find the cam you were talking about. Do you have a link?

They were probably talking about the stock cam or one of the shorter advertised duration aftermarket cams.

We are talking about using a cam with longer than stock advertised duration but keeping the .050" duration short enough so we don't push the stock ECM and injectors beyond their fuel flow limits in the rpm range you want to operate at.

It will be a custom cam. Download the Lobe List and see halfway down the 3rd page, Lobe# 1hs206278-2
https://howardscams.com/rt-4932-downloads.html
The intake lobe would be the 1hs206278-2 which has a long ramp with a 288 .006" duration.
We can go to a standard ramp for the exhaust to keep the overlap down and use the 1hf205280 lobe that has a 259 .006 duration.
Keep it at the stock 110* LSA
Last edited by pmuller9 on Wed Nov 22, 2017 10:00 am, edited 2 times in total.

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Re: Setting up a stock efi motor to run on 91 octane

Post #9 by Wesman07 » Tue Nov 21, 2017 5:26 pm

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Re: Setting up a stock efi motor to run on 91 octane

Post #10 by Wesman07 » Tue Nov 21, 2017 6:36 pm

I asked about your recommendation as well.

It looks to me that one was close to the crane 901 that we were trying to get away from.
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Re: Setting up a stock efi motor to run on 91 octane

Post #11 by pmuller9 » Tue Nov 21, 2017 6:39 pm

They didn't get the part about raising the compression ratio or increasing the .006" duration beyond 268*
The cam description clearly states that it is for engines with minor or no additional improvements.

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Re: Setting up a stock efi motor to run on 91 octane

Post #12 by Wesman07 » Tue Nov 21, 2017 7:34 pm

I should just call them. I also have to find a good machine shop or engine builder.

Any idea what kind of power this would make? I'm guessing 175hp 290lbs
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Re: Setting up a stock efi motor to run on 91 octane

Post #13 by pmuller9 » Tue Nov 21, 2017 9:31 pm

Wesman07 wrote:I should just call them. I also have to find a good machine shop or engine builder.

Any idea what kind of power this would make? I'm guessing 175hp 290lbs


It will take a phone call. The online forms do not supply the right information.

I'm hoping between the increase in compression and cam change to make just over 300 ft lbs of torque in the 2000 to 2500 rpm range.
Don't want to make a lot of power above that to keep the ECM and injectors from going beyond their limit and causing the engine to go lean.

To help with that since we are going with a longer .050" duration to get the lift we need, the cam will need to be advanced 4 degrees.
In order to keep the DCR in check with the cam advanced, the .006" duration needs to be more than the stock 268*

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Re: Setting up a stock efi motor to run on 91 octane

Post #14 by Wesman07 » Tue Nov 21, 2017 10:33 pm

What is the best way to advance the cam 4 degrees? A offset cam key with a cloyes adjustable get set?

Thank you for all of this by the way. It is the exact direction I wanted to go with this. Should be a great truck motor!
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Re: Setting up a stock efi motor to run on 91 octane

Post #15 by Wesman07 » Tue Nov 21, 2017 11:10 pm

Will the cam advancement change between the 270 and 280 degree duration?

Given the motor specs, Would you lean towards one or the other?

I would assume that the 280 would be on the safer side of things but less bottom end.
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Re: Setting up a stock efi motor to run on 91 octane

Post #16 by pmuller9 » Tue Nov 21, 2017 11:14 pm

You're Welcome. Glad to help

The Mr Gasket 987G offset cam key gives you 4 degree and the 988G gives you 8 degrees.
I prefer using all steel gears so the Cloyes gearset with the aluminum cam gear would be my last choice and would only use it if I needed another 4 degrees.
Last edited by pmuller9 on Tue Nov 21, 2017 11:32 pm, edited 1 time in total.

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Re: Setting up a stock efi motor to run on 91 octane

Post #17 by pmuller9 » Tue Nov 21, 2017 11:19 pm

The cam advance changes with the Lobe Separation Angle.
If the LSA is 110* like the stock cam then 4 degrees advance puts the Intake lobe center at 106* ATDC.
If the LSA is 112* like the Crane then 4 degrees advance puts the intake lobe center at 108* ATDC

Yes, a 280* intake duration would give a lot more safety margin.
The .006" duration doesn't affect the power band once the engine rpm is well above idle.

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Re: Setting up a stock efi motor to run on 91 octane

Post #18 by Wesman07 » Wed Nov 22, 2017 10:09 am

Ok. That makes sense.

I will have to call them. The guy just replied back and said " yes you could do that".

