had a few questions.. im going to be doing a cam, something similar to the 847 and i know you have to bring those things to around 6.4k. i was wondering if i just did a stock rebuild would the motor be able to handle WOT to 6.4k daily?? i say daily because i tend to run into quite a bit of races on my commute.

what would you guys recommend as far as the bottom end goes??

Jeremy

 

It all depends on how much money you want to spend on it.

 

It is not wise to run that kind of RPM on a stock bottom end. Eventually you will have problems as it is not designed to work that way. At a minimum you should change rod bolts and maybe open up the rods a bit to have better clearances. Of course new bearings are a must as rebalancing is as well.

Not only are you looking at the bottom end but alot of work has to be done up top as well. New springs and hardware will be required, as well as a quality valve job and some port work to accomodate the need of that cam. That cam is too large to be supported on a stock head and successfully run at that RPM.

 

i should have given more info on my plans. so right now im a student at wyotech and im finishing my core up right now. for the next 3 months ill be in hppt(high performance power train) building the motor. ill have around 2k or so to go straight to the motor.

I have an extra set of 643(think thats the casting number) heads which ill be porting in class.

I bought some parts whenever i had extra money. this is what i have so far (not much yet)

mcleod 7500 clutch disc w/ lt4 PP
gasket kit(head, exhaust, intake etc)
All necessary fluids.

wtb:
918 springs, chromoly PR's, ls7 lifters, 1.6rr, guideplates.
847 cam, stock replacment timing chain.

unsure as what to buy for the bottom end just yet still looking for some good suggestions..can anyone shoot me in the right direction?

thanks ahead of time for any help.

jeremy

 

The weak link in the bottom end can be addressed by heeding the advice I gave you earlier. The LT1 has very tight bearing tolerances and weka rod bolts which result in bearing failure at high to moderate RPMS. Simply changing the rod bolts will help out alot.

Thats all good so long as everything checks out good to begin with. You will find it cheaper to buy a new rotating assembly than to recondition the ones you have should they be out of round or whatever the case.

The 847 is a heavy lunger, meaning it needs deep RPMs to get going and run they way it is designed. To get there you will need gears and if auto a stall. As I said earlier port work is necessary as well. The 643 castings you mentioned are not favorable for porting.

It sounds like an extreme budget build to me, my best advice would be to invest into great machining, get your tolerances exact and then put it together with whatever you have. The cam isn't going to require anything more than extra air and of course addressing the rod bolt issue.

 

thank you for the info, i was doing some searching and found this.


http://store.summitracing.com/partde...0&autoview=sku

has anyone used this kit before and had any luck??

 

If you haven't bought anything yet DO NOT BUY ANYTHING! Wait until you get it back from the machine shop you never know what you are going to have to buy!

 

aww very true thanks for the advice

 

From what i have been searching it seems the 643 castings are better for porting because you have a little more meat that can be taken off. just seeing if someone could clarify that for me

 

i thought 374 and 643 are desired for porting with the 561s being the ones with less meat

 

When they changed head designs they took aluminum out of the head to make it lighter. It is approximately 2 lbs less material out of the heads. The earlier heads 374 had the most meat on them and were the heads that had the best potential to port. The later heads were lighter and actually flowed better as they are, but had less meat in the porting areas. If I am not mistaken the 643's will work, just not as much meat on the bone. It also depends on the port job you are looking to accomplish.

 

847 is an antique cam design. You need to forget ALL your plans, and look at what the best builders now are doing.

Short form:
Fully forged rotating assembly, spec'ed as light and strong as possible to spin to 7k+. (unless you're willing to do aftermarket electronics, the stock PCM runs out right after that)
Expect 2k-3.5k on the rotating assembly alone.

Get someone who really knows porting to prevent you from just hogging it out; you'll have a motor that will take forever to get to the revs and be worthless at anything except WOT if you do that. low lift and mid lift flow is at least as critical as max flow.

Consider larger valves. Expect big bucks on springs. 918 is not the be-all, end-all by any means. Consider shaft rockers, and definitrely invest in lifter that can handle the revs.

Figure 2 -5 k on the top end.

2k is far too small a budget, so reconsider the whole plan. Do a stock plus a little rebuild, use decent pistons, a very mild cam, good rod bolts, and good lifter, very very mild porting on the head, keep the revs down, and hit it with a 100 shot at the track... and it'll last a WHOLE lot longer than trying to spin it to the moon. It's often said, for good reason, the HP doesn't kill a motor but that revs do. It'll also be a whole lot more street friendly. That kit looks like a decent start, still need ARP rod bolts.

Lose the shorty headers in any case, you need long tubes to make power. Oh, add 1300, the only ones worth using on the big power build you mention in your post is the Kooks with the 1 7/8 primary and 3.5 Ypipe. On a mild build, you can use ANY long tube header; they all make similar power gains over shorties. You can go uncoated Hooker LTs for around 300 bucks.

And FWIW... unless you can afford to replace the 10 bolt rear, take it easy with the clutch dumps. One solid hook on sticky tires can easily kill a 10 bolt.

 

While I do not fully disagree with your post I don't think that is what the OP is after.

FWIW you can get a fully forged RA for under 2k, that includes balancing. If he were also looking for top dollar products then he could also do a H/C/I package for less using one of the more favorable porters and still have alot less into it.

The reason I don't fully disagree with your post is because I have well over 12k into my shortblock, but thats what I am after the best quality parts I can afford and standing up to some serious Horsepower and extreme RPM's.

Not everyone is out to build the fastest street/strip car on the planet. If you figure he uses an 847 and home ports his stock heads he is looking at no more than 380-400 rwhp, and thats if his heads flow in the 260 cfm range when done. I actually expect it to be in the 360 rwhp range given his mods etc. which by all means is still respectable and not out of reach for alot of his stock bottom end parts, Assuming most are good for 450 hp.

I don't care for the cam choice either especially given its a DD, or highly driven car. I personally think that the CC 465 or CC 468 are ofetn overlooked because they are not the bottom of the page cams. They would both maintain streetability, decent fuel mileage and the 465 makes HUGE torque spins relatively low and carries that torque with it across the board. It also works well with no port or mildly ported heads, and improves with port as any cam would. You could call it a custom cam by switching the LSA to 110 and then you would be no different than many of the other porters or custom cam guys abound as they all choose from a catalogue and change the LSA. I know that is gonna ruffle some feathers but show me a custom cam and I will show you an off the shelf grind very similar lol

 

Some shops actually design lobes themselves and pay to keep them proprietary.
LSA is the product of other variables not something that is independantly adjustable. How you go about adjusting it has a big impact on performance and people do get it wrong.

There is a LOT going on with a lobe and two cams with the same durations and lifts do NOT have to be all that similar.

 

That's fair and accurate. If you notice I didn't mention any names or point fingers