[RitorutoKyo]

Let's say that a .68 A/R SP67HO spools very well on a 8.5:1 compression TT engine. Since the Supra NA has considerably higher compression therefore more exhaust energy early on, how much bigger can you go while spooling exactly like the configuration above on a TT engine? Perhaps a .7 A/R SP73HO?

 

[btm7687]

or you could slap on a thicker headgasket and drop that compression down and run it like a TT....on ~8.5:1

 

[RitorutoKyo]

or you could slap on a thicker headgasket and drop that compression down and run it like a TT....on ~8.5:1

Well, I want to keep the low-end power, so dropping the compression is not going to happen. It's similar to how certain porsche turbos run 9.5:1 compression.

 

[BlackSupra93]

and just how much boost are you planning to run like that and for how long?

i think kdirty ran for alittle bit , 15psi on stock hg, but not completely sure...it was someone...

 

[RitorutoKyo]

and just how much boost are you planning to run like that and for how long?

i think kdirty ran for alittle bit , 15psi on stock hg, but not completely sure...it was someone...

How much boost? As much as 91 octane + a healthy shot of methanol/water can allow with 0 knock. Headgasket will be replaced and head will be ported.

 

[Rocky28072]

high boost and a lot of hp will NOT happen on high/stock compression.....especially shitty 91 octane.

 

[RitorutoKyo]

high boost and a lot of hp will NOT happen on high/stock compression.....especially shitty 91 octane.

I did mention adding methanol on top of 91 octane, otherwise boost will be limited to almost nothing. High boost will not happen, but I will aim for 1.0 bar at most.

Now I still want an answer. Original question:

"Since the Supra NA has considerably higher compression therefore more exhaust energy early on, how much bigger can you go while spooling exactly like the configuration above on a TT engine?"

 

[ThomsonCharm]

On your original question there are too many variables to accurately answer it. YES more compression will yield a quicker spool but I believe it close to impossible to throw you a figure from calculating a heat figure into how fast it will cause a mechanical figures behavior. Using Water/Methanol I have heard of good results but going to a SP67 or a SP73 turbo is a really big turbo for an application of only 1 bar. Both of those turbos are made to sustain much higher boost levels. Sure they will give you good numbers with low boost but what exactly are you looking to get here?

Also there are too many variables in the size of the exhaust housings of the turbo to answer that question as well. If I were to even guess on the difference I would think maybe a .73 SP67 would have similar spool characteristics as a .68 SP67 on a TT engine. BUT that is only a guess and even then I dont think the difference is going to matter as you wont necessarily take advantage of the top end power the larger turbine housing would give you when you only run 1 BAR of boost.

 

[RitorutoKyo]

The basis for the SP67 choice or larger is the ability to run higher boost levels later on when switching over to a TT bottom end.

 

[Bean]

i would run the smallest A/R you can; not for spool speed; but for efficiency... you'd be making your power below 1 bar right? so you want a smaller A/R (which has its peak efficiency at a lower boost level)