F-250 super cab 4x4 300 Turbo

motorsickle1130

Active member
Supporter 2019
Hello all. I've been thinking about a 300 build for a number of years, and just recently came into a 1978 f-250 4x4 supercab with Dana 60s front and rear. Truck is currently a mild 429, C6, with an NP205. Gears are 4.10s, rolling on 35s.
Donor is a 300, T18, with an NP 208 out of an ?1982 Bronco? Will most likely keep 205 in the truck, better ratio (1.96) and sturdier. Will be using the T18 for sure.

I've decided on an intercooled, blow through set up. Picked up an SA design book on Turbos, and have started working up some numbers.

Target: 8lbs boost, 10lbs max. wastegated for sure
Daily driveability, occasional towing/hauling. NO EFI, ECM, or the like to be installed. I will run guages, but will be sticking with analog wherever possible. Will most likely dyno for fine tuning.

I have a turbo that may or may not work. It's a T3 housing, garrett, off a ?VG30DET? (Nissan 300ZX) in need of a rebuild. I plan on running a larger inducer diameter, smaller exducer diameter, to keep the power band down lower; like in a diesel. I haven't crunched the numbers yet on specific diameters/trim.
Based on 8-10lbs, the math suggests 1500rpm to 4500rpm is a safe bet, though the efficiency could be a little better, but I am on a bit of a budget.
I have a machinist who's on board with a rebuild. Motor will be opened up, though the focus is on longevity. Still need to make a complete plan with him, and strip the motor down before purchasing parts.

QUESTIONS:
#1) Am I correct in wanting to use a smaller T3 for driveability/longevity, as opposed to what looks like a T4 most of the other posters on this forum are running?
#1b) If needing a different turbo housing, what do you think the best option is and why?
#2) At 8-10lbs boost, would stock grind cam w/ 1.7 rockers put out better low end torque, or bump up to a 252 cam? Goal is 400 ft lbs at crank (and hopefully? 15-20mpg). (it seems rediculous seeing it in writing, lol)

Thanks for whatever you have to offer, and I hope to be able give back what I hope to get out of the forum. :beer:
 
Not very familiar with that turbo but im using a t3 flanged he351cw holset on a efi headed motor and i have great low end results. Actually that was the area i was targeting as im developing a build that will eventually be in my 1996 1 ton crew cab long bed and i need all the low end i can find to pull out near 7k lbs unloaded. Also my results at 13 lbs of boost on pump gas was over 500 ftlbs at the tire and on the road i can achieve full boost at 1800 rpm. I can tell you that over 1500 rpm i can climb any hill around here in 5th gear. Thats in my half ton 4x4 right now but have no doubts it will pull around the 1 ton. The carb would be the biggest difference for me. Also i did advance the cam timing for additional low end. In my experience, if your looking for low end, the t3 will work just fine till about 4000 rpm. Now the other turbo specs may come into play as well such as turbine housing volume and wheel sizes and pitches.
 
Right on, much appreciated.
Here’s a picture of my rig. It’s going to need plenty of help elsewhere too, hence the goal of not going broke on just the drivetrain.
I’ll be searching around soon for info, but Any suggestions on head work?
 

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Very nice looking truck i love the 78s and 79s myself. Actually just found out where a 350 crew cab long bed is sitting. Havent found out what year it is yet and havent saw the front clip. Did you get that truck from south western pa? Ive seen one similar driving around in the past.
Im kind of at the head work point myself. I got arp head studs and have to order the felpro 1024 gasket. I thought i would have had problems with the stock hardware and gasket by now and then it would force me to get into the head porting and studs but so far so good.
There is alot of information about porting both carb or efi heads on the forum here including cutaways that show there isnt a ton of meat around the ports so it wouldnt be hard to blow thru. Some members here have flow numbers posted about a third higher than stock tho so there is still power to be found on these u flow designs!
 
The EFI head shrouds the intake valve in order to create swirl.
The flowbench shows restricted flow rates until the valve lifts above .350"
If you open up the chamber as shown on the right the mid lift flow picks up a lot.
The head shown below was installed on the block and the cylinder bore was scribed on the head surface.
Then the chamber walls around the spark was brought out to the scribe line.