I order to deck the block to the correct height, I would have to assemble, measure the top of block to top of piston, disassemble, mill.... correct?

Any other machining that should get done?
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Re: Setting up a stock efi motor to run on 91 octane

Post #19 by pmuller9 » Wed Nov 22, 2017 10:36 am

Wesman07 wrote:In order to deck the block to the correct height, I would have to assemble, measure the top of block to top of piston, disassemble, mill.... correct?

Correct. That is the most accurate way.

Are you doing a total rebuild with new pistons, rod and main bearings, valve job ...ect?

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Re: Setting up a stock efi motor to run on 91 octane

Post #20 by Wesman07 » Wed Nov 22, 2017 11:26 am

Yes. I will be building a second motor to keep the down time of my truck to a minimum. I don't like rushing motor builds.

I have about 250k and 150psi across the board on my current motor, so I should have an adequate amount of time.
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Re: Setting up a stock efi motor to run on 91 octane

Post #21 by pmuller9 » Wed Nov 22, 2017 1:48 pm

Just to summarize on the Howard cam profile.

Intake: The 1hs206278-2 lobe has a long .006" duration at 288* which will allow the cam to be advanced 4 degrees and still have a low DCR with a 9.4 static compression ratio.
Lobe specs: 288@.006", 206@.050", .444" lift with a 1.6 ratio rocker

Exhaust: The exhaust needs a short .006" duration to minimize the overlap between the intake and exhaust valve opening period.
If we go to a standard ramp lobe, the 1hf205280 lobe only has a 256@.006" duration.
Lobe specs: 256@.006", 205@.050", .448" lift with a 1.6 ratio rocker.

We want to keep a tight LSA to focus on low end torque rather than upper end power which might push the limits of the stock EFI system.
Staying with the stock 110 LSA would work great.

If you use one of the KB/Silvolite or Speed Pro/Sealed Power hypereutectic pistons, they supposedly have a 22cc dish.
At zero deck with a 68cc combustion chamber works out to a 9.4 compression ratio.
With the cam 4* advanced, intake lobe center at 106* ATDC, the DCR would be 7.3
Last edited by pmuller9 on Fri Nov 24, 2017 12:06 am, edited 1 time in total.

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Re: Setting up a stock efi motor to run on 91 octane

Post #22 by Wesman07 » Wed Nov 22, 2017 3:30 pm

Awesome. I'll have to call it in. I doubt they will have much input, as you seem to well versed in their cam profiles and know the build better.

I did not find the piston dish volumes listed on summit. I'm assuming the standard D dish, and not the round dish or the just the valve reliefs?

Should I go with standard ring thickness for longevity?
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Re: Setting up a stock efi motor to run on 91 octane

Post #23 by Wesman07 » Thu Nov 23, 2017 9:54 pm

I found these.http://www.jegs.com/i/Sealed-Power/844/H519P20/10002/-1

With the felpro gasket it should give me 9.44:1
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Re: Setting up a stock efi motor to run on 91 octane

Post #24 by Wesman07 » Fri Nov 24, 2017 7:54 pm

I tracked down a junkyard engine. Complete 1994 4.9, still running for $380.

Howard cams do not sell directly. They said try compitition products or summit... neither website showed a custom cam option for this motor... I will have to make some phone calls.

Pmuller, do you think the 288 duration will be too much? Any drivability issues?
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Re: Setting up a stock efi motor to run on 91 octane

Post #25 by pmuller9 » Fri Nov 24, 2017 10:33 pm

Wesman07 wrote:Pmuller, do you think the 288 duration will be too much? Any drivability issues?


The stock cam has 268* duration and is 4 degrees retarded with the intake lobe center at 114* ATDC.
The intake valve closes 68* ABDC.

An intake lobe with 288* duration advanced 4 degrees with the intake lobe center at 106* ATDC closes the intake valve 70* ABDC which is only a 2 degree difference.

The stock cam with both the intake and exhaust lobes having a 268* duration with a 110* LSA has 48 degrees of overlap.
As discussed, a cam with a 288* intake and 256* exhaust duration with a 110* LSA has a 52* overlap which is only a 4 degree difference.

