Evening, I want to make this my thread to chronicle and present questions I have on my build. I'm planning a build that would consist of an RD2-90 pump matched injectors (whatever code Racin deems suitable for me), possibly R&D cam, hx-35 turbo, custom exhaust, eventually as funds allow, studs, intercooler and maybe RD2-110.


My first question is I just purchased a 7.3 to rebuild and build while running my 6.9, and utilize larger head bolts. However I read all over about stay away from rebuilding 7.3s because of cavitation, are these suspicions well founded? I'm sure that this motor didn't have balanced coolant, but don't really want to swap it in and cross my fingers for a few months to build the 6.9. Is there any way to estimate wall thickness or check for near pinholes?

 

Nothing wrong with 7.3s... they cavitate more than your average diesel, but still only like 1 in 1,000 maybe. That said, if you want to rebuild it, simply have it checked for wall thickness (sonic checking i believe) also have the heads magnafluxed, especially on a 6.9. The 7.3 in my 92 cavitated around 140,000, sleeved 2 cylinders and rebuilt it. Has 265k on it now and no problems. Just run your SCA's (which you should do with a 6.9, and any diesel for that matter) and forget about cavitation. All that said, i would personally build a 7.3.

I have ran a hx35 myself, and i still stand behind what ive said for ages now, they are too small for a 6.9/7.3. I think you would be better off with an s360, however if youre set on using the holset, find a 14 or 16cm wastegated exhaust housing and consider a billet or 60mm wheel. For further information check out the dyno and numbers thread by racinNdrummin. Lastly, youre going to want to stud it when you put it together, not afterwords.

 

This build is also budget minded. I'm not really set on a holset it's just that my uncle's scrapyard has a ton of 5.9 cummins trucks sitting around so I can get them cheap, and take apart a cummins; win-win. I will look into the turbo threads for upgrades before I pull the trigger on one though.

 

You can get a 360 / 362 for 600 if that helps ya.

 

A problem with using a wastegated hx35 off a cummins is that they will all be wastegated at about 20psi which is going to be way too high to take advantage of the waste gate without swapping actuators.

Also, most of them have the actuator mount integrated into the compressor housing, and the cheap compressor upgrades do not have this housing. To go up in size the center housing must be machined (mill on rotary table) to make them fit.

I've heard repeatedly that the hx35 is too small, and I can understand why since the larger displacement of a 6.9/7.3 can spool a larger turbo anyway. Based on that, the turbo I'd probably be drooling over is the garret used in the PSDs. They obviously will be relatively matched for displacement, but have a really slick oil pressure actuated valve that can easily be wired to be an exhaust brake. Course use of an exhaust brake is a somewhat disputed issue on the IDI's.

Were I to have guessed *without reading other's experience*, I would have thought that a hx35 would be well suited due to quick spool. If you do go that way, there are a LOT of options for this turbo. Rebuild kits are less than $50, bigger compressors run about $2-300, and direct mount exhaust brakes are *plentiful*.

BTW I have done literally all hx35 mods listed above. For some engines (C-word) they work really well.

 

Think about this; an hx35 compounded with somthing s400 based. If you could get enough fuel to spool, I think it would be a pretty efficient setup

 

Is the issue mostly that the exhaust side on the HX35 is too small? I know a lot of Ford 2.3L Turbo guys run HX35's and are really happy with them, if I recall correctly I think they said the exhaust wheel is a little smaller than a T3 Stage III (which is what the factory ATS turbo has).


IDI's are weird when it comes to turbos because you almost have to treat it like a high compression gas engine (low boost) that can't rev past 3000 RPM.

 

I think I read that some cummins came with HX40s, maybe that's a better route. However I think the HX35 will work best for what I want and my methods of doing things. I can get a reliable turbo for next to nothing capable of 20psi, now admittedly I don't know turbos, I'm not able to read compressor maps past that oval is left and that one is right. From what I've seen and been told the HX35 is small but as funds allow I can get the compressor and exhaust housing upgrades to make it flow at or better than the S360/362 for less.<----correct me if I'm wrong


And for my truck which is purely a work horse seeing redline every other day on the street, heavy off roading checking cattle/screwing around, and pulling a stock trailer/equipment a turbo that is too small and responsive is better than too big without torque.

 

I have a 7.3 idit that i am getting prepped to drop in my truck, i have the idit in it now, i am gonna hack the restrictive hotside elbow off and weld in a 3" black iron 90 and weld a vband bung to it and put a new chra in it, from what i understand the stock turbos are plenty capable of providing good boost

 

7.3 will push a hx 40, may be laggy but will have less heat rise and make 20 + boost with 85-90 cc's you will want to decompress some and using a better cam will help with that, if you can work into the budget a inter cooler will hold down the egt's on long hills when towing. racer30 has a build on hear some ware you should check it out.

 

Take my advice or not... Ive ran an hx35, you dont want one, especially pulling. They are small, hot, and ineficient. Unless you pretend you have a 2400 rpm gov spring in there. I really doubt an hx40 would be laggy on a stock 7.3.

 

Alright guys just spent about 3 hours reading about hx35s, hybrids and hx40s...
Decided that while probably alright for a stock pump, an hx35 will, as I've been told be too small. So then I looked at 40s and the big price tag for the super 40 on top of all the don't screw around or you'll break a shaft stuff scared me away from that.


It looks like I'll have to drop some reasonable money on a Borg Warner, given the dyno evidence it looks like they work great, and if they're good enough for R&D to sell and use they'll work for me. On the down side it will probably take awhile to get enough $ to nab an S300 but I think it'll be worth it.

 

The Stage 3 wheel is just a tad smaller (negligible really) than the HX35 hot wheel... That being said, the HX35 is great on the 2.3T's (Im a 2.3T guy myself, at least I used to be), and that says a lot when paring with a 7.3L IDI. The thing is, The HX35 feels great on an IDI, is develops great torque (483wtq at 1800RPM) and spools excellent. But even with WG mods, the 7.3 was limited to 203whp at 18psi with the HX, tuned. We literally bolted on an S366 (Which should be too big right?) and made 40whp and 45wtq more with no changes... The best part is that we were putting over 500wtq out at 1700RPM with that setup. Bottom line, the IDI likes air...

 

If you are on a budget like you say, the HX40 is a good turbo to use... It takes the restriction of the hot side out of the equation... If you can find one cheap, it will be a good turbo. However, if you want an all around superior turbo, and I only say this because I have had Holsets, Garrett's and BW's all apart, the BW is going to be your best bet. I prefer BW because the bang for the buck is totally unbeatable, which is why you see most diesel trucks use them.

 

They are, but the T04B is, in general, a very inefficient compressor design. Don't know why but if you look at compressor maps the T04B wheels all have the lowest efficiency compared to others like the T04E and Holset.


racinndrummin, that's interesting...I really, really wanted to play with turbo sizing on my IDI but it's expensive to do and at the time it was my daily transportation so I never got a chance.


Curious, what are the specs on an S366 and what is that off of? I've been out of the turbo game for a few years now...