ok, I'm trying to take my time and build this one right. So the first questions start, compression ratios, what are people pulling off with pump gas, (cali. 91 oct.)

Q2- How many people have done a full floating wrist pin, any issues?

Suggestions on Rings and bearings, and any extra machining that LT1's like that most old school motor heads don't forsee.

I'm stuck in the middle of nowhere and I don't know who I'm going to have do my machining so if I get stuck going to "bob's metal grinding" I'd like for me to be able to teach him about LT1's instead of him learning on mine.


my plan is a reliable seasonal driver that I wouldn't have any doubts about driving from cali to dallas, making about 400rwhp with a small shot (125 wet) on top. I currently have a GM847 and a 4 bolt main block but I'm still head shopping.

 

First let me ask you a question...
Why are you building only a 355?
If all you want to do is spray and not rev the hell out of it (which you dont want to if you want reliability), why not build a 383?

If you are buying all new parts anyway, 383 parts cost identical to 355 parts. Only place you will have a problem is the oil pan, which stock can be made to fit, but an aftermarket pan is a good idea anyway to control windage (you can see close to 20hp just from that)

Its good that you arent thinking about the cam yet though, dont even start thinking about that until you have the heads in your possesion how you want them to be, dont buy a cam cuz you got a deal on it if you want to build it right.

Now, people are pulling off close to 13:1 im sure, but its all going to depend on your cooling system for one. The size of the cam you install, and also somewhat the design of the heads (ie chamber size and squish) a smaller squish wont detonate as easy as a large one. But the opposite with the chamber size, keep it as big as you can with the proper squish and compression you want. If it were me Id shoot for 11-11.5:1 thats a safe ratio that will still make good power.

Full floating pistons, dont knwo why there would be a problem there, cant get any better than full floating (yet). Rings...just get a good set of moly faced rings. Make sure you let your machine shop know what rings you are using, moly faced rings dont require as coarse a hone as other rings, a good machine shop should know that though.

 

I was just looking at that, the more i research the more i realize i need to learn, i found a 383 eagle kit with a cast crank (i was told a cast 6' crank is just as strong as a forged 350 crank) *shrug*

http://cgi.ebay.com/ebaymotors/ws/eB...190&category=0

are these good bearings? and will I need a fluid dampener?

 

ok I think I'm going with this kit, I talked to a builder down south that said he will grind the new crank to ensure that it is a true round then, heat treat it.

now I need heads. AI? LE? CM? port and pray? I wonder what power I'm looking at and how long this will last. keeping in mind I sitting on 2 GM847 cams. anyone selling a 58mm BBK?

 

A 383 is going to require a lot more head than a 355. For the street on lt1 castings i would stick with less cubes. You can easily meet your goals with a 355 and ported lt1 castings.

125 shot on top of that you could get away with cast crank, forged i beams (scat or eagle SIR), and a decent forged piston (SRP would be a cheap quality choice).

 

A 383 isnt going to require anything more than stock castings can provide. If youre going to get them ported, get them PORTED, and go with more cubes, even if theres less head you WILL make more power, whether its noticeable or not thats up for discussion, but in the long run a 383 will be more reliable, especially if you go with 5.7" rods over 6". And the difference will definitely be noticeable if you do get them ported well, like any of those companys you mentioned would do.

 

Stock heads simply dont have the cross section to suport a 383.

Taken from Bret..

 

I should a wrote that!

Good job Jared, some days I want to post stuff up like that again and again but hell I ever forget that I wrote it.

Basically that explains why you can get lots of power at high RPM with a LT1 head on a stroker, cause you can spin the thing before you overspeed the port.... well most times. If you spent lots and lots of time with a velocity probe and paid lots of money for the porting you could, but then you could have had more for less money.

Bret

 

This is basically a "how do I build a high HP LT1" question, and should be posted on LT1 Engine Tech. Moving it there.

 

First of all im curious how Bret got two different velocity numbers since the numbers in the formula are identical between the 355 and 383:

The 383 with LT1 heads @ 7000rpm....
(.00353 x 7000 x 3.75 x 4.03^2)/2.10 = 716 fps or around .59 MACH!

The 355 with LT1 heads @ 7000rpm....
(.00353 x 7000 x 3.75 x 4.03^2)/2.10 = 665 fps or around .55 MACH!

