best compression for whipple charged 408?
best compression for whipple charged 408? i'm looking at 2 different setups for a 408. One is fully assembled already and has 8.5:1cr, the other will be built by LME and will have 9.5:1cr. Which is better and why? Is 8.5 too low?
I would go with the 8.5 cr. My reasoning goes like this--
A 408 has plenty of torque.
Whipples are difficult to intercool-lower compression would help control knock.
Each point in compression is good for approx. 4% hp increase.
Each lb of boost is good for maybe 5-6% hp-several extra lb's boost per point cr decrease is possible.
Positive displacement blower negates any lag issues off-boost.
The only downsides I see are a slight decrease in fuel economy and a somewhat poorer idle quality if you run a big cam with lower compression. Since you're putting a big cube blower motor in a truck, I doubt the fuel economy is a priority, and some people like a choppy idle.
A 408 has plenty of torque.
Whipples are difficult to intercool-lower compression would help control knock.
Each point in compression is good for approx. 4% hp increase.
Each lb of boost is good for maybe 5-6% hp-several extra lb's boost per point cr decrease is possible.
Positive displacement blower negates any lag issues off-boost.
The only downsides I see are a slight decrease in fuel economy and a somewhat poorer idle quality if you run a big cam with lower compression. Since you're putting a big cube blower motor in a truck, I doubt the fuel economy is a priority, and some people like a choppy idle.
With 15lbs of boost i would go 8.5 C/R if the intention is to use pump gas due to what was said about the heat generated by the Whipple, but if you plan to run race gas then i would go with 9.5 C/R because it will make more power at the same boost level.
Good luck
Good luck
maybe I should elaborate. I'm at 15lbs boost now with my stock 6.0L and stock exhaust manifolds. I'll still be spinning the whipple at the same rate, but, i'm sure I'll only see 5 or 6 lbs boost on the 408/ASM headers. I do plan to run 93 octane gas most of the time, but, 100 octane at the track.
The other difference in the 2 engines is: the 8.5cr one uses "all pro" heads, I've never heard of them but i hear they're friggin expensive. This package is a 402 and is ready to ship. It's about $500+ more than....
this one which is a 408 with 9.5c. uses ET 240 heads. this one is about $500 cheaper and needs to be built. 5-6 weeks lag time
The other difference in the 2 engines is: the 8.5cr one uses "all pro" heads, I've never heard of them but i hear they're friggin expensive. This package is a 402 and is ready to ship. It's about $500+ more than....
this one which is a 408 with 9.5c. uses ET 240 heads. this one is about $500 cheaper and needs to be built. 5-6 weeks lag time
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I think it would be very foolish to run 9.5:1. You're going to be spinning that whipple to the max to make even 10 or 12 pounds of boost out of it, and running higher compression when that blower is pushing a lot of heat doesn't make sense. 8.5:1 all the way.
Originally Posted by eviltwins
I think it would be very foolish to run 9.5:1. You're going to be spinning that whipple to the max to make even 10 or 12 pounds of boost out of it, and running higher compression when that blower is pushing a lot of heat doesn't make sense. 8.5:1 all the way.
Cheers,
Mark
Why even screw around anymore? Even running a built 408 NA for awhile will be more HP than your putting out now. The power difference is like 3-4%, so go with the lower compression. That blower generates heat, and anything you can do to work around that, is something you should do.
I'd sell the whipple, but, i'd probably get less than $1500 for it. yeah. I have no idea what a F1R is. I'm probably gonna buy an engine this week. Either the LME 408 with ET heads(9.5:1), or the 402 GMC SKI has for sale with allpro heads(8.5:1).
They will be essentially the same price depending on which crank I go with from LME (eagle or callies).
eventually, i'd like to put on a bigger supercharger, maybe the twin rotex, or a turbo of some sort. I can't do the engine and that now, so, looks like the whipple may have to stay for now.
maybe running the 408 NA for awhile is a good idea. hmmmm
They will be essentially the same price depending on which crank I go with from LME (eagle or callies).
eventually, i'd like to put on a bigger supercharger, maybe the twin rotex, or a turbo of some sort. I can't do the engine and that now, so, looks like the whipple may have to stay for now.
maybe running the 408 NA for awhile is a good idea. hmmmm
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From: Mefis
Originally Posted by DanaliHD
...eventually, i'd like to put on a bigger supercharger, maybe the twin rotex, or a turbo of some sort...
Originally Posted by Pro Stock John
The power difference is like 3-4%, so go with the lower compression. That blower generates heat, and anything you can do to work around that, is something you should do.
But that is a race gas setup 