Need help getting best compression ratio for build.

[boosted99_420]

Ok so i am about to order some Wiseco pistons with Eagle H beams oe Scat H beams not sure which is best for my 91 talon but not sure of what compression ratio to get im looking to get about 400awhp from the build and will be using a 20g at about 25psi. I found a combo on ExtremePSI and not sure if I should get the 8.3:1 compression or 9.0:1 compression or just get the Manely 8.5:1. What would be best?

 

[donniekak]

What fuel?

 

[jayson427]

I would say 8.5 or 9.0 but if you did 8.3 or 8.5 u could run just 91 octane 9.0 you might have to run a little better octane.

 

[boosted99_420]

we have 93 octane here in Louisiana which is what i always have put in my DSMs ive had and old Conquest

 

[My1GLaser]

I debated over the same thing when I did my build, asked a lot of questions and researched the topic quite a bit. I went with 9:1 and am still very happy 4 years later. I have run 18 psi on a 14b all the way to 28 psi on an 18g with relatively little tuning issues. When I switched to an HX35 I also started blending in 50% E-85. Now I am really glad I went with at least 9:1!

I made sure the machine work was done well, and the combustion chamber was polished and had no sharp edges. I also did some extensive cooling mods to make sure I run about 170-175*. I was able to run 18-19* timing on 93 pump at 28 psi. That's my .02

 

[boosted99_420]

Thats what I was thinking was 9.0:1 and all not planing on haveing block bored out any but who knows we will see when I pick it up sunday if it needs to be bored or just honed. Im hoping just honed i really wanna have this thing on the road in a couple of weeks i need boost asap!! But still going to do more and more research dont wanna get to crazy on this ride its gonna be a DD. Got this one cause my Duster will be getting about 6 to 7mpg and thats not acceptable for a DD

 

[My1GLaser]

A stock block can have some decent taper even if the bores look relatively good. I had my block honed and all was good until I went to set the ring end gap. At the top my gap was .018" and I was happy til I pushed the ring about 2" down the bore and it opened up to .035"

I'm not positive on the exact number cause it was 4 years ago, but its like .001" of taper for every .004" in ring gap change. Basically it was about .004-.005 tapered but honed and looked real pretty. Had to order .020" over pistons and set my build back two weeks and I was bummed.

I have 18k on my first bottom end rebuild because I was willing to do it right the first time. I didn't ask my machinist to check for taper because I was unaware, and they didn't for some reason...I am sure you know this if you have a 6mpg Duster, but I wanted to throw it out there just in case you didn't

 

[5150DSM]

Higher compression will give you better off-boost power and drivability but without a very good tune (and good fuel) can limit the amount of boost you can run; that being said, higher compression will also let you make more power with less boost, its mostly in the tune.
If you are going to run fully tunable engine management and are willing to learn how to tune your car properly, then I would say go with the higher compression. In the end, it will be more fun to drive, potentially make more power than a lower comp set-up and challenge and improve you as a tuner. If you are looking for a more "plug and play" approach then go with lower compression, learn basic tuning and happily make power like thousands of other tuners.

My .02

 

[boosted99_420]

Yea the Duster is a pain in the butt 408 stroker and drinks and drinks and drinks. Lucky for me I bought a pre built one.

That's the plan is to learn tuning myself so I am going to do he higher compression. But before I order ill have block looked at and then looked at again. So ill hold off until I get it all looked at then I may be able to get everything at once.


Also I forgot but im pretty sure im right, but a Torque Plate is 100% needed for boring and honing on the 4g63 right?

 

[My1GLaser]

Also I forgot but im pretty sure im right, but a Torque Plate is 100% needed for boring and honing on the 4g63 right?

Haha, that's a loaded question! It depends on who you ask. If you have one readily available then use it. If you don't have the extra $250-300 then you can do without especially at 400whp. There is a recent thread on the topic when you have time to search it.

 

[boosted99_420]

Haha, that's a loaded question! It depends on who you ask. If you have one readily available then use it. If you don't have the extra $250-300 then you can do without especially at 400whp. There is a recent thread on the topic when you have time to search it.

Ill have to do that when im back at my computer my phone just dont work very well at all

Ok I found it im not worried about torque plating anymore