8.36.1 Compression What Boost To Run?

[17psi r33]

hi, i have a full forged and ballanced motor with all the good stuff inside and out, just not making the power im looking for, my motor was tuned at 20psi with a garret gt3076r im only at 70% injector duty and 60%afm left as in where there at in the last tune so heaps to go in both areas, and its only making 380rwhp, what i want to know is what psi can this motor handel? acl bearings, ballanced assembley, eagle h beam rods, wiesco 40thou oversised pistons, arp head bolt main bolt and rod bolts, ported polished flowed head, pom cams 256int 264exh, greedy intake, hks low mount cast manifold, 550cc injecrtor, watermethanol injected, fmic, bosche044 pump, pfc, ect also he (being the tuner) said he could back the timing off 8 deg retard and the peak power stayed the same which is odd so he said and it just spooled up faster and made more tourqe so not sure what the go is there.

[R31Nismoid]

Ask whoever built it.

No will know better.

[17psi r33]

Ask whoever built it.

No will know better.

surely others hav similar builds and have an idea of psi capabilitys of there motor? i just checking to see what others have gone for.

[bigmikespec]

As much boost as you can until it starts detonating and/or not making any more power...

[Deano45]

surely others hav similar builds and have an idea of psi capabilitys of there motor? i just checking to see what others have gone for.

Clearances play a big part in the psi capabilities of the motor. When you get the motor built, you normally work towards a goal including a turbo package, power and boost. The engine builder and machinist then work to these specs to build the engine. This is why the engine builder should be able to answer this question the best.

[17psi r33]

Clearances play a big part in the psi capabilities of the motor. When you get the motor built, you normally work towards a goal including a turbo package, power and boost. The engine builder and machinist then work to these specs to build the engine. This is why the engine builder should be able to answer this question the best.

ok was not aware of that, so what would be the problem with the timing issue then? i thought backing off the timin would mean the peak power would drop off linialy as well, excuse the crap spelling. what clearances am i asking for by the way? as in piston to valve?

[Deano45]

ok was not aware of that, so what would be the problem with the timing issue then? i thought backing off the timin would mean the peak power would drop off linialy as well, excuse the crap spelling. what clearances am i asking for by the way? as in piston to valve?

Piston to bore would be the most important one?

What motor is it? (sorry if I missed where it is mentioned)

Who decided on that compression ratio too?

[17psi r33]

Piston to bore would be the most important one?

What motor is it? (sorry if I missed where it is mentioned)

Who decided on that compression ratio too?

it an rb25det, forgot to mention that, when we were building the motor i was wanting around 500hp mark, so we went witha commetic head gasket 1.8mm to drop the compression down to run higher boost. and ill have to ask what the clearnaces are for the ring to piston as im not sure of that. i was hoping some one had a rought idea of what psi can be pushed through motors with that comp ratio, and why is the piston to bore the most important? is that for blow by or how well the piston stays center to the bore?

[R31Nismoid]

IMO the comp is too low anyways. With decent fuel these days and a good tune there isn't a need to drop it that low.

And hence as a result your power for 20psi is low, especially with WMI...

Sounds like something is missing also if you can pull 8 degree's of timing out and not lose any power.

So fix the problems you have now before going for more boost.

[Deano45]

it an rb25det, forgot to mention that, when we were building the motor i was wanting around 500hp mark, so we went witha commetic head gasket 1.8mm to drop the compression down to run higher boost. and ill have to ask what the clearnaces are for the ring to piston as im not sure of that. i was hoping some one had a rought idea of what psi can be pushed through motors with that comp ratio, and why is the piston to bore the most important? is that for blow by or how well the piston stays center to the bore?

OK.

I still a bit new to this stuff but have done a bit of reading and got a motor built for me last year.

The other thing that I should of mentioned is the oil ring gaps.

That and the piston to bore clearance will determine the boost that you can run. When you put boost through the engine, it expands the rings against the bore to seal it. With forged pistons they expand too as they heat up. Each different brand and even model of piston (depending on the material used) will have different clearances. the manufacturer normally supplies their recommendations on this and ring gaps, but you engine builder decides on this at the end of the day. My engine was built with tighter tolerances as I wasn't going to be running lots of boost.

I would up the comp a bit too for better response, as fuels and ecus/tuners are pretty good these days.

As i said i am only fairly new into this game compared to other people on here, but that's why I surround myself with people who know what they are doing, and I am happy with the results.

So go back to your builder and have a chat with him. Possibly even get your tuner to talk to your engine builder and they might be able to work out what's going on.

[17psi r33]

IMO the comp is too low anyways. With decent fuel these days and a good tune there isn't a need to drop it that low.

