1987 408 Stroker comperssion

Oct 2, 2018
13
1
13
USA
Hey all,

Sorry if this isn't the correct area to post this, as this is more engine specific than it is vehicle specific. though you could say that i plan on dropping this into my 97' fox and that i want some help on the motor for it. otherwise, i couldn't for the life of me find an engine specific forum here.

so anyway. I've got a 74' 351w that I'm wanting to stroke to a 408. I'm going with a 4" RPM forged crank, 6.250" forged Eagle H rods, and forged JE Twisted dome 1.230 Pistions with a -19cc dome. Zero Decked, overbore to 4.030.

750-800 cfm Carb, .037 gasket, Edelbrock Vic Jr heads with a 60cc chamber, and a Edelbrock Super Victor Intake. (The rest shouldn't matter for my combustion ration as of right now, lets assume the rest is pretty neutral). JE is claiming that my setup would get me 10.7 cr at a 58cc head, so with a 60 i imagine my cr would be around 10.5 give or take.

I don't think I'm using the online calculators correct because I'm getting an estimate of like 18.5 cr (kaboom). so i wanted an opinion from some guys that i figure have some experience with this.

Hows my setup looking so far (excluding the fact i don't have a cam chosen, but I'm looking at one to get me to about 6500rpm.) I'm trying to keep my CR at mid to low 10's on 93 pump fuel and decided to go NA instead of having a power adder.

Thanks in advance.
 
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I run 93 octane with 10.8:1 in the Georgia heat and I don’t have any issues. With aluminum heads and the right cam, detonation isn’t a problem. Personally I think if you’re not running mid 10s or higher on a good n/a engine you’re missing out.
 
Oh yea? higher 10's on a n/a? i guess thats where the forged parts come into play...

What do you think on the setup so far? im fairly new to building up a motor from scratch. i dont see how i would be getting an 18+ on my cr so i must be using the calculators wrong. im thinking the JE estimate of 10.7 should be alot closer to what id be getting, but i just wanted some opinion incase there was something im missing.

Also, what cr would be considered too high for a 408? is lower 11's pushing it? i definitely want performance, but longevity is the #1 goal for me.
 
aluminum heads are more forgiving to CR and timing...
more CR less total timing, assuming you keep the same octane.

total timing on that engine should start at 26-28* to be conservative at WOT with 93 octane. all in by 2500rpm
vacuum advance in the cruise range to net a 36-40* timing so you can lean out the carb during cruise and not get a lean surge/buck.
vacuum advance at idle to net 16-20* timing.

Im an EFI guy so im not sure how you need to play with weights ect to achieve these values unless you run a programmable ignition box.
 
Below is from a calculator i am using. there is no way this is right is it? 16.49 CR??

1538502553683.png
 
My 393w is roughly 10.5:1 I use 93 and have had no detonation issues, still EFI.
Not sure why your cr is coming out so high , maybe try a different calculator to compare.
Are you choosing a -19 dome for extra compression?
I got the same result when I put your values into the below calculator.
Looks like you need to either choose a different/dished piston or heads with larger cc.


https://www.rbracing-rsr.com/compstaticcalc.html
 
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Ah, so i changed my dome on the calculator from -19 to +19 and my CR went to 10.9 (more like what i want).

Like i said, im really new to this, but for less compression, you want a negative cc right? for more compression you want a positive cc? so maybe either the calculators are weird, im misinterpreting the calculators, or JE's site is displaying the wrong integer...

so if JE's piston claims, it has -19cc (inverted dome i/e hollowed out piston head) then that lowers the CR, if its a positive cc (like 19cc) like an actual dome, then it increases CR..

or am i wrong?
 
Ah... copy that. thanks man, actually helps out alot. and that makes more sense the more i think about it. Thanks for helping a fellow prevent his block from going boom,lol. so if i could get around the 10.5-10.9 range with a decent cam, i should be cooking pretty good for a n/a.
 
Ah... copy that. thanks man, actually helps out alot. and that makes more sense the more i think about it. Thanks for helping a fellow prevent his block from going boom,lol. so if i could get around the 10.5-10.9 range with a decent cam, i should be cooking pretty good for a n/a.
You should be fine,i am 11-1 on 92 octane. 20+* at idle,30 total in very early. (no vac. advance)
 
Hey all,

Sorry if this isn't the correct area to post this, as this is more engine specific than it is vehicle specific. though you could say that i plan on dropping this into my 97' fox and that i want some help on the motor for it. otherwise, i couldn't for the life of me find an engine specific forum here.

so anyway. I've got a 74' 351w that I'm wanting to stroke to a 408. I'm going with a 4" RPM forged crank, 6.250" forged Eagle H rods, and forged JE Twisted dome 1.230 Pistions with a -19cc dome. Zero Decked, overbore to 4.030.

