331 build advice please

[simonjrwinter]

I'm going to build a 331 stroker, I've got a SCAT 9000 crank, and a nice set of world Windsor ali heads with 1.6 scorpion roller rockers. I'm probably going to get a set of H-beam 5.4 rods but what would anyone suggest for pistons? How about a cam? I want it to be a fairly powerful engine but not madly tuned, I'd rather have something that ticks over fairly smoothly and makes lots of torque than a real screamer. What sort of comp ratio should I be looking at?
Any advice greatly appreciated. Thanks guys.
Simon

[SSSnake]

Our engine builder used JE forged pistons and a custom grind hyd. roller lunati cam (.550 lift, 234 duration). Idles around 975-1000 with a nice lump to it. Pulls strong all the way up to about 6700.

Glenn

[David Biele]

Hey Simon,

If I were you I would talk with jmarsey. Check out his build.

David

[simonjrwinter]

Thanks guys, really appreciate it. Who is Jmarsey? if he's listed under the Build-ups section, I can't see it from the UK. The bit of the site I'd really like to see and it ALWAYS comes up as a 404 error...d**m

[jmarsey]

Simon,

The motor requirements you are describing are easy to achieve with a 331. Use a good set of heads and you'll be in the 400 - 425 hp area and torque in the same range. Keep your cr around 10:1. The 331 is a very good combination in terms of endurance and power from a short stroke motor. You'll be surprised.

I'm not an engine builder and my build specs won't be of much help to you. My recommendation is that you find a engine builder who can help you through the basic steps and keep you out of trouble. If you buy your parts through a speed shop / engine builder, spend money at their store, they may help you with advice, assistance and necessary machine work. Good advice goes a long way.

Questions you need to know for engine set up and cam selection are: how do you intend to use your car, street, track, other, will you be cruising for long periods, cars total weight, gear ratios as well as final drive ratio and rear wheel circumference.

JE pistons are very good. With a 5.4" rod and your windsor heads, JE should have what you need on the shelf. Once you get your complete rotating assembly, crank, rods, pistons, flywheel and damper, have it balanced. Also make sure end play and rod side clearances are correct for your application.

Take your time and do it right the first time. You will have a sweet little motor.

John Maresy

[simonjrwinter]

John,

Thanks for the advice, I had a look on the je pistons site and they seem to have everything I could wish for. The only thing is that the oil control ring is in the same space as the wrist pin. I've been told to avoid pistons like this as it creates an engine that uses exessive oil, is this an issue?
Thanks again.

Simon

[MJN]

Simon

You can get slightly shorter rods, 5.315", that will keep the oil ring out of the pin bore. I used those rods in my 331 and have been very happy with the choice.

[jmarsey]

Simon,

The oil ring / wrist pin relationship on a 331 je / srp piston is a non issue. The motor will not burn excessive oil. There are a lot of guys running this combination much harder than you ever will with no problems of burning excessive oil. You may be confused with the 347 combination which has had problems due to rod angle under road race type conditions. 331 is much more durable for extended high rpm abuse.

Don't sacrifice your rod length for a myth. The 5.315" rod was the hot set up in 69 and 70 as used in conjuction with the boss 302... trans-am rod length. It gave a better rod ratio / more dwell time than the shorter rods. The 5.4" rod is better yet, in fact it is very good. Run the 5.4" with je's and you won't have a problem. Oh yes, get an engine builder to help you. Did I mention that?

Best of luck, John

[agro1]

John - It sounds like you have, as you put it, a sweet little motor...Couple of questions though. How does your 331 compare to a 393 or a 408 W making about the same hp ? Is your 331 as reliable spinning it to 7200 rpms on a regular basis ? It would seem to me, for someone trying to lighten up a Cobra for the track, that your 331 setup would be the way to go...

[MJN]

Agro

Inertial loads increase with the square of the rpm. A simple calculation will show you that the inertial loads on the bottom end of the motor are 144% higher at 7200rpm than they are at 6000rpm. Does that answer your question on reliability? rpm makes HP but also breaks motors.

[scottj]

agro1,

408 vs 331

331 @ 6000rpm would have 5100lbs of tension loading, or 2100 G's (as in G-force) on the bottom end

@ 7200 rpm it would have 7300 # or 3000 G's of tension load.

408 @ 6000 rpm = 6600# or 2700 G's

408 @ 7200 rpm = 9500# or 3900 G's

The 408 at 7200 rpm is higher stressed, in tension, than the 331 at 7200 because the longer stroke creates higher piston speed. At 6000 it's almost the same as the 331 at 7200

numbers are approximate, I used 1100 grams as the reciprocating weight for both engines which is probably light for most 408's so the actual numbers would be even higher.

[jmarsey]

Agro1,

This thread sould be in "small block talk". Your question is an interesting one. There is no fast answer. You are on the brink of the whole BB vs SB argument. And I mean that in a good way. But I don't really care.

Let's keep things in context. My motor is anything but "sweet". This is not a street motor. I can spin it to 8500 rpm but I don't want to make power there. little motors have to spin to make power. The rotating assembly is zero-balanced which reduces stress at high rpm. Yes, wheight and how the engine makes hp and torque is why I went with my combo. If you just want to make big hp and torque well then by all means build a bigger motor. Much easier. There is much to consider when you start thinking about how you want the motor to behave. Yes, the more revolutions per minute, the more wear & tear. But so what. The term is called "freshening"

Think about why motorcycle engines are made as such. 289 vs 427. It's a great topic.

Help Simon. He's in the UK and needs a motor.

John

[scottj]

jmarsey,

I love this subject but I hate that term.
Turning my 434's 8000 rpm brings up "freshening" every 300 miles.
Scott

[jmarsey]

Scott,

Ahhhh, now that's a real motor. Now we're talking.

John