[image]https://www.dropbox.com/s/0k6115t6fst229s/Unshrouded%20EFI%20chamber%202.jpg?raw=1[/image]

With the larger chambers you now have the option to install larger valves.
For low rpm work the Chevy 1.84"/1.60" valves are sufficient. They are 4.91" long versus 4.75" for the stock EFI valves.
The benefit of the longer Chevy valves is you are no longer restricted to (less than) .500" valve lift as with the stock EFI valves.
This way you can use a short duration cam and use the 1.73 ratio Scorpion roller rockers to get higher valve lift.

Porting can consist of just working the valve guide bosses in the bowl and cleaning up the ports.
viewtopic.php?f=22&t=77808#p599298
 
First things first, love the truck, and the direction of your build. Most turbo builds are more oriented toward hot rod type performance. I honestly think my turbo 4.9 f150 would stomp my 460 powered tow rig on the dyno in both hp and tq. That said my 300 isn't set up for towing, and I think of it was it would be a very good option over the big block and diesels. I'm running an hx35 t3 currently, I find it to be plenty responsive under 2000 rpm. I don't think a t4 is really needed for your very mild goals. However I'd be hesitant to go too small to, with my hx35 I can drag the brakes at 2000rpm and build as much boost as I want (one of my data logs shows 15psi at 1700rpm) moving a heavier vehicle and or towing a trailer will have a similar effect. That load will help spool the turbo, and one sized too small could just be un needed for this application. I would upsize in cam if it was me. If you search around for the n/a tow builds the comp 252 and 260 as well as other similarly sized cams build great low end and midrange torque, the same will go for a turbo build. Advancing the stock cam is an option as well. You can make 400ftlbs with a stock engine and boost, anything you do to the cylinder head or slightly upsizing cam will just make it easier to hit your goal with less boost. My trucks running megasquirt efi so I can't really give any useful information on the carb aspect of your build.
 
Thanks for all the great info!

-Nope, not in PA; I’m South of Portland Oregon.
I swapped a guy for my 2005 F-250 diesel. He got it from down by the CA border. It’s got a Canadian build code. The truck is mostly free of rust, and no major cancer. I’ll post some more in the intro section.

-Thanks for the head flow info. I’m going to try to sit down with the machinist/builder this weekend, and lay out the plan.
-I was leaning heavily toward the 252, seems like a good mid range set up. I’ll probably end up dropping it in and going N/A at first while finishing up fabrication, and then try to tackle install over a long weekend.

-I’ve actually done an about face on the EFI. I’m now thinking of going with the Holley Sniper EFI. Having self learning, instead of what would probably be 2 months worth of tuning, sounds way better. The reviews are mostly positive, especially the more recent ones.
 
-Any suggestions for a good source for turbo rebuild kits?
-I know it’ll no more difficult since I’m not certain about the origin of my unit, but I do plan on stripping it down and miking everything to at least know where I’m starting.
 

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Well, the teeth (or blades) could be in better shape, but I got 1.830" and 2.368". Puts it at 46.482mm x 60.1472mm, approx.
Straight across, equals 59.723 for trim. I'm guessing trim doesn't come in 3/4 measurements, so probably should be 46.5mm x 60???mm and 60ish trim? I'd like to bump the compressor to at least 62 trim, but maybe I should just replace the bearings and seals for now and see how it rolls?
There's a ding in one of the blades thats approx 1/32 to 1/16 deep and wide. That seems like a pretty big deal at 110,000 rpm. :eek:opsie:
 
A Garrett GT2860R has a 47/60 compressor wheel and is shown as a turbo for Nissans.
It also shows the turbine housing with a T25 flange.

It is small for a 300 six and the T25 turbine housing will choke the 300 early in the upper rpm range.
It would be good for very low rpm torque.

A ported head would push the turbo beyond it limits and run it into the choke zone.
You could try a stock EFI head with some intake valve unshrouding and use the stock cam with the Scorpion roller rockers to get more valve lift.
Advance the stock cam by positioning the intake lobe center at 110* ATDC.