There will be no issues

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Re: Setting up a stock efi motor to run on 91 octane

Post #26 by Wesman07 » Sat Nov 25, 2017 9:42 am

Yeah your right... it all makes sense. It's just the very different from what most people use for the same rpm range.
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Re: Setting up a stock efi motor to run on 91 octane

Post #27 by Wesman07 » Fri Dec 01, 2017 5:54 am

I just took a trip from Pennsylvania to Missouri and back. The truck weighed in at 6300 pounds. The air temp were around 50 degrees. Engine temp was on the low side.
Going through the Mountains in Kentucky i was able to stay in 4th gear through most of it, but I started to hear some knocking. So I switched to 89 oct, and it helped but every so often I would still hear a knock.
So my question is, am I shooting too high for my dynamic compression given my application?
The motor is stock beside and advanced cam. Based off the calculators I've used, it should have brought me from 7.5 to 7.8:1. This new set up would put me at 8:1..... is this correct?
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Re: Setting up a stock efi motor to run on 91 octane

Post #28 by pmuller9 » Fri Dec 01, 2017 11:40 am

I'm using the .006" closing point to calculate DCR based on the stock 268* duration.

The stock cam closes the intake valve 68* ABDC.
If you advanced it 4 degrees the closing point is now 64* ABDC.
My calculator shows a DCR of 7.134 with an 8.8 SCR

If we use a cam with a 288* intake duration and advance it 4 degrees with the intake lobe center at 106* ATDC the intake closing point is 70* ABDC.
The DCR is 7.172 with a 9.3 SCR which is the same.

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Re: Setting up a stock efi motor to run on 91 octane

Post #29 by Wesman07 » Fri Dec 01, 2017 12:31 pm

Ok great! It was user error on my end. thank you!
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Re: Setting up a stock efi motor to run on 91 octane

Post #30 by pmuller9 » Tue Dec 12, 2017 1:35 pm

Wesman07 wrote:Howard cams do not sell directly. They said try compitition products or summit... neither website showed a custom cam option for this motor... I will have to make some phone calls.

I talked to Billy Fisher from Howards Cams at the PRI show in Indianapolis this past week.
He said that they are willing to sell cams directly but it is a lot cheaper to go through someone like Summit where the cam cost less and you get free shipping. He was just trying to save you money.

I called Summit and they said you can order any cam through them if you supply them with the cam info which is the cam core number and the grind number which you would get from Howards cams.

I also talked to Crower at PRI and they said that they have over 10,000 cam lobe profiles and would be glad to make what you need.

I would be willing to work with either of the two companies and get the info you need to order.

Did you get the 1994 engine from the wrecking yard?

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Re: Setting up a stock efi motor to run on 91 octane

Post #31 by Wesman07 » Tue Dec 12, 2017 10:18 pm

I have not... I am still working on the logistics.

I have found a local machinist who I hear is good but a little pricey, and I would rather pay for quality.

I also found an engine stand to barrow... but the location is stil in question. I am pretty maxed out in my garage now, two Dirtbike's, my parts inventory, a welder, tools and a wood stove. Sure I could fit it, but it would be tight.

I also plan to move in the spring, so I need to double check the engines health and consider a plan B if the engine will hold up for a while.

I'm temped to buy the cam now, being that it is the hardest part to get. I think I can build this for under $2,000
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Re: Setting up a stock efi motor to run on 91 octane

Post #32 by pmuller9 » Tue Dec 12, 2017 11:24 pm

Quick question
EFI engines are listed as being available from 1987 but you list your truck as a 1986.
Did your truck come with EFI as a late model 86?

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Re: Setting up a stock efi motor to run on 91 octane

Post #33 by Wesman07 » Wed Dec 13, 2017 5:40 am

Nope. I did the EFI swap back in 2006.

86 was the last year carburetored. I got so dam frustrated trying to keep the original motor running right that converting to EFI was the easiest solution.
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Re: Setting up a stock efi motor to run on 91 octane

Post #34 by Lazy JW » Wed Dec 13, 2017 10:24 am

Yup, the 86 had the Dreaded Feedback Carburetor (DFC). It combined all of the worst qualities of carburetion and EFI into one pathetic piece of garbage with none of the good qualities of either :twisted:
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Re: Setting up a stock efi motor to run on 91 octane

Post #35 by Wesman07 » Wed Dec 13, 2017 11:38 am

Was that the only year for feedback carbs?

