Actually look up the samurai spec. Book calls out 199

 

So in this case where does the extra psi come from?

 

It has to come from the temperature rise and I am shocked it has that much effect.

P1V1/T1 has to equal P2V2/T2

 

My 7.8:1 302 is in the 140's. :noidea: I have seen 4 banfer build near 300 in n/a aps.

 

408w with 8:1 does 155-160 cranking.

 

If I did my math correctly, the temperature only has to increase about 15 degrees F to make a significant difference.

Solving for T2, correct?

T2=(T1*P2*V2)/(P1*V1)

In a 10:1 engine V1 is 10 times V2, P1 is 1 atm and P2 can be 13.6 atm(200psi), T1 can be 21 deg C(~70 F)

subing in

T2=(21*13.6*1)/(1*10)

I get this equals 28.56 deg C, or about 83.4 deg F, 13.4 degrees difference.

 

will cranking rpm have an effect on a compression test?

 

The temperature is absolute temperature so you must add 460 when useing temps in F.

 

http://www.turbobygarrett.com/turbobygarrett/tech_center/turbo_tech103.html

Andy is correct.

See formulas in the middle of the article.

Tom Vaught

 

I used the metric system? Should it be kelvin? I forget. If it is, then I get t2=373* K.

 

http://www.unitconversion.org/unit_converter/temperature-ex.html

use this

Tom Vaught

 

What about quench? On my Na motors i always kept that to around .042 with steel rods with .038 gasket. Most My engines were all around 11.1 and ran great on pump never no deto. Do guys do this with turbos? I had a 410 windsor this motor was about 10.2- 10.4 It cranked at 195 psi !

 

https://www.theturboforums.com/smf/index.php?topic=120797.0

https://www.theturboforums.com/smf/index.php?topic=123236.0

 

Thanks, Now here is some good reading i'll be gone for a while Sorry for hi jacking John

 

I rode in a car with a setup similiar to mine but with 8 to 1 comp instead of my 9 to 1, it was a dog off boost. Those 4% loss estimates for 1 point drop in comp don't seem to tell the whole story, otherwise we would all be happy running lower comp.

 

I second this. I had three engine builds for my truck. 383 chevy, 2 mpt70's, RHS 180 heads with 8.8:1, 8.25:1, and 7.8:1 static compression. Only pistons and head gaskets changed between the three. Here's a breakdown of the performance on 8psi with each.

Ratio ET MPH Cranking PSI Timing Quench

8.8 10.91 123 145 26 20cc dish .018 shim head gasket .040
8.25 11.01 121 135 30 31cc dish .018 shim head gasket .040
7.8 11.38 118 125 30 31cc dish .040 mls gasket .062

At 14 psi the differences were apparent also. Never ran the 8.8 on 14psi at the track but on the street is was way nastier than the 8.25.

8.25 10.57 127.5 24
7.8 10.82 124 26

The drivability got worse and worse the lower it was. Spool time suffered as well and fuel consumption increased noticably street driving. All three used the same 91 octane from the same station. Seems to me the quench distance played more of a role than the actual compression change. As with everything other engines could be different and with a cam change and some other things it could be evened out a bit but I'll take the higher compression and lower boost anyday and run the right fuel for higher boost power. Its a more efficeint engine anyway you slice it.

 

this may be a dumb question and bordering on hijacking but why do i see smaller engines, say a 4g63 able to run 20+ lbs of boost without detonating on pump gas but with my 5.0 id be scared over 15 psi?

 

Are you talking stock for stock? Those guys running 20+psi on a stock dsm are pushin their luck anyway. I bet the only diffference is that their rotating assemblies and blocks can handle more HP without letting go. Detonation is detonation. They don't have shitty Iron heads from the factory, but they still have to run rich conservative tunes or naturally they will detonate. That might have a little tighter quench from the factory or somethin stupid like that. But, from what I understand alot of factory turbo car's actually run hyper pistons. It shows how conservative they must tune them right out of the box. Anyway, with aluminum heads on a 5.0 you can easily run 20psi without detonating. People do it every day all over this board. You just need a 4 bolt block and a roto assy that can handle 750+hp. Thats the difference. You run a little stocker dsm up to 20psi they might make 300whp. Do that to a alum headed v8 and you have a low 9 sec car.
-end rant-

 

A first gen 4G63 had a compression ratio of 7.8:1. They are known for having poorer response than the later generations that got 8.5:1 compression but can take more boost and make more power.

 

That's something I think about too. My thoughts, FWIW:

-They have to; i.e. us big V-8 guys would too except that we can make 1,000HP fairly easily (read: low boost.)

-Inline engines always seem more stable compared to a V-configuration. I may be off base on that but I've seen the notion echoed by others. The bottom ends just seem to be able to take more abuse.

-This one might be a stretch but does the uneven firing pattern (bank to bank) cause cylinder to cylinder inconsistencies that could effect detonation? This would be fairly easy to test; you could make a standard twin system for any given V-8, turn up the boost until you run into issues, then swap to a different hot side with 180-degree headers and retest.