blown 83

iTrader: (1)

I am finally ready to start putting together the 8-71 blown 355 that I have gradully over the last year and a half gathering parts for.
I measured all my main clearances about 5 times each just to be sure. I have a fairly steady hand with a micrometer and snap guage, and took my time so I am sure that these clearances have been read correctly.
I came up with 1) .0025
2) .0024
3) .0024
4) .0023
5) .0037
The crank is a Eagle 4340 forged piece and the bearings are standard size clevite 77 H-series.
I believe the clearances on #1 trough #4 are fine but #5 bothers me.
So I guess my question is
1) what is a good clearance to shoot for on the mains when building a roots blown small block.
2) I am conserned about #5. It is the trust bearing and I have heard that some people run it about .0005 larger than #1-#4 but .0012 larger than of my other bearings seems too much.

This is a fairly roudy 355, I will give a few more specifics just in case it helps in answering.

it is a 350 4bolt main block bored .030.
the eagle 4340 crank I mentioned above
clevite 77 H-series bearing on everything
eagle 4340 H-beam rods
JE 24cc dish pistons
BDS designed/Isky ground solid roller cam specs are
(266/276@.050 .656/.672 lift with 1.6 rocker on 110 lobe sep)
1.6 ratio shaft mounted roller rockers
AFR 210 heads w/2.08&1.60 valves
Weiand 8-71 blower
2 650 holley double pumpers
every thing is studded and bottem end is balanced
compression comes out to just under 8.0:1

Hope someone out there who builds blown motors a little more than me can help me out. I have shelfs full of parts but I cannot go much further on assy of this motor until I get this worked out.

on another note I just wanted to complement you guys on the great tech that comes out of this column. The stuff some of you guys put together is nothing short of awsome.

thanks again

Kingtal0n

My Opinion:
Bearing Clearance...
<b>eagle 4340 H-beam rods </b>
Those are heavy...
<b>266/276@.050 </b>
And thats alot of High RPM potential
--
You want things a little looser then, a real tight motor will suck up a bunch of power turning it over at high rpms...
but too loose... and it will bang around... But:
You have boost. Boost will soften the blow up top.
I would just leave it. What would you do to change it? Buy a different bearing for that one main? That might not be conduvice to long engine life.
Thats just my opinion, and somone may have a different answer.

JAY4SPEED

Whew thats a tough call, GM factory specs are:

Production #1 = .0008-.0020
Production #2, #3, #4 = .0011-.0020
Production #5 = .0017-.0035

Service #1 = .0010-.0015
Service #2, #3, #4 = .0010-.0025
Service #5 = .0025-.0035

Crank Endplay {Thrust} = .0010-.0070

What bothers me about this is that the #5 main is the first to get oil from the pump. If the bearing clearance is too big there it may drop oil pressure to the rest of the engine. My suggestion is to call your machine shop if they build race engines and see what they recomend. Other than they you can try to select fit a bearing. I know most machines shops do this. They have a big box of bearings and try them one by one untill they get the spec they needed. Any production bearing will have varances in clearance. I do know that .001 undersize bearings exist {undersize meaning bearing inner diameter}. There was a problem with mid '90s pickups at the dealership that had a knock at startup and the fix was to install .001 undersize main bearings. They were made by AC Delco but were for 1 piece rear main seal blocks. May be worth investigating but also may put you on the tight side of the spec. I'd try the select fit route but I dont know how your going to get your hands on a big box of #5 mains.

Wish you the best of lock and please let me know how things turn out, I was planning on the exact same set up on a 400 with a 8-71, but now may be going with a stroked LS1 motor. I'm interested in what numbers your turn out when you get it running. Good Luck!

blown 83

iTrader: (1)

thanks for the feedback,

I called the machine shop that I had do all my balancing, machining, and they also build race engines. I told them the situation and they said that the clearances on #1 through #4 were good and that they like to see the #5 about .001 larger than the other 4 main journals.

These are the clearances they said were good for what I am doing, now for a every day car the same clearances may not be correct. They are a H-series bearing, which is more of a race bearing.

To Jay4speed, yes there are several different bearing sizes to help you achieve a certain clearance you are shooting for. For more info on that go to the Clevite 77 web site (not real sure what it is right now), it tells what sizes are offered.

The shop I had do my balancing and machining was AMS Racing out of Louisiana, They did good work and do most anything askied for a good price. I have been stationed in italy for almsot 5 years and it is hard somtimes to get someone to work with you on the phone, but they really helped me out. I definitaly recomend them if you are in their area.

Also if any one has been doing engines similar to this and have some good advice, I'm all ears.

And about the H-beam rods being heavy, I will get back with you. I have a chart that the machine shop gave me that has all the weights in grams. I will get that chart tonight and let you know what they weigh.

thanks again

89ProchargedROC

Ya, they are heavy....but they hold up to a ton of abuse as long as you dont plan to rev the **** out of them

And even then they will last a long time before breaking. There is a guy over by cz28 that has a lot of experience with cup racing motors that all use carillo rods and all the foreign h-beam rods are just copies of that. He even said without changing them to the honda journal to make them lighter....they will still last quite a few races before they bust one and they are CONSTANTLY spinning 8000-9000rpm

And honestly, they aren't TOOO much heavier than a comparable i-beam rod that will hold up to the power level and be in the same price range. I like to compare the Lunati Pro-Mod rods to the carillo clones because they are just as good as one another but the lunati rod comes with a better rod bolt already (arp 220,000psi) where most of the carillo cloners only come with the medium bolt (arp 190,000psi). So you kinda have to add in the extra $80 for the better bolts and you come out pretty close

just my humble opinion

Kingtal0n

my eagle H-beams were all 648 grams a piece.