I just remember it being a total birds nest with vacuum lines woven in, around and in between everything.
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Re: Setting up a stock efi motor to run on 91 octane

Post #36 by THE FRENCHTOWN FLYER » Wed Dec 13, 2017 2:50 pm

I think '85-'86.
FORD 300 INLINE SIX - THE BEST KEPT SECRET IN DRAG RACING

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Re: Setting up a stock efi motor to run on 91 octane

Post #37 by woodbutcher » Wed Dec 13, 2017 10:21 pm

:( My 84 had the feed back carb,until I did some"surgery".Junked it and the TFI ignition,and went to a non feed back and DS2.What a sweet difference.Went from 8MPG to 16 on the hiway.That also got rid if a plastic grocery bag full of wires from under the hood when I removed the stand alone computer from under the dash.Oh yeah,The DS2 box and distributor was strictly plug and play as the hook up for it was in the truck wiring harness.
Good luck.Have fun.Be safe.
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Re: Setting up a stock efi motor to run on 91 octane

Post #38 by Wesman07 » Wed Dec 20, 2017 11:59 am

I think this is one of the best ways to build a 300 EFI truck motor, and keep the factory fuel system. Simple, cheap, reliable.

But, If I wanted the option to take this one step further... im assuming that would involve head work and a stand alone?

Would head work alone yeild any benefits?

Would modifying the head affect our cam selection?

The reason I'm asking is because it's easy to swap out the ECM for a Stinger Pimp (basically a plug and play ms3), it's just getting it to run right is the hard part. I'd rather not build two heads or mess with the cam we selected.
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86 f150 300 efi with advanced stock cam. Np435, Dana 60/ 10.25, 35" BFG's, four link front suspension with 12" travel fox coil overs, custom deaver leaf pack in the rear.

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Re: Setting up a stock efi motor to run on 91 octane

Post #39 by pmuller9 » Wed Dec 20, 2017 2:02 pm

Adding the Stinger Pimp would make life with this project a whole lot easier.

You can now use a wide band O2 and stay closed loop the whole time and let the ECM self learn as you drive based on the A/F ratios you choose.
You can also change the size of the injectors as needed which eliminates the engines HP restriction of the stock injectors.
You also get full control over the ignition timing
Cam selection still has the same considerations for a higher compression zero deck piston with peak torque around 2000 rpm.

Head work should mainly consist of removing most of the intake valve guide boss and contour the remaining part to allow better flow around the valve stem area.
Keep valve sizes stock to maintain swirl and high velocity at very low rpm.
Just a clean up around the port walls with miniumum material removed.

Optional: Use the Scorpion 1.73 ratio roller rockers made for the 1985-1996 head for additional lift.
https://www.summitracing.com/parts/scc- ... /make/ford
Would recommend switching to the longer non EFI valves to increase retainer to valve stem seal clearance and allow wider selection of valve springs with 1.700" installed height.

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Re: Setting up a stock efi motor to run on 91 octane

Post #40 by Wesman07 » Wed Dec 20, 2017 4:15 pm

Ok, the hand work I can do and would enjoy doing. The longer valves and roller rockers arnt that much more work for the machinist, are they? Just need screw in studs?

So this would roughly add $1,500 to the build... total around $3,000. What kind of gains could I expect? Worth the price?

I would guess the rpm range would be extended to 4-4500, mainly seeing a increase in peak horse power?
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86 f150 300 efi with advanced stock cam. Np435, Dana 60/ 10.25, 35" BFG's, four link front suspension with 12" travel fox coil overs, custom deaver leaf pack in the rear.

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Re: Setting up a stock efi motor to run on 91 octane

Post #41 by pmuller9 » Wed Dec 20, 2017 4:19 pm

The rocker arms are pedestal mount and are supposed to be a bolt on item.
Haven't used one yet to see how straight forward they are to install.

The increased lift and higher velocity port should improve power everywhere.

The 300 six has 50 cu in cylinders same as the 400 V8.
The 300 head ports are way undersized for the cylinder size and as you improve the port flow there is an increase in torque even at the low end.

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Re: Setting up a stock efi motor to run on 91 octane

Post #42 by Wesman07 » Wed Dec 20, 2017 7:36 pm

Do you have a rough guess on the power out put?

Im just trying to justify the extra 1500 bucks and the time to learn mega squirt
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Re: Setting up a stock efi motor to run on 91 octane

Post #43 by pmuller9 » Wed Dec 20, 2017 10:43 pm

So I thought about it.
I suggest staying with the original plan of working with the stock ECM.
IMO it would be wasteful to use the Stinger Pimp for just a few extra HP since that unit can support so much more.

I still would do the port work in the bowl area around the valve guides and use the longer valves with Comp 903 springs set at 1.700"
They have the same rating as the stock springs on the non EFI heads.
Stay with the stock rocker arms.
Custom cam as planned.
Zero deck pistons.

The Stinger Pimp would work great with a turbocharger and about 500 ft lbs of torque starting at 2000 rpm.