Next, seems to me that that 40 thousandths of a mach isnt going to make a HUGE difference..and that is at 7000, what happens under 7000, if you give it enough cam to spin to 6500-6700 it would probably be very happy there, if the bottom end was up to it of course, and thus it would HAVE to make more power than the 355 assuming there is still enough air for the 383, and I mean were not talking drastic CI increase numbers here, and LT1 heads CAN flow pretty well.

Just seems to me that if the 383 makes more torque at all RPMs, which it sounds like it does, than how can the 355 be more powerful if HP is a function of TQ and RPM? If the 383 makes 400lbft at 6500 and the 355 only makes 399lbft at 6500 than the 383 is more powerful, thats an exaggerated case, but for the same amount of money the 383 made more power, am I wrong?

Plus, forgot to mention the fact that the 355 has to spin 500 rpms faster than the 383 to reach max power according to the calculation, so for a street car like he wants, to be durable, he would rather keep it below 6500 IMO, if not farther to keep really good reliability.

Actually now Im really confused, I just looked at the equations a little closer, and I read it backwards, the 383 pulls more max port velocity than the 355, right? So how does the prove that it makes less power? Seems that a higher port velocity would be good, thats what everyone wants from a head is high port velocity right? How is this making the 383 less powerful is what I dont understand.

I can see all this discusion leading us to the point that the difference in power between say a 396 with lt1 castings power increase over a 355 is negligable based on cost to hp increase ratio, but were talking identically priced engines here, and I cant see you proving to me that the 383 will actually make LESS power than the 355 at reasonable street RPMs, maybe at 10000 rpms, but at 6500 and below, prove to me that a 355 with as good of lt1 castings you can buy (say LE or AI), and a 383 with same heads and as well designed camshafts, will make more power, and I will shut up.

I wont argue with the fact that a lt1 headed 383 will puke way out at close to 7000 and up, but 90% of lt1 owners dont operate near that, and especially not over that. I could see a 355 max effort lt1 making more power @7000 than a 383 since the 383s torque is going to drop off at or around 6500 no matter the cam, but the 383s increased torque will hold it over at and slightly above that rpm.

IE: 383 @ 6500rpm 415lbft = 513hp
383 @ 6700 rpm 400lbft = 510hp

355 @ 6500rpm 370lbft = 457hp
355 @ 6900rpm 390lbft = 512hp

So assuming street reliable engine, we would want the 383 no?

 

Jon,

Note the correction....

This is what you should be more concerned about.....

Where the max power could occur if given the right setup and the min cross section areas are addressed to make sure they are maximizing their airflow thru that restricted space.

Now generally a stroker will make more power with a motor since it will produce more power in a similar RPM band. The guys out there who have taken advantage of the smaller motor do so thru RPM.

Here is a hypothetical.....

I'm going to make this simple, same tires, same tranny, same 4th gear pull on a M6 with no losses thru the drivetrain.

If you can create 420ft lbs of TQ at 6400rpm (which is the HP peak) in a 383 with LT1 heads and the optimum gear ratio for the combination is a 3.73, at HP peak you will develop 1566.6 ft lbs at the tire.

Now say that the 355 makes 395 ft lbs of TQ at 7000rpm (which is the HP peak) with the same heads and the optimum gear ratio for the combination now is a 4.10, at that level you now have 1623.45 ft lbs at the tire.

You lost 6.33% TQ at HP peak at the motor but gained 3.63% of TQ at the tire. The gearing is 10% higher in the 355 / 4.10 combo but it ends up with more TQ at the tires.

RPM potential in drag racing is a big thing, it even plays out in Pro Stock.

BTW in that example the motors both are producting roughly the same HP 526HP.

Bret

 

Yah, Bret, I figured it was just a typo, cuz i got the same results. Just wanted to point it out. I dont want ya to think Im getting cocky with you since (cliche) youve forgotten more than I probly know at this point, but it all just doesnt make sense to me.

 

It's ok to be cocky....

Reread that last post now that I edited it.

Bret

 

Ok, well I was arguing for no reason then. You and I both understand that it is better to make tq at a higher rpm so you can take advantage of gearing. But thats where my discussion went astray is because I was speaking about keeping RPMs down to a reasonable speed to keep the everyday street motor alive longer. Which Im guessing you would agree with me then that a 383 would be a better choice if you want to keep your engine speed down.

Not being completely experienced in racing as much as Im sure you are. Would that necessarily mean that the 355 will be quicker? If you can launch the 383 harder off the line and get through the 1/8 quicker than the 355, could you not hold out since the 383 will be running out of rpm/gear at the end of the track?