SBC 400 verses 383 question

[gretchen/jason]

So i picked up a SBC 400 block for 100$ , still has the stock bore size 4.00 . Although its a 2 bolt main i figured id have the machine shop make it a 4 bolt main . I was thinking of doing a 383 stroker but i figured 400 CI would be better then 383 .

 

Id like to know if a 383 would have the same /more /or less torque then a SBC 400. Ive noticed that heads for a 350 are the same for a 400 sbc . Is it just bore size that makes it a 400 CI block or stroke ?

 

Like i said i just figured bigger cubes means more power , then since i have a supercharged 350 and since it fits of course on a 400 i figured a supercharged 400 would be way way better then a 383 .

 

Im sure i know the answere to my own question im more looking for pros and cons of a sbc 400 verses a 383 stroker

 

Jason

[dr_hunt]

The stock bore size on a 400 is 4.125 inches. The stock stroke is 3.75 inches. The good casting # for the 2 bolt main ends in 509. Converting it to 4 bolt main is a good idea if your planning on making more than 500HP IMO.

 

IMO there are no cons to a 400 vs a 383 if you are using the same parts. Both take good heads to realize the potential of the larger cubes.

 

The 400 can use a larger cam and will make more tq and consequently more hp.

 

For most street builds opt for the 5.7 or 6 inch long I beam/hbeam rods versus the stock 5.565 rods unless you happen find a set of new/used eagle 5.565 h beam rods on Ebay, which I have seen a time or two.

 

Remember it all comes down to parts selection to make it all work properly and spend most of your money on heads followed by rods IMO.

[gretchen/jason]

I did find a crank that uses 5.7 inch long conect rods . Also found one with 5.565 but couldnt find any rods for that anyplace so it seems id use the 5.7 rods .

As for heads i have a set that i had reworked . I forget the measurment of watter presure the guy used but it was set for my altitude 6,000 ft above sea level . The head flowed 250 cfm with a .490 lift with a 1.94 intake valve and 230 cfm same lift with a 1.50 exhaust valve .

 

Ive been told that these are good numbers not sure im not so up to date on these things but the cam i was going to get had a .500 intake lift and a .530 exhaust lift due to the supercharger . I was told i needed to worry about exhaust flow not intake flow so much .

 

Ill check the casting numbers but i figured if im hitting 12.9 seconds in the 1/4 mile with 300 or so wheel horses then i shouldnt need to go over 500 horses . Or at least 12.9 is what my G Tech meeter is telling me " The ones in the catalog is what i bought " They are somewhat accurate id figure maybe a 13.1 1/4 mile . Heck last car i owned pulled 17.0 in the 1/4 130 crank horses in a 3,300 lb car . With a bit of NOS of course .

 

Jason

[280zwitha383]

Best of luck to you. I really like it that you're diving into the deep end already without knowing a whole lot about everything (insert smiley with large cahonas here).You are REALLY going to have to do your homework because you're REALLY going to have to stay on top of this s/c whatever and if you don't already have someone to mentor you locally then I would suggest finding someone.

 

As far as the cranks, unless I'm missing something 400 cranks should be the same regardelss of rods. It should be the pistons that have the wrist pins make up the difference.

[grumpyvette]

DR HUNT gave you some good info, but ID also point out that 400 blocks REQUIRE the heads are drilled for extra steam holes in the heads (your local machine shop can do this)

and ID also point out that the COMPRESSION RATIO, cam sellected and rear gearing must match to get the most from the combo!

your 400s larger bore helps breathing potential and larger bore surface area helps tq. the added displacement helps also, over a 383.

now I don,t know the intended use but if your intent is to maximize the power curve (mostly race vs street use)youll need at least a 10:1-10.5:1 cpr and a cam in the 230-245 at .050 intake durration range and a drive train set up to operate in the 3500rpm-6400rpm band (usually a manual trans or auto with a 3500 rpm stall converter and 3.73-4.11 rear gear

just some basic ideas

 

http://airflowresearch.com/articles/article074/A-P1.htm

 

http://airflowresearch.com/articles/article093/A-P1.htm

[gretchen/jason]

Ah yes i was told about the " steam holes" I checked the heads i have and they allready have the steam holes in them lucky me i guess .

 

My intended use is street /strip . I do drive it to work everyday also and i dont bother to take it on the highway . As of now i have a stall converter with a 3-3,300 rpm stall . When i had the stock gears in my z i think they were 3.54 something like that , the rpms would rev to about 3 grand before the trans reall started to grab .

 

I now have 4.11 gears for the 1/4 mile setup and the rpms go to about oh 2,800 before the trans starts to really grab.

 

I also agree with Drhunt . I have a friend who is a ex Indy car cheif mechanic he worked with now lets see if i spell it rite Jaque Lazier and he knows a few things about engines and such . He has helped me out a little bit . And thanks to the Hybrid z members for theire advice also .

 

Jason

[dr_hunt]

According to Grumpy Jenkins and GM steam pockes would develop in street engines that never saw over 4000 rpm, which is what Grumpy is referring to. I drilled the holes on some 882 heads back in the 70's and when I took it apart to rebuild it the holes were plugged with the typical rust that develops. Since then I never put them in and have logged over 225K street miles with a 406 and sportsman 2 heads without a problem. Nowadays I hardly even stay under 4K rpm.

 

I'm not sure if that's a fact or myth, but in my experience that's a myth, and I think that is attributed to the high efficiency aluminum radiators and high flow water pumps of today that we didn't have back then.

 

BTW Mr. Lazier is a well respected knowledgeable mechanic that is widely known worldwide. That's great if he can help you.

[jt1]

The head flowed 250 cfm with a .490 lift with a 1.94 intake valve and 230 cfm same lift with a 1.50 exhaust valve .

 

That's pretty impressive. What kind of work has been done to them?

 

John

[gretchen/jason]

For jt1

 

The heads had lets say a major port job done to them just a 3 angle valve job is all on the valves but i got valves with "skinny " stems to for more flow . I wish i had a way to show how the guy ported the runners and such but he calls it the Waterfall affect . Something he showed me against a stock head , and told me about how the air slams against the walls of the runners .

 

He then grinds the piss out of them and kind of makes the air want to follow a pathe he created so itthe air flows in or our and kind of goes ofver a ledge like a waterfall towards the valve . in the case of the exhaust its backwards of the intake of course .

 

I watched him bench flow one head and he injects a colored powder into the air stream and watches how it flows through the runners and around the valves very cool i must say . if it looks as he called it " sloppy air flow" he grinds some more .

 

Took the guy 3 months to do it not bad for crap what did i pay 400$ for the port job , not including the springs and valves . He only installed springs with a .500 max lift i may go a bit stiffer not sure the cam i want to use only has a .490 lift should be good enough on a small block 400 .

 

Jason