...?

My next mod is gonna be rods. I was thinking about it today and would like some feedback on this subject. I figure while the rods are out throw some 9:1 pistons in and and drop the boost down a bit.

Anyone have input on this, it's appreciated. I'm pretty sure it would work, and possibly quite well, but I'd like to hear some other opinions on it.

Cree

i would think you could get more power from a lower compression ratio and higher boost levels but idk...

JJ@WMS has been doing this for a while with good results. Less boost, but more power. Can't run as much timing, but you don't need it to make the power.

If your going to replace rods, ya it would be a good idea to throw some low comp pistons in it. Also I would keep the compression around 9.5:1. If you go to low it might hurt you in the HP department or you will need to throw a lot more boost at it.

Brad

if u do a search on f150 bout jdm, u can see that jdm is actually building some of his new motors with a 9:1 compression ratio. cant remember the results right off hand

JJ@WMS has been doing this for a while with good results. Less boost, but more power. Can't run as much timing, but you don't need it to make the power.

Yeah, I knew JJ was running motors like this, but I don't know the likely hood of him sharing any info with a lil guy like me. Doesn't he have some Eaton trucks in the low 11's off spray?

If your going to replace rods, ya it would be a good idea to throw some low comp pistons in it. Also I would keep the compression around 9.5:1. If you go to low it might hurt you in the HP department or you will need to throw a lot more boost at it.

Brad

Our STOCK compression is 8.4:1, so its higher for us. DAMMIT Rob, why is everyone taking my idea? Ive been plotting this for a while. More power, on less boost sounds great to me.

Cree - your low rpm torque will be fantastic with that setup and with the right setup / tuning, will pull very strong on the top end. As previously said - lower the timing and watch the A/F and you'll be great with it. I've done this same thing with other suoercharged engines with nice results. Also got around a JLP engine today with 9:1 and stage-3 cams - beautiful sounding lope.

Bird

some custom venolias with stainless dykes rings to seel in that boost would be nice then send thm in to get lightend. that may not be a good thing for the longevity of the motor though

http://www.venolia.com/ my buddys have used there stuff in our AMCs for years

anyone know what sise the wrist pin and crank journals are can you do an offset grind and stroke a 5.4

Cree - your low rpm torque will be fantastic with that setup and with the right setup / tuning, will pull very strong on the top end. As previously said - lower the timing and watch the A/F and you'll be great with it. I've done this same thing with other suoercharged engines with nice results. Also got around a JLP engine today with 9:1 and stage-3 cams - beautiful sounding lope.

Bird

Sweet. That's what I want to hear. Now I just gotta scrape together the cash for it. :(

Boost makes more power than compression does. You won't change much either way going from 8.5:1 to 9:1. I don't trust much of what some of these "tuners" claim.

The general consensus is that you run enough compression to keep throttle response "snappy" (8.5-9.0) and let boost make the power. Building a 12:1 motor and trying to put boost through it isn't going to work out very well. ;) (I'm exaggerating a bit)

Damn I must have not turned on instant email notification. Well, JJ has been pretty upfront about what he is doing to motors over on nloc. Might wanna ask him a couple of questions off the boards.

My honest opinion is that if you go from 8.4:1 to about 9.1:1 then all you would have to do is lower the boost, say from 6#'s to 4#'s, and take some timing out, add a touch of fuel and you should be good. Or get it on the dyno again and let someone tune it for it.

Damn I must have not turned on instant email notification. Well, JJ has been pretty upfront about what he is doing to motors over on nloc. Might wanna ask him a couple of questions off the boards.

My honest opinion is that if you go from 8.4:1 to about 9.1:1 then all you would have to do is lower the boost, say from 6#'s to 4#'s, and take some timing out, add a touch of fuel and you should be good. Or get it on the dyno again and let someone tune it for it.

Well, I know that Dave's (Screaming01L) truck is turning 10's on I think he said 15 psi out of a KB. I know he's got stage III's in everything, so I'm not sure how much of a difference that makes.

Boost makes more power than compression does. You won't change much either way going from 8.5:1 to 9:1. I don't trust much of what some of these "tuners" claim.

The general consensus is that you run enough compression to keep throttle response "snappy" (8.5-9.0) and let boost make the power. Building a 12:1 motor and trying to put boost through it isn't going to work out very well. (I'm exaggerating a bit)

Yeah, I'd thought about all that. I was just thinking along the lines of maybe you could meet somewhere in the middle, say like you wouldn't have to run as much boost to make the same power, etc..

I dunno, like I've said, I know N/A motors up, down and all around, but I don't know a lot about forced induction yet. I'm still pretty new to this game.

I am still in the planning stages of my engine build, but I may end up going with a bit higher compression, and less boost with more nitrous.

What about my set up?
L33 is 9.9:1 CR and I am going to FI w/Radix.

What if I added AFR 205 Heads (mega $$) ??

I'll throw out some numbers here... and this is on a pump gas configuration, no nitrous. Obviously if you're going to sacrifice street power for race power, this may not apply.

Let's say you have an 8.5:1 motor and you've got it tuned perfectly for 10 psi. EVERYTHING remains the same except the pistons which you install to change the compression ratio to 9:1. You will have to lower the boost to ~8 psi to run the same amount of timing as before. The rule of thumb is that each full point of compression is worth about 2% increase in hp. So, you get a 1% power increase from compression, but you lose roughly 10% because you can't run as much boost.

I dunno, like I've said, I know N/A motors up, down and all around, but I don't know a lot about forced induction yet. I'm still pretty new to this game.
I'm in the same boat

i know a guy that is a nitrous guru and severl people that have excessivly fast N/A cars but no one with a lot of experiance in forced induction

I think you also have to look at the type of blower being used. If the blower has no trouble breathing to 20psi and you only plan on running 10psi and it is very efficient (IE very low heat) then going low compression and upping the boost some would be good.

Now take a small blower that starts to really heat things up after 7psi then going higher compression and keeping boost low would be a better option IMO.

That is what I'm doing anyway since the Radix maxes at about 10-11psi and really kicks in the heat at that point. Its working well so far but I need to change my cam, retune after the 90mm TB and see what it can do. Ohh and keep my pressure steady. My peak HP was on 4.8psi :(

Hey Rob, i can get a good deal on Manley Rods and Pistons. Let me know on here, or SVTP if interested.

It'll probably be end of summer before I can start getting parts together, but I will keep that in mind bro. :cheers: