#58630 - 06/22/10 08:18 AM
piston question- beaten to death!
|
dodgycanuck
Active BB Member
Registered: 01/08/10
Posts: 115
Loc: Milton, Ontario, CANADA
|
So I know this has been gone over a few times, but I need a final word on this............
I cannot, at this time, afford forged pistons for my supercharged 250. I am only going to be running a pretty stock engine with a cam and the supercharger. Factory 5.5lbs of boost (which only comes on above 3/4 throttle).
Which pistons would be better, stock cast, repro cast or hyperutectic?
I am pretty hard on my vehicles. I so desperatly want the inline back into my car that I cannot wait for the funds to buy forged pistons. I will drive the car this way until I have saved enough to pull the engine and build it the way I want it!
Opinions, again. PLEASE.
Cheers!
|
|
Top
|
|
|
|
|
#58639 - 06/22/10 01:23 PM
Re: piston question- beaten to death!
[Re: efi-diy]
|
dodgycanuck
Active BB Member
Registered: 01/08/10
Posts: 115
Loc: Milton, Ontario, CANADA
|
After reading Leo's book... he mentioned that for street use and not more than 6psi, factory cast pistons are ok.
panic~ I am using an eaton m90 with the high vacuum by-pass, as you said. All the reading I have done on these leads me to believe that boost will only build once the bypass valve closes... which only happens at around 3/4 throttle and up. As for the 5.5psi boost, everything I read on the 3800 performance forums say that the factory dia. pulley creates this amount. PLEASE, correct me if I am wrong... it has happened in the past (me being wrong)!
I have been in contact with Tlowe about a vacuum canister that will retard timing. I am not 100% clear on the operation of this unit, but I have spoken with another person who is using the same thing on a similar engine. He is very happy with it.
|
|
Top
|
|
|
|
|
#58642 - 06/22/10 04:34 PM
Re: piston question- beaten to death!
[Re: dodgycanuck]
|
panic
Active BB Member
Registered: 01/11/05
Posts: 1340
Loc: Hempstead, Long Island, NY
|
If you're using the stock pulleys the blower speed will be the same, but the boost may not match. Your cam, ports and valves don't match the 3.8, your 250 is slightly larger than the 231" 3800, which may change the boost level, as will how big your manifold plenum is.
Again: that valve is vacuum-sensitive, when it closes doesn't depend on throttle opening or RPM but on falling vacuum, which is affected by gearing, chassis weight, exhaust backpressure - long list. I assume this a draw-through with a carb adapted to the Eaton intake? How big?
|
|
Top
|
|
|
|
|
#58649 - 06/23/10 05:56 AM
Re: piston question- beaten to death!
[Re: Mean buzzen half dozen A.K.A. Hank]
|
dodgycanuck
Active BB Member
Registered: 01/08/10
Posts: 115
Loc: Milton, Ontario, CANADA
|
I will be using a carter 600cfm for my carb. I am making a manifold which will be the similar to the clifford one, only with a larger plenum. I will also be making an adaptor for he carb... basically a 90 degree elbow for the carb to sit on top of.
Hank, I will look at the link you posted when I get a few more minutes... I am supposed to be working now.
|
|
Top
|
|
|
|
|
#58654 - 06/23/10 07:14 AM
Re: piston question- beaten to death!
[Re: panic]
|
dodgycanuck
Active BB Member
Registered: 01/08/10
Posts: 115
Loc: Milton, Ontario, CANADA
|
I have two... a carter 6oo or a holley 500 2 barrel. I'd rather use the carter because I find them easier to work with. I konw it is too much carb, but it is what I have to work with for now. Eventually it will be efi or tbi.
|
|
Top
|
|
|
|
|
#58663 - 06/23/10 09:01 AM
Re: piston question- beaten to death!
[Re: dodgycanuck]
|
tlowe #1716
12 PORT ADVERTISER
Active BB Member
Registered: 04/01/04
Posts: 2327
Loc: Dysart, Iowa
|
The vac can I make will pull 10 degrees out with boost. Can't remember right now how much it adds with vacuum.
|
|
Top
|
|
|
|
|
#58669 - 06/23/10 12:53 PM
Re: piston question- beaten to death!
[Re: panic]
|
dodgycanuck
Active BB Member
Registered: 01/08/10
Posts: 115
Loc: Milton, Ontario, CANADA
|
What are you going to do about the power system?
