Hey guys, this is my first time messing with a turbo setup, so id rather it be on something that i dont mind wrecking (either the motor or the whole truck) since i didnt pay that much for it and since its not a daily driver. The vehicle is a 1985 Dodge Ramcharger that came stock with a 318/4 speed/4x4. I put another motor in it because the old one is seized, though it is another 318 that i bought. lets make this short before it gets out of hand lol.

1985 Dodge Ramcharger
318 c.i.
727 Torque Flight
stock 1/2 ton axles
33 x 12.50 x 15 General Grabber red letter tires:

block is mostly stock over than a very very mild cam (not sure on the info as previous owner installed it and doesnt remember what it is other than being very very mild.

Edlebrock performer 318/360 intake

currently has a 650 cfm Edlebroke carb, but ill be switching to a Holley 4150 850 cfm (as seen on a build by Motortrend years ago)

stock heads and rotating assembly

radiator relocated to the rear since i cut the roof off (this truck is offroad only as i bought it with no title and i cut the roof off lol)

i just need some basic help on deciding what size turbo i need for a single and or twin setup. i want to do this mainly for fun but to also get introduced to the turbo life i suppose. this is a beater truck that will be abused and hurt and put back together multiple times as long as i have it. i found a turbo on amazon that i want to use to keep it cheao as ill probably blow turbos by getting mud in them (i know its gunna happen)

if you need any other info, let me know. im staying as cheap as i can seeing as i only gave 600 for this thing lol. thnks guys

 

I using a magnum 360 in my plymouth with a 78/75 from On3, as a remote setup, and it works really well. the 850 holley you want to swap to is going to be a lot of carb for your setup, I'd recommend staying under 750.

 

650 cfm carb, and a gt45, or s366. Don't be sucked into a large turbo, especially for off road.

 

the reason i was going with that carb is because i saw an easy way to mod it to work with a "blow through" setup from Motortrend. only have to spend an extra 50 bucks for the solid plastic floats so they dont rise during boost.

 

thank you, ill look into those. ive seen several posts where people were recommended those options. im assuming they are good for the money ad a decent setup?

 

What's your hp goal? That determines everything really.

 

The gt45 is very cheap, and has proven itself many times. I would prefer the 366 if it were mine because it's a bit smaller than the gt45, but they're more money. I recommended these because they're cheap, and are great for a first build. There are smaller turbos that would spool quicker, and be biased more towards low speed torque production, but low rpm boost is tougher on parts, and requires a good tune to manage cylinder pressures.

 

So I don't have alot of experience with carb engines, so if im wrong or going the wrong direction, I trust someone will correct me. But looking up an '85 318 says it does 140hp @3,600rpms, this works out to 202cfm. The 318 @ 100% volumetric efficiency would be moving 331cfm @ 3600rpms. 202÷331= 61% ve. That's terrible.
This is where things get fuzzy for me since I don't have much experience with carbs. But an 850cfm carb flows 30% more, bumping up the stock 650 carb flow of 202cfm by 30% gets us to 263cfm, which bumps ve up to 80%, a much better number.
BOTH carbs will make whatever power you want, using the 650 will require more boost than the 850, but the 650 will probably be better on the low end vs the 850. Or, the 850 will make more power than the 650 at the same boost number.

We'll assume 10psi as boost pressure @ 74% compressor efficiency, running through a 70% efficient intercooler on a 60° day. 10psi is a 1.68 pressure ratio, with a compressor outlet temp of 171°F, this leaves us with 93° out of the intercooler at 9psi, or 1.61pr. Density ratio = 1.51, so new airflow is 305cfm/212hp for 650 carb, 397cfm/276hp with the 850. Seems odd I know, but that's also at the lowly rated 3600rpms, higher rpms will raise this number for sure.

Single vs parallel twins, single is simple, twins will spool sooner but require some extra plumbing. Me personally id go with twins, I feel like they could package neater, and the smaller turbos come with internally wastegated housings, again making packaging easier.
So for a single look for a compressor map that will do 23lbs/min for the 650, 30lbs/min for the 850, at a 1.68 pressure ratio. Twins you'll divide that lbs/min number in half, but the pr stays the same.
Exhaust side will require a 1.4 pressure ratio at 25lbs/min for the 650, 27lbs/min for the 850. For twins divide the lbs/min in half.
Looking at the gt45, it's too big to do 10psi at 3600, the gt4094 looks like a better match, this is also based on me assuming 1200°egt, if it's higher that will help to drive the 45.
A pair of gbc20-300s, or the older gt2052's will work perfect, but won't be the cheapest option.

Again, if I messed anything up, correct me, I had to assume stuff like egts, and flow through the 850 carb.

 

Agreed, the gt45 is on the large side for the application, but for less than $200, it's been a go to for many here for 300+ cid. You're selection is much more technical than mine, mine is primarily based on what ive seen here, and supposed compressor map for the China GT45. The 318 responds nicely to some simple upgrades, so with the better intake, assumed better exhaust, and a mild cam i'd guess it's 200+ fwhp pretty easily. The 650 carb is better on this primarily for the signal strength, and a 650 is plenty of carb for 200-250 hp 318.