750-800 cfm Carb, .037 gasket, Edelbrock Vic Jr heads with a 60cc chamber, and a Edelbrock Super Victor Intake. (The rest shouldn't matter for my combustion ration as of right now, lets assume the rest is pretty neutral). JE is claiming that my setup would get me 10.7 cr at a 58cc head, so with a 60 i imagine my cr would be around 10.5 give or take.

I don't think I'm using the online calculators correct because I'm getting an estimate of like 18.5 cr (kaboom). so i wanted an opinion from some guys that i figure have some experience with this.

Hows my setup looking so far (excluding the fact i don't have a cam chosen, but I'm looking at one to get me to about 6500rpm.) I'm trying to keep my CR at mid to low 10's on 93 pump fuel and decided to go NA instead of having a power adder.

Thanks in advance.

That should be a pretty solid setup. Victor Jr is a good head, should flow plenty good for 408ci. I would’ve personally gone with a slightly bigger head if starting from scratch (like 225-240cc), but you’ll have a mean street engine.

Your bottom end will be solid as well. You’ll have a good time.

Looks like you’ve got the cr figured out. Like was stated, mid-upper 10s is perfect for a n/a build.

A buddy of mine has an old non roller 351w sitting around. That’s gonna be the next build, As soon as my wallet recovers from the last lol.
 
That should be a pretty solid setup. Victor Jr is a good head, should flow plenty good for 408ci. I would’ve personally gone with a slightly bigger head if starting from scratch (like 225-240cc), but you’ll have a mean street engine.

Your bottom end will be solid as well. You’ll have a good time.

Looks like you’ve got the cr figured out. Like was stated, mid-upper 10s is perfect for a n/a build.

A buddy of mine has an old non roller 351w sitting around. That’s gonna be the next build, As soon as my wallet recovers from the last lol.

Nice, sounds good.

Yea, after reading more and playing around with a calculator and looking at whats available, i think i found a setup that can get me what i want.

70cc Heads with a +5 Flat SRP piston will get me 10.5 which is good enough.

Or i can do a 6.2 rod under a 60cc head with an ICON +11 piston and get 10.9

That brings up another question. when it comes to pistons, whose good enough, who the one to go to if i can, and who should i stay away from?

Because i have 4 different formulas right now to get me different CR.

there is the two i mentioned, then i can get 10.7 CR with some DSS GSX pistons, or i can get 11.1 with some howard cam pistons.

Ive heard ICON and DSS GSX are a little iffy when it comes to reliability. which makes me not want to do the 10.9 or 10.7 builds (even though those are the numbers out of all 4 builds i like the most.). i would do the 11.1 build with howard but i feel 11.1 might be pushing it for 93 pump fuel, though someone on this thread does claim to run a 11 build. which leave me with a comfortable 10.5 build, but i cant find reviews for SRP. hows their reputation?

EDIT: Dont know why i couldnt find anything earlier, but another look over the web shows SRP as an offshoot of JE, so i imagine SRP should be a pretty good brand. still, what about the others? any opinions on a 11.1 CR build running 93 pump?
 
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I used SRP pistons in my 393w, good quality.
I applaud you for taking the leap and building/sourcing your own engine.
It gave me great satisfaction when I built mine, I also asked a ton of questions and
had help from a very knowledgeable friend.
Keep in mind "quench" when playing around with all these different piston/head combos.
I believe optimal quench with steel rods is somewhere around 0.038-0.043. Probably doesn't
make a ton of difference if your not looking to get every ounce of power, but since your building
it why not get close, imo.
 
I used SRP pistons in my 393w, good quality.
I applaud you for taking the leap and building/sourcing your own engine.
It gave me great satisfaction when I built mine, I also asked a ton of questions and
had help from a very knowledgeable friend.
Keep in mind "quench" when playing around with all these different piston/head combos.
I believe optimal quench with steel rods is somewhere around 0.038-0.043. Probably doesn't
make a ton of difference if your not looking to get every ounce of power, but since your building
it why not get close, imo.

Yea thanks man for mentioning that. i have just recently been reading into "Quench". Interesting stuff.

I believe in doing what makes you happy, and i do this stuff (read, car stuff) for fun/as a hobby so i figure why not experience the whole thing and get the satisfaction.

Alot of people can say theyve bought a aluminum 408 shortblock, or that theyve bought a stroker kit; but how many can say they built it from scratch and make it exactly how they want you know?

Thanks again bud.
 
I'm using a set of SRP pistons in my 331, machine shop that did my block work said it was one of the lightest he has seen for off the shelf. They even eliminated the oil support rail for the wrist pin. The are holding up fine after 9 years. 475rwhp NA.
Yes 10.5-11 is doable if you have the quench. I am 0 deck at 10.5 but still run a bit of race fuel just to be safe. Like half gallon per tank, the leaded fuel smells nicer with no cats also.