Power system?
|
|
Top
|
|
|
|
|
#58679 - 06/23/10 08:11 PM
Re: piston question- beaten to death!
[Re: panic]
|
dodgycanuck
Active BB Member
Registered: 01/08/10
Posts: 115
Loc: Milton, Ontario, CANADA
|
I didn't realize I needed to change any of it. I figured with it beging a draw through it would work the same as normal... was that a wrong assumption?
|
|
Top
|
|
|
|
|
#58692 - 06/24/10 06:31 AM
Re: piston question- beaten to death!
[Re: 56er]
|
panic
Active BB Member
Registered: 01/11/05
Posts: 1340
Loc: Hempstead, Long Island, NY
|
|
|
Top
|
|
|
|
|
#58694 - 06/24/10 07:42 AM
Re: piston question- beaten to death!
[Re: panic]
|
dodgycanuck
Active BB Member
Registered: 01/08/10
Posts: 115
Loc: Milton, Ontario, CANADA
|
I was just on the turbo forums... there are guys on there that claim to be running upwards of 30psi boost on CAST pistons. Obviously they would have some serious electronics for detonation suppression, but 30psi! Holy crap! There was a youtube link for a guy who made a 1/4 mile pass in his dart(?) making 25psi.
I like to imagine that my lowly 5-10psi would be handled, but who can say for sure.
food for thought... If I am spending the serious money on detonation suppression equipment, to ensure the life of my engine, are the forged pistons REALLY required? I understand that they are stronger and will handle the greater pressures, but if it is the detonation that has to be worried about...
|
|
Top
|
|
|
|
|
#58706 - 06/24/10 02:10 PM
Re: piston question- beaten to death!
[Re: Harry 6674 II 5760]
|
badsix
Active BB Member
Registered: 08/19/08
Posts: 59
Loc: oregon
|
as per Blower Drive Srvice compression chart at 6.5 compression then you inject 24# of boost their (chart doesn't go any higher) you end up with an enine that has 17-1 compression at full boost. thats only at 24# their are varibles such as cam timing leeky valvs that figure into this, but this sound like a lot of BS. if your thinking of running a blower get one of bds's catologs it has alot of info on drive raios, boost, compression ratios and a lot more
|
|
Top
|
|
|
|
|
#58707 - 06/24/10 04:53 PM
Re: piston question- beaten to death!
[Re: badsix]
|
panic
Active BB Member
Registered: 01/11/05
Posts: 1340
Loc: Hempstead, Long Island, NY
|
It's nice that they take the time to put this stuff up there, but even better if it were correct.
Their "math" is simply multiplying the static (mechanical) compression ratio by the pressure ratio, using 14.7 as ambient atmospheric pressure. (24 boost + 14.7 ambient) ÷ 14.7 = 2.63 PR. 2.63 × 6.5:1 = 17.1:1.
Except, that's not what happens in the engine.
Their purpose is to predict the equivalent static CR with the same knock characteristics as a normally aspirated engine, and they simply made this up.
The compression ratio never changes regardless of boost, the cylinder pressure changes, and the actual math is quite different.
Read my article:
http://victorylibrary.com/mopar/blower-engine5.htm#ECR
|
|
Top
|
|
|
|
|
#58714 - 06/24/10 08:02 PM
Re: piston question- beaten to death!
[Re: dodgycanuck]
|
Bob s Performance
Active BB Member
Registered: 05/03/00
Posts: 8
Loc: Moca,Puerto Rico
|
I have a new set of pistons 30 over for a 250 chevy. They are
forged with a dish , good for turbo.They are new TRW.The price is $300.00 for the set.Bob.
|
|
Top
|
|
|
|
|
#58849 - 06/30/10 02:06 PM
Re: piston question- beaten to death!
[Re: Mean buzzen half dozen A.K.A. Hank]
|
Bob s Performance
Active BB Member
Registered: 05/03/00
Posts: 8
Loc: Moca,Puerto Rico
|
No.These are not TRW L 2396. These are TRW L 2289 .030 over.They are flat with a .073 deep with 8.5cc cup.They do not have a chamfer.Comp. distance is 1.655 and they use 1/16 x 1/16 x 3/16
rings.These are press fit.Sorry for the delay on answers, but my
computer was damaged last week from a thunder storm.Bob
|
|
Top
|
|
|
|
Moderator: Webmaster
|
|
