More questions about my 383 stroker project... I'm shooting for "only" 400HP,max rpm will be below 6000... I guess I don't need a forged crank or H-beam rods..

Some cranks require longer rods, some don't... Is there any advantage/disadvantage when using 6" rods vs. 5.700" rods ?

Connecting rods: bushed or press fit rods ?? What's better and why ?

The following parts seem to be a good combo and are reasonable priced (Ebay) - the detailed description is below, will this combo work ??
Scat 9000 crank: $190
Speed pro pistons $220
Scat I-beam rods $180

With my Edelbrock aluminum heads (64cc) the CR will be 9.8:1 with these pistons - since I already have the heads and don't want to buy another pair it appears I'm limited in my piston choice unless I want 12:1 CR


Crank info:

Scat 9000 Crank Crankshaft 383 Stroker Chevy
- fits 1985 & older small block Chevy 305 and 350 blocks with the 2 piece style rear main seal. It is an internally balanced 3.750" stroker crank .
It has stock 2.100" rod journals and stock 2.449" main journals and requires stock style rod and main bearings in standard size like the CB663P and MS909P Clevite 77 P series bearings .
This crank weighs approximately 49 1/2 lbs. It is an internally balanced style shaft with the counterweights profiled for 6.0" or longer connecting rods.
Note: You cannot use 5.565" and 5.7" rods with this crank because of counterweight to piston clearance issues.




Rods info:

4340 I Beam connecting rods from Scat Crankshafts.

This rod set is a 6.0" rod length, 2.100" diameter (large journal rod pin), and bushed fit .927" diameter wrist pins. It is .300" longer the stock rod length for the 302, 305, 307, 327, and 350 V8 engines.
Approximate rod weight: 580 Grams
Scat's 4340 I-Beam rods are forged from a high tensile 4340 steel and are designed for high strength and fatigue resistance. They much stronger than stock OE rods and also the 5140 I-beam rods other manufacturers supply.



Piston info:

Part #: H140CL40
Brand: Speed Pro

Set of skirt coated hypereutectic flat top pistons with 2 valve reliefs from Speed Pro. Set includes 8 pistons with wrist pins and pin locks.
They fit 4.060" (4.030" available) over bore small block Chevy 350 V8 engines using a 6.00" length connecting rods and 3.480" stock stroke cranks.

Piston Specifications:
Part# H140CL60
Dome Style - Flat 2VR
Comp. Height 1.260"
Dome -5cc
Compression Ratio 64cc 9.85
Ring size: 1/16 1/16 1/8

(1) Compression ratio is figured using stock 9.025" deck height

 

Those rods and crank are fine I would go closer to 11:1 CR myself and put in a nasty solid roller cam for 500HP

 

I'm too scared to break stuff "back there" - reliable 400HP should be more than plenty for me.... but I may give it some more thoughts... 10.6:1 CR pistons are available, too

 

3 months after you get 400HP you will want 500HP

 

Why go stroker if you only want 400 HP.

 

i agree...look at me.

 

Though i haven't built a stroker mtr i have priced 1 out many times. But the hardest part is to find the correct weight parts for the crank to balance. I'm talking 'bout rod and piston wieght to match crank throw weight. I see u know the 5.7" rods won't work but 6" rods come in different weights too as do pistons. Not much info written on this but they need to match or the crank balancing becomes difficult and very expensive.
U need to contact the crank mfr for this but from what i've seen the rod weights are important/critical.
BTW it looks like ur pistons choosen are for a 3.48"/350 crank - not for a 3.75"/383. 350 pistons will not work in a stroker 383 - u need to find the correct piston for ur stroke and rod length.

Well if the parts are correctly choosen and then matched up by weights then its even possible to skip balancing. I know many won't believe this but actualy the mtr can tolerate small weight mismatch as there is quite a lot of crank flex during normal operation.
Weight and tolerance accuracy on new/modern parts is very good from new maching processes. Well just food for thought here as it may save u a few $$$.

U will probly want the block decked down close to zero and be aware this will increase compression also. I think ur running Edelbrock alumin and anything less than 10.5 c.r. should be ok.

Well enough for now and let us know what u decide on before purchase if u need help. I wouldn't buy anything until i could match the crank weights and find useble c.r. first - make a table and list.

cardo0

 

cardo0, you're rght... the pistons are for a stock crank... I looked at so many different pistons that day it's unbelieveable

I am also looking at complete rotating assemblies, they seem to be the better deal as they're already balanced.

How much will decking the block effect/increase the CR ? If I'm getting a rotating assembly with advertized CR 9.8:1 - what's the CR after decking (and what's the average amount removed from the block ?)