I would expect high torque from off idle with good power to 3500 rpm.
Somewhere after that point both the small turbine housing and the drop in engine VE will kill the power.
 
motorsickle1130":35mxpver said:
-I’ve actually done an about face on the EFI.
Im going to guess you were in the military at some point :LOL:

And as far as this build is going, i am very interested and please keep us updated thanks.
 
I am also interested in this. I have been playing with a desktop dyno on a similar build.

Pmuller9:

I have a stock efi motor with an advanced cam and must say the dynamic compression is very high for a 5,000lb truck. Loaded at 6,000lbs I need to up the fuel octane to 89 or higher. Without a knock sensor, I would go back to the 4* retard cam setting.

Your prescription to the cost effective KB S3117H pistons on a similar build in a recent thread seems like the hot ticket.
 
Wesman07":1ybv9dct said:
Is there a rule for the relation of dynamic compression and boost?

It's not that simple since the intercooler efficiency is also part of the equation and the efficiency of the compressor making the boost.
Both of those contribute to the final air temps in the intake manifold.

The question becomes, How much do I need to lower the compression to decrease the cylinder temps during compression to compensate for the increased air temps coming onto the cylinder.

Then you have to consider how long the engine will be operating under boost.
Will it be for a short blast just for fun or am I hauling heavy loads for long periods of time.
 
Thanks for the explanation, that changes the way I have been thinking. Matchbox is extremely helpful.

So Intake temps are a factor of PV=NRT, turbine efficiency, and inter cooling. How do you figure combustion temperature?

Sorry for hijacking. That will be my last question.
 
Wesman07":34g7jts0 said:
How do you figure combustion temperature?
You don't.
Autoignition for gasoline is around 500* F +/- depending on octane.
You can figure the air temps using the dynamic compression ratio but your calculations will come in high because it doesn't acount for the presents of gasoline which is a liquid that absorbs thermal energy and the effects of quench.

In general if an intercooler is being used you can drop the DCR about 1/2 a point for short term boost and up to a full point for long hauls with heavy loads.
On a 300 six where the DCR is normally 7.0 for 87 octane gas, that would be a drop to 6.5 or as low as 6.0 and that gives you room to use a higher octane pump gas if needed.
 
Don't worry about highjacking; these are all great questions and somewhat over my head, which tells me I need to do more research.

Talked to my machinist the other day; hopefully I haven't already mentioned that. Long day, already forgot half the posts. He thinks I'm nuts for wanting to ditch the 429. I'm supposed to be coming up with a parts list and something of a complete build layout. Haven't had time yet between starting a bathroom remodel and wifes pregnancy related stuff.

Still need to hit up Jobbers Services up in Portland to see if they have a decent forged crank. That's the only part I'm concerned about finding, aside from verifying that the block and head are solid.
Will also need a parts list for the drivetrain swap and will most likely rebuild everything, axles included.

Thing ran the front tank empty the other day. Pretty sure it's tuned way fat and probably only getting 6mpg at best. There's reason #1
The suspension is definately shot and the steering isn't tuned in the slightest, in addition to needing a new PS pump.
I'll try to stay on topic with Turbos next post.
 
Pmuller9 is one of the best teachers I know. All of this was over my head too just a few months ago.

I’m curious about jobbers and the forged crank. I know of a big vender selling “forged” cranks, that apparently are not forged at all.
 
Hopefully this one goes through...

I’m not going to mess with the Nissan turbo, and instead will pick one up from cxracing.com
They don’t have a lot of options for compressors in their turbos, or maps, but I figure they’re close enough and in my price range.
I’m getting down to the wire on pulling the trigger on parts.

Is there an off the shelf cam combination that fits 8-15lbs of boost with 1.7:1 roller rockers?
What’s a middle of the road piston rod?
For above cam, and 2000-5000rpm range, what size turbocharger is a good fit for a 7000lb 4x4 truck on 35s with 4.10s and a Ford T18?

I’ve been going round and round on turbo sizes, and am no closer than when I started.

Oh, and here’s the interior:
AB4AD5D2-AED6-4AFF-94A1-34898F75B04F.jpeg
 
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