Aluminum heads for 93 351 lightning efi

[rjrobin2002]

I am wanting some aluminum heads for my 93 351w with explorer efi.
It currently has gt-40p's

The thing is I also plan to add a torqstorm supercharger down the road.

Would I technically need to go up from say 170cc to 190cc after adding the supercharger?

I plan to keep the lightning upper and lower intakes to keep it mostly ford and low profile and know I will be limiting some HP not switching intakes.

What's yalls thoughts? Would a another cam be needed, I just spent $350 on this one.

 

[Broncobowsher]

The better the naturally aspirated power, the better the boosted HP.
I remember reading up on an old article where they were reaching a power limit as the stock heads just could not flow more even with the boost going up.

 

[EFI Guy]

You don't NEED to buy bigger heads just because you are boosting it. I would argue port size is a little less important when you force feed it, up to a certain point.
"Boost" is nothing more than a measurement of restriction. Bigger heads result in less restriction, so you might measure 3psi on bigger heads and make exactly the same amount of power at 5 psi on smaller heads.
I like to see minimal valve overlap on a boosted application. That cam has just a tad more overlap than I would like to see, but is still mild enough that I would run it anyway. There's plenty of hotter setups out there.
If you do decide on bigger heads, then it might be worth going higher lift on the cam with less duration. That cam matches the maximum usable lift of GT40's.

 

[Broncobowsher]

To that, running 3PSI of boost with a good flowing head over 5PSI with a restrictive head is less air temperature rise. Boost increases intake air temperature which hurts power and makes for detonation sensitivity. More reason for better flowing heads. Just don't be disappointed with low boost numbers and be happy with the power it makes.




Then add more boost...

 

[DirtDonk]

With modern heads, what would be a desired compression ratio? Given the choice of cams, of course.

 

[73azbronco]

My understanding is boosted engines use a lower CR.

 

[nvrstuk]

LS engines are running over 10.5:1 and running boost. About what everyone has said. Flow, quench, CR, timing, HOT intake air , centrifugal or screw. Waaay cool timing control and knock (detonation) detectors allow a lot higher compression ratios than the old days

 

[73azbronco]

I'm just saying, for a guy adding adders, LCR is the way to get increased boost potential. Otherwise, need to have a tuner look all this up.\\You really can't just slap a turbo or supercharger on without really doing some legwork.

PTP, jeep uses the 3.6 naturally aspirated, they make a supercharger for it. No one uses it. Too many bad results.

 

[nvrstuk]

With modern heads, what would be a desired compre ssion ratio? Given the choice of cams, of course.

8.5 to 9.5 whatever ... but there are so many variables that can be compensated for now compared to just 20 yrs ago, allowing you to add boost. I built my last 418 at 9.4 CR so I could run boost after I quit running to the tiniest towns (low octane gas) in BC fishing- figuring on a couple #'s of boost for some streetable HP. It's sitting in my shop... Last LS engine that was supercharged that I worked on was 11.0:1. Unheard of numbers 20 yrs back. It was in a '69 Chevelle. It could idle down main street in 3rd gear at 25 mph and light the tires up in 3 rd gear at 60mph when he floored it. Wicked car. Sold it as it was a lot to handle, $77K.

 

[Broncobowsher]

With modern heads, what would be a desired compression ratio? Given the choice of cams, of course.

And there is a little story. Working on a variable compression ratio engine. High of 14:1 and a low of 8:1. Runs on 87 octane. Light cruise, 14:1 to squeeze all the power it can from the fuel when there is little cylinder filling. Get on it, 25 PSI of air to water intercooled boost on 87 octane and 8:1 compression. Modern stuff is pretty amazing.

The old days people would build engines for boost and drop the compression into the 8s, even lower. And not running that much boost. Modern engine controls (good EFI) can let you run, lets say 15 PSI on about 9:1 compression on premium pump gas most of the time. Providing the engine is built correctly, good quench pads and height, good heads that handle heat well, good spark plug placement in that head, sharp edges that lead to hot spots taken care of. Dropping water temp down a few degrees (180 instead of a 192 thermostat) helps.
Then there is always water/methonal injection that can be added to give a little help under boost if you overdo it in the build.