Well, yeah...you're right!

BUT, he said he was only going to 45psi...the 60lb 12v springs won't wave any trouble with 45psi at less than 3200RPM! I think this is what he was shooting for

Now if we were talking about me, you're exactly right. My springs will need to control 75-85psi, and at 3500-4450+/- RPM when drag racing. I'll definately "need" some more help
Chris

 

would advancing the timing make the valves "float" lower in rpms???
I am running 18* timing with the stock gsk and the valves start to float at about 2500rpms.

 

Shouldn't...how do you know it's valve float?

Chris

 

up until this past year when curts truck went to an open truck they ran cummins 60lb springs with there hardened retainers and titanium keepers. this was spinning over 5500 rpm they just changed the springs at the end of the season each year.

 

RJohnson has since put on Don's springs...also tested the old ones he took out. Wonder why he hasnt chimed in yet??? HEEEEEEYYYY ROWLAND!

 

Have not chimed in cause they are talking 12v's.
Like Ben Franklin said "Better to keep quiet, and let people think you may not know... than to speak out and prove it to them."

I tested my 24v factory valve springs (106,000 miles on them) and there was some fatigue... 15 to 20 psi at intake valve (lobe) compression, down from 150 psi called for. Is this a lot? Fatigue may be worse at exhaust compression... did not have time to test. Don's springs are rated at 200 psi for intake compression (.325"), and were all right on... +/- 5 psi.

I have seen no noticable difference in driving on the street with the new springs (under 2500 rpm).... was not expecting any.

Biggest surprise was condition of the Valve Seals. Have since learned these are a high wear item, on 24v's only, for CTD's over 500-550 HP. About 1/2 were chewed up in varying degrees. A few were really bad! I replaced them all.

RJ

 

Correction! I did notice one difference from Don's Pro Sportsman Springs. Took me a week to realize what it was and that I did not have a problem!

Noticed at track I was 4-5 psi lower than normal max of 65 psi. Took me a week of thinking about it to realize - better breathing results in less boost pressure build up! Make sense?

RJ

 

Couldnt have been the fact that the temp at the track was 15-20* cooler the second time around? That would lower boost? NO?

 

Cooler, denser air will increase boost, if anything.

If an engine uses all the air it is offered... you end up with 0 boost pressure... right? So doesn't it follow that more efficient use of the air my turbos provide to the engine would lower boost pressure?
It's the old 'flow vs pressure' quandry!
That's what I came up, anyway.

RJ

 

Sorry RJ, cooler denser air makes the chargers work easier...more O2 in cool air than hot air, engine doesn't need 65psi anymore, 61psi will do the same job if it's cooler!

Chris

 

Agree that charger does not work as hard to build a given pressure, but.....I don't think that's the same thing?

RJ

 

Colder air will net more boost but also a denser air charge.
Warm air will net a lower overall boost number with a less dense air charge.

 

Bingo. And if my truck would build boost in 90 degree weather like it does in 20 degree weather twins would be obsolete. We use to equate a 10 degree temp change with 10 hp in the gasser turbo world.

 

Apparently I stand corrected...I must have forgotten something from winter to summer

Or it could be that I never have the same charger on long enough to see how it acts in both temperatures....I'll bet that's it

Chris

 

I'm sure that's it.
But it does get confusing because I deliver to Colorado (7000') 1-2 times a yr. and always loose 10-12 psi boost at altitude from thinner air... no matter how cold it is.

So does my 'more efficient breathing equals less boost pressure built up' make sense?
DO Helix cams lower boost pressure?

RJ