For street/strip use of a small block 400ci, what would be the biggest valve size you can go with?? People tell me that bigger valves, such as 2.08 are not that great for the street, and people tell me its good because your motor breaths better. What exactly happens when you go with too large of a valve size? I figure, a 396 big block motor comes with stock 2.07 intake valves and has almost the same stroke and piston size as my small block 400, and they are torque monsters. Im going to be running 6 inch rods also, so the rod ratio will be close too. I have a set of Brodix heads with 2.08 intake valves, should I use them on my 400, or is that too much? Any info will help, thanx.
11-13-2002 11:15 AM
I think that you would also need to take camshaft specs into consideration when talking about your valves. After all, it doesn't matter how big your valves are if the cam isn't holding them open for long enough.
11-13-2002 12:11 PM
[quote] RULE #1 THERE IS NO REPLACEMENT FOR DISPLACEMENT!!! <hr></blockquote>
Can't remember who told me that rule :confused: But I believ in it srongly :D :D :D
11-13-2002 07:26 PM
rule no.2 Ain't no substitute for cubic inches!
11-13-2002 07:59 PM
Rule no. 3: there's no prize for no size...just kidding
11-13-2002 09:07 PM
lol, Is that the same for valves though????? What cam should I use?
11-13-2002 11:51 PM
I have never heard of large valves hurting an engine... as long as you you have a cam that lifts them enough and long enough it should be better... I mean any engine I have seen with opened up vavles or larger vavle head run alot better. I mean that is why you need a decent bore in an engine... so you can get decent vavles in them
11-14-2002 12:13 AM
You will have to be very careful with your cooling situation on these motors.
If you have the blocked bored especially. The 2 center cylinders are sistered together(share the same center cylinder wall), any boring and little too much heat will crack out the center cyl. wall...then you'll end up with a 400ci anchor.
Some people love these motors, personally I wouldn't have one shoved up my ***** if I had enough room for a whole truckload.
I would probably save my cash and go with either a stroker motor or step up to a Bigblock. Also your parts availability is limited to pretty much this motor only.
Like I said that is just me though...
11-14-2002 01:49 AM
Going to test that rule about overboring a 400. Took mine to 406 for my 53 chev. The 400 ran fine before boring, wanted the extra cubic inches and torque to offset the weight of the 53 belair. Running a 4 core rad. and a seperate trans cooler. Plenty of cooling fans and a fan shroud. Will know more this next summer.
11-14-2002 07:21 AM
I would suggest that you get a hold of some of the cam manufacturers to get a recommendation for cams. There are a lot of different variables and what has worked for one person very well may preform like crap for the next person.
11-14-2002 09:37 AM
I got this motor off of an old guy that never went over 50 mph ever. So the motor is in excellent shape, it still has the cross hatchings in it from the factory bore. Im not too worried about cooling problems because it will be a standard bore, and I havn't had any problems with it yet, I used it a for the summer in my camaro.
I don't know where these people are coming with when they say that too big of valves are not good, They said with 2.08 valves, my motor won't start running well untill 4000rpm, but I guess they don't know what they are talking about.
Are those Desktop Dyno programs accurate??? I was thinking of matching up a cam using that program.
11-14-2002 10:47 AM
Well, it's a good place to start, but I wouldn't take something from one of those as the final word. Like I said, check with a cam manufacturer. I'm sure that they would be able to match a cam up to your current specs or the specs you want.
11-14-2002 11:07 AM
The bigger valves wont effect where your engine makes power,but it might hurt performance all over.When putting larger valves into your heads you need to make sure you have suficient clearance around the valve inside the combustion chamber,as well as proper clearance between the edge of the valve and the cylinder wall if the camshaft is really big.Bigblock combustion chambers are wider thn smallblock chambers which gives the valve more room to breathe,and the valve are canted toward the middle of the chamber so that they open away from the cylinder wall,and any 396 built for performance will benifit from having the top of the cylinder bore relieved in the area of the intake valve.In the case of the smallblock,most stok production heads dont have enuff material to support installing the bigger vlaves because if you relieve the chamber as needed you will cause the head to become thin.On many small aftermarket heads you wont have enuff room for a bigger valve,but you usually can have the chamber cut to clear the valve.400's have a big bore so you might be able to keep the reshaped chamber matched to the size of the bore.After installing the bigger valves,you need to blend the bottom seat angle into the bowl area as well.any time you can put bigger valves in any chevy engine and do the job right,the engine will make more power all over the rpm range and more torque as well.In all chevy engines,both bigblock and smallblock,the intake valve is a bottle neck,and as long as you are putting the bigger valve in right,the engine will kep making more power.Good luck.
11-14-2002 01:18 PM
Thanx for all the info. Im not actually putting larger valves in my heads, I have a set of Brodix aluminum heads that already have the 2.08, 1.60 valves that I am putting on my 400. Would I benefit If I had the top the cylinder bore relieved around the intake valves for more clearance,(like the 396 you explained), or would I be fine with the way it is?
Thank you for clearing up that bigger valves are better. I was all confused for a little bit there.