Newbie build in progress need advice on CR and Quench

[Kapper]

Hi Everyone, I am new to the stroker builds, but have been doing a great deal of reading and now I'm in the progress of building a 4.6 stroker. I have some questions regarding CR and Quench height that I need advice on. First here is what I am building.

Renix 4.0L
4.2 Crank
4.2 Rods
Standard .030 13cc dish Cast Pistons
Comp Cams 68-231-4
94 HO head Ported and Polished 58cc C.C.

Using the 4.0 stock Deck Clearance .0215 in the calculator I get SCR 10.07:1, DCR 8.8:1, and Quench is 0.0655.

With everything I have read, the CR values seem high for a daily driver/weekender. I am wondering if the notorious knock and high octane requirement is based on the SCR or DCR value.

Quench also seems a bit high but this is using the stock deck clearance rather than measured. The deck height is at stock and all the parts are off being balanced so I can’t measure the actual. I would like to be ready to decide if I need to deck the block by the time they return to the shop from the balancer.

OK so here are my questions:

Does anyone know the deck clearance with stock 4.0 deck height using 4.2 crank and rods with standard 13cc pistons?

Is SCR of 10.07 and DCR 8.8 likely to require high octane fuel in order to avoid the knock?

Is the Quench of 0.0655 acceptable or will I loose all the power I have been shooting for by not decking the block?

Sorry if these are familiar questions. I can find some posts that come close to answering these but they all seem to be for strokers using 4.0 rods and custom dish pistons or some other variation of recipe. As a newbie I just don’t want to make costly mistakes because I failed to ask stupid questions

Thanks for any help. God bless!

[astjp2]

I had 15.8 cc pistons and ported and polished head, offset ground crank .020, zero deck and felpro head gasket. had about .050 quench. Compressions were too high 204-212 psi at 4500 altitude. Worked with carb but not on my 94 wrangler, so I had Oleshot dish the pistons to 20.0 cc's hopefully that will fix my compression problem. Tim

[lafrad]

I did something very similar...

4.2L crank offset ground to add 0.015", have Oleshot enhanced pistons (20cc), and decked the block to get the pistons zero decked (or a few thou thereof)... quench ends up in the 0.040" area. Run Crower Stage 2 "Compu-Pro" cam: http://www.crower.com/products/camshaft ... 6-hdp.html installed *straight up*. (the cam came with 4* advance ground in, I used an adjustable set to set that back to 0*

have no issue at all running 87 octane when its under 50* out... and 89 for the rest of the year. I get a little bit of stutter when its over 90* with 89... its not really knock (that I can hear), but its not 100% happy. Solved with running 91/93 for the HOT months... a simple tradeoff for the nice throttle response and better MPG's of enhanced compression.

[gradon]

If using a .043"HG, then deck clearance will be .0295", quench will be .0725", SCR 9.96:1 and DCR 8.7:1. According to Dave Vizard, premium pump gas can only support up to 8.5:1 DCR on an iron head before compression knock takes over. He recommends aiming for a 8.25:1 DCR. I didn't heed his advice and have a 8.56:1 DCR and mine pings lightly in closed loop from 2.2K-3Krpms at sea-level when using 93 octane. I will fix it by biasing the O2 sensor output with the AEM FIC and running richer than 14.7:1. I recommend using pistons with larger dishes or have someone dish them for you.

[Kapper]

Thanks for the good information guys. It sounds like I'll need to have the block decked and try to gain some CC's somewhere to bring down the CR. Any reason why dishing the pistons would be better than removing some material from the Compression Chamber? Other than the work of course.

I appreciate the advice.

[herbiehind]

there's an article on this site somewhere(sorry ,cant say exactly) that deals with quench .(the squishing of the mixture to the center of chamber) . from what i gather , if you remove material from the cahamber to gain volume , you'll lose some quench maybe . it's alot to think about when looking to cc the head and all . i'm baffled as hell . just gonna use a known good formula for mine . found it . go to faq's and go to compression ratio q's . you are correct . you can do same thing with chamber work .