tblentrprz

Didn't see anything about application. What's the intended use? What rpm do you plan to run at? RPM window will help focus in on cam specs which will provide insight into DCR. This will help define SCR. 91 DCR 8.3

Fuel choice - E85 (105) and 91 are miles apart with regard to compression and tune. Run E85 with nothing less than 12.5:1 SCR. Maybe someone can chime in with E85 DCR experience and limit.

You could run 91 in a pinch with a flex sensor and tune that adjusts accordingly or a "91" tune to load in a pinch (assuming no knock detection to keep engine safe).

FCar2000TA

iTrader: (7)

daily driver. 1/4 mile track a couple of times per year. 90% of the time will be spent under 5k. I have zero intention of ever going over 7k.

70cc MMS LS7 heads.

4.155" bore 4" stroke with piston oil squirters

Darth_V8r

iTrader: (4)

My old 428 ls7 build ran 91 at 12.3. Dynamic compression was at 8.5. IVC was very late.

FCar2000TA

iTrader: (7)

How big was that cam? I do not want anything bigger than the equivalent of a mid 230s LS1 cam.

Corona

Now you 🖕ing..

Corona

Darth could possibly spec your cam Also...

Darth_V8r

iTrader: (4)

It was 248/255 solid, so it drove like a 242/250. And that cam basically drove like my 237/245 solid cam in my 346, which drove like a 232/240 hydraulic. If you are wanting to stay in the more moderate stuff, then I would keep compression down, as your dynamic compression will be too high or else you'll have a rather anemic engine for its size. On a mild cam, I usually would stay around 11.1-11.5 static compression on 91. Bigger cam, more compression.

For example, if you went with that solid roller I pulled out of mine on 91, 11.6 would be about perfect. If you were to go with something smaller like a hypothetical 236/244, you'd want to be more in the 11.3 territory.

I guess the short answer is you'll need to decide your cam based on RPM and desired driving characteristics, and then choose compression to suit.

Double06

iTrader: (1)

Mid 230s will not get you there you need to be in the mid high 240s if you are running a 114 lobe separation. At 12 to 1 compression (if we are going of dynamic compression ratio of 8.5 or so) you will need the intake valve to close in the late 70s/low 80s. With the 230 you will be at like 70-72 or so which give you a dynamic at like 9.0+ which is too high (assuming 12 to 1). Not saying something might not work - but you hate to find out you were wrong and have to run some race gas all the time for maybe like 10-20 hp if you had just gone with 11 or 11.5 to 1 compression. If you are in the mid 230s you probably want to stay below 11.5 to 1. Go to Wallace Racing calculators and look at the dynamic compression calculators.

Che70velle

iTrader: (6)

What intake are you running here with Tony’s heads? Tony is in Cali and could easily set you up in a simple email or phone call with exactly what compression and camshaft to run with his heads. It’s what he does all day, every day. He would be the guy to ask here for specifics.

FCar2000TA

iTrader: (7)

I emailed Tony and he replied last night with 11.25:1. So that is the target.

Mickyinks

mid 230 cam in a 433ci isnt the same as if it’s in a 376ci ls3..... big cubes eat up duration.. I daily a 454 with 255/269... if I get old n senile and tame it down the smallest I’d go would b mid 240s

FCar2000TA

iTrader: (7)

I will be going with Tony's FAST or MSD intake. Which ever he recommends. I would assume it will be FAST since I will not be above 4500 very often.

FCar2000TA

iTrader: (7)

4" stroke" 6.125" rods, 70cc heads. Now to find pistons that will get me close to 11.25:1

Darth_V8r

iTrader: (4)

I didn't realize you were going with Tony's heads. For some reason I thought you were using regular ls7 heads. I learned a hard lesson that I hope will benefit you:

Heads with really good port velocity will tame a cam. That 248/255 in my old 428 build (remember that's 242/250 hydraulic equivalent), I could drive 20 mph in fourth gear and pull uphill. When I swapped in Tony's heads, we deliberately went quite aggressive on the cam at 256/270 (251/265 hydraulic equivalent) and .100 more lift vs the old cam. The car drives exactly the same as before. but gained over 100 HP and 70 lbs torque. Meaning, I can still pull uphill at 20 mph in fourth gear.

So, knowing that you have Tony's heads, I think you'll find a cam in the mid 240's is surprisingly easy to drive on that 434. With that 11.25 CR, my guess is Tony has your IVC at 050 in the 48-50 degree range, which will make it quite torquey. Now, seeing that you're rarely going to clear 4500, less cam definitely makes more sense. Just don't be afraid of it. If you run a DCR calculator, on 91, you want to stay right at 8.5. So, as said earlier, your IVC determines your ideal compression ratio

For what all that is worth, anyway...

gnx7

iTrader: (28)

I run 11.25:1 all day on 91 octane... if I were in your shoes get the 11.9:1 pistons and in a pinch you can simply splash in some Torco octane booster if you can't get your desired fuel. It is silly IMO to overbuild your motor like you are and never plan to spin it to 7000rpm? Why not? You are using some of the best parts money can buy.... enjoy it!

I have a 13:1 compression 441 (4.190" bore, 4" stroke/AllPro LS7 heads) with 252/260 .714" Cammotion LLSR I plan to run on e85 and in a pinch I'm going to do the same thing..... add 91 and some Torco. The flex fuel sensor in the Holley EFI will work its magic to get the A/F ratio correct.

FCar2000TA

iTrader: (7)

Your threads with Tony's products are why I am going with MMS. Not to mention that HE answers his e-mails, not someone who works for him.

FCar2000TA

iTrader: (7)

I have never been in a situation where I can afford to have a motor like this built, so to me, 7K RPMs is crazy racecar stuff. I cannot comprehend a daily driver motor that can spin that high. I will only go to the drag strip a couple of times a year, so I might get into the 7000s as I get more comfortable with the motor.

FCar2000TA

iTrader: (7)

Looks like Carrillo BLSR1204-030, Mahle 930226755, and JE 311988L pistons are listed as 11.5:1 with 70cc chambers.

Double06

iTrader: (1)

Remember when you do the Wallace Racing dynamic compression test you use the advertised closing duration (not the .050) number. In your case if you go mid 230s you will be in the 70-74 degree range of intake closing (if they only give you the .050 number add about 26-27 degrees to that. So say 46 + 27 = 73 degrees).

Lsbmer

That's why there is more to choosing compression than cam timing. Heads 260fps or 360 or in-between. Does intake flow what heads do? . Put a duel plane on a engine that had a single plane. And high compression.