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Loukas Has Questions About V8SHO Engine Mods

New 6/3/05

Hey guys,

How can one increase compression in our V8 SHOs? Could the cylinder heads be shaven down? Are there any performance pistons that are available for our cars? What about the air intake manifolds...can they be changed to get better air flow? or How about performance fuel pumps...how do those work? and do they work at all? Someone had once told me that adding a bottle of 104 or 110 octane can help. Is that true? and is it safe for our cars?


Loukas Zannopoulos
98 SHO

Let me try a serious answer.

Pistons would be expensive, OE pistons have a very subtle dish. My concern with any solution would be valve to piston clearance.

I think V8 pistons at either side of the combustion chamber are already with in squish range of the head. So to raise CR changes must be made in the combustion area under the valves, which is busy area and it needs to be clean for flame propagation.

As you mentioned, a thin head gasket is the least expensive option but only if you want 10,000 gaskets.. No replacement gasket is available. Our head gasket is complex and trouble free. I don't know that it is easy or inexpensive to develop a thinner head gasket. 8 Pistons or head mill would be cheaper.

On the plus side, the stock 10.25 CR tolerates 87 ROM gas just fine. So maybe you can tolerate a slightly height CR with high octane?

You may have a CR > 10.25 if you already have carbon build up on your pistons.

An alternative way of looking at this is to just change the ignition timing with a chip from FPS. A chip is cheaper than pistons, heads or a custom head gasket and gets the same results.


You have mentioned nothing about brake or suspension upgrades. So lets just talk motors.

1) Are you welded? If not, do that yesterday. Do complete PM and inspection, struts in good shape and radiator clean for best cooling? Save for an ATX fund.

2) consider an UDP. ~ 5 hp

3) consider a cold air air filter mod. ~ 7-10 hp

3) consider Bullet muffs. ~ 5-10 hp

4) Get a chip from Doug Lewis (FPS)

------------------------- Then

5) Kirk has big bore butterflies, you can consider a head job with porting and lightweight valves and 3 angle valve job. Matching gaskets. You could get your heads milled a small amount. ~ $1,000?

6) Doug Lewis is the NOS god with kits up to 200hp. This is the least $/hp. For 25-50 you might DYI from help on the list. For 50+ Hp talk to Doug and do it right.

7) Get a shift kit from Doug Lewis, I know it's ATX but not motor but it will help a lot. $110 + Labor

8) Rumors of 4.0L V8SHO exist, running examples: population=zero. In theory it is possible, it it wise and prudent? I don't know, it is unproven. It could help torque, esp off the line a whole lot.


Have you ever visited FPS in Atlanta? It is the Mecca for SHO mods. If I had a project in mind for my SHO and say $10,000 to burn. Doug can do the work and give good advise. I would recommend a visit to Doug for any performance oriented SHO owner, even if they don't have a project in mind.

Set up a budget and a schedule, I would not go for an open ended arrangement with any shop.

Say Doug gets you in the low 14's, then if you want, need more performance Doug can do that too. If you make any serious Hp and drive hard you will need to also learn about our AX4N. Doug is also the guy for that.

Because a SHO is FWD it is best to have reasonable performance expectations. If you want a 12 sec car I would not even open the hood on a SHO. Go get a mustang.

Carter has a blown V8SHO, only example I know of. I don't think Carter is making any more examples of the breed. But it is possible. Carter is generous with advise. what are your skills like?

Having HP and good ET are two different issues. SHO have tall gears, poor traction, FWD and no low end, it will never be an ET monster.

wanna go real fast, Go get a mustang.


<<As you mentioned, a thin head gasket is the least expensive option but only if you want 10,000 gaskets.. No replacement gasket is available.>>

Our head gaskets are already the thinnest I have seen on a street vehicle.

Carter Fuji

Compression - J&E (Pistons) - http://www.jepistons.com/ - will make anything you are willing to pay for and it will cost a boatload. You would need custom domes with machined valve reliefs. If you go the custom piston route you may as well bore the block for extra displacement. The bottom end of our motors can definitely handle the higher compression. Shaving the heads/thinner gaskets = NO. We are already at the point of piston meets valve at TDC. Air intake manifold - Extrude Hone - http://www.extrudehone.com/powerflow.html - for larger/smoother runners. Having the heads ported and polished and blending the combustion chambers will yield small benefits if any. Larger valves and seats may work too but only VERY Slightly. Our 3.4 Liter intake runners are already TWICE the size of a stock 5.0 Liter - How much more can you flow with normal aspiration? Fuel pumps - Regular high perf Mustang pumps need only slight mods to fit into our fuel tank setup. I have a photo "How to" on the V8 site somewhere but can't find the link for you. Unless you are Supercharged or go over a 75 shot of Nitrous it will not help, the Fuel Pressure Regulator will simply return the excess flow to the tank. Octane boost - waste of time and money. It will make you idle rough but that is about it.

