342 replies to this topic

[Struggler]

I have two 400 cranks if your keen, one std/std, one 10/10.

[dattoman]

Haw Haw
Sorry mate but I know all about things hitting things with cranks
Mine as you know had rods hitting block to start with and now rods hitting camlobes
Not sure if the 400 has the same issues but make sure he checks that too

[Tiny]

Heya Gents.

Firstly thanks for the offer struggler. I considered tis option with my own crank.. getting it ground and just go again with my bits, but we've gone too far with the new crank/balancer/flexplate to take any of it back... we're right in the middle so it's kind of a "stuff the cash... Just do it for the better engine" situation! I just have to work harder

Chop: I never knew and to be honest i always thought there was only 2 chev rods.. 5.7" and 6"! But hey.. ya learn something new all the time! Your right, its cause the counterweights hit the bottom of the pistons. THe crank is designed around the 5.7" or 6" rod combo that "everyone" uses! Problem is.. this means new rods AND pistons for me as it alters compression heights
As for cam shaft, i wont reveal too many details yet ( mostly because i dont know/cant remeber them ) but it's about 2 steps up from mine with a bit more lift but not alot more duration from what i remeber talking about today!

We're also going up 0.5 :1 in the compression ratio.. So that should wake this bastard up

Lostit: Not 10s mate.. well.. not aiming there yet, but if she hauls off mid 11s consistant and is as drivable as she is currently i'll be a happy boy.. If it goes faster then i'll be an even happier boy! LOL!

Datto: Yeah I know I know.. just another one of life's little tests! We're going to make sure of everything in dummy assembles ( like the one that found this slight problem) for all things including coil bind ( we checked for it and it *SHOULD* be fine) and piston to valve clearance as well.

Chevy: We're going for a crower cam ( i think!) and the cam we took out is a Camtech cam. Basically we're not happy with the casting of the camtech although the grind was fairly good for its design in my opinion.
I'm more than happy to have mark assemble my motor. I've seen his workmanship and attention to detail and i like how he operates! I'll get down there to watch/do as much as i can but he's a fair hike from me so i'm happy for him to do his work.

Chop: I probably have the knowledge to asseble the motor after helping/watching on so many with Cliff, but i dont have a nice clean room in which to do it along with all teh washing up area and some of the tools required to do the job. That's why it's alot easier and "safer" to have someone you trust do it for you and pay him what he's worth!


I'll have to find some more piccies of the monaro from aeons ago for ya and get them posted.
As for the colour... I Could tell ya.. but then i'd hafta Kill ya



No seriously... It's a custom "TINY" red and i'd rather not give out the recipie other than to say it's only made up of 3 colours and not one of them is orange

Cheers

[Tiny]

Chop: I get where you're coming from now! And to be honest i dont mind revealing cam specs as its a book cam! If it were some super secret custom grind to make a bazillion Hp it may be different

Correct me if I'm wrong and i probably am.. But wouldn't having a longer rod INCREASE the piston velocity?
I follow your thinking though, and if that is the case then it makes sense that you are right!

Greg: That's pretty well the decision i came to mate. TOo far gone to go back now and it can only make for a better engine in the long run!

Greg, or SOMEONE... can you clear this one up? Will the 5.7" rod combo increase or decrease piston velocity?

[Tiny]

Heya greg

Yes mate the new crank IS internally balanced! This was a surprise to us when it was off to get balanced cause normal 400s ( i did say my engine was a straight up 400 previously) are externally balanced!

What you have described is what my limited brain power told me, and what i had learnt so that's a big *PHEW* in relation to piston velocities!

We had a look at a 6" rod combo, but on saturday we couldnt source pistons to suit the combo. The problem is i cannot afford to wait for a custom set to be made! The block was also zero decked to suit the old setup.

Now.. We worked out the compression ratio of teh old engine was 10.25:1, and using the 5.7" long rod and the aries piston from the rocket catalogue ( that are in stock and available) will give us 11.2:1.. they have a 5cc dish.. We worked out that a 9cc dish would give us smack on 10.7:1 comp ( which is our ultimate aim), require a minimum of machining and stuffing around and be a pretty decent combo for my intended use. I will have a chat to mark and see if there are any other pistons in stock elsewhere that would suit a 6" comp height and see what we come back with.

The heads will flow.. infact.. this change will help the heads work more to their potential! And we chose a cam from the book that suited the rev range a fair bit better than my current cam, but is a bit more radical thank what ive got now.

So that's the ins and outs of what we've done and why we've done it, and ALOT of it comes down to time and money yet again... I MUST have this car running ASAP as ive got a wedding that i simply cannot miss, and i am also skint and cant devote any more funds to this engine!

