[Brad3112]

Working on a street 428 motor going in 67 gto. Rest of car. 4.10 12 bolt posi, m21, headers, 66 tripower. Engine 68 basic stock, 4 bolt, been cleaned up .005 over. Stock pistons, rods, 62 heads. "Rebuilt" before I got it so I took tomachine shop to see what I actually had. All stock except crower cam 60244 and adjustable rocker studs. Kinda weird cam, as specs say it requires 11:1 compression. It seems to have a lot of overlap so thinking they were trying to compensate for the high compression with this cam

So now question is what to do with it. To get 9.5 compression with these heads I get into custom $750 pistons and one recommendation was to do that and go with a comp cam XE268H. This recommendation came from Butler so prob a pretty valid recommendation

Previously I had a similar 428 with the RAIV cam with high compression and like the semi rough idle. I know the RAIV cam is completely different than the XE268H cam and has some overlap but not as much as the crower that's in it now. Guess there is some thought that the overlap actually lowers the actual C.R. A little from the actual calculated C.R?

I don't want it to sound like a SBC sitting at a stoplight. I like the RAIV idle, but also know that's a 50 year old grind and cams come a long ways since then

Any thoughts? Suggestions? Also anyone of any pistons available? I can get flats or up to about 14cc dish which is still prob a little over 10:1. Even those pistons are $600, so not drastically cheaper than the custom ones.

Would be convenient to run pump gas, but not against adding some octane out of a can.

 

[PontiacJim]

No Pontiac ever sounds like a SBC. What are you looking to get out of the engine - more streetable?

You only have 2 options to lower compression, either purchase a set of heads with larger chambers or the custom piston route. Keeping the compression under 9.5 is the way to go for pump gas with 9.5 being the max with iron heads, but this could still be problematic. Closer to 9 or 9.3 is what I would shoot for. Getting the correct quench distance between the top of the piston and head helps in running higher compression.

My observation, why 4.10's in the rear end? Are you spinning the 428 up around 6,500 RPM? The big cam will bleed off some compression at lower RPM's, but you will pick it back up at the upper mid to upper RPM's. I suspect the 4.10's make the engine/cam more tolerable on the street like a high stall converter.

 

[Brad3112]

It is a street car. Not really planning on racing. The 4.10 I agree are a bit low, but I found the 12 bolt posi all together with the gears for a good deal. I had planned on putting different set of gears in the Muncie. I had seen sets where 1st gear was still the same and then they spread the ratio out a bit and 4th became an overdrive. Actually 4th was still 1.0 ratio and 3rd gear became overdrive by switching the 3rd/4th shirt lever upside down. Now I can't find who made those

Heads are all redone and would rather keep the 62s and change out pistons since I want to clean it up with a .030 bore

 

[bigD]

Here's a few thoughts:

(1) "...not against adding some octane out of a can..." Use a good octane booster, like Torco Accelerator, with flat top pistons.

http://www.torcousa.com/torco_product/un_acce.html

http://www.ebay.com/itm/TORCO-UL-ACCELERATOR-CASE-OF-6-32oz-CANS-/222255510776?hash=item33bf75f4f8:g:tUgAAOSwwPhWiaPX&vxp=mtr

(2) " Would be convenient to run pump gas..." Switch to E-85 fuel, if it is available in your area. There is plenty of online info about E-85.

https://www.google.com/search?q=e-85+for+high+performance+cars&rlz=1CAACAO_enUS682US682&oq=e-85+for+high+performance+cars&aqs=chrome..69i57.12106j0j4&sourceid=chrome&ie=UTF-8

(3) If you go with higher octane fuel & flat tops, you can by forged Auto-Tec pistons. Auto-Tec will move the pin location to wherever you need it, to get near .000 deck height. The last I heard, they did not charge any extra for the pin relocation. The price for pistons/pins is just over $500 shipped.

https://shanonsengineering.com/collections/ebay-motors-parts-accessories-car-truck-parts-engines-components-pistons-rings-rods-parts/products/auto-tec-small-block-pontiac-400-428-455-flat-top-pistons

(4) If you go with the higher compression, I agree that the 60244 is too big. If you run a Crower, the 60243 would be a decent cam. My favorite would be an 041 clone, like the Melling SPC-8, with Rhoads orginal lifters with the Super Lube option. The Summit 2802 would be the cheapest decent cam for it.

https://www.crower.com/camshafts/pontiac-287-455-compu-pro-hydraulic-cam-284-hdp.html

http://www.ebay.com/itm/Engine-Camshaft-Stock-MELLING-SPC-8-fits-68-70-Pontiac-Firebird-6-6L-V8-/131527250214?hash=item1e9fa29126:g:yOwAAOSwUKxYmGhq&vxp=mtr

(5) I think the Auto-Tec/Race-Tec customs are the best price you'll find for custom Pontiac pistons. Might be slightly less than $600 shipped.

https://shanonsengineering.com/pages/about-us

https://shanonsengineering.com/collections/ebay-motors-parts-accessories-car-truck-parts-engines-components-pistons-rings-rods-parts/products/auto-tec-small-block-pontiac-400-428-455-flat-top-pistons

(6) If you go custom & drop the CR down to a safer 9:1, I'd consider a Voodoo cam, either 262 or 268. The Voodoo cams are said to have a smoother closing ramp, which eliminates the noise which is common with the CC XE series cams. Most of the engine builders & street guys on the PY forum recommend Voodoo cams, instead of the XE cams.

Voodoo Hydraulic Flat Tappet Cam - Pontiac V8 262/268 - Lunati Power

Voodoo Hydraulic Flat Tappet Cam - Pontiac V8 268/276 - Lunati Power

But, a Summit 2802 with Rhoads lifters would probably be a decent choice also.

https://www.summitracing.com/parts/sum-2802?seid=srese1&cm_mmc=pla-google-_-shopping-_-srese1-_-summit-racing&gclid=CjwKEAjw3KDIBRCz0KvZlJ7k4TgSJABDqOK7Yk9bb432aOWc-HABZUtciV3hhkEp0RdBbalUYhCrKhoCD8_w_wcB

(7) If you use regular lifters, I'd go with Crower Cam Savers, and if you use Rhoads, I'd go with the Super Lube option.

Crower 66056X3-16: CamSaver Hydraulic Flat Tappet Lifters 1955-Up Pontiac V8 | JEGS

https://www.summitracing.com/parts/rhl-9518l/overview/make/pontiac

I am not a Pontiac engine building expert, by any means. And, I have not personally used all the products mentioned here. But, I have built & raced several Pontiac engines, & have used some of these products. And, I can read what others have experienced & posted on Pontiac forums. So, this is just a disclaimer. No need for anybody to question my expertise, because I admit I have none. Just trying to offer info that might be of help to the OP.

 

[Brad3112]

So help me understand the Deck Height. Why do i want to get it to .000. I think it has something to do with getting the piston as close to the heads as possible to avoid detonation........but it would seem that the further up I bring the pistons (if they are sitting lower now) that it would increase my CR even more?

 

[bigD]

So help me understand the Deck Height. Why do i want to get it to .000. I think it has something to do with getting the piston as close to the heads as possible to avoid detonation........but it would seem that the further up I bring the pistons (if they are sitting lower now) that it would increase my CR even more?

Yeah, it would increase CR slightly. But, as mentioned, it will decrease detonation possibilities caused by a large quench distance.

So, the best combination would be the correct CR, close to .000 deck height, AND a quench distance of around .040.

But, obviously, to achieve all this, with 75cc or smaller #62 heads, will require dish pistons, if you wanna use straight pump gas.