Mark IV Bowtie Main Caps

I am putting together a blown alky 540 that will be used mostly for bracket racing at 20 lbs or less boost. I would like to know what everyones thoughts are on the strength of the stock main caps and if I should be looking at billet replacements.

 

Milodon

 

I've run billet caps and factory caps, spayed and straight bolts and my thought on the chevy's is the most important thing is to have good tight cap registers in the block to help keep the caps from walking.

i've also found that having a very high quality crank helps also by not flexing and knocking the caps out of alignment

 

Main Caps

I used to run a Merlin III block (similar to the Bowtie IMO) and I ran with just the cast straight caps with no real problems. We ran 27PSI boost. It seems to me that if your not going to spin the engine real high, I kept it around 7800RPM, the regular cast caps should be OK. Bearing always looked perfect, just make sure your are keeping an eye on things regularly (should be anyways). I agree with making sure your caps are registered well, good and straight with straight main bores.

Sounds like you will be fine IMO

Corey

 

What kind of times did you run and how heavy was the car? Clutch or converter?

 

I am building a similar engine BBC 523ci with Bowtie block standard caps. Would a main girdle help any or just run it like it is? Thanks

 

steel caps

i use to run mark IV marine siamese block, I kept shrinking the caps, with 25# of boost with a 8-71.
It would spin a main bearing.
I think i have a set of steel caps in the shop if you are interested.

 

main caps

We run a stock block 468, short fill, stock 4 bolt caps with studs with a Mooneyham 10-71 on carbed E85, around 22lbs boost, rpms are 7500-7700, a few times hit the limiter at 8000, had some early tuning issues running lean, popped a panel and bent 1 pin. No problems with the mains whatsoever, bearings came out looking real good, no sign of walk on the caps either. The stock 4 bolt caps with studs hold up well in our nitrous motors as well...big loads of nitrous, but we keep rpm-s under 8000 in those as well.

 

Do those botie blocks have dowel pins? I'd pin the mains. We ran a concrete filled .190 over 69 school bus 427 block with 13:1 and #43 boost, it pulled the head studs out and bent all the wrist pins mains looked perfect. I probably should have known not to put a alky injection 1471hh on a single stage nitrous type bbc but it went 7.08 194 on the third pass in my doorslammer back in the 90's it was pretty cool up here in alaska and it was what I had



I think the iron caps would be fine esp. if they're tight in the registers annd or dowel pinned

 

Most steel aftermarket caps that I have found are for conversion to 4 bolt from 2 bolt and most are splayed. Milodon may make replacement caps but their site can be a little confusing. They also do not make a rear main cap as far as I know. Program engineering has everything but they are pricey. Howards makes a rear main, but I believe all of the rest of the caps are conversion caps.

 

No dowel pins. I have 2 tall deck bowtie blocks and one was a twin turbo boat motor that made 1100 hp and no problems with the mains. I have worked on engines that had dowels and still had fretting on the parting surfaces. I am retired and have to watch the budget and would like to use what I already have without breaking the bank. I do have a Merlin block with billet main caps but it is dry sump only and there is no room for the pump due to the narrow frame rails on my dragster.

 

Caps

We were running low 8's @ around 165MPH but we had lots of tuning, car was right around the 3000lb mark with a dual disc clutch and Lenco.

Corey

 

Have run both styles on Bowtie blocks. When using stock caps the block was filled. The racer I sold it to broke a trans, overrevved and broke a rod, and caps and block were the only salvageable thing left. The other one has billet caps on all even the rear. Has ARP studs and always have rotating assembly balanced. It has a 14-71 SSI. Have never had any main/crank issues (now blown head gaskets and melted pistons--that is another deal lol). This is tractor pull (mini) application but still BBC. Just my experience. JW