Thanks for the tips greg, I'll give you a call this week when i have some more numbers ( cam specs etc) and see what you reckon. So far i'm fairly happy with this new combo.. it's a step above what i had, but a step below the ultimate ( 6" combo)

Cheers!

[Struggler]

In regards to the piston speed, think of it this way. Regardless of rod length the piston still has to travel the distance of the stroke so many times per minute. As Greg said, the longer rod will leave TDC slower, gain speed around mid distance and slow down again at BDC (compared to the short rod combo). It has travelled the same distance in the same time as a short rod motor, however it has travelled faster (ever so slightly) around mid stroke distance, and slower around T & BDC.

In regards to rod length, the current thinking at the top levels of motorsport all agree that the rod should be long enough to connect the piston to the crank ie there are a lot more important things to consider than the length of your rod (!!!). Having said that, a benefit of a long rod is the ability to use a shorter piston, this makes for a lighter rotating assembly and less drag on the bore wall (due to shorter piston skirts). Whats the difference ? I have seen the same engine run both a 5.7" and a 6" rod on an engine dyno and the difference was negligable (I've even forgotten which was in front) less than 0.5% on a 600HP engine which could be due to anything. The difference in durability however, could be more measurable (due to the lighter weight and less friction). Is it worth the $$$ ? Only you can decide.

Hope this helps rather than confuses.

[TerrA LX]

you have come this far, go the 6 inch rods.

[Tiny]

Gday Struggler.. Clear as mud

No seriously it makes sense to me! From what i was told the main reason is the piston side loading.
As you said in the end it all comes down to the mighty dollar and i've blown teh budget BIGTIME on this already and as such i'm not prepared to get pistons oranised for a 6" combo.

TO be honest.. the only reason i'm not reverting to my original combo is that we've gone too far with the parts that we have and ive got a good price on a set of 5.7" rods. As long as they do as-good a price on the pistons i'll be happy.. otherwise.. it's back to the drawing board!

ALX: Mate i wish it was that easy, I can understand why you say that... I said it yesterday myself.. But money and time relegate me back to the 5.7" combo ( Otherwise its back to square one!)

[TerrA LX]

i hear ya. there is always a trade off somewhere, and there is always next time.
oh did i say next time.
good luck with the new combo, something tells me a mandatory cage will be next.

[Tiny]

hehe thanks ALX...

Cage!? I'm not counting my chickens mate ... infact.. i dont *WANT* a cage!

Cheers

[Tiny]

I think thats right Chop cause of th extra dwell you can work with a bit more overlap.

Anyway.. i'll let ya know how right you are when the engine is run in and dyno tuned to perfection

[Tiny]

Cheers Dave!

I dont know the part no off the top of me head but i do remeber talking with mark about it and he said Yep it was for a 5.7" rod!
We didnt realise the stock length was 5.56"!

I'm not worrying about the 6" combo.. if i was doing this to be an all out race thing then i'd be concerned but i didnt even want to go THIS far let alone stress about something else so "minor".

We calculated most other things over the weekend, so there shouldne be any other dramas even witht he new cam, but yeah piston to valve will be ckecked before the pistons are sent for machining... We've gotto take 4cc out of the piston anyhow so if it needs valve relief we can do it then!

Cheers and will keep ya updated!

Off to work now... Christ knows i need the $$$!

[Tiny]

Heya Tuffgong! Mate i didnt see this reply till now! Sorry!
Thanks heaps for the offer though i really appreciate it! We've sourced all the bits and priced it all up and Mark is helping me out IMMENSELY! So i think were good for parts now!

To answer your question Dave, I've decided to bite the bullet (so to speak) and go for it. We're going with the 5.7" combo, and going for all the good bits!
So a fast rundown is:
Scat 4340 Forged Crank ( think i remembered the numbers... it IS the better one!)
SCAT forged H beam rods
Aries Forged pistons
Crower ( i believe) camshaft
"Coolface" lifters - Also crower brand i belive.

We're going up in the comp to about 10.7:1 to help make this combo work better, and it looks like my top end will do the trick. The springs should handle the new camshaft without dramas and pushrods should work out fine.

So all in all it's a complete new rotating assembly, all the machine work, balancing and all the good gear and i simply had a heart attack at the bottom line!

Looks like a $6500 job...Or thereabouts... That should include carby being re-worked and tuned, as well as the steering component rebuild that Mark did for me too!

So from an initial quote of $1000... to this.. has hit me badly.. but it really is the right way to go ( no corner cut).. and should see a more reliable, more powerful MORE FUN engine to get me down the strip!

That's the long and the short of it guys!
Thanks for your advise and assistance and i'll keep you posted further as things progress!