Building bracket race N/A motor... What stroke????

[gmsux]

Lot of different opinions on this subject with good points on both sides. I'm building up a 351 dart block and need to choose between the 3.75" or 4.00" stroke crank. Tell me which one is better and why! No rules for me to worry about and I'm shooting for 13.5:1cr, N/A use only.

Part two... Whose cylinder head would you use and why??

[racer7088]

4 inch because it slow everything down and will make your stuff last. Your NA so you don't need crazy piston height.

[racer7088]

AFR 205 if your on a budget. It can make around 625 as is. from there you can go up in power but the cost starts climbing faster.

[TEA93]

I WOULD CALL TOTAL ENGINE AIRFLOW IN BOWLING GREEN KY. HE HAS ALOT OF EXPERIENCE W/ ALL THE AVALIBLE HEADS HE WILL POINT YOU IN THE RIGHT DIRECTION. ASK FOR BRIAN

[racer7088]

GMSux,

It depends on how much money you want to spend and how fast you need to go as to what head you will go with. Heads that flow over 325 will take you farther than the AFR 205 but again will go up exponentially in price. The Dart block has a little longer cylinders so you could even do the 4.100 crank if you wanted to make a little more power and keep it even lower. You could do Yates stuff and have a 1000 HP engine if you really have the cash. I've helped dyno some 1000 HP 434 Chevy stuff but again you're talking 35,000 dollars but it's still radically cheaper than doing it with 358 inches and 10,000 RPM like they did in Truck. You could have 625 HP for under 8,000 probably with the AFRS. The Victor will get you to 850 HP or a little more for less than the Yates stuff but you will need shaft rockers etc.

The cubes you choose will set up your rpm so don't go too small or you'll end up HAVING to spend some crazy money on valvetrain. Wear piles up FAST when you turn the rpm up.

[gmsux]

Tks for the feedback everyone!

As far as a 4" stroke goes, how well do they tend to balance internally? Does it take a lot of Mallory???

I know piston speed will increase significantly with the 4" vs 3.75" stroke, will this require a bigger head such as the TFSR?? A blended and polished TFSR will outlfow an AFR 205 I believe.

What kind of RPM range could I expect out of a 13.5:1 408 with large solid roller and 320cfm heads??

I don't have mega bucks, so I have been leaning towards the TFSR's which can be bought quite reasonable and blended and poslished myself since I have experience in doing this. I might even be able to do this with a flowbench to improve consistency.

With the current engine in my car it ran a best this season of 10.77 @ 125.80mph. I'd like to run 10.00 @13X.XX N/A. Not interested in all the gear to run 9's. Car weighs 3000lbs w/me in it.

[racer7088]

The piston speed that the engine will nose over at is more dependent on your heads than the stroke. The stroke will just slow RPM for reliability and you'll usually make a little more power since your inertial losses are lower at lower RPM. If you want more power though of course you can go with more cylinder head and you will again turn more RPM as you said but then you might be in the outer limits with the 3.500 or 3.750 etc., whereas the 400+ inch engine will keep you in more reliable RPM ranges.

With the 408 or 418 you'd probably peak by 6500-7000 depending on intake and cam but not a lot more with only a 320 cfm head. You'd already be in the mid nines with an engine like this at 3000 lbs. I don't think the TFSRs are that good for that type of an engine but wouldn't be horrible. They are really big in cross section and the ports are too low for the valve angle they use. I'd still stay with something like the AFR 205 and be able to use cheaper headers etc. Also the TEA Hi-Port sounds very nice since I think they still make headers for that head too. A 1 7/8 header would be nice.

[racer7088]

With a lighter bobweight you can easily internally balance a 408 whereas it gets very tricky on the smaller 347 type deals that have tiny counterweights due to the low decks. The amount of heavy metal required depends on how heavy your rods and pistons and stuff is which is figured into your bobweight. The lighter this is the easier it will be to go neutral. Custom cranks can be ordered to go neutral at a certain bobweight or lighter.

[gmsux]

Originally posted by racer7088
With a lighter bobweight you can easily internally balance a 408 whereas it gets very tricky on the smaller 347 type deals that have tiny counterweights due to the low decks. The amount of heavy metal required depends on how heavy your rods and pistons and stuff is which is figured into your bobweight. The lighter this is the easier it will be to go neutral. Custom cranks can be ordered to go neutral at a certain bobweight or lighter.

Ok, is it worthwhile to internally balance a 408W then??

[gmsux]

Originally posted by racer7088
The piston speed that the engine will nose over at is more dependent on your heads than the stroke. The stroke will just slow RPM for reliability and you'll usually make a little more power since your inertial losses are lower at lower RPM. If you want more power though of course you can go with more cylinder head and you will again turn more RPM as you said but then you might be in the outer limits with the 3.500 or 3.750 etc., whereas the 400+ inch engine will keep you in more reliable RPM ranges.

Can you elaborate on how more stroke decreases rpm range? Keeping the engine more reliable is very important to me. I would like to have it so that it did not need freshining for about 3-5 seasons. Valvespring changes every season don't bother me.

With the 408 or 418 you'd probably peak by 6500-7000 depending on intake and cam but not a lot more with only a 320 cfm head. You'd already be in the mid nines with an engine like this at 3000 lbs. I don't think the TFSRs are that good for that type of an engine but wouldn't be horrible. They are really big in cross section and the ports are too low for the valve angle they use. I'd still stay with something like the AFR 205 and be able to use cheaper headers etc. Also the TEA Hi-Port sounds very nice since I think they still make headers for that head too. A 1 7/8 header would be nice.

Hmm, you keep mentioning 205's, but what about the 225's? I read Brian Tooley's response about how the lower lift #'s are not as good as the 205's. Is this why you say to use the 205's? The Highports seem good too, but they cost more than the 205's do when you buy them ported. Having 9sec. power is no problem. just de-tune it a bit to run 10.0001 :D

[racer7088]

GMSux,

I don't know if it's that worth while to internally balance one at 7000 rpm and down but it wouldn't hurt. Above that I probably would since it will increase your reliability. The 351 even with the big 2.75 or 3.00 mains is a pretty stiff crank so they don't bend as much as some smaller cranks do. If you have the smaller 302 mains I probably would internally balance it.

I think the AFR 205s aree just a very good price point right now. They flow a little over 300 for real and would make over 600 with 13 to 1 and a good intake and cam easy but yet not spin to the moon. Something like the Victor head or TEA's ported Hi-Port would flow more and make more power and turn more rpm with everything else the same. With the AFR race ready SBC 227s I've seen 650 hp with similar specs. They have a longer port so they're not much different than the Ford 205s.

[racer7088]

I think the 225s would probably make even a little more power but you need custom headers so if you already doing that they would work too I think. The 205s are a very good deal though and I haven't seen the 225s in action yet.

[gmsux]

Thanks for the feedback Racer 7088, you have been very helpful! I'll be spending some more time working out the details...

:D

[Dave Bandt]

gmsux,

I have a set of Victor Sr's for sale that went 300 CFM on the intake @ 0.500" and 370 @ 0.800. The combo was good for an 8.65 @ 161 on an 11.9:1 motor with a 400 shot. It made 700HP on motor and 980HP on a 250 shot and i have the dyno sheets to prove it. I am upgrading to a set of BF 202's this winter so i'll be selling my cam, intake, heads, and headers as a package if you are interested....or i can possibly split them up. Email me at dbandt@evtac.com if you are interested and i'll give you more details.

Dave
aka Snowstang