Hope this info helps.
 -- Eric Lehmann

Ok, thanks Carter, I learn from the master.

Another thought. I knew a body man with a light weight CRX. He got the car on a default, it needed a front clip. Well Honda has a lot of weight in the bumpers and bumper absorbers both ft & rear.

He was able to purchase a one piece fiberglass replacements for rear bumper, & front bumper/ hood / fenders that cut 300-400 # off the car front and rear and it made his 1800# car into a 1300# which % wise is a killer mod. (unlike a CRX no such off the shelf part for a SHO exists, yours would be the first)

Remove the outer fenders and the body colored engine well (part that holds the upper strut tower) is actually part of the chassis, you don't want to remove that.

My CRX friend noted that his car now had a glass jaw (and ass) and if he so much as hit a squirrel he was pooched. This makes the car a trailer queen, unfit for daily street use.

Say you could make a tilt nose V8SHO? Might be able to save 200#? It's all bad weight in front of the front wheels. Someone else would know what a budget for that may be. I guess $5000+?

Say you can knock off another 100-200#? Might get down to 3200# curb weight? It is car specific so the amount of weight varies and yes the car would not be safe in the event of an accident.

But it would cost tons less than an chassis aluminum SHO.

If you have too much weight of your own it is pointless, (like I do) but if you are a 110# driver and money is no object?


If we had a simple head, one could eliminate a head gasket and O ring the the head gasket, but we don't have a simple head. I wonder how much we could mill a head? I suspect not too much.

Thanks Carter.


see also









There is not a lot of material to be shaved, plus shaving the heads or decks on a DOHC motor entails all kinds of other things, as the cams and intake are all now spaced differently, and must be spaced back up. I would even say that if I had a warped head on any SHO engine, I would scrap the head and get another, rather than shaving it.

Getting custom pistons made is the “cheapest”, and actually the easiest, way to do this. The other advantage here is that you could have your heads ported, polished, and the combustion chambers cleaned up & CCd, and get pistons to recover any lost compression and add more, if desired. There are already a few folks who got custom pistons for V6 SHOs, and piston makers can make up about anything you want. Not as cheap as 410 off-the-shelf Chevy V8 pistons, obviously.

Stock fuel pump produces more than the engine needs.

Higher octane fuel will slow the car down, plus cost more. The car runs on 87. As with any car, the best gas has the lowest octane that you can run without pinging.

Ron Porter

The CR is 10:1 on the V8 (9.8:1 on the V6 SHO). The engine is already an interference engine, and I doubt the piston-head spacing is that tight (compared to an 11:1+engine, especially an OHV engine).

Piston makers can handle whatever you want to do. Granted, this is not a “weekend bolt-on mod”, but if I were tearing down any SHO engine, I would go with higher CR pistons to really use higher octane fuel.

Then, the chip upgrades with timing adjustments will be more useful.

I would say that a higher CR piston will do far, far, more than anything that can be accomplished with a chip on a stock motor.

Ron Porter

Good point, shaving heads on a DOHC V8 will cry havoc with valve / cam timing. I still think it will require considerable study to increase CR with modified pistons because of combustion chamber design. Polishing the combustion chamber will lose compression. See www.SHOCLUB.com  photos. The V8 combustion chamber actually has small flame troughs for ignition propagation.

see http://www.shoclub.com/membersonly/shoheads/imagesheads/v8combchamb.jpg

for what we have to work with.


Sorry to confuse you. My point about temperature was in reference to the temps created from raising compression, oxygen content of the combustion chambers or advancing timing require the counteraction of the use of a "slower-burning" fuel. The fuel of itself does not burn hotter of course but does net less BTU as opposed to lower octane pump liquid.

Again, sorry for the confusion.

Carter Fuji

John Hrinsin went with Wiseco pistons (http://www.wiseco.com/) and had the custom made. When he first got them, he said they were so pretty that he hated to put them into the engine!

He went with an overbore, and offset-ground Manley Chevy rods, to get 3.4 out of his V6, plus he bumped the CR to close to 10.5:1, IIRC. Getting custom pistons ties together a number of mods like this.

Ron Porter


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