Websy21

iTrader: (34)

Funny you said it, I am also changing from 8.5 to 9.2 on a 408, 91 and meth. Last minute change while it was buing built. Fell more comfortable with the off boost power running a bit more CR.

52172

iTrader: (2)

I am running 9.8:1 makes great power on pump.

ninetres

iTrader: (35)

Yep. Better spool, and it will help down low with the big cam I am running. I am also adding a dual alkycontrol kit so I am not SUPER worried. I have seen all kinds of cars running GREAT times at ~9.5:1 with a stock bottom end, and 6.0 heads. Turbos seem to like it.

LS1LT1CAM

since everyone is on this topic of high compression
I am building heads up street race car for the nmca with a 70mm turbo (max size limited to)
will be intercooled
I am putting a ton of compression in this thing 12.2 to 1 with 52 cc heads

my question is how am i going to keep from putting heads gaskets on this thing every weekend

as far as boost as much as it will make (how much timing will be safe)

hannes_slanec

That is very interesting topic and I want to mix up with.

My project is a 1968 Impala convertible SS427 (clone)
and I plan to run it with:

a 4l80E

3,08:1 12bolt Positraction (many of you will say why that high but I have just bought it that way and think my engine will have enough torque to move it and that way I have nice overdrive ratio because- Gasoline in Austria/Europe where I live, 1,95$ per liter!!!)

twin turbochargers

BBC 540cid mark IV rebuild, balanced and blueprinted

http://cgi.ebay.com/ebaymotors/ws/eB...3DR2%26fvi%3D1

with hydro roller cam setup and a Vortec 7400 EFI


Now my question:

If you read the description that engine will make 12,00:1 with closed chamber heads and 10,00:1 with open chamber heads.

I want to drive 95 octane and so the compression ratio will be to high for turbos.
Now I also ask if I get it done with a thicker head gasket.

I dont want to come toooo low with the compression as I dont want to loose my nice torque which would also cause more fuel consumption in the daily stop and go traffic. I think about relaxed 9,0-9,3:1 compression and only a mild boost to give an additional punch in the mid and high range when my tire slipage is already over and I have traction again.

Is it done with a thicker gasket and a lower boost pressure and what pressure would you recommend?

Any camshaft recommendation for a BBC stroker with:

Twinturbos

EFI

which only got low boost preasure

high torque

and which shall not need unnecessary much gasoline (I know it will not take less but evan by a big displacement engine there is a window from -until and I would prefer to be on the lowest possible point with that setup)

If you have a recommendation please state all specs I need for an order as I am not a cam specialist. I am advised and supported by a friend and dragracer but he dont want to believe that a EFI engine never got that radical cams as a carb engine (at least I was told so at www.raylarengine.com, I was in contact with them as my first engine for that project was a Vortec 496).

Any help highly appreciated

Hannes

Got Me SOM

iTrader: (2)

Hannes buy a motor that is desgned for turbos, you're gonna spend more money trying to reengineer that motor to make it work for your application.

You want to lower the compression with new pistons NOT headgaskets.

Keep it around 9:1 to make it pump gas safe.

With 540 cubic inches I'm sure you'll have PLENTY of torque.

I am skeptical to buy things off ebay. I would contact a known engine builder like Shafiroff or Nelson Racing engines. You'll need to tell them what size turbos you are running and they can design the engine around that criteria.

good luck .

hannes_slanec

Yes but I would pay 20 000$up for such an engine. Nelson is surly I very able guy to that but not the only one in the whole USA.

For my opinion I made a very nice deal and this guy got a usual shop outside of eBay, it is not a private seller.
He got a lot of positive feedbacks.

10:1 is 10:1 whit what pistons does not matter. I ask the same question than the thread starter did: Can I come low enought with a thicker gasket.
And like him, I also try to keep high enough with the compression to keep my low end tourqe and only to give just a little boost to make my
engine more punchy in the mid and high range.

By the way, do you know Nelsons video 66´Impala 572cid for jerry covington (see it at www.nelsonracingengines.com).

Sorry to say but he says at that video that the Impala got 5000+pounds.
I have a 68 Impala what is the same body (65-70 Impala/Caprice/Bel Air/Del Ray), it is the convertible and therefor more heavy as it got a stiffer frame to compensate the missing roof and it only got 3750 pounds.

Such a light car (for me it is not that heavy for the size) with that displacement and a 6speed???

What nonsense 572-6speed. I am sure Nelson took thousend of dollar for building that car but that for I dont need a pro.

He also run biiiig engines only on 9,0:1, sorry bit I have another opinion. Usual street cars with aspirated engines using pump gas should drive 10,0-10,5:1 to have efficient power.

Else I take a smaller one with higher comparession.


Thanks Hannes

elky489

iTrader: (1)

what about a 11 to 1 406 with a pt98?

hannes_slanec

What the hell is pt98?

Thanks Hannes

bluecamaroz28

http://www.forcedinductions.com/productpte.htm

elky489

iTrader: (1)

its a big dick 98mm turbo.

zapp168

iTrader: (7)

With my old build, stock bottom end 5.7, with patriot heads running 10.5:1 with 11# of boost....I beat the living daylights out of it..pulled it for the new set up, and I would honestly say after inspecting it I would just install it into another car without a problem!

Rickys S/C Z28

iTrader: (13)

so what is folks running now days?? i see that this is kinda old but i would like to see if the thinking is the same?

cablebandit

iTrader: (37)

10.3-4:1 for me....

DanZ28

iTrader: (5)

I'm staying 9.0:1 on mine with Q16. I think it just depends what you are doing with the car. With a tune, you could run almost any CR but making it optimal is another story.

jfg455

iTrader: (5)

We run 9.1:1 w/10psi on pump gas and no meth w/ no more than 15* of timing. Bump it to 15 psi w/ meth and pump gas. still with no more than 17* timing.

CBIII

iTrader: (6)

So im secondguessing my build and toying with the idea of going turbo again.
Setup is forged 408, ~11.7:1 with -1.5cc dish pistons and fully ported 5.3 heads (73cc chambers).. Im looking at going l92 top end, but not sure what that would do to my compression. Ill be converting to E85 regardless and im told it allows for more forgiveness with a tune. I JUST built this engine and would like to do this without replacing pistons right away if I possible. Anyone?

vaticano

iTrader: (8)

I'm running at 11.4:1 with 12 psi using E-85 and have had no issues. I"m hoping to put in new pistons +10cc at 13:1 this winter with the same setup.

CBIII

iTrader: (6)

wow!! Im looking to go turbo though.. in the thread it mentioned that sc's are more forgiving with higher compression though?

NemesisC5

How much does E85 cost per gallon? I'd like to see the result of the CR bump going from 11.4:1 compared to 13:1

FWIW, I am an advocate of higher CR