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what bore size would you recommend for DART block?

6K views 13 replies 4 participants last post by  Freshmeat 
#1 ·
I am looking into building a Dart short block up using the 8.7" deck height block (I don't want to cut bonnet so 9.2" or 9.5" block will not fit) looking at 360

If I go with the Dart 8.7" block that comes in 4.125 bore but can be taken out to 4.185 safely, what should I take the bore out to considering it is my street car, or is it not worth taking bore past 4.125?

Also Dart states that max bore and stroke recommended is 4.185 x 3.5, is it worth going straight to this or should I go 3.4 stroke and less bore?

I am looking at using Scat 4340 forged internals, what do you think of this brand?

What brand and port size heads do you recommend that I use?

I was looking into using Edelbrock RPM2 intake, will this be a good choice for flow capacity and usable rev range, if not what others may be better?
Thanks guys :hy:
 
#2 ·
I think you should go more bore and less stroke- it'll leave the bottom end stronger to have shorter rods/crank throws, in my opinion.

The RPM set-up would be a good run. Are you EFI? They make a great cam/lifter kit, hardened pushrods, heads, intakes, etc that are all designed to work together, which leads to another point:

Keep your parts matched up. Edelbrock didn't put over six decades of research and development into their packages for you to go and mix up their heads and intakes and cams and whatnot- they're designed to work together and they do one Hell of a job. Go with the 2.02" intake valve design on your heads and be sure to get pistons that are notched to clear those ungodly valves.

As far as the bottom end goes, unless you're blowing it, boosting it, or juicing it, you really don't need a completely forged bottom end. If you're going to do it, though, do it right. It's a long argument between Scat and Eagle, but do what makes you happy- I don't feel like starting a fight.

Most importantly, though: KEEP US UPDATED ON YOUR PROGRESS!! We'd like to know how your build is going and we definitely want to see some dyno charts when it's done! Good luck.

Oh- Edelbrock also sells a great double-roller timing assembly for only $60. I'd greatly recommend that.
 
#5 ·
If I use the 4.125 bore with a 3.4 stroke in the 8.7" deckheight block and use 5.7" rods then I get a 364 ci motor, by increasing the bore up to 4.185 then i get a 374ci motor. The 8.7" deckheight allows the use of longer rods so the rod ratio is much better making for better durability I believe.
With the heads what port size are recommended for street use, 185 or 205? Also would I still go with the 2.02 intake valve size?
I am thinking of going NA to start with but may look at blowing it later if wanted, enough is never enough from what others have said!
Any comments or suggestions appreaciated.
Thanks for replies :hy:
 
#6 ·
I kept mine at 4" bore as I'm turbo induction..With 3.25 stroke/ 5.4" rods as used by most 347's..To get compression low enough I had to use custom C.P pistons with 27cc dish..Something you are going to have to make your mind up what you want to do? If forced induction 8.5 for blow and lower with turbo to make untold torque & power..All up my chamber size is 90cc....Yes low comp...But SAFE!!! Carefull with notching piston too close to bore as any detonation will blow through where there is any weakness..Using bigger bore puts you deffinately in custom piston field!! Have you checked the $$$ of them ?...Bloody expensive!!!
 
#7 ·
A few notes:

Racer- there is no problem going 4.185 with the block if that's what he wants to do. Dart doesn't charge $2500 for weak blocks. I do understand what you mean about leaving more meat, but I also know that high RPMs hurt long rods and that Dart blocks are damn near bulletproof.

Blown- if you want to start N/A, start that way and if you want to add a turbo later, just switch to the 27cc dished pistons as mentioned. I've seen STOCK (130,000 miles) 302s with STOCK intakes, heads, pistons, crank, rods, etc. (okay- they did add a main girdle) running sub-11s and over 500hp.

EBXR- piston companies know how to notch pistons to clear the valves. If he's running high compression with boost, then he needs to be shot, but that's probably the only time the notch could possibly be seen as a weakness. Also, it's not expensive to order pistons as high as 4.185" bore. Forged aluminum pistons with 4.185" bore is another story- maybe that's what you're thinking about.

Blown, back to you- I don't know how rich you are, but from the parts you've listed, you're looking at investing $7,000 in this motor, minimum, if you assemble and install it yourself. If you're going to do that, go ahead and run Edelbrock's Victor or Victor Jr power package and turbo it with the dished pistons mentioned above. That's my opinion. It makes absolutely no sense to waste a Dart block and forged rotating assembly on a N/A motor that isn't running on alcohol. That's my opinion. Again, keep us updated and keep asking questions- good debate going here.
 