 

Agreed, better airflow components to get ve% up closer to what the 850 would do would be ideal. I would have to know what max rpm is to calculate how close he'd be pushing the 650 carb. @6,000rpms he'd be at 625cfm, assuming cam and intake bumped up his ve% to 75% vs stock 61%.

I know the gt45 is cheap, but I'm not convinced it's the right choice. I think twin gbc20s would be better suited for the trail/ mud running he'll be in.
If he wants to go cheap single, a gta4294 off a Detroit 12.7 would be better than a gt45, only around ~$400 and is internally wastegated, saving money on an external gate and its extra exhaust plumbing. But at the end of the day it doesn't matter what I think lol. Up to him and his wallet to decide.

 

The GT45 definitely isn't the best choice, just throwing it out there. I think a S360 or 366 would be where i'd personally look. My math for cfm is different, a 318 at 75% ve, and 6000 rpm is 414 cfm. My understanding is that cfm requirements don't change with boost, just the density. 650's are commonly used on engines making 600+ hp, especially on something with a relatively low na hp number.

 

Yep, your right, I had a brain fart and quoted 625cfm at the turbo inlet. 414cfm is correct. I'll also agree an S361 or 363 would be a good candidate. Although I'm not a big borg fan, except I think their efr turbos are pretty kick ass.

 

I'm not sure I would want a small quick spooling turbo on an off road rig. The last thing you want is a torque hit that is difficult to control when you are in 4 low buried in the rocks. Something big that will be a little lazy seems about right, keep wheel speed up when you need it but have a chance to roll out before boost kicks in when you are in the slow stuff. GT45 seems about right. One of the s300 series from an industrial application with the larger hot side could work too, and tend to be available inexpensively.

 

For mud, you don't want the characteristics that a big single gives. I work in mud daily as a drainage contractor. A big single will plant you in the middle of your tracks. If your stuck and backing up, you need the power to get speed and momentum up to get through.
You want ~40mph wheel spin to clean the tires out, I don't see a stock 318 spinning 4 33" tires at 40+mph.

 

MQ was a little vague on what the intended usage was. To be competitive in open class mud racing will require a couple of thousand horses. (Turbos and blowers put you in the BigBoy classes). Of course, it’s only money. ‍♂️

 

I cant fathom a gear ratio where you would not be in boost at 40 mph wheel speed in mud, even with an extremely lazy turbo

 

I’m jumping on the GT45 bandwagon with this one, and I’d just build the edelbrock for blow through since you already have it.
There’s a good thread on this forum on how to do it.

 

honestly. i dont really have a goal. im building this truck to have fun in and be my entrance to boost applications.

 

man....that was alot lol. thank you for the input brotha! i dont know much about the cam, the guy i bought the motor and trans from said that its a very mild cam, but he was using the factory 2bbl carb for some reason with the stock intake. i dont think he really realized how much power he was missing due to that, but i have a holley 4150 carb, and an edlebrock performer intake on it currently, along with custom headers i hade from cutting the long tubes up and making my own thet face forward with plans to run atlease a single. im gunna run it n/a until i get all the parts i need. im also going to give comp cams a call and see what the reccomend and offer for some type or turbo cam or any cam that will work for what im doing.

 

to answer some questions i didnt realized id get asked:

this truck is just a toy for mudding, some crawling, trail riding, and just having fun

NOT a competition truck at all

this is going to be my first ever turbo vehicle and build

i was originally looking at some cheap amazon turbos because i know at some point, mud is going to destroy them

i was looking at a gt35 turbo for around $169 on amazon

im doing this so i can learn how to setup and tune turbo setups, and because i was going on a trip to MOAB Utah in April with a bunch of Isuzu guys to crash the ride with my brother and our friend (both of which have isuzus lol) and i wanted to be the only one making anything over 75hp lol

at some point, i am swapping to some dodge 2nd gen 3/4 ton axles i got off a 1997 2500 gasser for cheap as well as the transfer case because i know im going to break these axles at some point, even with 33s because these Dana 44s are very weak.

for anyone wondering about space, i have relocated the radiator to the rear behind the seat with a shroud to protect me and my passenger in case anything goes wrong, so that gives me a good bit more room in the engine bay. when i get a chance, ill try and upload a picture on here for you guys to see. but for now, all my current progress is on my Facebook, TikTok, and Instagram. (foREVer1492 on TikTok, garymaddux2000 on Instagram, and Gary Maddux from Cullman AL on Facebook)

so above all, this truck is just to have fun in, if i blow it up on first start up, no big deal because i have another engine. its almost a "i dont care about it" kind of truck. so im just having run with it, doing things i normally wouldn't do to a truck. im not going for the most bad ass truck, or the best looking, or even the fastest, much less the best crawler to ever exist.