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Some Punk Kid
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I don't want this to be a "is a 2 bolt main alright?" thread. But I know a lot of you guys have experience with all these chevy 350's. I do not believe i am running a lot of horsepower on this motor but I still want to ask as I want as many opinions as possible. The machinist/engine builder swears that the stock bottom end is fine for my setup for what I am running and I know he has seen his share of 350's and he says if anything is gonna go its the front main whether it be 2 or 4 bolt. I was fully prepared to at least buy new connecting rods but he said stock rods WITH stock bolts is A OK for my motor. So here is the question that I am getting at will this engine run fine and strong for a long while. This is the engine as follows:
1970 2 bolt (300 horse block by the numbers)
stock re-grind crank 20 thou bearing undersize
stock con rods/bolts
speed pro forged alum 10.2 C/R pistons
comp cams 270H magnum hyd flat tappet. 224 @ 50 thou / 1.5 rocker
GM stocker heads 76cc no porting / comp cams double springs
Weiand Stealth manifold / Probably either the street avenger 570 or 670 carb -Im leaning towards the 670
Mallory HEI ignition

The cam operating range is 1800-5800 RPM. And that is what I planned on keeping the engine speed in.

Thats the setup. I also have another side question. What kind of ponies do you think will be coming out of this block? And will it hold up in that RPM range of 1800-5800? Thank you for any response
 

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When your making around 500 dyno proven horsepower, then I would worry about it, but as it stands your about 290 horses short as a rough estimate.
 

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I wouldn't say that it has to be "dyno proven horsepower" because the horses that run off the dyno are not any tamer. But 500hp seems to be a good level to switch at, sure some have gone alot higher, and some have had caps walk at 400hp but 500 seems a good rule of thumb. As for that cam and parts list- it shouldn't be a problem at all for a 2 bolt- unless you strap a 250 shot of nitrous on it.
 

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I said Dyno proven since it`s not very likely that one can put one together the same as someone who did so and tested it on a dyno and think`s they`ll get the same result. In just about all cases, they don`t tell the fine details of the build, they give the basics of the combination and that`s about it. We ran a 2 bolt 400 in the early 90`s that had 200cc dart II heads, forged dome pistons, a 240 duration flat tappet cam, with a 350 horse big shot nitrous plate, we never had any problems with the bottom end during the whole race season. This engine was never on a dyno and we didn`t have any magazine dyno results to compare it to, but we estimated it made 425 horses off the bottle. In the next race season we ran into a problem with 2 of the pistons, when the ignition was failing around 4000 rpm and the nitrous activated, it started popping out of the exhaust and cooked 2 pistons, but the bottom end looked fine.
 

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Hard to compare a 2 bolt 400 block as those caps are much wider and are much more stable in there registers at our shop we use a good 4 bolt for any engine over 400 horse and anything over 500 horse we install splayed caps in fact the only 2 bolts we have worked with in the last 4 or 5 years is the old 327 blocks and even on some of those blocks we have installed all billet caps 3 played centers and a front billet and a straped the rear main cap.
 

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I'm not a small block person,but for a little peace of mind you might want to consider upgrading to a set of ARP rod bolts and maybe even a set of their main bolts or even a stud kit.
 

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Race it, Don't rice it!
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Why are you using a dual spring with a small cam and low rpm?


I'd worry about the cam before the mains in this case.
 

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Some Punk Kid
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Discussion Starter #8
johnsongrass1 said:
Why are you using a dual spring with a small cam and low rpm?


I'd worry about the cam before the mains in this case.
My fault. Its a single spring with a damper spring in the middle. Comp cams part 981-16. They are recommended by comp cams with the cam I have. I know its not a huge cam but its going to mostly be running on the street not the track. I thought 470 lift / [email protected] duration was pretty good for the street.

DoubleVision - You think its only gonna make 210 horsepower? I just want to make sure I'm catching your 290 short statement.
My goal was ci=hp. 210 would be very short of this goal.

CNC-I have read a past post of yours about 2 bolts. I feel your opinion carries pretty good weight as you see a lot of mishaps I am sure at the shop. This engine will be kept below 6k rpm do you really think it will have a problem on the bottom end(mains/rods). The machinist I went through was very very very sure everything would be fine down there. Its just something in the back of my mind and I like second opinions.
 
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