I have a set of '77 351m heads out of a truck. I would like to spend some time and a little bit of money to make a good street head for my 400. How hard is it to port alittle at home? Gasket match maybe? I thought I read somewhere to leave the intake side alone. I know to match the springs with the cam, but do they make better guides and studs for the 400? Also what about valve size? Right now the 400 has a wieand intake, holley 4160 600cfm, cloytes double roller, Badger flat tops and a isky 256 supercam(might change to the xe256), headers and 2 1/4 duals with an h-pipe.

 

Don´t enlarge your valves , just polish and enlarge your exhaust bent ratio, that should do the trick, hey how did you match the springs with your cam? do you have any procedure ?

 

If you are looking for studs and guide plates the 351M/400 head use all the some stuff for a 351C, any machine shop shold be able to mill down the rocker mounts and put in studs, and again for rockers any 351C stud mounted rocker will work you will also need hardened push rods for use with guide plated and taller valve covers to clear roller rockers if you got with them. As for the port work the exhaust does need more work than the intake, but i would check over the intake side and remove any rought castings it might not help alot but it won't hurt you at all. The 351M/400 head is almost identical the the 351C 2V thats why you can use just about any valve train part from a Cleveland except pushrods. Looks like you might be dumping a lot of money in your heads might want to check into TMIs Aussi heads.
-Johnboy

 

I have done a set of heads for a 400 that turned out pretty well, except I did not go to flat top pistons to raise the CR. It was ten years ago and I didn't know where to get flat tops at the time.

I have ported quite a number of other heads, mostly SBC, so I know what to grind and what NOT to grind. It is just as important to know what NOT to grind as it is to know where you do need to grind.

These heads don't need much as compared to SBC heads. Chevy heads have sharp edges below the valve where the port makes its turn. These heads are cast with some radius at that point rather than sharp edges. For street use, the most important part of the ports on most any head are on the short side radius, meaning the part below the valve where the mixture must turn the sharpest and make a hard turn. If this area is SLIGHTLY rounded with no sharp edges, it will help greatly, especially at low valve lift, which is what you have with most street cams.

SOOooo..... take out any rough casting spots, but do not polish. Make sure that there are no sharp edges below the valve and smooth everything around the valve boss. Also match porting to the manifold doesn't accomplish alot, but it doesn't hurt anything either.

If you have never done much or any head porting, use a dremel with a small burr. It will take more time, but will keep you from grinding too much. Using a large burr on an air die grinder will take away material TOO fast for someone who has never done this before and will very likely result in a head that flows worse than it did originally.

As far as studs goes, Crane used to sell a stud kit for this engine that is easy to install and works quite well for street use. It allows you to have adjustable rocker arms. For economy and effectiveness, with this stud kit you can use Big Block Chevy rocker arms. This gives you a large selection and they are less expensive due to availability.

In my case I did not use flat top pistons, but milled the heads to the max which I think was .040 or .060. I am told that this results in 8.7 CR. This engine is using an RV Cam, 600 Holley and Edelbrock performer along with manifold dual exhaust and works pretty good. I keep thinking I need more CR, but I will probably leave it as is. It pulls my 5,000 + pound truck along pretty good with the 31's and 3.50 gears that I currently have on the truck.

Good luck,

 

OK, round off the exhast ports in the sharp radius, Keep the valves, knock off any sharp edges on the intake side, and look for clevland valve train. The bbc rockers have a 1.73 ratio? Where can I get a taller valve cover if I need it to clear the rockers? as for matching the springs, when you buy your cam, the manufacturer recomends getting a valve spring to match the lift and ramp of your cam. Thought about aussie head, but what would that put my cr at?

 

The only Crane valve train conversion I have seen is #52655 and it uses 7/16 studs for the 351C not the 3/8 BBC the kit is $86.99, I would check the machine shop prices as I feel conveting to the standard studs is better and might not cost any more since the heads sound like they are going to the machine shop any way. Just my $.02
-Johnboy

 

using 7/16 sounds better than 3/8 anyway. I'll have to look at crane to see what the kit all includes. Thanks for the part no., it probly saved me alot of time.

 

Yes, the aussie heads will probably bring the compression up too far for running on pump gas.

Yes, the rocker ratio of the BBC rockers is 1.73, but as opposed to 1.76, if you improve the flow of the heads it will more than make up for the few thousandths loss in valve lift. At .500 inch valve lift with 1.76 ratio, 1.73 ratio rockers will only result in the loss of about .0085" of valve lift.

Anyway, I only used the BBC rockers for reasons of economy. You are not limited to using them. There are 1.76 rockers available.

 

I thought the 400 had 1.73 ratio, i'll have to look. Does it look like I can use the old rockers in the crane 52655-16 kit? Save some money for rollers later.

 

It does appear that the 400 has a 1.73:1 rocker ratio. Is there any room for improvement in the bowls? I can't say as if I've ever had the valves out of one of these heads myself.

 

You will not be able to reuse the pedital rockers with any form of adjustible valve train to my knowledge, but if you go with the Crane kit you can just install the heads as is and add the kit later on. I actually plan on going with that kit in the near future to try to eliminate a very slight lifter tap on my truck after it warms up that kinda stuff just drives me nuts.
-Johnboy

 

Yes, that's why I used the kit in the first place, so that I could adjust the valves to ensure that there was no valve train noise.

For some reason I was thinking that the 400 rockers were 1.76 ratio, but I could easily be mistaken about this.

Yes, there is a little room for improvement in the bowls, but not as much room for improvement as with an SBC head. These ports are cast with some curvature to them, unlike the SBC ports which have a few sharp, machined edges to break.

 

the oem rockers will fit with the 52655 kit, just not adjustable right?

 

Wrong! The OEM rockers are pedestal. The kit provides a stud so that you can use adjustable ball rockers. You also can use roller rockers as long as you have valve covers that will fit over them.

I noticed in the Summit catalog that one of the particular rocker arm offerings for the 335 engines was the exact same part number as that for a Big Block Chevy. The BBC rockers and ***** really are the most practical choice unless you're building a very serious engine in which case you will want to use roller rockers.

Don't bother with the roller tip rockers. It has been proven that the roller tip does not roll very well. It's all or nothing, either standard BBC rockers or roller rockers. Don't mess with the in betweens.

 

why waste any time, money or effort on post 75 heads? they have terrible un-improvable exhaust ports. just get a set of pre 75 castings to start on!