Mods, move if this isn't advance enough...

If no one know of my ailments, I have recently found I need a new shortblock. Here's the question:

Stock ported LT1 Castings. Are these going to be enough to support a well build 383??? They flow great, but I need to know if the intake runner size of the stock casting, even when ported, is going to choke the motor of air at the upper end of the powerband. Or, will I be ok, since I'm getting a custom cam??

 

I don't put stock LT1's on a 383 because they just can't feed the thing enough air for my tastes. A well built 355 could use them no problem.

BTW what happened to the motor?

Bret

 

Stock ported LT1 castings would be fine on your 383. Jordons ported LT1s ran low elevens and eventually even faster with those heads and a hydraulic roller at first. I know I rode in it quite a few times. Good ported LT1s can move decent air like 275 up to 285 CFM which is sufficient to make over 550 HP on a race engine or an easy 450-500 HP on a hot pump gas street engine.

 

Well, I know the heads were moving 272 CFM @ .550, an d most likely more up top. I wasn't concerned about the flow as I was the intake runner size choking things up.

Bret,

They did a compression/leakdown test, and got the following:

1 -- 220
2 -- 205
3 -- 185 with about 35% leakdown
4 -- 220
5 -- 160 with 45% leakdown
6 -- 215
7 -- 200
8 -- 210

My guess is that when the car was on the dyno the first time the motor just couldn't take it. Joe told me it started to spark knock because of the lean condition up top which is why they shut it down. But, having dropped compression on two cylinders seems to be the concensus that it's my problem, as everything has been checked prior. When the shop called my they were like "uhhhhh, we found your problem." in a very disconcerting voice.

I'm going to have to use the stock castings no matter which way I look at it. I am scraping hard to come up with the cash for a fully forged bottom end in the first place (having thought of giggle juice, but they're probably only thoughts). I believe they'll be fine, I just won't be able to really take it to the limit up high. Dyno will tell I guess......

 

Well you could always take the plunge and do a 355. The stock crank can handle most abuse people throw at it. It's not like we have 500hp circle track motors here.

Usually a LT1 casting will need more camshaft since it has a smaller cross section and less flow than a aftermarket casting.

Bret

 

I'm quite intent on the 383 at this point but the 355 will be in the back of my mind as a backup if it's going to cost too much. The extra TQ is very enticing.

 

383 is about 8% bigger than 355. If torque relates to displacement, that's not huge. Of course with same heads, etc. total area under the usable torque curve won't be a huge difference either. Especially if you are head flow limited, 355 looks better and better, and cheaper.

425+ RWhp (approx 500+ FWhp) 383s often have better-flowing heads than yours....but not always. Better flow can mean less cam and more mid-range torque.

My $.02

 

This head thing seems to be the $64,000,00 question.

Ronald Tiggs made 441 RWHP using a 236/242 cam with ported LT1 heads in a 383. I made 450RWHP/451 torque in a 396 with the same cam and GTP LT4's flowing 282 cfm. Also made 466 rwhp with the same heads and a 246/253 cam.

Guess it all in what your looking for as that pretty good power especially when you have the dyno sheets to back it up.

I'd like to see a bit more objective information regarding "afermarket castings" and the results people are getting. I'm frankly sold that aftermarket castings can more than likely produce more power but for some reason people are a little short on hardcore results.

Real dyno numbers work real well for me. Anyone got any?

 

Well, looks like a 355 may be my motor now. Just got off the phone with a company, balanced blueprinted motor, Eagle ESP Forged Crank, H-Beam rods, Diamond Ultra Lite pistons with valve reliefs and 11.0 compression ratio, ect. ect. for $2800. I'm probably going to leave myself wondering if the 383 would have been better overall, but this fits my budget much better.