 

[QUOTE=RedBad1979]
I am also looking at complete rotating assemblies, they seem to be the better deal as they're already balanced.
Just a recommendation here, we see a number of "pre-balanced" assemblies in the door here, and I can tell you this, DON'T order it that way. Let someone you deal with locally and trust to balance the ***'y We've had more issues with customers over these "already-balanced", that we often have them there and show them on our balancer(s) how far off they actually are. You'd be amazed! Thank's Gary in N.Y.
P.S. Another reason I have against this procedure is this: if you have any "fitting" to do at pre-assembly, such as flycutting pistons, cam to rod issues, etc., you've wasted a balance job.

 

I'm with Gordonm, if you only want 400hp go with a 350. No need to waste the extra gas, just build it right. Spend the extra money to buy some nice heads and a roller cam.

And I've been told that 6" rods tend to make slightly more hp at high rpms. So if you don't plan to spin past 6K it's not worth the extra money and especially not worth the extra clearance work and the added cost of a small base circle cam that you would need.

 

Well most stock blocks are 9.025" deck hieght and that puts the piston tops down .025" in the hole. And zero decking reduces deck to 9.00" to bring the top of piston flush with deck of block. This allows a .038" compressed gasket to bing the head within .065" for a good quench effect. U don't want less than .035" quench to prevent pistons smacking the heads due to tolorance or stress/elongation at high rpms. And quench is a good thing as it will reduce detonation more than the increase in c.r. would cause it - but the higher c.r. adds pwr too.

So let me crunch some numbers for Ya:
volume removed is = piston bore area times deck hieght change
pie X (4.030"dia/2)squared X .025" = 3.14x(2.015)squaredx.025 = .319 cubic inches

Well now for ur Edelbrock heads with i assume 64cc chambers:
64cc X .06102in/cc = 3.90528cu-in
piston vol = pieX(radius)squaredXstroke = 3.14x(4.03/2)x(4.03/2)x3.75 = 47.81cu-in
gasket vol = pieX(radius)squaredXcompressed hieght = 3.14x(4.1/2)x(4.1/2)x.038 = .5014cu-in
there is also a crevise vol between piston and cyl wall but so small i will leave out (but u can measure for ur self).
So now we assume completly flat-top pistons (no dish or u would have to add this vol in too) use (chamber vol + gasket vol + deck hight vol + piston swept vol) and divide by (chamber vol + gasket vol + deck hight vol)
= (3.9053+.5014+.319+47.81)divide by (3.053+.5014+.319) = 13.34 c.r.
But with zero deck hieght = (3.9053+.5014+47.81)divide by (3.053+.5014) = 14.45c.r.

So were talking over a full point of compression.
Be my guest and check the math.
But again with dished pistons the c.r. would be lower and so would the c.r. change from change in deck hieght.

Ok throw in that 5cc dish and i get 12.44c.r. before decking and 13.39c.r. after.

10cc gets u down to 11.66c.r. before and 12.48c.r. after decking.

15cc dish = 11c.r. before and 11.7 c.r. after

Well my recommendation is save urself some money and stay a 350" (ok 355").

I appoligize i didn't mean to ruin ur plans but this may say u plenty of headaches and $$$. cardo0

 

Cardo0, thanks for taking the time to respond so detailed.

I looked at some more online catalogs and the number of useable 383 pistons is more than limited if using 64cc heads... the only pistons with a 16cc or 18cc dish are on Summit's website. SUM-CSUM383KIT or ESP-B13052L030

Speedomotive offers assembled 383 short blocks and stroker kits, they advertize 10:1CR or less with 64cc heads. I wonder what pistons they use

My plan is to get a 4-bolt main block and have that machined, therefore I'll need a new rotating assembly (355 or 383) anyway - I don't want to re-use my cast crank out of my L-48. Nothing wrong with that engine so I don't want to rip it apart... this also means I have a lot of time to get prepared for my first homebuilt engine

I'll definately look into the 355ci kits - with 10:1CR and a nice cam it should be a huge improvement over what I have now

 

Get a newer 1 piece rear main seal block out of a truck (if you really want a 4 bolt but it is not necessary) which will be set up for a roller cam and get a 383 rotating assembly, will cost about the same as building a 355. You will be able to use a bigger cam to get a touch more hp and a lot more torq at a lower rpm level as compared to a 355.

Just my .

 

If you buying a new crank , I'd build a 383 for the money . At the mild HP your wanting these Speedpro's will hold up .

Look here for other piston selections . Click applications , then Speedpro .

http://www.21cgt.com/FMWebCatalog/default.htm

Most local Speed shops can sell you the parts you need at a good price . If there is a problem with the parts , it's their's to deal with and dealing locally if problems arise is so much easier .

Get the part numbers you want and call around , you might be surprised ...FWIW