And hence as a result your power for 20psi is low, especially with WMI...

Sounds like something is missing also if you can pull 8 degree's of timing out and not lose any power.

So fix the problems you have now before going for more boost.

this is where im mot sure what to look for? could that be cams not dialed in properly? what would be that cause for being able to retard the timing with no hp differance, changing comp would be an option but dont want to remove head just yet till im sure the comp is the problem. what do you mean something is missing?

[Harey]

hi, i have a full forged and ballanced motor with all the good stuff inside and out, just not making the power im looking for, my motor was tuned at 20psi with a garret gt3076r im only at 70% injector duty and 60%afm left as in where there at in the last tune so heaps to go in both areas, and its only making 380rwhp, what i want to know is what psi can this motor handel? acl bearings, ballanced assembley, eagle h beam rods, wiesco 40thou oversised pistons, arp head bolt main bolt and rod bolts, ported polished flowed head, pom cams 256int 264exh, greedy intake, hks low mount cast manifold, 550cc injecrtor, watermethanol injected, fmic, bosche044 pump, pfc, ect also he (being the tuner) said he could back the timing off 8 deg retard and the peak power stayed the same which is odd so he said and it just spooled up faster and made more tourqe so not sure what the go is there.

That timing thing does sound strange, as R31Nismoid said look into that first.

I would drop the timing back to just before it starts to drop power and then start increasing the boost. Lots of people run 20psi on standard compression engines so with low compression you will need more boost.

[tridentt150v]

If it is the 0.63 exhaust housing you probably won't get to much more out of it anyway. And that could be why you can back off that much timing??

[GTScotT]

IMHO 380rwhp is excellent power for a well tuned RB25 of any spec running that particular turbo.

BUT, the fact your using WMI tells me your either running a leaner tune or lots of timing.

If its lots of timing I bet thats the fastest 380rwhp you have ever seen, so I dont know why you would want more.. BUT, if the WMI is there for the sake of leaner mixtures then you may want to speak to your builder about the motor. Tolerances may be sloppy, although thats simply speculation and I would take it up with the builder.

A dyno read out wouldnt go a stray right now.

[rob82]

If you can retard the timing 8degrees from MBT (Minimum best timing) and not loose any torque you have built a non dynamic engine. This maybe due to low compression pistons combined with larger duartion camshafts. The other problem with thicker head gaskets is that you reduce the squish clearance which has a huge effect on timing sensitivity.

You should be able to put a bit more boost into the engine to give you more cylinder fill but anything more than about 25psi with that turbo on an RB25 is pushing you outside the efficiency of that turbine. I would try that first and if the engine is still unsensitive with ignition timing changes then I would be putting a thinner head gasket in to raise your static and dynamic compression.

[17psi r33]

IMHO 380rwhp is excellent power for a well tuned RB25 of any spec running that particular turbo.

BUT, the fact your using WMI tells me your either running a leaner tune or lots of timing.

If its lots of timing I bet thats the fastest 380rwhp you have ever seen, so I dont know why you would want more.. BUT, if the WMI is there for the sake of leaner mixtures then you may want to speak to your builder about the motor. Tolerances may be sloppy, although thats simply speculation and I would take it up with the builder.

A dyno read out wouldnt go a stray right now.

ha ha ha well actually it spools up alot faster and made heaps more talk, im getting dyno sheets in an hour so ill post them then, and i was wanting around 450rwhp cause its got the 0.82r housing not the 0.63 and the clearances were set to what wiesco said the clearnace was for that type of piston ill have to look it up, they were 40 thou over sized teflon coated pistons if that helps.

[17psi r33]

ha ha ha well actually it spools up alot faster and made heaps more talk, im getting dyno sheets in an hour so ill post them then, and i was wanting around 450rwhp cause its got the 0.82r housing not the 0.63 and the clearances were set to what wiesco said the clearnace was for that type of piston ill have to look it up, they were 40 thou over sized teflon coated pistons if that helps.

ha ha i mean more tourqe, see what happens when people are readiing what your typeing out laud when your typeing!

[Harey]

Yeah I think 450rwhp is a big ask from a GT3076 with 0.82 housing with only 8.36 compression on 98 fuel.

[Adriano]

TBH i would consider using a different head gasket. At the moment you are basically wasting a WMI setup, as with that comp you dont need it. Run probably the thinnest gasket you can get(.9 i think) Then with that exhaust housing and good tuning, you should see 320-340rwkw, but i doubt any more.

[tridentt150v]

Go a 1.06 rear and you will see a bit more [and more lag], but you really need to think about upsizing, or an RB30 plus lift your CR to +9.0 and use that WMI kit as it was intended.