The Top DSM Community on the Web

For 1990-1999 Mitsubishi Eclipse, Eagle Talon, Plymouth Laser, and Galant VR-4 Owners. Log in to remove most ads.

Please Support RTM Racing
Please Support Fuel Injector Clinic

Revs for HX40 Setup

This site may earn a commission from merchant
affiliate links, including eBay, Amazon, and others.

This site may earn a commission from merchant affiliate links, including eBay, Amazon, and others.

GSXDNA

15+ Year Contributor
256
14
Nov 19, 2007
Los Angeles, California
Did some searching, but couldn't find quite the answer I was looking for.

My profile is up to date, but here's a quick summary of my relevant mods:
  • 7-blade HX40, .70 a/r, T3
  • Brian Crower 272/272 cams (otherwise stock 1G head)
  • Stock valve springs
  • 2.0L 6-bolt bottom end w/ (newer) oem 2g pistons, 1g rods
  • Stock IM
I'm currently running 34psi on a 50/50 e85/91 mix. Have a dyno appointment next week, and am trying to decide how high to take the revs. Looking for any thoughts on (1) the likelihood I'll make more power past 7.5k RPMs and (2) the safety factor in bringing the RPMs up to 8k, 8.5k, etc. on my setup. Thanks an advance for any helpful info.
 
Last edited:
Your limiting factor is the valve springs..

I just dynode a hx35 Setup at similar boost and I went to 8600rpm without concern. however, I was stock cams with updated valve springs.
 
Your stock spring are most likely beyond their service limit, being close to a 20 year old head and components. Using aftermarket cams on weak springs is asking for trouble.

If you do no want to fork out the money for high end springs, beehives or duals, I would look into BC or manley single springs, and use the stock retainers. 16 springs from manley can be had for around 80-90 bucks.
 
Springs are certainly next on my list, and I do plan on getting something a bit more high-end. I just haven't gotten around to them yet. I've never dyno'd the car with this turbo setup, and the opportunity just came up, so I'm curious to see what it puts out as it stands now.

Maybe I'll just take it to 7.5k for now, and wait to go a bit higher until I get new springs.
 
Yeah, I've actually only been going to 7k on the road. I'll probably go up to 7k the first few pulls, and if I'm within a few hp/tq of some nice round number, go to 7.5k on the last pull.
 
The dyno is just a number generator. Risking the motor isn't worth the occasional "that's cool" people will reply with when you tell them how much horsepower you make that they don't generaly care about to begin with. Just take it to 7.5 and be satisfied with the fact you know it has more in it.
 
@bastarddsm - to me, subjecting a stock bottom end to 600whp is a bit more crazy than running stock springs on my setup. But, if it does grenade before I can put some springs in, that gives me an excuse to finally build the motor :)
 
Keep running stock valve springs at that much boost, and it won't matter what you want, you'll be picking up pieces.

I have heard that high boost is hard on springs from a few people now. Why is that? I have a hard time believing cylinder pressure has anything to do with springs. Springs keep valves closed. Cylinder pressure keeps valves closed. They generate forces in the same direction and never oppose each other. Cams push against the springs and cylinder pressure (to open up the valve). Maybe I am thinking of this wrong? I understand the high rev part being bad for springs/valves...
 
I have heard that high boost is hard on springs from a few people now. Why is that? I have a hard time believing cylinder pressure has anything to do with springs. Springs keep valves closed. Cylinder pressure keeps valves closed. They generate forces in the same direction and never oppose each other. Cams push against the springs and cylinder pressure (to open up the valve). Maybe I am thinking of this wrong? I understand the high rev part being bad for springs/valves...
For simplicity's sake say your intake valve is 1 square inch. If you start with 70lbs of seat pressure, and add 30psi of boost to the back of the valve, you now have 40lbs of seat pressure.
 
Plenty of people have made and currently make big numbers on stock springs. Definitely not the best way to do things but it's being done all the time. Personally, I would run the first pull to 7500 or so and see how the dyno graph looks. That will tell you how far you can rev out on your next pull.
 
I had same turbo same cams on a stock 2g head and i reved to 8250 all day, and wish i would have reved to 9k at the track but didn't have valve springs installed. The dyno will be able to tell you where your peak curve ends though.

Also, was on 38psi on c16

Edit: i never said i had a stock bottom though, were talkin stock head.
 
Last edited:
You'd have a hard time convincing me to rev over 7500 with 15 year old rod bolts, at 34 psi, on a stock intake manifold, with 2g compression, and stock springs. You're taking a spring that's already only seeing probably 50lbs of seat pressure, which isn't linear throughout the springs travel, and fighting against it with 34psi*surface area. You're also on an ethanol/91 mix which means you're tune likely isn't "spot on" cause you don't know the exact concentration of ethanol. I'm not saying don't rev it out as long as you want, I'm just saying that numerous people have had failures from just having one of the variables I listed that you have.
 
Many thanks to everyone for the replies - this is all very helpful. Sounds like it's time for me to start reading up on spring options.

@UrbanSmoker - how long were you running an HX40 @ 38psi on stock springs for?

@jakelandry - The bottom end has about 15k on it, so there (hopefully) shouldn't be any 15yr old bolts. The tune has a good amount of safety dialed in. Even when I do run a few gallons off (either way) with the mixture, I still get no knock across the board and AFRs are still in a safe range. That said, I still have concerns spinning it much past 7k.

I'm very curious to see what this setup will put down at 7-7.5k. It's a mustang dyno, so it'll likely be a bit less than I'm hoping for.
 
Many thanks to everyone for the replies - this is all very helpful. Sounds like it's time for me to start reading up on spring options.

@UrbanSmoker - how long were you running an HX40 @ 38psi on stock springs for?

@jakelandry - The bottom end has about 15k on it, so there (hopefully) shouldn't be any 15yr old bolts. The tune has a good amount of safety dialed in. Even when I do run a few gallons off (either way) with the mixture, I still get no knock across the board and AFRs are still in a safe range. That said, I still have concerns spinning it much past 7k.

I'm very curious to see what this setup will put down at 7-7.5k. It's a mustang dyno, so it'll likely be a bit less than I'm hoping for.

I'm sure you'll be satisfied. Regardless of what a piece of paper says, it's still just as fun to drive after you dyno as it was before.
 
i was running on the 38psi for 6 or 7 track runs and i had the hx40 on the car for 2 years motor has 13k on it stock springs are from my stock 99 head also have stock 2g intake mani

Still have all the same except now i have a twin scroll 6466, and i have BC 276/276 cams and Bc dual valve springs with BC cam gears to install and I'll do the 9k thing more safely.
 
I run the pretty much the same setup but with stock cams and I have revved as high as 7500 at 30psi. I don't feel comfortable revving that high on the stock springs for any period of time and I wouldn't recommend it to anyone else either. Also, I didn't see any mention of upgraded rod bolts, so I would consider that a limiting factor on a high revving application.
 
Support Vendors who Support the DSM Community
Boosted Fabrication ECM Tuning ExtremePSI Fuel Injector Clinic Innovation Products Jacks Transmissions JNZ Tuning Kiggly Racing Morrison Fabrications MyMitsubishiStore.com RixRacing RockAuto RTM Racing STM Tuned

Latest posts

Build Thread Updates

Vendor Updates

Latest Classifieds

Back
Top