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Re: Setting up a stock efi motor to run on 91 octane

Post #44 by Wesman07 » Thu Dec 21, 2017 6:06 am

I had seriously considered going to turbo route, but the time and money that it would take to do it right turned me off. I would be investing way too much into just one area of my truck. I would also never feel comfortable saying things like "sure babe, just take my truck". And I would probably say things like "now watch your egt's".... I just don't need that.

So back to what you were saying... I can do the mild port work at time of rebuild, and even put in the longer carb head valves with out messing anything up. That's a good thing.

The added lift from the roller rockers
would be too much for the stock computer?

It would be a huge luxury to be able to have the option of running the stock computer.

I'm not putting the stand alone in the "No cagagory" just yet.... if this motor could hold 300lbs/ft for an extra 1,000 rpm... that's an extra 60hp... 260hp/300lb/ft
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Re: Setting up a stock efi motor to run on 91 octane

Post #45 by pmuller9 » Thu Dec 21, 2017 11:19 am

Wesman07 wrote:The added lift from the roller rockers
would be too much for the stock computer?

As you raise the engine torque which requires more fuel, you hit the HP limit of the injectors/ECM at an earlier rpm.
That's something you would have to monitor with a A/F ratio meter. As soon as you see the A/F ratio start to go high then you know the injectors and/or the ECM is at the HP limit.

Wesman07 wrote:I'm not putting the stand alone in the "No cagagory" just yet.... if this motor could hold 300lbs/ft for an extra 1,000 rpm... that's an extra 60hp... 260hp/300lb/ft


If you want the head to breath enough for 300lb/ft at 4600 rpm you go to the next level.
In order to keep the cam duration relatively short for low end torque, the burden for flow is on the head.

SBC 1.94" intake and 1.60" exhaust.
The combustion chamber walls are laid back to unshroud the valves and you trade (Kill) swirl for volumetric efficiency.
A lot more work in the bowl area.

You start by bolting the head to the bare block and scribing the cylinder bore diameter to the head surface.
The chamber walls around the spark plug are pulled back to the cylinder bore scribe line.
Then using a template scribe the lines for the intake and exhaust valve relief. It will mostly be the intake valve side of heart shape that needs to be pulled back.
Here is a finished example.
https://www.dropbox.com/s/c2wxpsuq25rp1 ... 3.jpg?dl=0

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Re: Setting up a stock efi motor to run on 91 octane

Post #46 by Wesman07 » Thu Dec 21, 2017 12:43 pm

You bring up some very good points. So if I stick to the original plan, I would still run the risk of going beyond what the stock computer can handle. I would still need to check this with a wide band. And if I do run lean, I would need to limit my rpm... or is it possible to run lean through out the entire rpm range at wide open?
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Re: Setting up a stock efi motor to run on 91 octane

Post #47 by pmuller9 » Thu Dec 21, 2017 1:20 pm

HP is based on fuel flow so the fuel flow limit equates to a certain HP limit which also equates to torque x rpm / 5252 something you already know.
For a certain HP point, the higher the torque, the lower the rpm.
You would have to limit the RPM with the stock EFI system if the mods push it beyond its HP limit.
No problem with WOT till you reach the HP limit.

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Re: Setting up a stock efi motor to run on 91 octane

Post #48 by Wesman07 » Thu Dec 21, 2017 2:45 pm

That makes sense if the computer stays in open loop. At wot the computer falls back to closed loop, ignoring the o2 sensor and runs off of a fuel table that's programmed in its memory. So if this motor makes more power at say 2,000 rpm... what is telling to computer to add more fuel at wot?
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Re: Setting up a stock efi motor to run on 91 octane

Post #49 by wallen7 » Thu Dec 21, 2017 3:42 pm

You got your loops backwards open loop is cold starts, wot thats when you get extra fuel from look up tables in the eec processor. Closed loop it run off sensors, tp and speed to get stoichiometry ( basically 14.2 af ratio )

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Re: Setting up a stock efi motor to run on 91 octane

Post #50 by pmuller9 » Thu Dec 21, 2017 4:19 pm

Wesman07 wrote: So if this motor makes more power at say 2,000 rpm... what is telling to computer to add more fuel at wot?

The computer looks at the Manifold Absolute Pressure (MAP) sensor which corresponds to the vertical position on the fuel table.

Wallen7 is right. You have your loops backwards.
At low engine loads the ECM is in closed loop mode with the O2 sensor.
It is a narrow band O2 sensor whith a center response around 14.7
Once the load increases to the point where a richer mixure is needed it must open the loop (disconnect) from the O2 and use the fuel table.

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