#9 ·
I must correct a few things.that are applicable to Aussie....Custom pistons cost around $1800 Au for a set, rings included....For top quality ...
In my combo with Twisted Wedge heads attention was paid to inlet valve notch NOT going too close to edge of piston as some off the shelf are...Obviously if you need clearance you must!!!
Plus we had the top ring alittle lower than a N/A piston...To keep it away from heat as much as possible..
On a 8.7 deck block there would be way more room in this area..
The reason we used the Oliver rods was they have oil feed to pin, which we used as a piston cooler to squart oil under piston...As these rods are designed to work on dry sump engines where the vacuum they produce pulls oil from this area so they adapt an oil feed...Sounds very Jap but in this case Yank...

Bore size???
I'd go the bigger bore..But keep in mind in turbo situations a long stroke engine and SMALL bore will tolerate more boost before detonation in most cases..The flame has to travel further, plus scavanging exhaust from cylinder is better with smaller bore.. Generally ....
A bigger bore will unshroud valves also.But forced induction this isn't an issue....
 
#10 ·
Freshmeat said:
A few notes:

Racer- there is no problem going 4.185 with the block if that's what he wants to do. Dart doesn't charge $2500 for weak blocks. I do understand what you mean about leaving more meat, but I also know that high RPMs hurt long rods and that Dart blocks are damn near bulletproof.
I actually meant leave more meat in it, so that it has something left for a future routine rebuild, or a piston failure that scuffed the bore.
 
#11 ·
Racer said:
I actually meant leave more meat in it, so that it has something left for a future routine rebuild, or a piston failure that scuffed the bore.
Understood.

EBXR- I understand what you're saying, now- forgot you folks are Aussies. Up here in America, a set of forged aluminum pistons only runs between $500-800(USD). I'm not familiar with people having pistons custom-notched... I guess that's because up here, we have everything more readily available.

I'll be talking to you more about your turbo ideas in the future... I'm thinking about halting the engine build for my wagon, getting it reliable and installing the air ride and nicer wheels, then calling it complete.

But then, I'll have this extra 351W laying around with nothing to do... time to find a Mustang with a shot motor! :priest:
 
#12 ·
What sort of HP and TQ levels do you guys think will be possible with this engine, bearing in mind it is for a street car, which means that although it is not really a daily driver, it still has to maintain drivability.

I have not contacted any cam manufacturers yet to ask for recommendations, what sort of questions should I be asking of them and what sorts of general descriptions should I be giving to them for street driving (although spirited at times) and maintaining enough drivability to be happy still.

The same goes for talking to engine builders, I am now seeking quotes from three engine buillders and want to make sure I am asking the right questions and giving smart criteria to them for what I might need for quick street car that weights approx 1700kg that I want to do 11 sec 1/4 at least, it must be still retain a good level of drivability, although I do want a rumbly deep sounding very powerful V8!!! Also how can I confirm that what they tell me is good advice and not just what is easy or puts most money in their pockets?

Gear box (T56, TKO, or is T5 ok) driveshaft and diff/axles/centre/ratio what recommendations? :hy:
 
#13 ·
For good all round I'd say 2031 or the SVO F303 or the std cam with 1.72 rockers...
All will make around 400 rwhp and over 800 nm tq..Hard to measure on chassis dyno..As its ealy a calculatiom...
Heaps of guys in the States have made over 500 rwhp with std cam..Diffrent dyno's there though, they don't load engine up the same..
T5 just cuts it on n/a V8! Having said that I drove mine for some time with 280 rwkw..BUT I took it "real" easy....
T5/6 or TKO...Is the way to go... Oh and twin plate clutch...
 
#14 ·
He's right- keep your stock cam or close to stock and run a 1.7:1 roller rocker. Either steel or aluminum, it's your choice- but the aluminum are three times the price.

For the transmission, maybe be saving up for a T-56 or TKO, but run the T-5 until it gives out. I'd highly recommend a Redline style transmission fluid, though- it'll make a world of difference. Twin plate clutch, just like the man said.

For gears, I'd say don't go over a 3.55:1 ratio. That'll help the engine rev a little better without making it obnoxious.

Do you have access to Edelbrock parts in Australia? (I'm obsessed with Edelbrock ever since I realized how great the products are.) If you can, get their RPM Power Package. It's all designed to work together, so it'll be your best performance per dollar. It takes the guessing out of matching up your parts.

See what the shops tell you, then post it up here and we'll tell you if they're taking care of you or screwing you.
 
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